Well I first got into the whole DIY projector about a year ago. I bought a Dukane 4000 off ebay as well as an nView ViewFrameTFT projection panel. The lcd is old and of mediocre quality but you gotta start somewhere right?
So while I wait for my LL parts in the mail to build the standard 15", I got to thinking. The setup I had with the OHP was usable and I didn't want it to go to waste so I decided to rip apart the OHP and the ViewFrame and build an enclosure while recycling the parts I had on hand. So as it sits now, I have ripped out the lighting assembly and switches as well as removed the fresnel from the OHP. I also stripped the casing off of the projection panel. I'm all ready to go but I have a few questions.
First of all, the fresnel out of the OHP is something I am confused about. After extensive reading on this forum, I have learned that there are really two ways to use fresnels in the projector. Split, or unsplit. The fresnel I salvaged when looked at from the side, looks like it's actually two fresnels fused together. I'm assuming ohps use unsplit technology so I also assume that this 'one' fresnel contains both the fresnels needed. What i'm unsure about is how far I'm going to need to have this fresnel from my light source.
My other question involves the triplet that I salvaged from the ohp. It's a 327mm triplet but being the beginner that I am, I'm wondering how far I need to have that lens from my lcd.
So to sum it up, I'd like to know how I tell how far I need my fresnel from my light source and how far I need my triplet from my lcd. Thanks for your help.
Full Version: Using The Guts Of An Ohp
You really should check out the Lumenlab Guides (Basic and Pro) under the tools section of the forum index. They answer all these questions and a lot more...
in the nutshell:
-Your OHP fresnels will not be big enough to fit the entire 15" LCD. You can either live with the cutoff, adjust the monitors effective resolution with Powerstrip, or get new ones. They are in fact 2 fresnels fused, which can be carefully split if you want by running a xacto knife or something similar along the seam.
-Distance from light source to rear fresnel is determined by the rear fresnels focal length. If you don't know that figure for your OHP's fresnel, and still want to use it, you can approximate it by measuring the distance from light to fresnel in their original OHP configuration.
-Dukane's 327mm triplets are nice. You can definitely use that. You want to put the lens a bit beyond its focal length from the thing you are focusing on -- in this case the LCD. Exactly how far is determined by your throw (distance from lens to screen). So you'll need to build some adjustability there.
Hope that helps.
in the nutshell:
-Your OHP fresnels will not be big enough to fit the entire 15" LCD. You can either live with the cutoff, adjust the monitors effective resolution with Powerstrip, or get new ones. They are in fact 2 fresnels fused, which can be carefully split if you want by running a xacto knife or something similar along the seam.
-Distance from light source to rear fresnel is determined by the rear fresnels focal length. If you don't know that figure for your OHP's fresnel, and still want to use it, you can approximate it by measuring the distance from light to fresnel in their original OHP configuration.
-Dukane's 327mm triplets are nice. You can definitely use that. You want to put the lens a bit beyond its focal length from the thing you are focusing on -- in this case the LCD. Exactly how far is determined by your throw (distance from lens to screen). So you'll need to build some adjustability there.
Hope that helps.
QUOTE (sensibull @ Dec 15 2006, 10:48 PM) 
You really should check out the Lumenlab Guides (Basic and Pro) under the tools section of the forum index. They answer all these questions and a lot more...
in the nutshell:
-Your OHP fresnels will not be big enough to fit the entire 15" LCD. You can either live with the cutoff, adjust the monitors effective resolution with Powerstrip, or get new ones. They are in fact 2 fresnels fused, which can be carefully split if you want by running a xacto knife or something similar along the seam.
-Distance from light source to rear fresnel is determined by the rear fresnels focal length. If you don't know that figure for your OHP's fresnel, and still want to use it, you can approximate it by measuring the distance from light to fresnel in their original OHP configuration.
-Dukane's 327mm triplets are nice. You can definitely use that. You want to put the lens a bit beyond its focal length from the thing you are focusing on -- in this case the LCD. Exactly how far is determined by your throw (distance from lens to screen). So you'll need to build some adjustability there.
Hope that helps.
in the nutshell:
-Your OHP fresnels will not be big enough to fit the entire 15" LCD. You can either live with the cutoff, adjust the monitors effective resolution with Powerstrip, or get new ones. They are in fact 2 fresnels fused, which can be carefully split if you want by running a xacto knife or something similar along the seam.
-Distance from light source to rear fresnel is determined by the rear fresnels focal length. If you don't know that figure for your OHP's fresnel, and still want to use it, you can approximate it by measuring the distance from light to fresnel in their original OHP configuration.
-Dukane's 327mm triplets are nice. You can definitely use that. You want to put the lens a bit beyond its focal length from the thing you are focusing on -- in this case the LCD. Exactly how far is determined by your throw (distance from lens to screen). So you'll need to build some adjustability there.
Hope that helps.
Thanks for the help.
I have read the guides but I was still confused about how to determine the focal length of the fresnels. I also neglected to mention that while I am waiting for supplies for a 15", the nView lcd that I have is only 9" so there isn't a problem with how big the fresnel(s) are. Are the fresnels only fused at the edges?
About determing the fresnels focal length: Since there is a mirror in the ohp that reflects the light to the fresnel, do I measure the distance from the fresnel 90 degrees down to the mirror? Also, is there any other way to measure it's focal length because this method doesn't seem to be the most accurate?
So when mounting the triplet, how much adjustability will i need? I've read a couple inches is all that is needed and I just want to confirm this.
Thanks again.
QUOTE (dunks @ Dec 15 2006, 11:39 PM)
also neglected to mention that while I am waiting for supplies for a 15", the nView lcd that I have is only 9" so there isn't a problem with how big the fresnel(s) are. Are the fresnels only fused at the edges?
I believe so, but I haven't split any myself (plan to soon). There have been several instances of members cracking or otherwise destroying the fresnels while attempting to split. There are also success stories. Proceed with caution and please don't hold me accountable
QUOTE
About determing the fresnels focal length: Since there is a mirror in the ohp that reflects the light to the fresnel, do I measure the distance from the fresnel 90 degrees down to the mirror? Also, is there any other way to measure it's focal length because this method doesn't seem to be the most accurate?
Yes. Total distance between light > mirror > fresnel. One other method is to take the fresnels outside in the sun. Slowly lower them down towards the ground until the light is focused into a point. Distance from ground to fresnel will be the FL.
QUOTE
So when mounting the triplet, how much adjustability will i need? I've read a couple inches is all that is needed and I just want to confirm this.
The guide recommends 50mm/2 inches of movement. In my first build I gave it a little more just to be safe.
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