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Alternative Imaging Methods
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Old January 12th, 2006, 07:01 AM   #16
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Ack, free bandwidth is having problems....
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Old January 12th, 2006, 08:27 AM   #17
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looks like those links are up...
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Old January 12th, 2006, 10:24 AM   #18
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Link still not working. even light on the back ground (or frame), wall, sky, etc.
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Old January 12th, 2006, 10:46 AM   #19
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I'll repost these elsewhere tonight. Dan, what's the purpose for the evenly lit footage? I had a slight mishap with my latest GG (slight contact with case flange=swirl mark in middle of frame) last night, so I may have to wait a day or two for the new blanks. I can only imagine how careful you must be with your screens! For me, it costs about $2, for you ... a lot more.
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Old January 12th, 2006, 11:28 AM   #20
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Quote:
Originally Posted by Dennis Wood
Dan, what's the purpose for the evenly lit footage?
Im guessing he is asking you to film that in order to test for any vignetting.

Looking foward to seeing your footage
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Old January 12th, 2006, 12:25 PM   #21
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That's right! Vigneting. (That's why I asked for frame size earlier as well).
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Old January 12th, 2006, 12:56 PM   #22
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I get it. I just used a 500 watt on a white wall to check myself. I had to move the achromat back a bit and extend the tube about 1 inch to allow the GS400 to zoom beyond the vignette in 16:9 and still allow focus. I can now zoom in well beyond the vignette at the expense of a 1" increase in length. Shooting 16:9 (with about 15% larger field of view on this cam) requires a bit more zoom then shooting 4:3.

There's a difference between my F1.4 50mm and the 28-130 F4.0 zoom lens in terms of the rear lens aperture and effective GG area.

Other than masking a "test" GG with a 24x36 frame, is there any other way to determine the actual effective frame area?
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Old January 12th, 2006, 01:04 PM   #23
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Dennis,
I would put a 36x24mm frame in the adapter. You say your zooming past the vignetting, but try not to zoom into a smaller area then 36x24mm, as the more you crop this size, the less benefit you get from the adapter in terms of DOF.
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Old January 12th, 2006, 01:23 PM   #24
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One "other way" is to use a real camera (mounted with the same lens) and frame something to have a reference for the framing. Top/bottom, L/R.
That is what the 24/36 shows you. Then, (same distance, same lens on adapter), see the video framing. Zoom-in and out till you get the same frame as before. Zoom-in (most likely) to avoid vigneting and "guess" the frame size (by proportions)
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Old January 12th, 2006, 01:33 PM   #25
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Good ideas fellows. I'll just use my trusty Minolta SLR body on a tripod mounted next to the adapter. I printed out a couple of sheets of paper with a 1/2 inch grid. I should be able to just set up the two cams equidistant from each grid for comparison. Those links appear to be up again...
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Old January 12th, 2006, 01:51 PM   #26
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Dennis,
I dont think your ground glass is diffusing the light enough, as it looks like your getting ghosting issues.

Check this by holding up your glass to a light bulb and check if you can see through it. If you can read the writing on the bulb then its not diffused enough. This badly efects DOF.
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Old January 12th, 2006, 01:54 PM   #27
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Wayne, are you referring to the red fringing on Tigger? If so, the cam seems to do this with or without the adapter. Apparently it's a DV compression issue. The GG is a temp one at 2mm, but it is very diffuse. It was blasted with fine media, whilst spinning 1000rpm on my "jig", at about 60PSI, about 1 metre distance.

Is there something else you're seeing?
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Old January 12th, 2006, 02:02 PM   #28
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Dennis,
On the lunch box, I can see as it goes out of focus, you are getting ghosting. This is where some aerial image is passing through the glass and not being diffused. The lines on the box should be more blurred/diffused. This ghosting gives a very hazy/smeary effect in the 'out of focus' areas
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Old January 12th, 2006, 04:11 PM   #29
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You have a good eye Wayne. So you're thinking more diffusion is required...

I'll have the new GG's in a few days, so I'll experiment a bit. Other than a visual check, are there any other methods of determining whether diffusion is sufficient? I 've seen a few POC tests using lasers shone through the material onto a backing screen. Being that I don't have a laser, have you found anything else that would give an indication of diffusion levels?
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Old January 12th, 2006, 04:21 PM   #30
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Dennis,
Just to confirm if im correct, please try holding the ground glass up to a bright bulb as i said, you should not be able to see details coming through.

Another thing I do is hold the glass about 5cm away from the green LED on my PC speakers. It should be a complete blur. If you can see the hard outlines/edges of the LED through the glass then it is not diffusing enough. You dont want any aerial image getting through.

Is the method your using simple sandblasting? If so what grit size are you using? It maybe that it just needs blasting for longer to complete the 'etching' on the acrylic surface.

I really think your on to a winner with your adapter here!!!
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