I was doing some thinking last night. What if you had this setup:
25mm - 27mm arc Bulb -> 330mm Back Fresnel -> 550mm Field Fresnel -> LCD -> 450mm - 480mm f9 Process lens
The arc size (arc * field / back) would be between 41mm and 45mm and the diameter of the lenses (focal length / f#) would be around 50mm - 53mm. Would it be possible to get all of the light into the lens with this setup? Using a 330mm back lens reduces light output, but is it really that much???
I did find those opaque projectors. I'm having a hard time finding one that has a 14" x 11" stage. OHP with a 14" x 11" stage and a triplet would work too. I don't suppose those are very common huh?
25mm - 27mm arc Bulb -> 330mm Back Fresnel -> 550mm Field Fresnel -> LCD -> 450mm - 480mm f9 Process lens
The arc size (arc * field / back) would be between 41mm and 45mm and the diameter of the lenses (focal length / f#) would be around 50mm - 53mm. Would it be possible to get all of the light into the lens with this setup? Using a 330mm back lens reduces light output, but is it really that much???
I did find those opaque projectors. I'm having a hard time finding one that has a 14" x 11" stage. OHP with a 14" x 11" stage and a triplet would work too. I don't suppose those are very common huh?
OHP with a 14" x 11" stage
Probably non-existant!
You can figure out how much light you would lose changing from a 220 to a 330 condensor fresnel. If you are good with 3-D math, then have at it. Or you can do it graphically: Just draw a full-scale drawing of a 17" fresnel with light coming from 220 or 330 mm away. Measure the ratio of the angles and then square that to get the difference between the two designs.
I forget the answer, but it is quite a lot. 😀 (Determining the correct answer is left as an exercise for the student.
)
That is why people try to use a pre-condensor lens with 330 mm fl fresnels, to capture more of that light. Unfortunately, that magnifies the image of the lamp arc, so it is just as large as it would be using a 220!
Just keep watching eBay: There is one fellow in San Diego who sells opaque projector lenses almost every week. Maybe he is on vacation right now.
Probably non-existant!
You can figure out how much light you would lose changing from a 220 to a 330 condensor fresnel. If you are good with 3-D math, then have at it. Or you can do it graphically: Just draw a full-scale drawing of a 17" fresnel with light coming from 220 or 330 mm away. Measure the ratio of the angles and then square that to get the difference between the two designs.
I forget the answer, but it is quite a lot. 😀 (Determining the correct answer is left as an exercise for the student.
)That is why people try to use a pre-condensor lens with 330 mm fl fresnels, to capture more of that light. Unfortunately, that magnifies the image of the lamp arc, so it is just as large as it would be using a 220!
Just keep watching eBay: There is one fellow in San Diego who sells opaque projector lenses almost every week. Maybe he is on vacation right now.
I fell upon a thread from a while ago with amcorp and yourself (guy) talking about opaque lenses.
http://www.diyaudio.com/forums/showthread.php?threadid=50385
Said he bet it would cover a 19" screen although he only tested it with a 17". It's interesting. Will have to keep an eye out for lenses.
Yeah, now that you give the exponential relation to for distance and brightness.... Longer distance is worse (don't feel like getting the triple integrals out, but squared stuff grows and shrinks QUICK). So, I will keep to the 220mm lens. 550mm fresnel is in my future. Just have to get the parts. sigh
http://www.diyaudio.com/forums/showthread.php?threadid=50385
Said he bet it would cover a 19" screen although he only tested it with a 17". It's interesting. Will have to keep an eye out for lenses.
Yeah, now that you give the exponential relation to for distance and brightness.... Longer distance is worse (don't feel like getting the triple integrals out, but squared stuff grows and shrinks QUICK). So, I will keep to the 220mm lens. 550mm fresnel is in my future. Just have to get the parts. sigh
"Determining the correct answer is left as an exercise for the student"
my teacher used to say this all the time 😀.
my teacher used to say this all the time 😀.
I came across this lense on ebay. Would it work for a 15" widescreen lcd?
forget to add link haha
http://cgi.ebay.ca/Nikon-Apo-Nikkor...ryZ30076QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
forget to add link haha
http://cgi.ebay.ca/Nikon-Apo-Nikkor...ryZ30076QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
process lenses
Either one of these lenses would give you a very precise image. Process lenses are used for turning "camera-ready artwork" into lithography master plates. So they have very wide Field Of View, and they are corrected for projecting a flat object onto a flat photosensitive plate. They are usually optimized for 1:1 projection, but would still work very well at 10:1. (Most 15" DIY projectors operate around 7:1.) They are also apochromatic, which means that they have correction for chromatic aberration at red, blue, and green light wavelengths. So no funny color fringes around white characters on a black background.
The only problem (beside the high price!) is that they are not very wide. It is difficult to get much light through them, so you don't get a very bright image. You really have to tune the fresnel focussing perfectly, to fight for each lumen.
There are other options that are much cheaper (and wider), but not quite so sharp: Several online DIY stores sell a triplet around 300 mm fl (ie. $30 US), and some sell (or will shortly sell) better triplets in the 450-500 mm fl range. You can also get an opaque projection triplet for <$100 US with a fl of 457 mm, that is very wide.
I have a process lens that gives me very well-defined black screendoor between the pixels. I have an opaque projector lens that gives me grey screendoor between the pixels. The opaque projector lens image is much brighter. I can't even SEE the screendoor from more than 5 feet away, so why pay 4 to 10 times more for the process lens?
Either one of these lenses would give you a very precise image. Process lenses are used for turning "camera-ready artwork" into lithography master plates. So they have very wide Field Of View, and they are corrected for projecting a flat object onto a flat photosensitive plate. They are usually optimized for 1:1 projection, but would still work very well at 10:1. (Most 15" DIY projectors operate around 7:1.) They are also apochromatic, which means that they have correction for chromatic aberration at red, blue, and green light wavelengths. So no funny color fringes around white characters on a black background.
The only problem (beside the high price!) is that they are not very wide. It is difficult to get much light through them, so you don't get a very bright image. You really have to tune the fresnel focussing perfectly, to fight for each lumen.
There are other options that are much cheaper (and wider), but not quite so sharp: Several online DIY stores sell a triplet around 300 mm fl (ie. $30 US), and some sell (or will shortly sell) better triplets in the 450-500 mm fl range. You can also get an opaque projection triplet for <$100 US with a fl of 457 mm, that is very wide.
I have a process lens that gives me very well-defined black screendoor between the pixels. I have an opaque projector lens that gives me grey screendoor between the pixels. The opaque projector lens image is much brighter. I can't even SEE the screendoor from more than 5 feet away, so why pay 4 to 10 times more for the process lens?
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