Is a fresnel lens necessary for building a projector? I've been looking at different designs and have find one that doesn't use a fresnel at all; instead, it uses a mirror to reflect the image towards a triplet lens. I have also read on a different forum that fresnels can blur the projected image.
What are the ramifications of not using a fresnel?
I want to use two lights that should produce 20,000 lumens.
Full Version: Is A Fresnel Lens Necessary?
I think I have seen pics of that design you are referring to with the mirror and two bulbs, and my analysis concludes that its pretty much garbage 
Take a look at the results people are getting here with fresnel lenses and tell me if they look blurred. I am steadfast with my assertion that a single MH bulb, two fresnels, and an triplet delivers the best results for a DIY projector without straying into extreme modifications.
Take a look at the results people are getting here with fresnel lenses and tell me if they look blurred. I am steadfast with my assertion that a single MH bulb, two fresnels, and an triplet delivers the best results for a DIY projector without straying into extreme modifications.
QUOTE (tameone @ Dec 11 2006, 04:22 PM) 
I think I have seen pics of that design you are referring to with the mirror and two bulbs, and my analysis concludes that its pretty much garbage Take a look at the results people are getting here with fresnel lenses and tell me if they look blurred. I am steadfast with my assertion that a single MH bulb, two fresnels, and an triplet delivers the best results for a DIY projector without straying into extreme modifications.
Take a look at the results people are getting here with fresnel lenses and tell me if they look blurred. I am steadfast with my assertion that a single MH bulb, two fresnels, and an triplet delivers the best results for a DIY projector without straying into extreme modifications.Yeah I have decided to go the overhead projector route. I'm going to actualy create an enclosure for the OHP, replace the lens, and maybe upgrade the light.
I'm looking for a small compact portable OHP that will not take up to much space.
how is a mirror that reflects the image towards the projection lens supposed to focus the light?
unless yer talking about a parabolic mirror
unless yer talking about a parabolic mirror
OHP conversion is a great way to create a good image with a very low budget.. good choice!
I didn't try to remove the rear fresnel but I know some have experimented with multiple lights.
I can say that removing the front fresnel and using a mirror is the same as just removing the front fresnel except the image is reversed with the mirror.
What I mean is that if you have a straight split fresnel design and you remove the front fresnel the center of your projection will be bright but the edges much dimmer and may show circular darkness on the edge, at least it does for me with the standard LL triplet and a 15 inch lcd.
When I used a mirror and faced the lens upwards towards the ceiling the image was smaller because the ceiling is closer but no matter where I placed the fs mirror in relation to the triplet or the lcd I still had that darker outside circle. The image was complete so the triplet saw the whole panel it seems the light on the outer edges just wasn't focused right. When I placed the triplet lens back facing forward with no mirror the same effect was visible on the screen.
Maybe the LL pro lens with a smaller panel might work because it would allow more of the light through the triplet but then you wouldn't really need a mirror in front. In my limited test I saw a small but obvious loss of brightness and contrast. In my split format I also lost a bit of size because my normal placement of the front fresnel magnifies a bit. Maybe someone with a lux meter could verify this effect on various areas of the projected screen.
I can say that removing the front fresnel and using a mirror is the same as just removing the front fresnel except the image is reversed with the mirror.
What I mean is that if you have a straight split fresnel design and you remove the front fresnel the center of your projection will be bright but the edges much dimmer and may show circular darkness on the edge, at least it does for me with the standard LL triplet and a 15 inch lcd.
When I used a mirror and faced the lens upwards towards the ceiling the image was smaller because the ceiling is closer but no matter where I placed the fs mirror in relation to the triplet or the lcd I still had that darker outside circle. The image was complete so the triplet saw the whole panel it seems the light on the outer edges just wasn't focused right. When I placed the triplet lens back facing forward with no mirror the same effect was visible on the screen.
Maybe the LL pro lens with a smaller panel might work because it would allow more of the light through the triplet but then you wouldn't really need a mirror in front. In my limited test I saw a small but obvious loss of brightness and contrast. In my split format I also lost a bit of size because my normal placement of the front fresnel magnifies a bit. Maybe someone with a lux meter could verify this effect on various areas of the projected screen.
QUOTE (tameone @ Dec 11 2006, 11:22 AM)
I think I have seen pics of that design you are referring to with the mirror and two bulbs, and my analysis concludes that its pretty much garbage Take a look at the results people are getting here with fresnel lenses and tell me if they look blurred. I am steadfast with my assertion that a single MH bulb, two fresnels, and an triplet delivers the best results for a DIY projector without straying into extreme modifications.
Take a look at the results people are getting here with fresnel lenses and tell me if they look blurred. I am steadfast with my assertion that a single MH bulb, two fresnels, and an triplet delivers the best results for a DIY projector without straying into extreme modifications.If it's the one I saw also it uses reflection off the panel instead of passing a brighter light through the lcd panel. Someone posted a link to this model recently. Very similar to the upside down tv idea but might be a bit better because it sugggests a brighter lcd but obviously it's not in the true diy pj league.
QUOTE (gumshoe99 @ Dec 12 2006, 06:50 AM)
If it's the one I saw also it uses reflection off the panel instead of passing a brighter light through the lcd panel. Someone posted a link to this model recently. Very similar to the upside down tv idea but might be a bit better because it sugggests a brighter lcd but obviously it's not in the true diy pj league.
Yes. I got the idea from this site: http://www.audiovisualizers.com/madlab/lcd_proj.htm
It's basically an opague projector. Using this design with a backlight is basically the same thing as an overhead projector??
QUOTE (mmiikkee @ Dec 14 2006, 11:24 AM)
Yes. I got the idea from this site: http://www.audiovisualizers.com/madlab/lcd_proj.htm
It's basically an opague projector. Using this design with a backlight is basically the same thing as an overhead projector??
It's basically an opague projector. Using this design with a backlight is basically the same thing as an overhead projector??
yes thats the one.. its complete crap
I just purchased a lot of 7 overhead projectors from ebay for $75 from a company that is local to me. I'll keep what I need and sale the rest. 7300 lumen 500-thing watt metal halide bulbs...
QUOTE (mmiikkee @ Dec 14 2006, 01:04 PM)
I just purchased a lot of 7 overhead projectors from ebay for $75 from a company that is local to me. I'll keep what I need and sale the rest. 7300 lumen 500-thing watt metal halide bulbs...
hehe thats a pretty good deal. OHPs are a great starting point.
QUOTE (tameone @ Dec 14 2006, 06:28 PM)
hehe thats a pretty good deal. OHPs are a great starting point.
Too bad I just butchered my LCD screen
maybe i can find the lcd screen on ebay and use the rest of the parts....doubtful
QUOTE (mmiikkee @ Dec 14 2006, 02:41 PM)
Too bad I just butchered my LCD screen
maybe i can find the lcd screen on ebay and use the rest of the parts....doubtful
maybe i can find the lcd screen on ebay and use the rest of the parts....doubtful
you should be able to find a nice monitor on ebay with a broken backlight.
QUOTE (tameone @ Dec 14 2006, 08:13 PM)
you should be able to find a nice monitor on ebay with a broken backlight.
YEAH i had a nice cheap ebay $40 monitor until I cracked the screen DOH!!!!
I blame A.D.D. and crack rock.
QUOTE
It's basically an opague projector. Using this design with a backlight is basically the same thing as an overhead projector??
There are opaque style ohp like that with the light from above but the ones you want have the light below, underneath the presentation glass and transparency. Hopefully you can also get one that comes with a triplet and an external fs mirror. Some have a closed head with a lens then a 45 degree mirror then another lens built into one assembly. I never owned one of those so don't know if they are as good as a triplet.
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