| Justinjay |
I have a reflector idea...
Hello everyone. I have spent about a month now gathering parts to build a projector (reflector included).
It seems that one problem people are having here is finding a decent reflector to focus all of the light from giant metal halide bulbs to a small point (BT-28's and BT-37's (what I have)). People are resorting to sheet metal and glueing little mirrors ect..
All of our problems would be solved if we all had a reflector like Marklar's! I have checked with my lighting supplier, and yes, custom ordering this reflector alone would be expense, about $80.
I talked to a customer service representative from seattle lighting, and he said he had a reflector in his garage he would give me for free. So I drove to his house and picked it up. Here it is:
The problem is that it is just too small for a BT-37 lamp (I have a 1000w). It can burn cardboard, but not all of the light is concentrated to a small point. I have tested the projected image, also this reflector leaves a dark spot in the middle of the screen due to the arc tube construction. (Yes, convex lens mounted to the front)
I was thinking... There are many mixing bowls out there. A lot of them have mirror like finishes. Some of them are deep and shaped like maklar's reflector.
Of course, these bowls are probably not deep enough, this picture is just to give you an idea of the reflectiveness.
Yes, MIXING BOWLS might be the answer! We might have to look hard to find the right size and shape, but this might work.
robv60 originally brought up this idea in the IRC. I just wanted to make it known.
Please tell me what you guys think. PLEASE, I am desparate for a good reflector! |
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| Justinjay |
| Woneill what do you think about this? |
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| remp |
Justinjay
I searched all open forums and found three posts regarding mixing bowls that you might find useful.
In the bar at the top click search.
In search page change the radio button from show as threads to show as posts. Type in mixing bowl
Undream I think found a very suitable bowl for $5
Hope this helps. |
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| Justinjay |
| sorry I havn't figured out how to search yet. Now I know |
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| Justinjay |
Would be nice if I could buy this bowl separaty without the mixer. Looks about the right shape!
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| woneill |
Hi Justinjay,
What a cool and interesting idea!!!
While the bowls don't look like pure parabolas, or ellipses, the MH bulbs are not point sources either...
I'm sure it would be worth it to many of us to try these cheap bowls out by taking a MH bulb, holding it inside the bowl, and seeing if it can be positioned to give the desired light pattern. As you found out, an even illumination (with no rings or hotspots) is a must, while a parallel, or focussed beam, or hybrid output can be manipulated one way or another... ;)
It can't be much worse than many of the reflectors being used successfully today, and is probably a lot better!!! (Of course, the insides will need to be polished...)
I must ask you, however: 1000W???
:eek: :eek: :eek:
Are you planning on getting a sun-tan while you watch your films/football???
:cool: :cool: :cool:
Bill. |
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| Justinjay |
No. I read that the arc of a metal halide lamp produces little UV, and besides, ordinary glass (like the outer envelope on the bulb) are opaque to the ultra-violet.
BTW, I got much better results with the reflector now. I cut it so the bulb can fit deeper into the reflector. Also, I found out that my convex lens was not at the focal point.
Basically I am trying to copy Marklar's design, but make it a vertical projector.
1000w Metal Halide is VERY VERY bright and hotter too. The concetrated light burns carboard much like the sun does with a magnifying lens.
Sunglasses are a must have when working with these bulbs!
I would say it is about as hot as my original OHP bulb which was 600watts. Not bad for effieciency. |
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| woneill |
Hi Justin,
I was actually joking about the suntan thing - you are right about the UV.
My worry with the 1000W bulbs, though, is twofold:
1) The heat you mention needs to be blocked from the LCD. For something so powerful, look at cold mirror options, or an IR blocking filter - a film was identified by mycamel (I think) in the other thread that blocks/reflects 85% of the IR, while transmitting 85% of the visible light.
2) You might reach a point where your panel is operating outside of its design parameters, and literally cannot block out enough of the light to give you a good dark black and a high contrast ratio for the screen size you choose.
This is the reason why they talk about contrast ratios when they give projector parameters. Ideally, you want the blacks to be black, and the whites to be white. Poor brightness gives you black blacks, but grey, dim whites. To much brightness with poor contrast gives you white whites, but washed-out grey instead of black.
Nobody here has suffered from this problem yet, but if you couple a 1000W bulb with a really good reflector, you will definitely be outside of the envelope compared to the people here.
I DO hope it works for you though! You might have the answer we have all been waiting for!
Hmmm... Thinking about it, if your lamp was too bright, you might still be able to do something really cool: Xblocker identified a commercial projector that uses parallel beams of light and TWO LCD panels to achieve a high contrast ratio. If you could get your beams REALLY parallel, then the light lost through the second LCD (if properly aligned) would be much less than in the first panel, but your contrast ratio would be massive - comparable to the commercial units of today...
It just keeps on getting more interesting...
Bill. |
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| icculus |
| i actually work with one of those mixers( or pretty close). the bowl has abig dimple in the bottom. and it's pretty difficult to get an extra one from kitchenaid. definitelt not parabolic |
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| woneill |
Icculus,
In any of these bowls, the bottom would probably need to be removed with some kind of cutter for actual use so that the MH bulb could be fed in. For testing, it would probably suffice to position the bulb the "wrong end in," just to see of the beam profile would be useful.
The thing about the profile is that while a Parabolic profile would be ideal, the bulbs themselves are usually not. Thus, it becomes a question of compromise, and the biggest thing that seems to be compromised here at the moment is the brightness of the image due to inefficiencies in both the reflectors and the panels.
The panels are a topic on their own, but if we can get a reflector that, when working with the real-world MH bulbs, gives us an output beam that allows us, in some way or other, to use MOST of the light produced, and not just a small percentage, then we will have made much progress.
This is very much a "suck it and see" exercise in many cases, and for the prices on some of the bowls, it could turn out very worthwhile. Or, it could come to nothing. In which case a few of us will have some extra cheap aluminium mixing bowls with polished insides... ;)
You never know...
Bill. |
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| Justinjay |
I was chatting with Marklar in IRC last night, and I found out that he is using a condenser lens after his reflector to spread the light out onto the LCD.
I changed my mind. My reflector will probably work quite well. It concentrates all of the light to a small point and burns a hole in cardboard. It's just my convex lens is not the right type. I need a condenser lens instead of a projection lens from an OHP. I found one on surplus shed that looks exactly like the lens of Marklar's.
Anyway, yeah he showed me a picture of his lens. It looks exactly like this one:
I liked the look of these kitchenaid bowls becuase they are the same shape as his reflector.
Acually you can find some on ebay. Type in "mixer bowl" instead of mixing bowl.
This one is a little expensive, but looks like it would work:
http://cgi.ebay.com/ws/eBayISAPI.dl...item=2038920500
These bowls are advertised as having a polished interior and are mirror reflective. If you go this route make sure that you don't get a "brushed steel interior" becuase it is not shiny at all.
Some new bowls are pretty darn shiny!
I am basically trying to copy his design as far as the reflector and condenser lens goes.
BTW, I would rather have problems with the projector being too bright than being too dim. It seems everyone is having the latter problem |
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| woneill |
Definitely - being too bright is a problem everybody would like...
Just make sure you are not too hot...
Bill. |
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| gaff |
Bill,
That seems like it is exactly what I was looking for, except you already bought it.:D
I've seem some similar ones online so tell me how it works out.
Gaff |
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| woneill |
Hi gaff,
The only reason I bought it was because nobody else seemed interested, and they DO say that they have more...
Send them an email and see what they say. If you can't get one from them, then since I blocked you, you can have mine for what it costs me. Currently I'm at $10 plus shipping, and waiting for them to contact me with the shipping costs...
What really interested me is that they quote the normal retail price for these things at $22. At this price, if they work, it is not really worth using anything else.
The prime reason I ordered one was to see what they are made of, and if, for $22 they are worth pursueing as the new standard; maybe we can all have a beast like Marklar and Justin. From the protograph, it looks like they are made of the same cold reflectors that the OHP bulbs use...
I personally am looking for a really cool parabolic rather than elliptic, because I want to experiment with a more parallel beam, a 100W bulb, and two panels for the contrast...
Bill. |
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| gaff |
Bill,
Thanks for the offer but I think I will save you the trouble. I have seen Altman "Super" Reflector Kits that are supposed to work in the 360Q's also for around $30. My main concern about the reflector is the diameter. I have a 400W Metal Halide bulb and don't know if the reflector will be big enough. It looks like I will definitely have to make the base hole bigger to fit the bulb through though.
Gaff |
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| Justinjay |
Did I show you this picture yet?
I think my reflector will work quite well.
Also, the size of the BT-37 lamp I have does not really matter because the light is all focused to that small point.
*cough cough** If I hold the carboard up to the reflector long enough it will catch on fire!
I consructed a light-holder and a sheet metal cover for the front of it with an opening in it about half the size of the reflector's opening. (seems to help concetrate more of the light to the point)
Now I am waiting for that condenser lens I ordered from surplus shed to arrive, I hope it does a good job of spreading that light out onto the LCD.
So much for the mixing bowl idea for me. This reflector was a pretty good deal at $0.
In case you are wondering it comes from a HALO recessed HPS lighting fixture (not sure of the model #)
Anyway I can't wait to see the final results! |
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| woneill |
Hi Justin,
Wow!!! :eek:
Make sure you get a GOOD IR blocker. We don't want to see pictures of your LCD panel looking like that - they are very sensitive creatures...
Bill. |
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| Justinjay |
I heard that low-e film is available at any hardware store such as Home-Depot or lowes.
Will this stuff work? It is designed to be put on windows.
Or will I have to buy special glass?
I'll have to pick some up on my next trip to the harware store when I pick up some black laminate for the project.
This project has been going very fast for me, thanks to the DIY projector thread!
Also I have a design like Marklar's to follow.
I would say my projector will be finished in less than a month |
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| woneill |
Justin,
Try this from the main thread (II):
| quote: |
Posted by mycamel on 07-09-2002 08:04 PM:
Lightbulb Heat reflection film
While trying to figure out how to keep my panel cool, I ran into this. Its a film used for stage lighting in high power lights to kill most of the heat while allowing most of the light to pass. Cost looks to be $20 for 1 square foot.
http://www.premier-lighting.com/sal...t.htm#screenout
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Bill. |
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| Justinjay |
Bad link, Woneill.
Could this be the forum trying to shorten the link?
Try it without the ..... My browser puts that in the URL |
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| mycamel |
I've ordered one of those ellipsoidal reflectors too, but the 'buy it now' price went up to $11. It appears to be exactly the same as the one in the Leko I got yesterday. The relector is just too small to be used with the large 400w MH, so I guess I'll be buying one of the smaller 400w MH bulbs so I can get the light source into the focal point. The smaller ones seem to be identical to the larger ones but with a smaller envelope and correspondingly shorter expected life.
FYI - The Leko is set up with an adjustable holder so the bulb can be moved into optimal position within the reflector. Then the whole bulb housing can be slid within the lens housing to position the bulb and reflector with respect to the output lens. After analyzing it, I've decided to sell it rather than try modifying and using for my projector. |
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| mycamel |
I received a sheet of this stuff Friday. Its very thick and nearly clear, with little optical distortion. I held it in front of my monitor and noticed only a slight grayish tint. As you might expect, one side is labeled to face toward the bulb.
I haven't tried really using it yet, as I'm still trying to settle on a bulb and reflector combination. Should work great though, as its designed to be used with much hotter lights than I'll be using! |
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| woneill |
| Excellent!!! :D :D :D |
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| Gunawan W |
When we talk about point source light, actually we don't need big reflector too, ideal is just slightly bigger than point source light itself.
Together with direct light beam, the reflector will spread another half of the light beam (undirect) and must cover the whole fresnel panel in front of the lamp to produce near perfect parallel light beam, am I right?
Someone said, I forgot the name, that half sphere can be used to produce parallel light beam, with placing the light source at 1/2 of the sphere radius? Is it true? If it works then why we use parabolic reflector? Since half sphere is much easier to make than parabolic to get the same result (parallel light beam). |
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| woneill |
Hi Gunawan,
With a point source, if you are only going to use a tiny percentage of the light emitted by the bulb, then the reflector doesn't need to be very big. In the classic point source thing, only a small amount of light from the bulb goes in the direction of the screen.
You get higher uniformity that way, but at an overall reduced light level. If you use shorter focal-length fresnels, then you can use a bigger solid angle of the light from the bulb, but then the uniformity suffers big time with the intensity fall-off tending towards 1/r^2 where r is measured from the center of the screen. Also, the fresnels aren't as good at the shorter focal lengths...
As for the parallel beam, if the radius of the sphere is BIG compared to the width of the beam - then yes, the output of a spherical reflector will approximate to a parallel beam. The reason is that the base of a parabola approximates very close to a spherical surface very close to its axis.
The problem with using a spherical reflector is that you get spherical abberation - exactly the same as with a lens. This is why the a lens generally works "ideally" if its radius of curvature is much bigger than its diameter...
Thus, you can use spherical reflectors very nicely in telescopes if the radius of the sphere is MUCH bigger than the radius of the mirror.
Otherwise, we would all be using soccer balls and tinfoil to generate pure parallel reflectors...
Bill. |
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| HokieTT |
| What's the word on that reflector from eBay? I'm still trying to find a reflector solution, and my local lighting store is dragging its feet trying to get me a Markar-type downlight reflector. If the eBay one's big enough for the 400W MH, I'll try that. |
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| woneill |
Still waiting...
I'm working offsite, and it is supposed to be delivered to the office. I'll maybe get it on Friday. |
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| mycamel |
| quote: | Originally posted by HokieTT
If the eBay one's big enough for the 400W MH, I'll try that. |
Like Bill, I bought a couple of those to play with too. Based on dimensions given on eBay, they appear to be the same size as the one in the Leko I bought earlier – about 6” at the top with 3/4” opening. I tried a ‘dry-fit’ of the top of my larger 400 MH bulb into that reflector and found that I couldn’t get the light source in deep enough to reach the focal point. The reflector fit almost like a cap on the top of the bulb, directly in contact with the glass. I immediately remembered undream’s experience with the aluminum foil and the fried bulb!
I’m hoping it’ll work out with a smaller MH bulb. I bought one of the smaller envelope Phillips 400w MH’s from Home Depot, and when I receive the reflectors from KayeLights (eBay seller - http://www.kayelights.com/) intend to try modifying the bulb opening to allow the base to fit through. If I can get part of the light source into the focal point with some (at least 1/4”?) of air space between the glass and reflector, I’d be willing to try it with some forced-air cooling. |
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| HokieTT |
| I'm a tad confused about the bulb sizes. I do remember when I got my bulb at Home Depot, they had 2 sizes...a HUGE one and a smaller, but still very large, one. I bought the smaller one. Now, my question is, which one are you referring to with your tests? Did you find a third, 'baby-sized' buld? Or did you start out with the monster one and are now progressing to the one I had? Mine cost $31, I believe. The huge one was much cheaper...under $20, I think. Thanks. |
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| mycamel |
| quote: | Originally posted by HokieTT
Did you find a third, 'baby-sized' buld? Or did you start out with the monster one and are now progressing to the one I had? |
I wish there was a smaller 400w MH for about the same money. If anyone finds one, be sure to post please!
Yes, I started with the monster and that's the one that will not work with the small reflectors I'm referring to. |
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| HokieTT |
Okay guys, I'm at the end of my rope, reflector-wise.
My projector project (pun alert!) has been at a virtual standstill for 4-5 weeks now. The parabolic reflector I got from Edmund Optics just didn't cut it. I've had my heart set on trying an Ellipsoidal reflector (Marklar-type), but I just got screwed over by my local lighting company. They made me wait almost 3 weeks to finally tell me they hadn't done any looking into my situation and frankly didn't have any desire to. This after I printed out and brought in spec sheets and photos of the reflector, and talked for a while with the salesman about what I was looking for and the substitutes I would accept.
So basically, if no one can find a suitable reflector available for purchase online, I'm going to have to give up this project. I can't proceed any further without a reflector. I can't believe no one has found anything suitable yet.
Any help? |
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| woneill |
Hi Guys,
Back from the field... I picked up my reflector this morning, and as expected, it is too small for one of the 400W monster MH bulbs.
Its focal point is too close to its base, and the hole at the back is only 3/4" diameter. :(
It is definitely interesting, though. I can't figure out whether it is made of aluminium or aluminised plastic. I think, aluminium.
I will probably use it anyway, because I tend to prefer the smaller HMI/HQI Metal Halide bulb variants, and for these, it is perfect. They cost more than the big ones, but they are much smaller and easier to use efficiently.
Has anybody tried the idea posted earlier about using a cardboard/chipboard elliptical cut-out to "lathe" a wet plaster/clay block into a suitably elliptical dome that could be used as a base to form an elliptical reflector from aluminium foil/sheeting?
I think the idea was ingenious, because once the curves and shape is set (and the plaster/clay dry), it would be easy enough to cut and wrap a suitably sized 1mm thick aluminium sheet into a high quality reflector that would be more than accurate enough for the needs of the project.
Bill. |
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| bixs |
woneill;
I to purchased one of these reflectors. I agree it is too small for standard MH bulbs. I've been doing research on possible bulb alternatives and have found something that might work. The following links are to a 400W T-15 or T-17 MH bulb. For those who don't the "T" stands for tubular and the number (15 or 17) stands for the diameter of the bulb envelope in 1/8th's of an inch.
http://www.eyelighting.com/mhconversioncleanace.html
http://www.hellolights.com/400wat65iw.html
There are several great things about this bulb compared to standard MH bulbs.
1. Smaller size. It's approximately 2" in dia. and about 9" long.
2. Color temp of 6500k compared to 3000k-4000k.
3. CRI of 90 compared to 65.
4. Will run on a standard M59 MH ballast or a H33 MV ballast.
The manufacture's web site states that it should only be run on the H33 ballast, but every other reference I've seen says that it will run on either ballast. This bulb is quite popular for reef aquarium lighting. A quick Google search for "Iwasaki metal halide" should confirm this if anyones concerned.
The downsides are slightly less luminous output and a rated life of "only" 9000 hrs:).
I think this bulb should work with the reflector because the filament in the original bulb is oriented along the projection axis as will be this bulb.
I plan on enlarging the hole in the bottom of the reflector with 2 1/4" hole saw. This will allow adjustment of the bulb within the reflector to obtain an optimum output beam.
I've ordered the bulb and will post back with results as time permits.
Patrick |
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| Mitch |
Hey guys,
Why couldn`t you just build a sqaure rack and put bulbs all the way around the rack and in the middle to have an ( pretty much)evenly distributed light. Then stick it right behind the LCD. Of course you`ll need a lexan lens or something...
I don`t know much about this project yet so this might be a stupid idea...
Mitch |
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| woneill |
Mitch,
There is still debate on this topic in the main thread. I personally subscribe to this model being viable using 10/12 MR11 halogens with built-in spot reflectors and narrow beams.
The problem here is that the halogens operate at a lower colour temperature than the pure-white MH bulbs, and generate more heat per lumen.
The good side is that they are easier and cheaper to connect up than the MH bulbs - no ballast required - and allow for a much more compact light unit than the MH monsters. Also, our eyes/brains adjust much more effectively than people seem to think to changes in colour temperature, and the effects would not be very noticeable...
The trick here in these forums is to explore ALL ideas and contribute as a whole to as many different strategies as possible. That way, everybody's understanding increases, and the chances are, we will get more breakthroughs.
Bill. |
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| Mitch |
ok,
So has anybody tried this yet? If I was to build this square frame and put lights all around it, then stick a Lexan lens between the lights and LCD screen to keep the heat away from the LCD, it seems to me that this would give me an evenly distributed light.
I don`t have all my stuff to start this project yet or else I`d be contributing ideas out the wazoo! So please don`t think I`m trying to wiezel out of experimentin`.
Mitch |
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| mycamel |
Found these formulae in a patent (5,765,934) describing orthogonal parabolic reflectors:
Y=2{f(f+X)}.sup.1/2 where -f.ltoreq.X.ltoreq.0 Eq. (1)
Y=2{f(f-X)}.sup.1/2 where 0.ltoreq.X.ltoreq.f Eq. (2)
where f is a focal length of the paraboloid located on X-axis of a coordinate (X, Y);
I barely understand parabolic math! Anyone understand this one?
FYI - That same patent has some very interesting ideas which seem to apply directly to what we're trying to do with our reflectors - make non-point-source light behave as if it is. One thing which caught my attention was the use of optical fibers. Here's an excerpt:
The optical performance of a projection type display using a light valve greatly depends on the illumination optical system that illuminates the light valve, particularly the characteristics of the light source. Liquid crystal projectors use a light source such as a tungsten halogen lamp, metal halide lamp, and xenon lamp. These light sources are not an ideal spot light source, while the light emitted from a non-ideal light source is condensed by a reflecting mirror such as a parabolic mirror, elliptic mirror, and spherical mirror that have a substantially ideal shape. As a result, the image projected on the screen is not uniform. Manufacturing variations of the lamps are also a source of significant differences in efficiency, color temperature, and useful life of the lamp. Such differences cause non-uniformity in brightness and color of the projected image, deteriorating the quality of the projected image.
In order to solve the aforementioned problems, Japanese Patent Preliminary Publication No. 4-204883 discloses a liquid crystal projector using optical fibers. FIG. 11 shows a general construction of the prior art light source apparatus for the liquid crystal projector.
An illumination system is constructed of a metal halide lamp 11 and reflector 12, and the light emitted from the system is condensed by a lens 14a. The light is then incident upon a bundle 16 of optical fibers to which connectors 165 and 166 are connected. The bundle 16 of optical fibers includes a plurality of element optical fibers, and the arrangement of the element optical fibers at the end at which the light is incident are not correlated at all with the arrangement of the element optical fibers at the end at which the light is emitted. This ensures that light having uniform distribution of intensity throughout the overall light pattern is emitted from the light-emitting end of the bundle 16 even if the intensity of light at the light-incident end of the bundle 16 is non-uniform. The light is diverged by a lens 14b before illuminating a liquid crystal panel 6 which has a condenser lens 14c and two polarizing plates 60 and 61. The output of the polarizing plate 61 then passes through a projection lens 8 to project an image onto the screen. The projected image with a uniform intensity is thus obtained.
My head hurts, but its a good sort of hurt... |
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| mycamel |
| Here's Fig. 11 referenced in the patent: |
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| Mitch |
Good stuff, mycamel,
The only thing I don`t understand is the optical fiber part. how are optical fibers going to be beneficial to the distribution of light? I must be reading it wrong...
Also, how big would you guess those lenses are they are using? 3 or 4 Inches?
mitch |
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| woneill |
Mitch,
The reason for the optical fibres is to increase uniformity in the light hitting the LCD.
The idea behind them is that the optical fibres receiving the light from a particular area do not all output into the same area of the LCD. They are mixed and moved around so that any hotspots coming out of the light module are distributed throuought the area of the LCD.
Bill. |
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| Mitch |
ok, I get that now. However, I`ve been searching all over the internet and I can`t find out what an optical fiber is or what it looks like. Care to share?
Mitch |
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| mycamel |
| quote: | Originally posted by Mitch
ok, I get that now. However, I`ve been searching all over the internet and I can`t find out what an optical fiber is or what it looks like. Care to share?
Mitch |
Here's some starter info. |
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| remp |
Optical fibre is a (usually) very thin strand of high quality optical glass surrounded by a sleeve of a material with a different index of refraction . Then a protective coating is applied to protect from mechanical damage The idea is light rays entering at one end travel the length of the fibre with very little attenuation. Many telephone long distance links are fibtre optic. A fiibre optic cable can carry thousands of times as much as comparable copper lines or coaxial cables. Many buildings have a fibre optic backbone cabling system for high speed computer/ communications. One of the many advantages of fibre optic cables is the fibre can be bent around a shallow radii and the light inside is not lost or disturbed.
It follows the curve with very little loss by a process known as total internal reflection.
An orthogonal parabolic reflector is not a parabolic reflector. It takes a line source of light for example a long halogen fillament or any other long type filament, collects the light and focuses that light to a point. It does not in itself give you parallel rays as a regular parabolic reflector does. The advantage is it is the only type of reflector that can focus a line source light. Other types of reflectors such as elliptical or parabolic require a point source for best results. There is information and drawings on a orthogonal reflector in the video projector part 1 thread. |
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| mycamel |
| quote: | Originally posted by remp
There is information and drawings on a orthogonal reflector in the video projector part 1 thread. |
I should've used the search function - Good stuff there. Thanks! |
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| Gunawan W |
Hi guys,
what about rectangular parabolic reflector?
It's easier to make. It can be made in same size with the LCD panel. |
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| woneill |
Hi Gunawan,
Such a reflector is only truly parabolic along the central axis of each face. As you move towards the corners, each face only has parabolic characteristics in one dimension. In the other dimension, the face is a flat plane - giving the output beam a "floodlight" characteristic..
If LCDs were more forgiving of viewing angle, and we were using a primary objective that was larger compared with the LCD, then it would be good enough. But, even with fresnels guiding the output beam, much of the light coming from the LCD would never reach the objective.
Bill. |
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| Mitch |
Wha-ho! So light is actually traveling inside this fiber until the other end? Thats nifty.
Thanks for the help, remp and mycamel. |
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| remp |
Hard to imagine one fibre so thin you can hardly see it can handle millions of phone calls all at once or deliver gigabytes of computer data at the speed of light.
And its a relatively simple DIY project if you have a need.
A fibre optic bundle is not the only way to even out light from an imperfect reflector. A short optic quality glass rod with square cut and polished ends is used in many situations where imperfectly distributed light has to be made perfectly even. From what I have read on the internet many 3 panel projector manufacturers use a glass rod for this purpose. Will find the details if anyone is interested. |
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| Mitch |
Hey, if somebody would draw up a more detailed diagram of just the fiber optic part of (fig 11) from page 3, that would be neato... cause it wasn`t very helpful to us who know next to nothing about fiber optics. I have been researching though and I am learning a little.
Mitch |
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| Justinjay |
It seems like this is the kind of reflector we would need.
I tried looking at the images at the US patent website for the projection display but my browser would not load the images.
Is an orthogonal parabolic reflector shaped differently than a regular parabolic reflector?
How come with Marklar's reflector the light is all concentrated to that small point? (Looks like an ellipsiodal)
My reflector can burn cardboard but is that enough?
I am feeling some vibes right now. Not all of the light is focused properly with my reflector, but light shines everywhere. (I feel only a portion of the light is being utilizes)
Seems hard to find the focal point of this light becuase it is not focused in an orderly fashion
It doesn't seem like finding an "orthagonal parabolic reflector" is an easy task, or finding any suitable reflector!
I feel something homebrew will never do. Well at least we can try anyway.
Sigh sigh sigh |
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| Justinjay |
Don't forget....
I ask a lot of questions so you will have to put up with me for now.
I will post anything I can to help out with DIY video projection
This video section of this web site is all about homemade lcd projectors
and it all started with one post!
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Hi,
If there is anybody out there that is interested in sharing ideas on DIY video projectors, please let me know. I have several sources for parts, info and theory. I'd like to network with others who'd like to try this or who has worked on this type of project in the past.
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Does 3251 replies to this topic answer your question?
:D :D :D |
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| Gunawan W |
Woneill,
I know rectangular-parabolic reflector is not perfect, but it's very easy to make compared with circular-parabolic reflector.
Even with perfect circular-parabolic reflector which can produce perfect parallel rays, it still have problem with direct rays from light source which it's not parallel rays (the rays spreading away).
BTW, I found site explaining: How to draw a parabolic curve without any knowledge of Mathematics, here:
http://www.cc.jyu.fi/~hvirtane/cooker/node8.html |
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| woneill |
Hi Gunawan,
If the bulb is mounted with the filament longitudinally, then most of the light will be emitted transverse to the filament - into the reflector and out of the front. See my **** picture. This way tends to reduce the amount of light coming out of the front of the reflector directly from the filament itself. Though it doesn't eliminate it.
This is actually the problem with the theory behing the ortho-parabolic reflector. Its design is not to collect and focus MOST of the light from the bulb: its design is to maximise the amount of light that CAN be focussed.
Thus, while you WILL get a point source of light, you will also waste probably 90% of the light from the bulb in getting it.
The best bet, if you want the purest point source of light, is to use an elliptical reflector to bring the light to a point(ish), and use a small diaphragm to mask off everything except the brightest center of that point. You will probably not loose much more than you would if you went for the ortho-parabolic, and an elliptical reflector is easier to make/find.
Having said all that, with the LCD diffusing the output, I STILL maintain that treating the LCD as a self contained light source that decouples the output optics from the lamp optics, and trying to get an even illumination across its back face with roughly parallel light is more important than striving for ultra high optical quality in the light source phase.
A rough point source plus two fresnels, or a rough parallel source plus a single fresnel (before or after the LCD, dependent on taste) should give the LCD a decent enough illumination. If the majority of the light that gets through the LCD is fed to the primary objective then a high quality image should result.
Different screens have different effects - one of my sharp panels (8" QA 1100) is almost opaque, while another (10" QA 1000) is almost transparent. My 8" Spectra C is somewhere in between, and my DOA 10.4" Proxima 822 behaves like a pure diffraction grating. The opaque Sharp panel benefits most from parallel rays and putting a large lens immediately after it (fresnels work here, but I have recently acquired an 8" diameter lens from an elliptical stage light - awesome...) The others seem to be easy enough to work with in either configuration.
I seem to be rambling - so I'll stop now...
Bill. |
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| woneill |
Hi Gunawan,
Interesting diagrams - I like them, but they hilight a problem with parabolic reflectors that I have been mulling around with for a while: both your and my diagrams show the removal the light coming directly from the filament at the center of the apparatus.
The end result is the opposite of a hotspot - a black hole right at the center of the beam...
Would it be worth sunbstuting a small convex lens for the little blocking mirror in your diagram? If its focal length were suitable, and its diameter small enough (<= the diameter of the bulb), it would only affect rays coming from the front of the bulb, and collimate them to the same degree as the rear main reflector. The glass of the bulb itself would destroy the coherence any rays reflected through it from behind, so not much would be lost here.
What do you think?
Bill. |
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| cowanrg |
there is only one thing you need to know about reflectors.
light ONLY reflects at 90 degree angles.
woneill, your picture is wrong. rays reflect at right angles when they hit a reflective surface. that reflector would end up focusing the light into a point out in front of the reflector.
i have some good tutorials and reading about these things on my site, which im working on getting back up. if anyone could help me out, i could have it up much sooner. email me if you are interested. |
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| woneill |
cowanrg,
Actually, no. The angle of incidence is equal to the angle of reflection for a plane mirror. (see diagram)
Try looking into a plane mirror at a shallow angle, and see if the image you see is from right angles to your angle of vision or not.
Bill. |
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| Piston |
While eating dinner the other night, it dawned on me that if I could find a reflector like the salad bowl in front of me, I might have a good reflector.
My wife is great, I just hope she still cookes for me after I steal her salad bowl....Still with me?
Does anyone know what it costs to have glass aluminized, like what astronomers use to build their home reflector telescopes, because that is what I intend to do...what do you think???
I tooled a piece of glass and sanded a hole through it using my dremel, this took me 2 hours for a 1/4 hole. I said no way I'm doing this to fit the mogul socket, so I went to the acetylen torch, and that worked great in 5 minutes.
I played around with what reflection standard green glass has and positioned a standard 100W bulb inside, the focal point seems right for the job.
So the only thing stopping me right now is:
1: How much would this coating cost
2: If my bowl is arcopale, does it still work?
3: If I break the bowl, does the wife divorce me...
<P> |
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| Gunawan W |
woneill,
is this what you mean? |
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| Piston |
| Gunawan the image above is also what I have in mind, however, I think that building a mask to the size of LCD would help reduce the difused beam around the lens. Use the mask as you lens mount also. |
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| xblocker |
Salad bowl!? Hmm, hmm..
Any reflecting coating only make sense, if the curvature of that piece has spherical, elliptical or parabolic shape or it won't work!
Reflectors follow to the laws of geometrical optics!
xblocker |
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| woneill |
Hi Gunawan,
That's exactly what I was thinking of!
Now all we need to do is find a way to levitate the lens into the right position... ;)
Bill. |
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| insolace |
i don't know if anyone has posted this or not, but i found a neat site for reflectors that may be of use. it has a chart listing it's sizes and focal points etc, but it also looks like they might do a custom job.
http://www.carleylamps.com/reflectors.htm#Aluminum Reflectors
-eryk |
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| tahustvedt |
I don't know if it's useful to you guys but I couldn't find any mention of this here so just in case...
Have you guys considered car headlight reflectors? There are quite a few different shapes and sizes to choose from. :)
Also, to make the insode of a bowl reflective you could use chrome spraypaint. It's quite reflective (hey, it's chrome).
Tor Arne |
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| ace3000_1 |
Hey ya i got one of those lol they work well.
Trev:) |
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