how could we measure the lens quality?
does anybody know the keys for this meassurement?
charts... how do they work.... any information would be apreciated.
does anybody know the keys for this meassurement?
charts... how do they work.... any information would be apreciated.
scratches?
This is the nearest to where this question goes as far as I can tell without starting a new thread.
Can you repair scratches in lens coatings or use them without the coating? I saw a couple on sale that sounded great except that the coatings are scratched at one end from improper cleaning. Any ideas?
Thanks
This is the nearest to where this question goes as far as I can tell without starting a new thread.
Can you repair scratches in lens coatings or use them without the coating? I saw a couple on sale that sounded great except that the coatings are scratched at one end from improper cleaning. Any ideas?
Thanks
scratches & quality
I don't think a few scratches in the AR coating would matter much. The important surfaces for AR are inside the lens. The outer ones won't make much difference. I don't think you would see anything at all in the screen image.
There are places that will recoat lenses for you. I would try the lens first. I think it will be fine.
There are loads of lens quality parameters, most of which I don't understand. I know that spot size is a simple indicator. This tells you how much a small beam of light is scattered by all the different distortions and aberrations when it hits the screen. If the spot size at the maximum field angle is still small (relative to an LCD pixel size), then most of the distortions and aberrations have been compensated for in the design. That will give you a sharp image.
Other parameters important for projection are maximum field angle, barrel or pincushion distortion, and aperature size.
I don't think a few scratches in the AR coating would matter much. The important surfaces for AR are inside the lens. The outer ones won't make much difference. I don't think you would see anything at all in the screen image.
There are places that will recoat lenses for you. I would try the lens first. I think it will be fine.
There are loads of lens quality parameters, most of which I don't understand. I know that spot size is a simple indicator. This tells you how much a small beam of light is scattered by all the different distortions and aberrations when it hits the screen. If the spot size at the maximum field angle is still small (relative to an LCD pixel size), then most of the distortions and aberrations have been compensated for in the design. That will give you a sharp image.
Other parameters important for projection are maximum field angle, barrel or pincushion distortion, and aperature size.
Well what I'm looking at are some opaque projector lenses being sold on ebay and it would be nice to get one of those big ol lenses without having to buy and pay for the shipping of a bunch of heavy steel that I would only have to discard. These pjs are so heavy that the shipping is very expensive. I've checked around locally but apparently all of the schools have gotten rid of these kinds of things a long time ago.
OHP lenses
I have seen OHP replacement triplet lenses for sale pretty cheap on eBay. They were for upgrading an OHP with a duplet to have a sharper lens. If you can find one of those for sale, it would be pretty cheap to get it shipped.
Schools and businesses have moved away from OHPs, but they sold them off cheap to the public. You might find one of those at a local yard or garage sale, once the owner tires of it collecting dust. If you can find one that doesn't work anymore, that is perfect: $5 probably takes it!
I have seen OHP replacement triplet lenses for sale pretty cheap on eBay. They were for upgrading an OHP with a duplet to have a sharper lens. If you can find one of those for sale, it would be pretty cheap to get it shipped.
Schools and businesses have moved away from OHPs, but they sold them off cheap to the public. You might find one of those at a local yard or garage sale, once the owner tires of it collecting dust. If you can find one that doesn't work anymore, that is perfect: $5 probably takes it!
- Status
- Not open for further replies.