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Old January 28th, 2004, 01:35 AM   #61
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http://www.bealecorner.com/trv900/re...x.html#EIA1956

This chart which has been recommended before in these forums can help you gauge the lines of resolution that your system can resolve.
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Old January 28th, 2004, 07:59 AM   #62
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I've got another ground glass solution

I think I've stumbled upon another way to get high quality extremely fine ground glass. Use the stuff out of a hand held photographic slide viewer! I took a photo of mine at the link below.

http://uk.geocities.com/brian.wyndham@btinternet.com/index.htm

I've got a spare piece somewhere so I'm going to try basing my Aldu35 around this. Sorry if the photo is a bit poor as I'm still at the 'mess around with things roughly placed on a table' stage! But I tried the camera behind it and it seems to be a pretty sharp image. Now I just have to work out what kind of macro attachment I'm going to use (it's for an XM1). The Hoya combinations seem to be the best bet judging from what you guys have said yeah?

I'm really hyped for this!
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Old January 28th, 2004, 08:37 AM   #63
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simon, is the slide viewer GG glass or plastic?
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Old January 28th, 2004, 09:32 AM   #64
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http://www.knightoptical.co.uk/acata...ticscreens.htm

Just looking at that it states.

"These Plastic Screens have still greater diffusion than ground glass types, allowing an image to be back-projected on a large screen without `hot spotí, and have a grey tint to minimise reflection of ambient and scattered light"

Would that be ideal for GG?
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Old January 28th, 2004, 10:05 AM   #65
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Richard Mellor

Put some scocth-tape on it to protect the other side.

for the monitor is the resolution good enought?

Alain
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Old January 28th, 2004, 11:06 AM   #66
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John, yes, I the screen is plastic.

I am also trying an inversion technique using mirrors (I tried a mock up with some mirrors that were lying around and it works fine as far as getting the image the right way up is concerned. Because it's done with mirrors the left to right thing isn't an issue by the time the image arrives at the camera. The image comes out left to right correct). The setup would be more bulky than Alains original design, but I seriously want to look at a correct image in the camera viewfinder rather than invert in post.

The pentaprism idea will get you an image that is the right way up but not correct left to right if I worked it out correctly.
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Old January 28th, 2004, 12:51 PM   #67
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Stewart--

Sounds like the plastic diffusers from Knight optical fit the project needs to a tee. Any idea the prices of these? Maybe one of us should buy one to test and report the results.

It says that they can custom make them too, which is nice.
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Old January 28th, 2004, 01:26 PM   #68
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The price is on this page (from 9 pounds for 3mm thickness):
http://www.knightoptical.co.uk/acatalog/DiffusersPlasticscreensSquares.htm

I wonder why they're talking about gain, do they have a Fresnel on the incident surface?

Also, has anyone considered if diffusion screens from rear projection TVs could be used? They get scratched so often, I imagine I could beg at a local TV repair shop for a couple of throw-aways, find one where the center part isn't scratched, and just cut to size.
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Old January 28th, 2004, 02:08 PM   #69
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Test Chart

Here is the test that I did , sugested by Brett Erskine.

I have change the lens from the optex magnifier for a lens that I took from a old super8 camera that is mutch better and the size is the same .Whit the test chart I notice immediatly how much distortion I get from this magnifier,So I chane it

There is a bit of lost of sharpnes and in light .this is shot whit a normal 60W light.



http://www.kheops-tech.com/~ad3d/test-chart.gif
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Old January 28th, 2004, 02:48 PM   #70
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Not too bad. You'll need to fill the whole frame next time you shoot the grid chart. If you can't you wont beable to use 35mm cine lenses correctly. But it looks like your already just close enough for regular 35mm still lenses so no huge loss.

I noticed it was alittle soft and had some chroma distortion starting to happen as you go out towards the outside of the frame. Sounds like your using a single element magnifier. Swap it out for a two element lens like a achromat (diopter) or for the best possible results a three element lens called a apochromat (triplet). Make sure it has enough magnification power and retest with the chart. Should make your setup work perfectly.

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Old January 28th, 2004, 04:08 PM   #71
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I have just ordered 100x100 of the 3mm thick acrylic diffuser from knightoptical.co.uk

Will report back when I receive it, could be up to 7 days.
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Old January 28th, 2004, 07:01 PM   #72
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Brett Erskine

I talk to guy's that is an optic specialiste this evening and he say the same ting about the diopter,I need three lens for better result

I alway's thoug that one element is better than three in optic.
But no.

So I get back to work.

Alain
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Old January 28th, 2004, 08:00 PM   #73
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Alain make sure you dont just stack three of the same elements you are using right now. That wont work. Your going to need something called a achromat. Its at least two elements that are optically designed to work together to correct this problem. They are perminately cemented together when you buy them and are often housed in filter rings.

As far as having THREE elements its the same idea as I just mention. But in this case there is one more element that is cemented together with the other two. With this arrangement your sure to correct ANY possible barrel or chroma aberration. But there is currently conflicting information on the usefulness of the third element in the system as some say it only corrects for the UV part of the color spectrum while others say it also helps correct parts of the visible spectrum. Specifically the color violet.

Btw I think you finally convinced me that your ground glass is up to par with that last image you sent me of the resolution chart you shot. I didnt see any grain. Now lets all hope that the softness seen in that image will be corrected with the information Im giving here. Good luck everyone.

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Old January 28th, 2004, 08:04 PM   #74
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P.S. THREE element corrective optics like I described are called APOchromat. Microscopes use them and they go way past 10X power but are too small to use for our purpose. Its a proven solution. We just need to find them in a bigger physical size. 58+mm I would guess.
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Old January 28th, 2004, 08:36 PM   #75
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Hi Brett,
AFAIK Achromat or Apochromat lenses are designed to correct chromatic abberations only and do not correct for geometric distortions such as pincushion/barrel.
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