Hello all,
Sometime last year i bought a fresnel lens to use for my DIY projector. Since then i have been reading some of your forums here and there was something about doublet and triplet lenses. I think i might have a singlet lens im not very sure but when i find the specs i will post them.
I am using a CRT tv to project this image on my wall at home. I get an ok picture, but it is not as crisp as it can be. The edges are abiit out of focus and the middle is ok.
Know i heard somewhere that doublet and triplet lenses are better for this type of projection, is this true?
And would the doublet or the triplet lenses have a better focus and be clearer and also give out more light then the singlet lens?
Also if someone could please tell me where i can find these doublet and triplet lenses so i can buy one, and what would be the price?
Thanks in Advance
BRC
Sometime last year i bought a fresnel lens to use for my DIY projector. Since then i have been reading some of your forums here and there was something about doublet and triplet lenses. I think i might have a singlet lens im not very sure but when i find the specs i will post them.
I am using a CRT tv to project this image on my wall at home. I get an ok picture, but it is not as crisp as it can be. The edges are abiit out of focus and the middle is ok.
Know i heard somewhere that doublet and triplet lenses are better for this type of projection, is this true?
And would the doublet or the triplet lenses have a better focus and be clearer and also give out more light then the singlet lens?
Also if someone could please tell me where i can find these doublet and triplet lenses so i can buy one, and what would be the price?
Thanks in Advance
BRC
Let me just add, if i add a condensor fresnel lens behind the fresnel lens will it help absorb more light? And if so can you tell me where i can find them online and buy them.
a doublet or triplet refers to a projection lens, while a fresnel is a different animal. You can use a projection lens in conjunction with a fresnel, but a doublet or triplet would not replace one.
Hi BRC,
I as well as other folks have tried the CRT/fresnel (television) method to result in a dim image and only with focus in the center while the corners go blurry. This focus problem is often due to the fact that the curvature of the CRT glass causes it go out of focus. You probably could construct a curved screen to compensate for that but this isn't probably something that you'd want to do and again the dark image is hard to enjoy.
I for a while thought it was futile to try and make a projection television untill I found this site along with Lumen Lab.com and DIY Projector Company.com. The results posted by other builders is outstanding and was what convinced me to buld my own PJ. The light source of choice is the metal-halide bulbs that are extremely bright and have a long life, plus they're far more cheaper in cost in the long run when compared to commercial devices. Some folks just use an exisitng overhead projector, some just use the overhead projector's bulb as a light source (like I'm doing untill I save up for a metal-halide).
One thing to know is that a fresnel lens can only perform one task, one can either collate light or collect it. Collating is like how a lighthouse redirects the light rays into a parrallell beam that shines outward to the horizon (this is with the grooved side away from the light source). Now if you start with practically parallel light (sunlight) and flip the lens around (grooves toward the light) the lens now concentrates the light in a point that you can readily burn things with. This isn't condensing though.
So the reason why fresnels are used in the PJ's is to first collate the light so that it passes straight through the LCD screen. The second fresnel then takes that light and concentrates it for the projecting (triplet) lens to handle. I've purchased the standard lens set from Lumen Lab and the quality of the image produced is superb! The proper lens matched to each other make all the difference.
A condenser lens for DIY PJ's is actually tempered glass since it's placed rather close to the light source. This lens is an effort to grab more light for the first fresnel to handle, although some folks have gone without condensers. I've even seen some folks go without a reflector behind the bulb (fresnel lens agree best with a point light source).
I've drawn up some plans of the PJ that I'll be building and have performed some bench tests for my own trials with very promising results. Alignment of the light and three lenses is critical. A little measurement off affects the brightness greatly. The plans may help you see how the light is treated but the three lenses. You can see my projector project within my website at:
http://communities.msn.com/portraitsmore
Peace!
Chris B. in Iowa
I as well as other folks have tried the CRT/fresnel (television) method to result in a dim image and only with focus in the center while the corners go blurry. This focus problem is often due to the fact that the curvature of the CRT glass causes it go out of focus. You probably could construct a curved screen to compensate for that but this isn't probably something that you'd want to do and again the dark image is hard to enjoy.
I for a while thought it was futile to try and make a projection television untill I found this site along with Lumen Lab.com and DIY Projector Company.com. The results posted by other builders is outstanding and was what convinced me to buld my own PJ. The light source of choice is the metal-halide bulbs that are extremely bright and have a long life, plus they're far more cheaper in cost in the long run when compared to commercial devices. Some folks just use an exisitng overhead projector, some just use the overhead projector's bulb as a light source (like I'm doing untill I save up for a metal-halide).
One thing to know is that a fresnel lens can only perform one task, one can either collate light or collect it. Collating is like how a lighthouse redirects the light rays into a parrallell beam that shines outward to the horizon (this is with the grooved side away from the light source). Now if you start with practically parallel light (sunlight) and flip the lens around (grooves toward the light) the lens now concentrates the light in a point that you can readily burn things with. This isn't condensing though.
So the reason why fresnels are used in the PJ's is to first collate the light so that it passes straight through the LCD screen. The second fresnel then takes that light and concentrates it for the projecting (triplet) lens to handle. I've purchased the standard lens set from Lumen Lab and the quality of the image produced is superb! The proper lens matched to each other make all the difference.
A condenser lens for DIY PJ's is actually tempered glass since it's placed rather close to the light source. This lens is an effort to grab more light for the first fresnel to handle, although some folks have gone without condensers. I've even seen some folks go without a reflector behind the bulb (fresnel lens agree best with a point light source).
I've drawn up some plans of the PJ that I'll be building and have performed some bench tests for my own trials with very promising results. Alignment of the light and three lenses is critical. A little measurement off affects the brightness greatly. The plans may help you see how the light is treated but the three lenses. You can see my projector project within my website at:
http://communities.msn.com/portraitsmore
Peace!
Chris B. in Iowa
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