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Old November 8th, 2004, 03:33 PM   #16
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static adapter

steve I just got in the new groundglass from thorlabs.
started testing it and it looks as good as the optmo sigma . and it,s only $14
and I am getting sharp focus now with the tube system
it looks beautiful. I am sure you will quite happy when you put this on your camera.
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Old November 8th, 2004, 03:48 PM   #17
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Richard, is this the ground glass - http://www.thorlabs.com/ProductDetail.cfm?DID=6&ObjectGroup_ID=1132&Product_ID=36117

If so, this would certainly be alot easier than grounding down a UV filter with AO. Unless you still have to ground it?
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Old November 25th, 2004, 10:20 AM   #18
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Well, since I couldn't get my hands on any AO locally, I went with Silicon Carbide, but unfortunatly it seems to be too fine to get a good frosting on it... by the looks of the Aldu, his is completely opaque, whereas all I can get is a semi-transparant covering. Furthermore, I tried it out with the macro, and it looked like a spider's web down there... nothing but harsh grain, even after I went up to 400 (eventually I can go to 600).

Does anyone have any Silicon Carbide advice, or should I just try it with AO?
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Old November 26th, 2004, 08:06 AM   #19
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There was a reference to another site related to optical groundglass awhile back on one of the posts.

The grade you are using is a little too coarse. I think the grade in silicon carbide should be 1200 grit. I understand this equates with 5 micron in aluminium oxide.

Silicon Carbide is apparently inferior to aluminium oxide because for the same grade or size of particles, it had a tendency to drag long chips out of the glass rather than punch pits into it.

If you want to determine if your cam has the light performance to work with AGUS/ALDU appliances, see if you can get some 1x f-stop neutral density filter material as used for making gel filters to put in Bolex or CP16 motion picture cams. These have little frames you put the gel filter material into. The material comes in a folder and looks like very thin plastic sheet and cuts with scissors.

The AGUS/ALDU appliances seem mostly to lose between three and four f-stops of light so test with as many layers of gel in front of the lens until your camcorder says enough.

The SLR lens on front has some bearing on it as well. For best results use f1.8 of better lenses.
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Old November 28th, 2004, 01:44 PM   #20
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I've uploaded a shot of what I've gotten so far with the grade 600 sodium carbide, a spacer tube of cardboard and the lens at the appropriate distance...

http://www.keanufan.co.uk/camtest.jpg

This is obviously far from acceptable, but what I can't yet understand is how to stop it looking like a 1920's zoetrope... the vignetting is unbearable!! The scratches are also horrible (like you said Bob, cause of the SO) which leads me question weather or not it is possible to remove a clean focusing screen from an old camera, and using that instead of grinding a filter lens?
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Old November 28th, 2004, 09:28 PM   #21
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Steve.

From what I see, your camcorder has adequate light performance to deal with the AGUS/ALDU. Your groundglass is very opaque which cuts light transmission down.

The vignette is another matter.

I was unable to determine if it is from the close-up lens/macro, insufficient zoom-in available on your camcorder, or the Pentax lens on the front, being of insufficient wide aperture. Judging by the scale of the scratches relative to the circular image, I suspect your camcorder needs to be zoomed in closer through the vignette. The close-up/macro lens on front of the camcorder may have to be a larger diameter with step-up ring to enable mounting.

What close-up lens are you using?

If you are using no close-up lens at all and relying on the camcorder's own macro/zoom facility to get to the groundglass image, you may be running out of camcorder zoom range which would mean you are looking at an area on the groundglass larger than the projected image.

To test for this, draw a 24mm x 18mm rectangle and see if your camcorder/close-up combination will frame tightly on it. If it remains a small rectangle in center of your image, you will need a stronger close-up lens to bring the gg image closer to the camcorder.

Then you may need to add a close-up/macro lens to bring the groundglass object closer. Going out to the end of camcorder zoom, drops the light level as well with most products.

All input to the AGUS/ALDU ideally is with the SLR lens at its widest aperture, ideally an f1.8 if you can get it.

Don't take too much notice of my comments as they are largely guesswork.
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Old November 29th, 2004, 01:05 AM   #22
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<<<-- Originally posted by Bob Hart

All input to the AGUS/ALDU ideally is with the SLR lens at its widest aperture, ideally an f1.8 if you can get it. -->>>

Sorry for the ultra newbie question,but isn't it going to be better with an f1.2 or f1.4? (besides the higher price of cource)

Danny
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Old November 29th, 2004, 09:07 AM   #23
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Yes, but they don't come cheap. I think that was Bob's point.
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Old November 29th, 2004, 12:37 PM   #24
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got it!

thanks
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Old November 29th, 2004, 01:42 PM   #25
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http://www.keanufan.co.uk/camtest2.jpg
http://www.keanufan.co.uk/camtest3.jpg

These are the two newest photos that I've taken an f2.8 macro lens, so it gave me a better aperature to focus through. The problem is it looks like I've zoomed in, which I have, but I can't seem to find a way of getting a wideangle image. I'd have blamed the Macro lens, but the other one looked the same!
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Old November 29th, 2004, 04:28 PM   #26
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For a wide angle image you need a wide angle lens ;)

What is the focal length of your current lens?
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Old November 30th, 2004, 12:20 PM   #27
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The focal length is 90mm, but I also tried the 50mm and both gave a rather telephoto image. What is the ideal focal length to use?

Also, could the ground glass diffuser that Richard linked to be useful with my setup? Cause it seems alot handier than having to use a UV filter, if it would work.

Edit -

I discovered a UK place that sells GG Diffusers: http://www.knightoptical.co.uk/acatalog/DiffusersGroundGlassDiffuser207.htm

Would any of these be useful, since $60 for shipping to the UK from Thorlabs is a little expensive!
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