Re: Shadows, point source and projection.
If you used a fresnel between the light sources and the lcd panel, would it still create a "shadow"? I thought from reading here, the light would straighten out once it passes through the fresnel? Or am i deeply mistaken? 🙂
mycamel said:
If you used a fresnel between the light sources and the lcd panel, would it still create a "shadow"? I thought from reading here, the light would straighten out once it passes through the fresnel? Or am i deeply mistaken? 🙂
Hi Multiplexor,
The shadow is being caused by the LCD shutter on the surface of the fresnel.
The smaller the shadow, the less of the fresnel that is affecting the image, and hence, the less distortion to the overall picture. Ideally, you would have them flush, except then you get moire banding.
The problem with fresnels is the same as with any big lens - the bigger its surface, the more accurate that surface needs to be so that all light rays emanating from the same physical point get refracted to end up at the same point on the projected image.
With ANY big lens it gets difficult. It also gets difficult to reduce the focal length and maintain the lens size - again, the shorter the focal length, the higher quality the lens surface must be.
This is why most high powered magnifying glasses and lenses are either very small or very expensive.
The fresnel allows a very short focal length with a very wide aperture, but can only do this well if the light emenating from a point only gets refracted by a tiny localised part of the lens surface. In this way, the lens only needs to be made with the surface tolerances of a much smaller lens.
Bill.
The shadow is being caused by the LCD shutter on the surface of the fresnel.
The smaller the shadow, the less of the fresnel that is affecting the image, and hence, the less distortion to the overall picture. Ideally, you would have them flush, except then you get moire banding.
The problem with fresnels is the same as with any big lens - the bigger its surface, the more accurate that surface needs to be so that all light rays emanating from the same physical point get refracted to end up at the same point on the projected image.
With ANY big lens it gets difficult. It also gets difficult to reduce the focal length and maintain the lens size - again, the shorter the focal length, the higher quality the lens surface must be.
This is why most high powered magnifying glasses and lenses are either very small or very expensive.
The fresnel allows a very short focal length with a very wide aperture, but can only do this well if the light emenating from a point only gets refracted by a tiny localised part of the lens surface. In this way, the lens only needs to be made with the surface tolerances of a much smaller lens.
Bill.
Additional thoughts...
I would think of any convex lens (fresnel or otherwise) reducing the divergence of the light from a given point, rather than straightening it out.
In magnifier mode (light source closer than the focal point), the lens does not have the power to reduce the divergence so much that the rays re-converge at a new image. Instead, they simply diverge less, creating the impression to a viewer that they are coming from an object further away than the real light source.
In projector mode (light source further than the focal point), the lens is able to converge the diverging rays so that they all meet up at a single point in space. This point is the conjugate image of the original light source, and corresponds to the projected image. This is all focussing is: you move the objective lens until the diverging rays emerging from the LCD surface are re-converged at the screen.
This is one of the reasons a bigger objective increases brightness - more of the diverging light actually goes through the lens and gets refracted (converged) back to the same point on the image.
Regarding my point in an earlier post about parallel rays: they do not need focussing to produce an image. Thus, you could hold an LCD panel above the ground so that the sun shines down through it, and if it is a sunny day and the LCD does not cause too much divergence than you should see the shadows of the LCD shutters on the ground.
The more divergence, the closer you need to be to the ground before the shadows overlap each other and begin to reduce contrast. Too much overlap, and the contrast reduces to zero. Hence, closer is better...
Bill.
I would think of any convex lens (fresnel or otherwise) reducing the divergence of the light from a given point, rather than straightening it out.
In magnifier mode (light source closer than the focal point), the lens does not have the power to reduce the divergence so much that the rays re-converge at a new image. Instead, they simply diverge less, creating the impression to a viewer that they are coming from an object further away than the real light source.
In projector mode (light source further than the focal point), the lens is able to converge the diverging rays so that they all meet up at a single point in space. This point is the conjugate image of the original light source, and corresponds to the projected image. This is all focussing is: you move the objective lens until the diverging rays emerging from the LCD surface are re-converged at the screen.
This is one of the reasons a bigger objective increases brightness - more of the diverging light actually goes through the lens and gets refracted (converged) back to the same point on the image.
Regarding my point in an earlier post about parallel rays: they do not need focussing to produce an image. Thus, you could hold an LCD panel above the ground so that the sun shines down through it, and if it is a sunny day and the LCD does not cause too much divergence than you should see the shadows of the LCD shutters on the ground.
The more divergence, the closer you need to be to the ground before the shadows overlap each other and begin to reduce contrast. Too much overlap, and the contrast reduces to zero. Hence, closer is better...
Bill.
Gunawan,
i still haven't tried a 2. fresnel, cause i first had to change the distance between lamp and the 1. fresnel to get a rough parallel beam out. The lamp adjustment of my normal OHP only allow a small range of up and down. I hesitate of modifying it cause i probably will sell it. I've got a brandnew 3 panel projector from ebay which is miles ahead from my OHP setup. 800 ANSI, 120w UHP lamp, SVGA, over 90% illumination uniformity, zoom lens, it's great!
But i'm still interested into the questions discussed here, cause i wanna know, how things work!!
xblocker
i still haven't tried a 2. fresnel, cause i first had to change the distance between lamp and the 1. fresnel to get a rough parallel beam out. The lamp adjustment of my normal OHP only allow a small range of up and down. I hesitate of modifying it cause i probably will sell it. I've got a brandnew 3 panel projector from ebay which is miles ahead from my OHP setup. 800 ANSI, 120w UHP lamp, SVGA, over 90% illumination uniformity, zoom lens, it's great!
But i'm still interested into the questions discussed here, cause i wanna know, how things work!!
xblocker
hey u guys
ive been testing and its not going so well (ill tell you later tonight why)
i made a reflective light tunnel (it helped out ) but directs heat to lcd.
one very important queston i need answered. will the lcd work with out the front polarizer?
i might test that out cause of two reasons. #1 cause my lcd is almost shoot. #2 cause i want a way higher res. lcd.
talk to you later.😀 😀 😀 😀
ive been testing and its not going so well (ill tell you later tonight why)
i made a reflective light tunnel (it helped out ) but directs heat to lcd.
one very important queston i need answered. will the lcd work with out the front polarizer?
i might test that out cause of two reasons. #1 cause my lcd is almost shoot. #2 cause i want a way higher res. lcd.
talk to you later.😀 😀 😀 😀
xblocker
It sounds like you went the way of the tech head.
I still follow the thread and post every now and again but I am enjoying teh projector I bought on ebay.
I'm still working on building one but it has taken back seat to my hovercraft.
Joe
It sounds like you went the way of the tech head.
I still follow the thread and post every now and again but I am enjoying teh projector I bought on ebay.
I'm still working on building one but it has taken back seat to my hovercraft.
Joe
woneill,
for a further clarification, is it that what you mean? Two options here:
1. point light source (forgot spherical reflector)
2. several roughly parallel light sources
The gaps between light sources on #2 could be a problem!
tech head,
i knew the time would come....!
greetings
xblocker
for a further clarification, is it that what you mean? Two options here:
1. point light source (forgot spherical reflector)
2. several roughly parallel light sources
The gaps between light sources on #2 could be a problem!
tech head,
i knew the time would come....!
greetings
xblocker
Attachments
Hi Xblocker,
For the first diagram, I would say yes - definitely.
For the second diagram, I would not use the fresnel between the light sources and the LCD because the light beams are already effectively parallel (assuming parabolic reflectors). Producing the parallel beam is what the first fresnel is for in the top diagram.
If the light sources are small, and they have SOME divergence to each beam, they could be arranged close enough together to avoid gaps in the illumination.
Hexagonal packing would maximise light density.
Bill.
For the first diagram, I would say yes - definitely.
For the second diagram, I would not use the fresnel between the light sources and the LCD because the light beams are already effectively parallel (assuming parabolic reflectors). Producing the parallel beam is what the first fresnel is for in the top diagram.
If the light sources are small, and they have SOME divergence to each beam, they could be arranged close enough together to avoid gaps in the illumination.
Hexagonal packing would maximise light density.
Bill.
Damn, i indeed forgot to remove the 1. fresnel on second drawing! Thanks for hint!
I suppose, most of the people would prefer the single light source setup, less wiring, lamps, ballasts...,and also a large IR-filter would be needed.
xblocker
I suppose, most of the people would prefer the single light source setup, less wiring, lamps, ballasts...,and also a large IR-filter would be needed.
xblocker
Hi Xblocker,
Definitely, a single MH/Xenon lamp is easier to setup than many of the same.
One of the things I was thinking about, though, is the size of the big 400W beasts that everybody is using. They require a big reflector which has been hard to find and harder to make.
(The recent investigations into replacement stage lighting reflectors might give interesting results: they seem to be selling at $20-$30 for a high power elliptical reflector.)
Multiple (physically) smaller bulbs might also be easier to harness efficiently, and if we can utilise more of their output with better reflectors, we might not need to consume as much power to get a decent output.
Then, there is always the possibility of arranging multiple little MR11/MR16 halogens into a bank. If they were connected in series like Christmas tree bulbs, they could be wired directly across the mains with a fuse and a series diode to give them the DC drive that they need (but only by someone who knows what they are doing...)
They are definitely not as efficient as the MH bulbs, but they can be bought cheaply with a narrow beam (11 degrees) which might actually be more efficient in feeding the screen than some of the big 400W MH variants. They would DEFINITELY need both a UV filter and a very good IR filter, though. But, compared with the 50 hours you get from a single OHP bulb, a bank of these, drawing equivalent power, but lasting 2000 - 3000 hours may be a cool alternative for many people.
They would also allow a much more compact overall projector size - possibly down to a cubic foot.
Bill.
Definitely, a single MH/Xenon lamp is easier to setup than many of the same.
One of the things I was thinking about, though, is the size of the big 400W beasts that everybody is using. They require a big reflector which has been hard to find and harder to make.
(The recent investigations into replacement stage lighting reflectors might give interesting results: they seem to be selling at $20-$30 for a high power elliptical reflector.)
Multiple (physically) smaller bulbs might also be easier to harness efficiently, and if we can utilise more of their output with better reflectors, we might not need to consume as much power to get a decent output.
Then, there is always the possibility of arranging multiple little MR11/MR16 halogens into a bank. If they were connected in series like Christmas tree bulbs, they could be wired directly across the mains with a fuse and a series diode to give them the DC drive that they need (but only by someone who knows what they are doing...)
They are definitely not as efficient as the MH bulbs, but they can be bought cheaply with a narrow beam (11 degrees) which might actually be more efficient in feeding the screen than some of the big 400W MH variants. They would DEFINITELY need both a UV filter and a very good IR filter, though. But, compared with the 50 hours you get from a single OHP bulb, a bank of these, drawing equivalent power, but lasting 2000 - 3000 hours may be a cool alternative for many people.
They would also allow a much more compact overall projector size - possibly down to a cubic foot.
Bill.
RE: lamps and reflectors
Perhaps these could be of some use?
http://www.lithonia.com/library/specsheets/Indoor_HID/GS.PDF
I'm lost as far as the specs go, but someone knowledgable might be able to shed some "light" on the matter ;-)
Perhaps these could be of some use?
http://www.lithonia.com/library/specsheets/Indoor_HID/GS.PDF
I'm lost as far as the specs go, but someone knowledgable might be able to shed some "light" on the matter ;-)
my fresnel idea didnt work. but i think its be cause the mirror reflector make it seem as if there is 40 of these lights stacked togetter. kinda like when your in a room with two mirrors, one on oppissit sides of the walls, you see 50 etc reflections of your self. so basicly my light wasnt going in a some what forward direction as i plan it and it didnt work. i still think it might work with a different reflector maybe made of sheet metal but i think i got a better idea.
some one i work with said to make a funel. i thought of it be for just like alot of people probbly have but im sure every body think it might be the end of there lcd(i figered thats why every body puts there light about a foot or so away from there lcd). well i did a funnel with sheet metal.there is still some big holes i loose alot of light from, because i threw it all to getter using my setup that ive been working and telling you guys about. well lets just say im getting closer. im planning on making a new reflector/ with a funel/ and a very good cooling system.im gona try my best to get you a picture tonight of the results"the projected movie"but that might not happen cause its midnight in ca right now,and i need to find two AA baterys for my cam. if not tomarrow night i will post a pic.
😀 😀 😀 😀
ps. "i think" the front polvarizer is to send the light forward on a lcd. i might be wrong. so maybe if i take it off then set my delta IV projection lens right on the lcd (my projection lens has to be very close or touching the lcd to project)to do the same job as the polvarizer, sending the light forward,projecting the light, and sence one polvarizer is gone i might be projecting alot more light through the lcd. but i think that might only work with my projection lens or a setup that can catch the light right at the lcd before it gets destorted picture projection. hey its just a theroy i might try it unless otherwise noted. i dont sujjest you guys try to try this im just need some advice. if this dosnt work im probbly out of a lcd for a while.cash has been a problem lately.
some one i work with said to make a funel. i thought of it be for just like alot of people probbly have but im sure every body think it might be the end of there lcd(i figered thats why every body puts there light about a foot or so away from there lcd). well i did a funnel with sheet metal.there is still some big holes i loose alot of light from, because i threw it all to getter using my setup that ive been working and telling you guys about. well lets just say im getting closer. im planning on making a new reflector/ with a funel/ and a very good cooling system.im gona try my best to get you a picture tonight of the results"the projected movie"but that might not happen cause its midnight in ca right now,and i need to find two AA baterys for my cam. if not tomarrow night i will post a pic.
😀 😀 😀 😀
ps. "i think" the front polvarizer is to send the light forward on a lcd. i might be wrong. so maybe if i take it off then set my delta IV projection lens right on the lcd (my projection lens has to be very close or touching the lcd to project)to do the same job as the polvarizer, sending the light forward,projecting the light, and sence one polvarizer is gone i might be projecting alot more light through the lcd. but i think that might only work with my projection lens or a setup that can catch the light right at the lcd before it gets destorted picture projection. hey its just a theroy i might try it unless otherwise noted. i dont sujjest you guys try to try this im just need some advice. if this dosnt work im probbly out of a lcd for a while.cash has been a problem lately.
i think some stage lights might also have glass frenel lenses to spot the light.a stage light is seems to me kinda a good idea .
#1. metal housing already done.
#2. reflector included.
#3. glass fresnel.
#4. maybe just needs some little modifying.
but right now im sticking to what i got.
no picture tonight, maybe tomarrow night. note my projector works out right now for video game and movie (when day seens are playing) due to brighter colors.some night seens in movie dont realy hit spot(alittle dim)
one part of my goal is to see the picture clearly with out having the bightness adjustment up(exsample of brightness over kill,see undreams result picture of his video game projection).no offence cause this **** is really hard long technical project. but im geussing if undream video game projection is bightness over kill,his movie projection is probbly worse.thats what ive notice with my projector.games and cartoons look better than movies projected. so go figger.
😀 😀 😀 😀
#1. metal housing already done.
#2. reflector included.
#3. glass fresnel.
#4. maybe just needs some little modifying.
but right now im sticking to what i got.
no picture tonight, maybe tomarrow night. note my projector works out right now for video game and movie (when day seens are playing) due to brighter colors.some night seens in movie dont realy hit spot(alittle dim)
one part of my goal is to see the picture clearly with out having the bightness adjustment up(exsample of brightness over kill,see undreams result picture of his video game projection).no offence cause this **** is really hard long technical project. but im geussing if undream video game projection is bightness over kill,his movie projection is probbly worse.thats what ive notice with my projector.games and cartoons look better than movies projected. so go figger.
😀 😀 😀 😀
biteon said:
I received the lens for the Strand fresnel light I'd ordered, and can tell you that the fresnel is only good for what it was intended for! The prisims (ridges) are very wide apart, and the backside of the lens has a pebble finish to disperse the light. Great for stage lighting, but not good if you're trying to send the rays in a particular direction like we are. Our good old page magnifiers are more appropriate for that.
The reflector for the fresnel light isn't going to work for me either. The focal point is about 1 inch, but the light source of the 400W MH is farther than that from the outer glass envelope. So you can't get the bulb's light source in close enough to let the reflector do its job properly.
My leko (ellipsoidal with lenses) is supposed to be delivered today. I'll play with it and let everyone know what I find.
what do you mean brightness overkill? Those pics that I posted were with default brightness/contrast settings on the dreamcast and Sharp QA1750 panel, I have never even touched the brightness/contrast controls at all. Maybe I should have, could possibly get a better image. heh.
undream
on your web page the "june 9 sucsess pictures"
im looking at the pictures of your projection when the room is pitch black. the up side down picture looks good and sharp other than the fresnel is kinda projecting the light on the lcd unevenly.i had that probblem when using to many frensel lenses and the mirror made it seem as if i had 50 mh bulb stacked togetter. if you look at the two taxi intro projected pictures at the bottom of the page you'll see this
#1. your black isnt pitch black, its kinda faded alittle.
#2. the white letters are so bright that there glarring white light beyond the letters.
brightness over kill
your projection should be easy to fix that problem if its not fixed allready.
i figger that because
#1. on june 9 you werent even using a reflector there fore you still can get way more light passing through which will probbly make your screen look more brightness over kill but still good cause then you can adjust the bightness etc. settings and have enough light to work with.
#2. fu*king around with the fresnel etc. or something to make the light spread evenly on the lcd might be a easy job to.
ive seen your reflector with the cooling sys. and i still think you should change that if you havent already. your fans are taking away very important parts of your reflector and reflection of your light. maybe it better if you set it up so the fans arent in the way of the reflected light and also not attached to your reflector where your have to cut holes in your reflector. might also help making your light more evenly spread out.
to night when i post my picture you guys are gonna see some probblem that im having.for instantance my lcd is a tad bit bigger than my projection lens so the edges fade to black. the two boards i use to keep the lcd polvarizers intact only allows direct light around the perimeter there fore making the edges alittle dimmer. but i cant realy do notting about it unless i get a smaller lcd. when i bought my lcd i didnt know what i know today, or else if i did id get a supper high res and high contrass smaller lcd maybe a 3"-4" to go with my crappy projection lens. also if any one has a delta IV projection lens and has a problem with it cut the corners of the lcd picture there is something you can do to help that just a little bit. if you open the lens setup you will see a paper circle that you can take out to help alittle bit(not much). no i dont no why the paper circle is there but there is probbly is a good reason.
tonight im gona take a picture of a movie (dark seen and a day seen) then a pictue of a video game from the ps1 or if my sister lets, ill use her ps2(it probbly has better graphics).?'s etc.
😀 😀 😀 😀
on your web page the "june 9 sucsess pictures"
im looking at the pictures of your projection when the room is pitch black. the up side down picture looks good and sharp other than the fresnel is kinda projecting the light on the lcd unevenly.i had that probblem when using to many frensel lenses and the mirror made it seem as if i had 50 mh bulb stacked togetter. if you look at the two taxi intro projected pictures at the bottom of the page you'll see this
#1. your black isnt pitch black, its kinda faded alittle.
#2. the white letters are so bright that there glarring white light beyond the letters.
brightness over kill
your projection should be easy to fix that problem if its not fixed allready.
i figger that because
#1. on june 9 you werent even using a reflector there fore you still can get way more light passing through which will probbly make your screen look more brightness over kill but still good cause then you can adjust the bightness etc. settings and have enough light to work with.
#2. fu*king around with the fresnel etc. or something to make the light spread evenly on the lcd might be a easy job to.
ive seen your reflector with the cooling sys. and i still think you should change that if you havent already. your fans are taking away very important parts of your reflector and reflection of your light. maybe it better if you set it up so the fans arent in the way of the reflected light and also not attached to your reflector where your have to cut holes in your reflector. might also help making your light more evenly spread out.
to night when i post my picture you guys are gonna see some probblem that im having.for instantance my lcd is a tad bit bigger than my projection lens so the edges fade to black. the two boards i use to keep the lcd polvarizers intact only allows direct light around the perimeter there fore making the edges alittle dimmer. but i cant realy do notting about it unless i get a smaller lcd. when i bought my lcd i didnt know what i know today, or else if i did id get a supper high res and high contrass smaller lcd maybe a 3"-4" to go with my crappy projection lens. also if any one has a delta IV projection lens and has a problem with it cut the corners of the lcd picture there is something you can do to help that just a little bit. if you open the lens setup you will see a paper circle that you can take out to help alittle bit(not much). no i dont no why the paper circle is there but there is probbly is a good reason.
tonight im gona take a picture of a movie (dark seen and a day seen) then a pictue of a video game from the ps1 or if my sister lets, ill use her ps2(it probbly has better graphics).?'s etc.
😀 😀 😀 😀
First surface mirror
Is $30.00 to much to pay for a piece of first surface mirror that is 8" X 10" ?
Please advise
ap0the0sis 😀
Is $30.00 to much to pay for a piece of first surface mirror that is 8" X 10" ?
Please advise
ap0the0sis 😀
undream or someone
draw me out a cut section of your lcd. i just want to see how its set in the plastic housing(chassy).conferm front to back.thanks.and ill show you the problem with my lcd with the two board fix i did.i think but not sure but we might have simular problems in that area(with the lcd housings dimming light at the perimeter of the lcd).
😀 😀 😀 😀
draw me out a cut section of your lcd. i just want to see how its set in the plastic housing(chassy).conferm front to back.thanks.and ill show you the problem with my lcd with the two board fix i did.i think but not sure but we might have simular problems in that area(with the lcd housings dimming light at the perimeter of the lcd).
😀 😀 😀 😀
regular mirrors are cheap if you buy the 12"x12" tile size mirror package. but im not quite sure what a first surface mirror is.