Property, I'd recommend going with split fresnels. People who say it degrades picture quality havent even tried it... or they did try and did it wrong! Commercial single LCD projectors use the split method... you decide.
verbose mustafa, I'm waiting for a call back from the company now. I'll hold off before emailing you so that I might be able to quote you a price... if I dont get one by tonight I'll email you anyway with the details.
I'll also post all the info on the boards for the rest of you.
verbose mustafa, I'm waiting for a call back from the company now. I'll hold off before emailing you so that I might be able to quote you a price... if I dont get one by tonight I'll email you anyway with the details.
I'll also post all the info on the boards for the rest of you.
Property,
In your first example above, with the OHP screen before the LCD, the fresnel is actualy a double fresnel - just joined together. Some people have split one of these apart so now have two fresnels, and sandwitched the LCD in the middle. The advantage of this is that the light goes through the LCD parallel not converging, and therefore should provide a brighter image. The only problem with using two fresnels is they must be lined up exactly, and must have the same number of grooves. This is why seperating a double fresnel into two single ones is a good option - you already know that they will line up fine. Having said that, if they both have the same number of grooves per inch it should be possible to line any two single fresnels up together.
Hope this clears some things up for you,
Matt
In your first example above, with the OHP screen before the LCD, the fresnel is actualy a double fresnel - just joined together. Some people have split one of these apart so now have two fresnels, and sandwitched the LCD in the middle. The advantage of this is that the light goes through the LCD parallel not converging, and therefore should provide a brighter image. The only problem with using two fresnels is they must be lined up exactly, and must have the same number of grooves. This is why seperating a double fresnel into two single ones is a good option - you already know that they will line up fine. Having said that, if they both have the same number of grooves per inch it should be possible to line any two single fresnels up together.
Hope this clears some things up for you,
Matt
JCBKLYNY,
I have been following this thread and your ideas for the custom fresnels. I think this is the key for us all. Getting the right fresnels should make this all work very well.
When I see how good a picture some are getting with the split fresnel approach with non optimum fresnels we should be really persuing this.
Most of the the larger size fresnels with high lines per inch that I have seen have too long a focal length. The best one I have been able to find is an 18" focal length with about 125 lines per inch if my memory serves me well.
Please let us know what the cost for the custom single lens is. I will be using Alans triplet objective lens and I may have to have a fresnel with the correct focal length made up.
Hezz
I have been following this thread and your ideas for the custom fresnels. I think this is the key for us all. Getting the right fresnels should make this all work very well.
When I see how good a picture some are getting with the split fresnel approach with non optimum fresnels we should be really persuing this.
Most of the the larger size fresnels with high lines per inch that I have seen have too long a focal length. The best one I have been able to find is an 18" focal length with about 125 lines per inch if my memory serves me well.
Please let us know what the cost for the custom single lens is. I will be using Alans triplet objective lens and I may have to have a fresnel with the correct focal length made up.
Hezz
Hezz, FresnelTech wasn't really any help at all! so I'm going with someone gives a **** 🙂
Some new stuff - the 200 grooves per inch may not be possible or needed for a few reasons... and split fresnels may not be the answer after all!
1. the fresnels will be too expensive... no I wont say how much... just, trust me on this!
2. Alignment issues. 200 grooves matched perfectly without bonding them would be... well a pain in the ***!
3. a high groove count shouldn't be needed.
Let me explain. After many conversations with optical engineers I now understand that for this project split fresnels would actually degrade picture quality. Although it does brighten up the picture and send light straight through the lcd... a fresnel lens should never be used in the direct image path between the lcd and projection lens. If your getting rings on screen with a double fresnel behind the lcd... the fresnel is simply too close to the lcd.
The answer is just a larger double fresnel with a longer focal length for the top fresnel. The longer focal length changes the angle at which light passes through the lcd. So you can sit the fresnel further away from the screen, and still fill it.
So Lifter was right in that you need a larger effective area then 12x9 for a 12x9 screen... but a higher groove count behind the lcd isnt going to make any difference in picture quality.
Some new stuff - the 200 grooves per inch may not be possible or needed for a few reasons... and split fresnels may not be the answer after all!
1. the fresnels will be too expensive... no I wont say how much... just, trust me on this!
2. Alignment issues. 200 grooves matched perfectly without bonding them would be... well a pain in the ***!
3. a high groove count shouldn't be needed.
Let me explain. After many conversations with optical engineers I now understand that for this project split fresnels would actually degrade picture quality. Although it does brighten up the picture and send light straight through the lcd... a fresnel lens should never be used in the direct image path between the lcd and projection lens. If your getting rings on screen with a double fresnel behind the lcd... the fresnel is simply too close to the lcd.
The answer is just a larger double fresnel with a longer focal length for the top fresnel. The longer focal length changes the angle at which light passes through the lcd. So you can sit the fresnel further away from the screen, and still fill it.
So Lifter was right in that you need a larger effective area then 12x9 for a 12x9 screen... but a higher groove count behind the lcd isnt going to make any difference in picture quality.
Bottom line - fresnels should only be used as a light gathering lens... not imaging lens.
Now the price on these pre-cut fresnels (not sure of exact size yet) will be around $100.00 each.
It was recommended that I draw up the project in autocad for best results... which is what I'm doing now. I'll post pictures when finished.
Now the price on these pre-cut fresnels (not sure of exact size yet) will be around $100.00 each.
It was recommended that I draw up the project in autocad for best results... which is what I'm doing now. I'll post pictures when finished.
split fresnels
Well....Since I was first to split the fresnels I tend to disagree.....I saw no decrease in picture quality , but did see more even brightness across the screen, and I was able to use more of my 15" panel! Judge for yourself, Property!
(sorry I was tough on your 1st post)
Well....Since I was first to split the fresnels I tend to disagree.....I saw no decrease in picture quality , but did see more even brightness across the screen, and I was able to use more of my 15" panel! Judge for yourself, Property!
(sorry I was tough on your 1st post)
Attachments
Wow. That's a major turn of events. Well I guess the good news is that we won't be spending a fortune on fresnels.
Yeah, personally, brightness and light uniformity has not been a problem with my setup. The problem is that the lit area is too small (even with my 12.5x12.5" 305 fresnel). It just bareley fits if you put it directly against the fresnel, but of course you can't do that w/o getting rings.
Yeah, personally, brightness and light uniformity has not been a problem with my setup. The problem is that the lit area is too small (even with my 12.5x12.5" 305 fresnel). It just bareley fits if you put it directly against the fresnel, but of course you can't do that w/o getting rings.
Here is a though... How about not using a fresnel lens? Is there an alternate way to focus the light?
I know Lifter, at first I was told that a higher groove count would help then hear the exact opposite!
Proto5, I'm not saying you have a bad picture... not at all, but looking at the picture I DO see rings 🙂 Thats what I'm trying to avoid. I thought that with a 200 groove fresnel on top you wouldnt see those rings... and from what I was told by the engineer, with the fresnel in front of the lcd you'll always have rings. A higher groove count would help... but not solve the problem.
Verbose, I WISH we didnt have to use them... but the trick is using them the right way.
Proto5, I'm not saying you have a bad picture... not at all, but looking at the picture I DO see rings 🙂 Thats what I'm trying to avoid. I thought that with a 200 groove fresnel on top you wouldnt see those rings... and from what I was told by the engineer, with the fresnel in front of the lcd you'll always have rings. A higher groove count would help... but not solve the problem.
Verbose, I WISH we didnt have to use them... but the trick is using them the right way.
I still think that engineer is not being practical. For instance it is still better if the light is perpendicular though the LCD than a cone which is what you get with double fresnels behind the LCD.
Using the fresnel in the image path isn't so bad if done correctly.
What we really need is an aspheric fresnel but it seems like they are only available in the smaller sizes.
Can they build an aspheric fresnel in a large size. That would correct a lot of focusing problems.
Supposedly the fresnel can be moved 1-2 inches away from LCD to reduce or eliminate the ring effect ( in the single fresnel method).
Sure increasing the focal length will help to make the angle less extreme but to decrease the angle in any significant amount you would have to have an unrealistically long focal length. You would need a differet objective lens because to focus all of the light properly the objective should be no more than about 2" shorter focal length than the condesing fresnel.
Really who is going to want a 30 -40 inch or longer focal length. Your OHP won't adjust that far and will require a very long DIY enclosure. The other option is having a very large diameter objective lens so that the light cone from a longer focal length fresnel can be completely focused without having to be so far away from the LCD.
Still a single high quality fresnel that covers a 15 inch monitor and has 125 lines per inch and 14 inch focal length would be exellent. Better than anything that I have been abel to see from stock sizes.
Hezz
Using the fresnel in the image path isn't so bad if done correctly.
What we really need is an aspheric fresnel but it seems like they are only available in the smaller sizes.
Can they build an aspheric fresnel in a large size. That would correct a lot of focusing problems.
Supposedly the fresnel can be moved 1-2 inches away from LCD to reduce or eliminate the ring effect ( in the single fresnel method).
Sure increasing the focal length will help to make the angle less extreme but to decrease the angle in any significant amount you would have to have an unrealistically long focal length. You would need a differet objective lens because to focus all of the light properly the objective should be no more than about 2" shorter focal length than the condesing fresnel.
Really who is going to want a 30 -40 inch or longer focal length. Your OHP won't adjust that far and will require a very long DIY enclosure. The other option is having a very large diameter objective lens so that the light cone from a longer focal length fresnel can be completely focused without having to be so far away from the LCD.
Still a single high quality fresnel that covers a 15 inch monitor and has 125 lines per inch and 14 inch focal length would be exellent. Better than anything that I have been abel to see from stock sizes.
Hezz
Verbose,
You can hand grind a large lens from a plastic or glass blank but it is very time consuming. The question is has anyone tried to use a large convex plano lens to condense the light coming off of the LCD. For a 14 inch focal length it would need a fairly deep curve.
Surplus shed has some 7 inch plano convex lenses for realatively cheap but I don't know the focal length.
The curved side should be towards the LCD. If anyone has a small LCD and would like to try this I would be interested.
Buy the way, the more curve the lens has the more ill effects it will have on focusing unless the lens is aspheric. But I don't think you could hand grind an aspheric lens only a sherical one. If I'm wrong about that I would like to know.
Hezz
You can hand grind a large lens from a plastic or glass blank but it is very time consuming. The question is has anyone tried to use a large convex plano lens to condense the light coming off of the LCD. For a 14 inch focal length it would need a fairly deep curve.
Surplus shed has some 7 inch plano convex lenses for realatively cheap but I don't know the focal length.
The curved side should be towards the LCD. If anyone has a small LCD and would like to try this I would be interested.
Buy the way, the more curve the lens has the more ill effects it will have on focusing unless the lens is aspheric. But I don't think you could hand grind an aspheric lens only a sherical one. If I'm wrong about that I would like to know.
Hezz
I was going to sugest "carving" a fresnel, but i though it would be too time consuming. Actually, if i were to use a compass with a pin or some sort of way to cut the pvc, i could could make perfectly round circeles starting in the middle and working my way out. I may have to pollish or buff the thing for a while, but it may just work 🙂 (A very long shot). The next time im at tha glass shop i'll sak about really thin pvc. About using a condensor lens to spread the light, I agree that may be hard with a 15" lcd. Im sure it could be done with a 5" or smaller though. As soon as i pay off my creditcard and get have some positive income... Im going to go shopping at surpluss shed for some optics 🙂 . The good thing with me using hqi is that it is a smaller point light source... Unlike normal mogul stlye bulbs with the 2" ark 🙂 . HQI may be easyer to "capture" with a condensor lens.
I have been reading this forum for 2 days. My friend and I want to make a projector and proto5 has one of, if not, the best results (not putting others down at all cause we are impressed with the people here). Those images of his projections are awesome! 
Why does proto5 have more success? I think that is because he took a double fresnel and split it and some people have been trying two single fresnels. Two singles don't do the same job as a split double (I may be wrong) because the double fresnel's two pieces do different things with the light. proto5, can you post some more pics (how about something other than Harry Potter 😉 ) jcbklyny, you say you seen rings in that last pic but I can't, can you please show me where you see them? Thanks.
Why does proto5 have more success? I think that is because he took a double fresnel and split it and some people have been trying two single fresnels. Two singles don't do the same job as a split double (I may be wrong) because the double fresnel's two pieces do different things with the light. proto5, can you post some more pics (how about something other than Harry Potter 😉 ) jcbklyny, you say you seen rings in that last pic but I can't, can you please show me where you see them? Thanks.screenshots
I'll post some more screenshots and details this weekend....I got my new digital lightmeter to play with too!
I'll post some more screenshots and details this weekend....I got my new digital lightmeter to play with too!
Sandmanfvr,
A double fresnel is just two singles glued close together with thier contours aligned.
There is no special magic here. It's the light going through the LCD straight instead of at an angle and focusing the LCD's light output better that makes the split method work better.
I for one cannot see any significant spiral lines on Proto5's picture which leads me to believe that the split approach properly done can yield exellent results.
Hezz
A double fresnel is just two singles glued close together with thier contours aligned.
There is no special magic here. It's the light going through the LCD straight instead of at an angle and focusing the LCD's light output better that makes the split method work better.
I for one cannot see any significant spiral lines on Proto5's picture which leads me to believe that the split approach properly done can yield exellent results.
Hezz
Does anyone know how the fresnels are manufactured. I would think that they would turn a master stamper out of steel on a very precise diamond tiped CNC lathe and then polish the master somehow. They could then stamp out the fresnels in mass from hot plastic much like a record is made.
Any thoughts.
Hezz
Any thoughts.
Hezz
sandmanfvr said:I have been reading this forum for 2 days. My friend and I want to make a projector and proto5 has one of, if not, the best results (not putting others down at all cause we are impressed with the people here). Those images of his projections are awesome!
His may look the best from photos, but you have to rember that you cannot judge porjectors by photos. Other people could have just as great of results, but have a digital camera that captures a shitty looking image. YWH for example was the oly one who took real good pictures (though his projector was groundbreaking and amaizing). Many people had similar results, but they did not have good photos of there projected image. Im not saying protos projector is bad... That image looks great, but im sure many other people have the same if not better image quality wihtout using a fresnlel lens on top.
results
Verbose is correct.....
Anyone out there using a decent 15" panel and an Elmo 305 or other bright-*** OHP should get the same results! It is important to eliminate light leaks to get a decent image. A good digicam is paramount to getting a good screenshot-I use a kick-*** Sony F707 on a tripod and pause the DVD before taking the shot.
Verbose is correct.....
Anyone out there using a decent 15" panel and an Elmo 305 or other bright-*** OHP should get the same results! It is important to eliminate light leaks to get a decent image. A good digicam is paramount to getting a good screenshot-I use a kick-*** Sony F707 on a tripod and pause the DVD before taking the shot.
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