| xblocker |
multiplexor,
OHPs don't use a single lens for projection, they mostly have doublets or triplets for correction of spherical and chromatic abberations. A single lens can't do that!
xblocker |
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| amblix1 |
| quote: | Originally posted by cowanrg
hehe, yeah, it will come BACK up soon. you must be a newbie. when the site went down, it had over 35K hits :-)
ill try and get it back up this weekend. i had a problem with my host. and lost interest in the projector thing.
ill try though, there is a lot of good info there for newbies. |
sweet, do you have photos of a completed one, or screenshots? |
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| multiplexor |
| quote: | Originally posted by xblocker
multiplexor,
OHPs don't use a single lens for projection, they mostly have doublets or triplets for correction of spherical and chromatic abberations. A single lens can't do that!
xblocker |
hmm I see. I always thought when i looked at one, i would see a round lens which looked like it was one piece.
does surplusshed have a lens i could use then, without buying an OHP?
i'm gonna read some other threads and the wicki thing to see if more info exists on it :)
thanks for pointing that out though. |
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| cowanrg |
yeah, i have both. a few galleries of screenshots of various finished products. as well as pictures of projectors and such.
i just kinda left the project behind becuase at this point, there still isnt enough info to make a really great design. mine works FINE, but is nowhere NEAR consumer models, and i dont think we will be able to do one of those for under $500 for awhile.
btw - zark's design DOESNT WORK. plus, CRT lenses dont work for lcd panels. they were designed to work for the curvature of CRT tubes, so, either the middle or the edges will be in focus, and the other will be out of focus... they dont work for flat surfaces.
and, the LOA's (lights of america) that he uses are NOT good. i had one, just threw it away finally yesterday. they are bright, but the light goes everywhere, its FAR from focused.
| quote: | Originally posted by amblix1
sweet, do you have photos of a completed one, or screenshots? |
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| eebasist |
| for some reason i still believe that a crt lens will work.....i have 3 crt projectors at home. and i know the lens has two focus rings on it....one for the middle of the image, and one for the edges of the image.......would this allow it to focus to a flat panel? |
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| cowanrg |
here is the deal, you are taking a FLAT source and putting it into a curved lens. therefore, the distance from various points on the panel is longer or shorter, so the panel will look in focus in places, and out of focus in others.
its just how physics works. try it first, but back in the OLD diy projector thread, it was found that this would NOT work.
a CRT lens works with a CRT tube, they are both curved.... |
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| amblix1 |
| quote: | Originally posted by cowanrg
here is the deal, you are taking a FLAT source and putting it into a curved lens. therefore, the distance from various points on the panel is longer or shorter, so the panel will look in focus in places, and out of focus in others.
its just how physics works. try it first, but back in the OLD diy projector thread, it was found that this would NOT work.
a CRT lens works with a CRT tube, they are both curved.... |
damnit get your site up now hahahahaha j/k :)
what about using a fresnel before the LCD to concentrate the light into one spot, such as lighthouses :/ |
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| Mario007 |
| Umm most overhead projectors do use an fresnel light before the lcd to spread the light evenly to avoid hot spotting. Cowan I have a computer that is setup using apache webserver I would be willing to host or mirror your site if you want. |
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| eebasist |
| i wasnt aware that it was tried.....i was commenting that there are two focus rings for the outside and inside edges thats why i thought it could work....i do know how physics works, but i dont have the specs of crt lenses |
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| amblix1 |
| quote: | Originally posted by Mario007
Umm most overhead projectors do use an fresnel light before the lcd to spread the light evenly to avoid hot spotting. Cowan I have a computer that is setup using apache webserver I would be willing to host or mirror your site if you want. |
Ok thats what I thought, I knew OHPs use them but I wont be using an OHP. Well I guess all I need then is a good lens. Im not picky on quality, just something to play my video games on at night |
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| cowanrg |
possibly. i have the site done, and hosting done, it just got pulled because of some disputes with my hosting over traffic...
this site pulls a LOT of people when its up. i think i was doing like 4K page visits a day near the end. i forgot how much bandwidth was used, but its more than a cable/dsl can handle for sure. it was in the multiple GB/month range.
ill get it back up and see if i need a mirror. where you located?
| quote: | Originally posted by Mario007
Umm most overhead projectors do use an fresnel light before the lcd to spread the light evenly to avoid hot spotting. Cowan I have a computer that is setup using apache webserver I would be willing to host or mirror your site if you want. |
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| Mario007 |
| I live in Portland, Oregon west coast. Wow that sure is a lot of bandwidth. You might look into compressing your images a lot. Possibly a non intrusive banner ad would help you pay for your hosting? I will host as much bandwidth as I can for free in the name of diy projection. 320k upload. |
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| cowanrg |
nah, not near enough bandwidth thanks.
hosting is paid for. no worries there. its all setup, i just need time really...
images are compressed, max one is like 80k i think. trust me, its just a big site with a lot of visitors... thats all. once its up its fine. my hosting is like 100GB/month (i almost reached it the last month it was up :-) |
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| Mitch |
Cowanrg,
How do you know that Zork5150`s projector doesn`t work? Have you tried it or something? It seems like it WOULD work. Any reason you believe otherwise?
Mitch |
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| Mario007 |
| Simply because the lights of america flourcesents aren't very high lumen which means you would have to have an awsome reflector for them. Plus his lens is a crt lens which means as was already pointed out would give an out of focus look on the outside edges. But maybe he figured some way around that. Bending his lcd panel :) JK. |
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| icculus |
| zark's idea was quite similar to my first idea, as i was browsing my partsexpress catalog and saw the cheap auto lcds. if you look at the screenshots on his site, you will see that they suck a$$. bright in the middle, dim in distorted on the edges. its like the video version of a bagel. the crt lens forces you to put the lcd within 1"--actually less--of the lens. i busted apart a fuji crt lens i got for 6 bucks and there are actually some potentially usable elements inside. read the original thread--it's all inthere |
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| Mitch |
So his lens, the Delta IV, is no good for projecting?
Mitch |
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| icculus |
| buy one and try it , if you like. they're pretty cheap. apparently, they made a lot of these at some point. edmund has beesn selling them for years. i beleive theyre from the old scool huge front projection tv's of years ago. nothing wrong with them, but not really what we're looking for |
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| cowanrg |
uh, no... they ahve been tested MANY times, and proven to not work. the inside will be focused, but outside will be blurry. or vice versa.
| quote: | Originally posted by Mitch
So his lens, the Delta IV, is no good for projecting?
Mitch |
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| eebasist |
| oh well time to take apart one of my crt projector and find out what lenses inside are of any use to me, if any. |
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| biteon |
some one give me the perfect dimmintions to a parobolic relfector and ill try to make the out of alum. and sell them to you guys through ebay for cheap that of cource if they work out.where i work has alot of tools etc. that i can work with. but if this dose work out im only making a limited amount just for u guys. nonprofit work sucks after a while. we see how it gose.
:D :D :D :D |
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| Mitch |
Hey, thanks guys. You just saved me about $40.00.
As far as the Lights of America goes, they are 8,000 lumens and they are color corrected (I don`t know if color corrected is better or not). But I think 8000 lumens is bright enough...isn`t it?
Mitch |
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| Mario007 |
| 8000 lumens is not enough I think. You would defiently have to have a good reflector even then it would be dim. Use a metal halide although they are a bit more expensive they have good color tempature and are very bright. Most people are using 400 watt metal halide which seems to be good size. They output 40,000 lumens. ROTFLMAO on icculus comment that his pictures look like a video bagel. |
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| woneill |
Hi Guys,
Where (and whose) was the post a few days back about using a cardboard cutout to create a solid elliptical dome out of plaster/clay that could be used as a mold to build an elliptical reflector around using aluminium foil/sheet?
I remember reading it a week or so ago, but it seems to have been lost in the weeds...
Having seen the commercial reflectors from stage lights, I am sure that this is the answer to the reflector problem.
A suitably cut (like petals on a flower) aluminium disc could be wrapped around this dome, fastened in place, and its inside surfaces polished. It would be cool!
I THINK a suitably set-up elliptical arrangement would also eliminate the center hotspot situation that affects many who have used a parabolic reflector, or cylindrical + fresnel combination. But, then again, I might be wrong...
Bill. |
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| mycamel |
| quote: | Originally posted by woneill
A suitably cut (like petals on a flower) aluminium disc could be wrapped around this dome, fastened in place, and its inside surfaces polished. It would be cool!
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Bill,
The plaster mold idea is here on this page.
I liked your idea of the thin - petal approach, but wonder how easily it would conform to the shape required. The better the specular surface, the worse any imperfections will affect the light reflected off of it.
I still think it would be easier to use thinner, easily formed metal like foil, built up in many layers to obtain the wall strength needed. Sort of like paper mache, but using foil instead of paper. The sticking point (bad pun alert!) I think would be glue.
Biteon had suggested melting the aluminum together, but I don't think that would work unless you formed a complete mold and did a pour like a foundry. Otherwise you'd be essentially trying to weld it, and as far as I know, aluminum doesn't cooperate around oxygen.
Any adhesive experts among us? What sort of heat does super-glue handle? Would it start producing toxic fumes after we'd been watching our TV a while? Are there any epoxies made for automotive repair that could handle the heat? |
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| remp |
| Maybe something like that black gasket goo they use for auto engines. Gasket cement. Gasket replacemnt. May need highish pressure to work properly. |
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| thelaw |
| quote: | Originally posted by cowanrg
possibly. i have the site done, and hosting done, it just got pulled because of some disputes with my hosting over traffic...
this site pulls a LOT of people when its up. i think i was doing like 4K page visits a day near the end. i forgot how much bandwidth was used, but its more than a cable/dsl can handle for sure. it was in the multiple GB/month range.
ill get it back up and see if i need a mirror. where you located?
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I wouldn't be to sure cowan.
I host a very popular forum on my DSL line (512k/256k) I have ~13000 members and usually around 30 connected at any one time. Traffic wise this costs me around 700MB a day, on busy days though its usually around 1GB, recently it came up to 2.5GB in one day.
Beleive me, a well configured server on a dsl line can handle a hell of a load (this was my problem). I had to upgrade the server for a performance boost, the line was not the bottleneck. In my 2 years experience of home-hosting :) the hardest thing is keeping the server running.
Anyway, back to projection :)
Im all setup, sorry I havent posted pics yet, im still trying to get hold of a camera. I have an Elite Vision 4000 OHP that takes EVD Lamps, and my panel is a Spectra Pro (different to Spectra C)
I never thought i would get such a good projection on such a budget. It's amazing, the best thing i have ever purchased for home cinema is this panel and ohp. I had it setup yesterday on my outside wall, the picture was about 14ft diagonal. Amazingly it was still crisp and bright (this was about 11pm :) )
I am aiming to fit my ohp with a new MH setup though because i have a few problems::
1. The panel gets EXTREMELY HOT (REALLY REALLY HOT :) )
2. There is a small spot in the middle of the picture (the tungsten filament.
3. It would be nice to have a brighter image for ambient lighting
4. Im worried that in this state it would be a fire hazard to roof mount.
Also, I would like to upgrade the panel to an XGA QA-2500 and have emailed ISI to ask them to keep one reserved if they get a few in. If anyone is selling a Sharp QA-2500 please send me a private message.
Thanks ppl
cya, |
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| woneill |
Hi Mycamel,
Awesome original idea!!! :cool: :cool: :cool:
I was thinking that something like 1mm aluminium sheeting would be robust enough to hold its shape once formed, but ductile enough that it could be "forced" using blunt implements (and a small hammer - hammers are always fun) :) to conform to the curve of the dome.
The petals would overlap each other to some extent, and a solution as crazy as pot-riveting near the exit apeture might be good enough to hold them together in place without disrupting the output beam too much (the rivets would probably need to be applied from inside the reflector). The holes could be drilled through the reflector petals while they are still on the mold.
Even a crude and simple arrangement such as this would be better than most of the existing reflectors out there, and once polished, would probably be equal to many of the stage-lighting ones.
If nothing else, it would dramatically increase the amount of usable light from the big 400W MH bulbs.
Bill. |
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| woneill |
Mycamel,
Your foil idea is definitely a good alternative, though! High-temperature epoxy would be your best bet - it is what is used by the Xenon car headlamp manufacturers to glue the base to the bulb.
I don't know what the heat characteristics of normal epoxy are, but I too would be wary of superglue - it contains cyanide compounds. Not good!!!
Bill. |
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| jco9w |
For those of you who would like to use multiple lamps to get more light: Couldn't we setup the lamps behind a fresnel that would catch almost all their light, and focus it, and then at the focal point, we could put a diffusing lense (I am sure this isn't the right word, but I don't know the name of it), like the ones in the Elmos HP A305's, and 3M 9550 OHP's. For those of you who haven't seen these diffuser lenses, these lenses are real thick and go right in front of the bulbs in these projectors. This technique would conentrate relatively diffuse light, and then diffuse it out onto another fresnel, and the LCD panel.
Lamps Fresnel Diffuser Fresnel LCD Objective
} |
} | ) | LCD ()(
} |
This should allow you to use multiple light sources without hotspotting, I think.....
An update on my work: I got a fresnel, a diffuser lens and an objective lens from Inventory Solutions on Friday. I now have everything I need to build the projector. The objective I got has a variable focal length, you just rotate the mount to change the focus. This means I woun't have to have a moving part to the front of my box, which is a key!
Current parts:
Nview MediaPro LCD panel
4 1/2 in elliposidal downlight reflector
diffuser lens from Elmo HP A305
triplet objective lens from Elmo HP A305
fresnel from Elmo HP A305
400 Watt MH BT 28 bulb with MultiTap M59 ballast
My setup will be very similar to Marlakar's, but hopefully smaller!
J |
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| jco9w |
I was at Advance autoparts the other day, and noticed that they have chrome tape. It is very shiny tape, that could be used as part of a reflector, I think.
they also had aluminum tape, but not as shiny.
If you get a good mold, you could just use this tape? Not sure how well it would stand up to heat, though.
J |
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| Mitch |
| Where did Redevil Go? I`d like to find out more about his projector. If he`s getting a really good image, then ignoring his ideas would be really dumb... |
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| xblocker |
Concerning new ideas of reflectors: You guys should do a google search for 'solar cooker'. There are a lot of reflectors out there...!
Well, if they are good enough for optical instruments is another question, but it's worth a look!
xblocker |
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| mycamel |
| quote: | Originally posted by woneill
Even a crude and simple arrangement such as this would be better than most of the existing reflectors out there |
I guess the only real reason for pursuing our own reflector is to allow us to try optimizing the light from the 'cheap' 400w MH bulbs.
Got another question, but being that its reflector oriented, I'll take it over to the reflector thread. |
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| Redevil |
Hey Mitch
Just got back from trip.
Use a magnifying lens at end of bulb.
Using only 640x480 LCD panel.
Image looks perfectly good all around.
Make sure to build heat sink around ballast, gets hot.
Fan the bulb.
Then your good to go.
Later |
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| Undream |
My latest creation. $8 and 3 hours.
I havent mounted the bulb permanently in it yet. But, its going to be easy. Plastic planter and a plastic bowl, purchased at Walmart for $1.97 and $.50, respectively. I also havent done any testing with it yet (havent even hooked up the bulb.
But, it looks very promising. |
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| Undream |
couple more pics.
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| Mitch |
Redevil,
I have some questions about your particular design.
How long is the entire structure? What is the distance between the two fresnal lenses you use for light dispersion?
Also, what size is your LCD? I want to use a 14", but I have a 3 7/8" plano convexlens that was made for a Mitsubishi projection tv. Do you think that`ll be big enough to "suck in" the entire image of the 14", or will I need a bigger one?
Mitch |
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| Biglurchy |
| quote: | Originally posted by mycamel
Any adhesive experts among us? What sort of heat does super-glue handle? Would it start producing toxic fumes after we'd been watching our TV a while? Are there any epoxies made for automotive repair that could handle the heat? |
A good heat resistent epoxy solution would be JBweld, it has been used in many automotive applications including use on the egine block. How much heat it can stand exactly I'm not sure.
I'm almost certain superglue would break down past 120 degrees fahrenheit . Also doesn't seem like it would bond well to foil. JBweld will bond to most anything.
I work for a tool store and have access to a huge resorce of knowlege, coming from experts in all aspects of hardware related fields. Feel free ask any questions such as the "quote" above, and I'll do my absolute best to get the answers you need.
You guys have been a great help in my own project (still on paper), and would like to contribute as much as possible. |
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| amblix1 |
| can anyone find the specs of an Eiki LC 300 for me??? A friend wants to sell it for $200 working, but if I can get better looking building one I would rather do that |
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| Redevil |
Mitch
First you need to square off the light by using a metal box.
Use a piece of cardboard at each end of lens to see how the light pattern is turning out. This is also a good way to determine distance. Your panel will work, but will need a 400watt MH for
brighter image (bigger panel). The lens you have will work, but then you will need alot more distance from Plano to screen.
I got mine (5 7/8" Diameter Plano convex Lens) for 8 bucks at
the surplus shed. The total length of my projector is about 42"
long, but hey I dont care, you should see my 90" TV.
Perfect clarity on all four corners, no centre hot spots, and this is on a white bed sheet. My friends freak out on this.
Later |
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| eebasist |
amblix1
It looks like it is an older video only projector. Not a bad unit, but remember that the bulbs on these are expensive, i believe it uses a MH that costs 289.00 at bulbman.com so factor that into the cost and decide if its worth it to you |
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| amblix1 |
| quote: | Originally posted by eebasist
amblix1
It looks like it is an older video only projector. Not a bad unit, but remember that the bulbs on these are expensive, i believe it uses a MH that costs 289.00 at bulbman.com so factor that into the cost and decide if its worth it to you |
thats one part I dont like, I saw a screenshot and it looks very promising though. Whats the life expectancy on those bulbs do you know? Also do most commercial projectors have Zoom so I dont have to keep moving the projector going from 16:9 to 4:3, I want my screen to be 16:9 because as furniture it looks much better. Also with an OHP setup how do you do this? Just move the OHP back and forth? |
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| eebasist |
| with an OHP you move the whole system since its not a zoom lens. Not all commercial projectors have zoom, most of the cheaper ones obviously dont. The 160watt MH in the Eiki i believe is rated for either 1000 or 2000 hours, so you never really know how much life is really left on it. Although you could try and put a different MH bulb in there with a replacement ballast, but again it adds into the cost, if you want something to watch a couple hours a week and just throw away then 200$ is a good deal, but if you want this for long term viewing, it might not be as good a deal |
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| Mitch |
Redevil,
Thanks for your help. Drawing up those diagrams was above and beyond.
There are a few more things I had questions about. How big is your 2.5x magnifier? Is this a page magnifier sheet, or a round lens?
I just looked at the surplus shed and they didn`t seem to have any 5 7/8" PCX lenses. But they did have a 4 1/2 with a 12" FL. So I`ll proabbly get that.
I think I`m going to use two smaller MH lights instead of one big one. This might help with the light dispersion, plus I`m using a pretty big screen.
One other thing. On your diagram, your projector isn`t entirely in a box. Is this how it really is or did you draw it like that for "educational purposes"?
Oh yeah, just out of curiousity, how would you compare your projector to a regular tv?
Mitch |
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| theartoflife |
Hey all,
I'm new and didn't have time to go through the entire 1 and II threads, I hope this hasn't been covered already.
The start of Thread 1 talked about using LED's to light the projector. Using a convex refractive telescope mirror with the LED's in a doughnut shape would make a very bright light. This is the same format used in the desert to make plasma furnaces.
This could also work with regular bulbs.
After starting in the first thread on this topic I was stunned to see 184 pages. Maybe I can take a month off work and catch up so I can start building one of these. :) It would be great to have a summary of whats been covered so far.
-Steve |
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| Mario007 |
Mitch
I wouldn't reccomend using two small metal halides. Simply
because two ballasts,two bulbs,two reflectors. It's quite a bit more money and construction then a single bulb. For light dispersion use a fresnel before your lcd and a dispersion lens right after your light source.
ANYONE
We need a pinout for a sharp projection cable. Please checkout the thread: Panel Paranoia! VGA cable -» need help . Thanks |
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| Mitch |
Mario007
By dispersion lens do you mean like a magnifier. Cause when I searched for "dispersion lens", it gave me some sucky results. No place where I could actually buy one.
Mitch |
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| Mario007 |
| Yah I'm not sure of the techinical name of the lens. It's a bubble shaped lens. It helps disperse light which helped with my image that had a hotspot even with a fresenel. Check out Marklar's awsome website he used a lens like I"m talking about. |
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| Redevil |
Use only one MH bulb. A 400watt 4k-5.5k would be fine for you.
With two bulbs, you may end up with double image.
Only one point source is needed.
Thats why my reflector is made of sheet metal.
Before I tried a chrome reflector, and that ended up causing hot spots. The sheet metal gave me the chance to combine the back reflector spot with the front lens spot and not to overshoot the original spot.
The lens after the bulb is a round glass lens that is 4 1/2 inch
in diameter (it is curved on both sides). Your lens after the panel,
your plano, will work fine. It will need a longer distance, so you may whant to use first surface mirrors. And guess what I just
experimented with today. You know the stuff that they use on
cars, the mirror type material . The one that you see yourself on
one side, and the other right throught. Well I took my brothers
back windshield from his truck, it has that mirror stuff.
And there you go. It worked really good as a firs surface mirror.
My MH bulb is in a metal box, with the other box attached.
The rest has a dark towel over it for know. The picture is better then my friends 52" TV. I can see the lenticular lines on it, and whats worse, the line doubler causes alot of distortion. Jagged edges.
If you live in Canada or close to Sault Ste. Marie Michigan
come on down and take a look at it. It will blow your mind. |
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| daveb |
Ladies and Gentlemen, I've taken the plunge, and I'm sort of treading water, sort of drowning.
I've been hanging out here since April, and have followed these threads all through. I've been inspired by the successes. So I've gone ahead with a design of my own. It's a bit different than the others, but not too unorthodox.
I built a frame out of 1/2" threaded rod, and cut 15" x 16? plywood rectangles drilled through at the corners. I can mount these "shelves" at variable heights for complete control over distances.
So I've put the light on the bottom. Above it is the Fresnal, and ontop of that is the LCD. Above that is the lens and mirror assembly.
What do I get? An image that's about as bright as the one I started with before I gutted the 6 year old LDC Projector from which the panel comes. And that's about 200 lumens worth. Dim, dim, dim.
I think there's something fundamentally wrong with the configuration, but before I start fiddling with everything, I thought I'd ask them that may know for some suggestions.
Please see the photo attached. If more clarity is requried, I can profide more pix quickly. ( I took the one here about 20 minutes ago).
I feel like I'm so close, yet so far.
dave. |
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| daveb |
| This diagram of the tv room is the desired end state. The projector doesn't have to be pretty, because it'll be behind the back wall of the home-theatre. |
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| Redevil |
Daveb
Move the coffee can closer to the bulb.
Put a glass magnifying lens over the bulb (4 1/2" Diamater, 2.5x magnification). Mount the lens on a piece of sheet metal.
Leave 1/8" gap between glass lens and bulb.
Then move your panel higher, and stick another fresnel lens (or page magnifier) in between. Play with the added fresnel and panel til the light covers all for sides of your LCD.
Heat rises on these bulbs, put cooling fan on it.
Try the fresnel both (line side up or down) ways til image is good. |
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| Mitch |
Redevil,
With your design, is it possible to get your projector within a couple feet of the projector and still get a 4' x 3' picture? This is with scootin the lens backward or foward some, of course.
Also where is your fan located at? Are you blowing it directly on the bulb or do you have it behind the reflector somewhere?
i`m probably going to put a couple of fans back there. Probably one directly on top of the box, facing the bulb. Which poses another question. If I get the fan to close to the bulb, will the fan overheat?
I want to put another behind the reflector pulling the air out....or is that what you were using the heat sink is for?....
Mitch |
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| Justinjay |
Dispersion lens....
More commonly know as an aspherical condenser lens.
I got the lens marklar is using from surplus shed, it is called a Melles Groit Aspherical Condenser lens
It looks like a PCX but it is slightly (but unnoticeably convex on the flatter side)
I am giving up on my reflector I think. It does not concentrate enough light into the dispersion lens.
The results were OK, it was a little brighter than my original OHP (old 3M model), the image was uniformly lit.
But we are talking 1000w metal halide! I was expecting it to be much more brighter, but it isn't!
So, that being said, I am now upgrading to a Dukane 4500 (not very fancy, but much better than my antique 3M projector). The Dukane 4500 is designed for use of an LCD panel.
Once I find a better reflector, I will probably modify the lightsystem again; I don't want to leave a 1000w MH system lying around to long.
----------------------------------------
Hip hip hurray to Marklar for stumbleing into a nice reflector and having everything turn out perfectly. |
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| Gunawan W |
Redevil,
May I know, what is the purpose using 2 fresnel panel on your setup?
Is it to reduce focal length?
IMO, it's better placing the LCD panel between 2 fresnel panel, because in there the light beam is parallel.
It can be achieved if you placed light source at focal length of first fresnel, distance between 2 fresnel panel doesn't matter (close is better), but placed second fresnel panel close to LCD panel (arround 1").
daveb,
I think the big problem is your reflector, if you can find good reflector, it will increase your light output 50% or more.
Second, try to adjust your fresnel panel up and down until produce light spot as big as your lens diameter.
third, placed the LCD panel really close to Fresnel panel.
fourth, build enclosure for your setup, make sure light spreading from the lamp below fresnel panel doesn't mix with light beam above the fresnel.
fifth, adjust your objective lens up and down until you get focused projected image on the screen.
sixth, with 400 W MH lamp should produce enough light, maybe something wrong with your LCD panel.
Good luck. |
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| the whinner |
enyone tried to use light pipe?
here is the article about it from this site:
http://www.extremetech.com/article2/0,3973,18971,00.asp
since i know you will not read it, here is the quote also:
"The optics in a projector are used to channel the light from the lamp to the imaging engine and then to the screen, maintaining as much efficiency and accuracy as possible.
This task starts right with the lamp, with the elliptical reflector that is built around the lamp itself. As the demand for smaller and less-expensive projectors grows, the reflectors also need to be smaller. The smaller gaps offered by the UHP lamps make it possible to use much smaller (and lighter) reflectors on the lamps.
Another optical task is to concentrate and steer the light from the reflector to the imaging engine. This is also an opportunity to mix the light so that it strikes the imaging engine more uniformly. The light from most lamps will be brighter in the center, gradually diminishing as you move farther from the center. On a rectangular screen, the differences can be noticeable by the time the image gets to the corners.
One way to resolve this problem is to use a series of microlenses to integrate the light from the lamp and create a rectangular beam. Another interesting solution is to focus the beam from the lamp on the end of a rectangular rod. This rod may be constructed of polished glass or quartz, or its internal surfaces may be surrounded by highly-reflective mirrors. The light rays bounce multiple times within this light pipe, and emerge from the end as a uniform light beam with a rectangular shape.
Note the left curve is the cross section of the light levels entering the light pipe, and the right curve shows light levels leaving the pipe. " |
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| jco9w |
Hi--
I got started putting all my stuff togther this weekend, and ran into a problem last night. I have my setup exactly the same as Marlkar's: A 4 1/2 in. ellipsoidal down light, a OHP condenser lens (sorry for calling it a diffuser before, thanks JunstinJay for the correction), a OHP fresnel, a nview mediapro LCD, an OHP objective, a 400 W MH bulb, and a M59 ballast.
I checked out my downlight, by making the hole in the bottom bigger and sticking my 400 watt metal-halide bulb in it. Just like Marlkar I was able to burn carboard, it really focuses the light! So I figured if I put the OHP condenser in I would be good to go. HOwever the OHP condenser was a little different looking than Marlkar's or for that matter the ones I have seen on the 3M 9550 OHP's at work. The condensers I have seen are normally very thick glass, and exactly the way JustinJay described them. This lens was pretty thin. However, Inventory solutions sent it to me and told me it was in front of the lamp in a ELMO OHP, so I tried it out.
Well after putting it all together I found that in the middle of my image I had a dark spot, and that depending on where I put my objective the dark spot would resolve. Finally I took out the objective and the LCD and fresnel, and just looked at the light coming out of my "condenser" lens. I held up a white piece of paper in front of the light, and guess what? If I move the paper to the right distance I can read off the MH BT28 on the top of the bulb, on the white paper! The "condenser" lens was focusing an image of the bulb onto my paper! This is obviously not what I want, I want an even stream of light, with no image in it.
So today I ordered a condenser (same one as JustinJay) from Surplus Shed. I hope, that this is the problem, that this thicker lens will defocus the image of the bulb completely. Does anyone have any ideas of any other problem it could be?
Remember before putting in the condenser I get the exact same behavior from my reflector as Marlkar, burning through carboard...
I thought I was almost there. If anyone thinks it is something besides the condenser, let me know, but I took everything out of the optical path, one by one, and the condenser seemed to be the culprit of the spot (actually the image of my bulb) on my image.
J |
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| Mario007 |
| Yes I am too having your problem. I took a condenser lens and put it into my setup and then I was able to focus a picture of the bulb burning. While fun for a few minutes it is not good for projection. My condenser came out of a old beseler overhead projector like incadesent lamp old. |
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| Redevil |
Mitch
With my design it is not possible to get a large image at a close
distance. This is because my LCD panel is 10" Diagonal.
But if you can get a bigger Plano convex lens, say 12" then your in luck. I also tried two page magnifiers for the end lens (panel to screen, and it wasnt to bad (better with glass though). If you can get 2 glass frenel lens's with the lenticular line being fine (more lines per inch) the you should be good to go. Make sure that the
lenticular/ fresnel's are perfectly in line.
My MH bulb is in a metal box, and the reflector or any other shinny
stuff does not heat up. Therefore my job was to get the heat from
the bulb itself out. The only thing that I am doing is to have those
12Volt computer case fans (three of them) blowing air into the bottom of my metal box and a hole on top for out.
The heat sink is for my ballast (it getts hot). I have 2 pieces of aluminium about 12"x12" with heat sink compound on it and bolted the ballast between the two sheets. |
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| Redevil |
Gunawan W
The 2 lenses is to make the bright spot bigger, keep the light
square and parellel. Shorter distance.
It works great for me. I tried the reflector thing. If your using an
LCD panel use this method. Put a half curved reflector on the back
side. Make sure it is not mirror material, or it will creat another
beam or two. Use semi reflective material. I used one of those
stove pipe tubes or dryer vent ones. Something like that. |
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| Mitch |
Redevil,
Are your two fresnal light magnifiers glass or plastic? If they are plastic, it seems that they would get to hot and melt.....maybe not. I don`t know too much about them and what they can take.
Do you have any idea if they even make a 12" PCX? I`ve looked but I have seen any.
Mitch |
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| icculus |
| just curious if anyone is using a condenser lens other than the melles griot lens at surplusshed. |
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| Mitch |
Hey,
Me again. Maybe this is old news, but check out this link. It tells you, if you know how far away you want your projector to be to the screen, which lens to get. Look carefully at step two. It also says to use an achromatic lens instead of a PCX. (those aren`t the same thing are they?)
Theres some good stuff here.
http://www.vinci.it/Nuova%20cartell...or%20Design.htm
big link. Hope it works for ya |
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| Mitch |
Hmmm. i`m not so sure about that site. It says that if I want to set the projector 375mm (15") away from the screen, then I need a lens with a 18mm fl. Thats with a 20x magnification. Does that sound right to you guys?
Then I would need a huge projector lens to be able to see all of my 14" LCD...right? This is getting a bit more complicated. |
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| Redevil |
Mitch
The first lens after the bulb is glass.
The 2 page magnifiers or fresnel lens are plastic. Bought them
at Staples in Canada. I think you have a Home Depo there.
My setup runs horizonal. Any extra heat developed goes straight up. They do not get hot. All the heat is traped into the metal box housing and the heat is removed by the 3 fans. My LCD panel
is always cool, not ever warm. Left it on for three days straight,
panel still cool.
As far as the lens after the LCD panel, look into lenses used
for light shows. They may be 9 or 12 inches round. If you have no luck try putting 2 plano convex lenses (4"ones) 1 or 2 inches
apart in a home made rolled tube. |
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| Mitch |
Thanks Redevil,
I think I may have found something that is useful. I have learned that a Double Concave lens will take single light beam and throw it out at a gazillion different directions. (Towards the LCD, of course)
So heres my plan now.
After the Metal halide bulb I will put a single glass 4-7/16" condensor lens. A few inches after that a 3-1/2" dbl concave diverging lens. This will spread all the light out to the 2 following fresnal lens. After the last fresnal lens will be my LCD.
Now heres the cool part. I am going to size my 14" 1024 x 740 resolution LCD down to a 10" with the control buttons on the front of the monitor. This makes an amazing picture.
Then I will place a 6" PCX lens with a 14" FL in front of the LCD as the projection lens.
That sounds pretty good to me if I can get that lighting design to work good. Whadaya think about that?
Mitch |
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| Redevil |
Way to go Mitch
I think you have seen the light.
Thats what I think my glass lens is, it curves out on both sides
and expands the light. Try it with the condenser lens.
That sounds like a good idea, but I never tried that.
Keep on trying and dont give up. Once you are done, you will be so thrilled withe the results. People will start freaking when they
see it, and will want you to make one for them. A year ago I started with the 100"TV thing, moved on to better and better.
And now to perfect.
Be sure to have the fresnel in the right order. Makes a big difference. if you forgot look back.
Keep me posted
Good Luck
Later |
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| Mario007 |
| Mitch do yourself a favor and go to a store and checkout all the 14 inch lcd panels. Find one that allows image resizing try it out and make the image 10". Notice the tremendous distortion. Why shrink it down? It'll also let less light through then if you had the full 14" for the image. |
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| Mitch |
Mario007,
I wasn`t aware that it caused distortion when you shrunk it. If what you say is true, then that kinda suks. I know that when you shrink a regular monitor the picture remains bright and clear. However, I realize regular monitors are totally different than LCD`s.
Do you know this for a fact or is it more of a speculation...?
The reason I want to shrink the picture to 10" is so my 6" PCX will get the whole picture and it won`t be as much screen to pick up. Whereas if I leave it 14", the edges might not look so good with only a 6" PCX.
Thanks for the warning, though. I`ll make sure and check it out.
Redevil,
do you have a convex or concave dispersion lens. I think you said earlier that you had a double convex for the lens closest to your bulb. I might be mistaken.
What I found out tonight is that a double concave (both sides curve inward) does it really well. I don`t know if a convex works just the same.
But if yours works really good, then who cares, ya know?
It`ll be awhile before I start building mine cause I am in the middle of finishing out our attic where i`m going to put this thing. But after I get it finished I will definitely take pics and post them on here. |
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| Mario007 |
| I've played with the viewsonic vg150 and it distorted a lot. Use a projection panel as those are mainly 10" panels. I have never understood why excatly you want to use only 10" that is what I'm confused about. |
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| Mitch |
Like I said before. I`m afraid that if the screen is a full 14", my 6" PCX won`t pick up the full picture. Or else it might leave the edges kinda blurry since its not a big lens. See what I`m saying?
Do you think 1440 x 234 resolution would be good enough to be projected. Its one of those little 7" seat-rest LCD for cars. I`m looking more towards this anyway because of (1). They are cheaper. (2). They would be small enough for my 6"pcx. (3)My box wouldn`t have to be 19" wide. (4). I wouldn`t have to buy one of those expensive VGA to RCA adapters.
But, if this lens WILL pick up the entire picture, I would be willing to spend a bit more money to get a better picture |
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| jco9w |
Hi all,
Well I figured out my problem with the light bulb image being focused onto the LCd. As I suspected, it was my condenser lens. I grabbed a condenser from a 3M 9550 OHP, and popped it in my setup, and there was no lamp image. Moral of the story, make sure you get a good condenser lens.
Now, however I still can't get a bright image of my LCD screen from corner to corner. The focal point of the fresnel seems to be only about 6 inches past the LCD (measured by putting a white piece of paper in front of the LCD):
Lamp Fresnel LCD FOCAL POINt
} | || X
I thought it should be more like 12 inches past, that would make sense for an overhead projector. Because the focal point is so close to the LCD, the objective lens I have won't focus the image. When I move the objective further out, it focuses the image, but then it is dim, because a lot of the light cone is missing the objective lens. Does anyone know what is going on here? Do I have my Fresnel to close to the light source, does that matter at all? By all rights the focal point of the Fresnel should be about 12 inches, since it was from an OHP (well, 12 inches give or take).
Anyone know what is going on here?
At least I figured out the condenser lens problem
:)
J |
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| thelaw |
Is or has anyone used tubular metal halide lamps? the type that are in industrial fixings?
I am attempting to retrofit my existing quartz-halogen OHP with something brighter and longer lasting and these tubular lamps are the only thing that will fit in between the condenser on this particular ohp.
These things are damn huge in length and give off around 40,000 lm.
One more thing, is it possible to get hold of 400 watt double ended metal halide lamps? if so, please please point me in the right direction.
cheers, |
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| Gunawan W |
jco9w,Mario007,
distance between lamp spark/filament to the lens (convex / positive) must be smaller than it's focal length to get dispersion effect. Bigger than fl. it's start to collimate light.
Redevil,
with your setup, there are wasted beam of light after leaving the fresnel (see attached dwg1), because it's parallel beam, not collimated beam.
You don't need distance between 2 fresnel panel, you can put it close together to get parallel beam, just place the panel at 1 focal length distance to the lamp-spark/filament. (the 2 panel now act as single panel with new focal length=half of original fl. of single panel).
With drawing 2 setup, no wasted light, because all light beam goes to the objective lens.
Mitch,
please have a look at my spreadsheet at my website, it's explaining how to calculate lens, distance etc.
Rule of thumb, you need lens with diameter 1/3 of diagonal size of the LCD panel, to get whole image to be projected.
To get your setup work as your plan, you need to know the focal length and placing distance toward the lamp of condenser lens and concave lens, please do calculation before buying lenses to avoid useless lenses afterthat.
Actually to disperse light you can use either convex or concave lens, it depends on the distance of the lens toward the lamp.
jco9w,
if your fresnel fl.=12", then if your lamp at 12" behind the fresnel, you get parallel beam, Move the lamp further away, it's start to condense until the light beam covered your objective lens. |
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| Mario007 |
| Hey mitch you were wanting a 10" panel? Almost all projection panels are 10". If you want high res you can get a 1024*768 panel for about 200$ if you look hard. Projection panel is specifically designed for projection.Where as a desktop panel you can have serious problems with moving the driver board out of the way. Only thing I don't like is the contrast ratios of projection panels 150:1 where many desktop panels have twice that. Do whatever you want to do but if you read some of the posts in the first diy video projector thread you will hear some pretty bad stories of people killing their panels. |
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| jco9w |
Gunawan W,
So if my Fresnel's focal length is 12 inches, do I want the lamp 12 inches from the fresnel or the condenser lens 12 inches from the fresnel?
See I am confused because I have the Marlkar setup, with the lamp inside an ellipsoidal reflector, which has the light converging at a small spot (the burning carboard test proves this), then I have a condenser lens in front of that spot. From there a circle of diffused, but bright light comes out. Now I have to put my Fresnel/LCD combo at a point where that circle (which expands as you move away from the condenser) is as big as the LCD.
The point is that I don't have too much of a choice where I put the Frensel/LCD, however the spot where the circle is just big enough happens to be at least 12 inches away, but I still get the light converging through the frensel on the other side at about 6 inches away.
I will just have to play with this once I get my condenser lens.
J |
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| xblocker |
jco9w,
i don't understand your setup completely. Are you using an elliptical reflector AND a fresnel? How large is this reflector?
If it is able to generate a descending light cone, which 1. transmits complete panel and 2. has it's second focal point at the plane, where objective lens is, then you should not need a further condensor (fresnel).
If the reflector is smallel than LCD, an elliptical reflector doesn't work! Then it's better to have a spherical one, which doubles the filament brightness and as condensor(s) use the fresnel(s). You have to move then the lightsource until the light cone has it's smallest spot at objectiv's plane.
xblocker |
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| woneill |
Hi Xblocker,
I think the theory behind jco9w's design is that unlike the spherical arrangement that loses much light, the elliptical reflector captures MOST of the light from the bulb, and focusses it onto a single point - the new effective point source of light.
A condenser lens (?) is being used to diverge the light from this point source into a much wider cone of light than would be natural from the reflector alone - allowing the fresnel + LCD operate as expected.
The issues here involve the natural angle of divergence of the light coming from the reflector; the angle of divergence resulting from the condenser; the focal length of the fresnels; and the focal length of the objective.
jco9w,
I would suggest that if you are using OHP optics, then you should mimic the original OHP dimensions as much as possible: i.e. you want the divergence of the light coming from your reflector/condenser combination to be as close as possible to the original OHP as possible such that with the LCD panel fully and evenly illuminated, the rays hitting the fresnel can be traced back to an effective point source of light exactly where the fresnel's focal point would be.
If you are using a convex condenser, then you should check to see if you are merely reducing the divergence from the reflector, or converging it so much that you are actually re-focussing it through a new point. A concave lens might be better for this task if the light from your reflector is diverging too slowly. As mentioned the rays should be diverging at an angle equivalent to a point source placed at the fresnel's focal point.
Bill.
P.S. I'd draw a diagram but I can't draw... |
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| xblocker |
woneill,
i'm not sure if the setup you described make things better!
The new point light source, which is generated by the elliptical reflector isn't a real point light source, it's an image of the real source. Reflected lightrays pass this point and diverge again under the the same angle as they come. If i understand right, a concav lens should amplify this divergence and the light should go the usual way to fresnel -- LCD--...?
But what's with the direct light from the bulb? It's wasted and will add more scattering light to the whole arrangement! I think the lighting concept of OHPs which is made for large imaging areas is not easy to beat, and you have the advantage of using direct and reflected light together with a small spherical reflector, doubling bulb's filament. Efficiency of elliptical reflectors is no question, but IMHO only if they are used as primary condensors!
xblocker |
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| Redevil |
Gunawan W
I tried with the 2 fresnel lens an inch apart.
The resulst were blury in the corners.
Almost like having a round TV.
Then I also tried setup #2 and found that when I go to focus the
image, I can see the fresnel lines on the screen.
By puting it behind the LCD caused me to project the LCD image first, before seeing the lines on the fresnel.
As for as wasted light, Im only using a 250watt 4K MH bulb and
getting a very bright, clear and no distorted image.
And the room lighting does not need to be pitch black.
I have the lights on in the back of the room and the picture still looks good.
I did this on a trial and error basis, went throught what you guys
went throught, and after alot of confusion got it to work
beyond belief. |
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| woneill |
Hi Xblocker,
An image of the real source that acts as if it is a point source, and contains most of the energy from the original point source is actually hard to beat - it is a very efficient, directional, virtual bulb.
If the elliptical reflector is any good then all the light from the bulb will be projected through the point source image in the direction of the screen. If the divergence of the light from this image equates to the divergence expected by the fresnels then focussing the fresnels on this image is perfect - much more light than any other method.
Otherwise the rays from the projected image should be diverged to give the same angle as an OHP would do.
The other OHP optics could stay as normal except they take their input from this efficient virtual bulb instead of an inefficient normal one.
Also, in most elliptical arrangements, the bulb is fitted longitudinally so that most of the light is emitted along the transverse axis and focussed by the reflector into the point source image.
Compared to the spherical arrangement that loses most of the available light from the bulb, any light that does get directly through the front of the reflector will be negligible. (A small lens could be also placed in front of a transverse bulb to focus this light too - discussed in the other reflector thread.)
If you really wanted to be fussy, a diaphragm should be used at the focal point of the elliptical reflector to remove any off-axis light. The end result will still be much more efficient.
Bill. |
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| woneill |
Hi Redevil,
Well done - all successes are good.
When you put the fresnel after the screen, did you try it both ways around? Fresnels are directional - usually (but not always) they will only work with the rough side facing the LCD.
The trick is to get the fresnel as close to the LCD as is possible without getting the Moire lines from the fresnel interacting with the LCD.
If you have a laptop or LCD monitor, then that serves as a good way to test this out. Literally put the fresnel as close to the LCD as possible without getting the moire effect, and place your eye at the focal point. You should be able to see the screen being magnified and undistorted. If your eye is too close to the panel, you will not see the corners. If it is too far then you will see massive distortion. Fresnels as well as being directional have a very narrow viewing angle - your eye (the simulated objective lens) needs to be placed within a very narrow range of positions. The idea is to have the fresnel and objective matched so that they can interact to focus a reasonable sized image at a reasonable distance... (OHP optics are already matched to work this way.)
The correct fresnel orientation should collect most of the light from the panel - including the corners. If it didn't do this then something fundamental was going wrong - either the fresnel was the wrong way around, or the objective lens was too close to the LCD/fresnel, and was literally only getting light from the center of the light cone.
Bill. |
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| Redevil |
woneill
You are correct. The fresnel lens must be in one direction only.
In my case I do have the lines facing the panel on the back side
and yes it is close as possible. I removed the glass plate and replaced it with the fresnel. It was a ***** to cut the fresnel but I
managed. My image is so good that you can see the actual TFT
thin film transistor. This is at 640X480. My avermedia box, wich I use to interface the panel has the option to give me 800x600.
But to get that it uses a scan doubler (horizontal scan x 2)
It looks like **** in that mode. The image is so clear that I can
see the jagged edges when motion is viewd. But I will be hooking
in my computer soon. Cant wait. This panel can handel 1024x768.
When HDTV comes out I'll be ready.
Later |
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| Mitch |
Redevil,
What screen are you using? I mean what is the brand and the size?
Mitch |
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| Redevil |
Mitch
Right now Im using a white bed sheet. Couple of wrinkles.
Im doing the rear screen thing, and need to knock a wall down.
But I already have the screen material (Grey). I unrolled it, held it
in front of my projector and the image on the other side is good
in image and contrast (little less brighter). Make sure image is projected on dull side. The side you watch TV on is shinny. This prevents the light from going into the stuff behind.
The sreen needs to be streched over a square frame.
It is I think 52"H and 64"W
Later
http://www.rosco-ca.com/products/sc...oscoscreen.html |
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| Mitch |
i`m sorry, I meant what type of LCD are you using? The brand and size (in inches)?
Mitch |
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| jco9w |
HI-
Since there seems to be some confusion about my setup, I will elaborate. I have a MH lamp enclosed in an elliptical reflector. The reflector makes the light from the lamp converge to a point. At that point I need to put a condenser lens. This lens makes the light diverge in a cone. The rate of divergence, is I believe the problem. This rate of divergence of the condenser must correspond to the fresnel I am using, so that I get the light condensing through the fresnel and LCD to a point where the focal length of my objective can focus the light.
Schematically
reflector fresnel LCD objective
( | || }
woneil, I agree that I should match an OHP as much as possible, however I don't have the original OHP to look at. I realize that I must match the condenser to the fresnel to the objective, and I guess that is my problem. I think that my fresnel/LCd has to be closer to my reflector, however, the condenser must make the cone of light expand fast enought to encompass my LCD or I will get uneven illumination. Therefore there is some miniumum length that my fresnel/LCd must be from the condenser. This minimum length dicatates the focal length of the fresnel, and hence the focal length of my objective. The problem I am having is that they don't match each other.
I can't do much testing until I get my new condenser from surplus shed, so I won't be able to do too much till then. However, I do want to say that I think a elliptical reflector will help, NO MATTER WHAT THE SIZE! I will image your bulb light to a small point, which you can use as a point source. It is very efficent as woniel says.
Anyway I will keep in touch, and try and get some pictures tomorrow.
J |
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| Mitch |
hey, I gotta question. On those LCD screens that you can buy that don`t have a covering over them, they have two wires sticking out. One is red and the other is yellow.
Does anybody know what those are for? Are they for splicing a RCA cable to it. Cause its says they are made for DVD, TV, Cars, ETC.
Thanks,
Mitch |
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| Mario007 |
| Can you post a link or tell us more about the panel you are talking about? |
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| Mario007 |
| Mitch I hate to break it to you. But those look a lot like laptop panels and the fact that they are linking you to www.earthlcd.com is not a good sign. It looks to me like they are selling laptop lcds and making it look like they are specially designed for cars. |
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| noodles |
Hey everybody! It's been a while since I came here.
Anybody selling a cheap panel? If I can't get one, then I'll just go back to my computer hardware phase... then come back every month to check up on things. :D
I still have my nView Spectra with power adapter sitting here. I'm thinking it's a bad cord cuz the one I have now has a male/female adapter on it (for some reason, all the ones on eBay have the same thing. I figure they got the wrong cable too, so they're trying to ditch it. Coincedence?) Still going For $20 + shipping. Unless somebody's nice enough to find me a male VGA to female EGA cable. |
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| Mitch |
| okeedokee. Thanks for the info. Your probably right. |
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| tech head |
I think I have finaly figured out why some people can get a good image and some can't.
Everything must match...
The light source must sit at the focal point of the first fresnal and it must iluminate the entire lens.
next the panel
next another fresnal
and finaly the objective lens.
The hard part is, the second fresnal lens creates a larger virtual image of the lcd. The objective lens must have a focal length that is equal to or greater than the diagnal of the virtual lcd but is also large enough to catch the entire light cone from the second fresnal.
Now for #s
light => fresnal 12"
panel as close as possible to first fresnal
panel => second fresnal 1"
second fresnal=> objective 12"
assuming 12" fl on both fresnals and 13" fl on the objective lens.
I am going to buy the rest of the parts I need this weekend and see if it works.
Wish me luck
Joe |
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| Undream |
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| jco9w |
Undream, tech head,
I totally agree. You have to match ALL the optics up. Marlakar was partially lucky, and partially smart. Using all the stuff from a single OHP was smart, he was lucky to have all that stuff :)
There are 3 condensers available at Surpuls shed, two have similar f #'s, and one is much faster. I ordered the Melles Groit one, and will check that out.
I found this website which is partially useful for those of use trying the Marlkar method, but mixing and matching optics:
http://www.cairnweb.com/tech/tech_lamp1.html
This site is talking about a Xenon lamp, but the principles are the same. It explains why with no condenser you get a donut beam (which I get). It then at least partially explains how the focal lengths must match up.
J |
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