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Old August 3rd, 2005, 12:36 AM   #1
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Help with some basic questions about the adapter

'ello, I just need a few answers to some questions I have after extensively reading into what's going on here:

Does the position of the GG matter in terms of the SLR lens? How do you determine the distance from the SLR lens to the GG? Does that matter, or can you just manually focus it to get it focused on the GG?

Read the "35mm adapter parts list." What is up with that c-mount? Do I use step rings on that motha or do I dissassemble it and glue on a step ring? Will the c-mount work for other than Canon FD lenses?

Is there noticable grain with 1500 grit ground glass when in a static adapter? Should I be worried?

How do I troubleshoot vignetting and distortion? Is my only option to play with the positioning of the GG and condenser? Which makes me wonder...

Is a plano convex lens (PCXL or whatever) a "condenser?" Why does Richard's design (the one I'm constructing) call for only one when I see many other designs use two, one on either side of the GG?

Why is Ashlee Simpson still a celebrity?

Thanks, and sorry if I sound like an idiot.
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Old August 3rd, 2005, 05:52 AM   #2
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Hi Ben,
I've been reading this forum for over a month now and have built a working static adapter/prototype. Hopefully I can answer some of your question:

Quote:
Originally Posted by Ben Winter
Does the position of the GG matter in terms of the SLR lens? How do you determine the distance from the SLR lens to the GG? Does that matter, or can you just manually focus it to get it focused on the GG?
The best way of setting up the correct distance from the SLR lens to the ground glass is to focus the lens at its 'infinaty' setting, then point the lens at far away objects (like trees in the distance). Then adjust the ground glass distance untill the far objects are in pin sharp focus. This way, you are able to use the entire focus range that the lens was designed for, and the numbers on the lens showing distance will have true meanings.

Quote:
Originally Posted by Ben Winter
Is there noticable grain with 1500 grit ground glass when in a static adapter? Should I be worried
My current prototype is using the 1500 grit ground glass from optosigma. I can quite easily see the grain in all lighting conditions, mostly noticable in 'out of focus' area's and also while panning. This ground glass also has another annoying property in that it lets too much 'areil image' thought, that is light that hasnot been diffused. Although this gives a brighter image, you get a 50%-50% mix between diffused and non diffused light, which in turns kills the DOF. this is most apparent on bright areas with strong contrast.

Quote:
Originally Posted by Ben Winter
How do I troubleshoot vignetting and distortion? Is my only option to play with the positioning of the GG and condenser? Which makes me wonder...
In my experience, using a condensor solved my once BAD vignetting. But the type of lens you use will also have an effect. The faster the lens the better, and try using one with the biggest 'hole' at the back of the lens (im not sure of the correct term, im not a lens guy;) )

Quote:
Originally Posted by Ben Winter
Is a plano convex lens (PCXL or whatever) a "condenser?" Why does Richard's design (the one I'm constructing) call for only one when I see many other designs use two, one on either side of the GG?
I think the term 'condenser' is miss used on this board, so I have read anyway. I think the true meaning for 1 condensor is acually 2 plano convex (PCX) lens working together. I think the reason people are using the 2nd PCX lens is to correct the barrel distortion from the first. This is the setup im using:
35mm---GG|)-----(|DVcam

Both PCX lens are the same. Some people are using the PCX in between the SLR lens and the GG, but I dont like the sound of it. But you should test it out for yourself.

I hope that helps somewhat.

Regards,
Wayne.
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Old August 4th, 2005, 02:25 PM   #3
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Thanks Wayne. That clears up a lot.

About this 'areil image' problem you talk about: would closing the aperture on the lens do anything to help that? maybe letting in a bit less light will prevent "overloading" of the diffuser, if that's even possible.
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Old August 4th, 2005, 02:44 PM   #4
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looks like it does, but you then widen the DOF.

Wayne
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Old August 4th, 2005, 08:16 PM   #5
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I don't think you sound like an idiot. That was a perfectly reasonable line of questioning. To which the answer is, because her sister is one and because they have a great publicist.
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Old August 9th, 2005, 03:21 PM   #6
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Got my optosigma glass today, and tried it out. I don't have a step ring yet for it so I'm stuck just holding it to the front of my camera. Here's what I got:

With broken 50mm lens(won't go to infinity for some reason, and aperture is broken)
http://www.astronautradiomusic.com/Test1.jpg
http://www.astronautradiomusic.com/Test2.jpg
With working lens, but I didn't zoom in enough to get rid of slight vignetting:
http://www.astronautradiomusic.com/Test3.jpg
http://www.astronautradiomusic.com/Test4.jpg

Keep in mind there's still a PCXL on the way that was backordered.

I had to zoom in all the way to get rid of vignetting. Should I be doing that? I'm using +14 power macro lenses (a +4, then a +10, then the thorlabs tube, is that the right order?).

Thanks for ze help.
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Old August 9th, 2005, 03:37 PM   #7
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Do you need +14 worth of macro? Looks like you are getting a lot of chromatic abberation from it. I got away with just a +4 on a GL2. I'd say use as few macro lenses as you can get away with. You probably wont need so much once you get your PCX since it will increase the usable image area that isnt all vignettey.
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Old August 10th, 2005, 01:10 AM   #8
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I don't quite understand why that is either. In fact, I've recently had to up it to +15 after adjusting the location of the GG to the SLR's focal point. Don't you just put it to manual focusing mode and then turn the ring all the way to the right (camera facing away from you)? It's weird.

This is a video of what it looks like--Oddly enough, no chromatic abberation, although is this more likely to occur with things further away?

http://www.astronautradiomusic.com/dofpracsmall.wmv

EDIT: By the way, I'll be selling this adapter (including the non-broken 50mm SLR lens) for $200 in about a month or so in preparation to build another one. If anyone's interested, contact me now so I know.
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Old August 10th, 2005, 07:19 AM   #9
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I think what I used to do with my GL2 was zoom in on the GG and turn on autofocus for a few seconds to let it focus and then go back to manual and zoom out to the correct framing on the GG. I found that with the GL2 you can often focus closer if you allow autofocus to do it for you, but also when focused very close, it can be inconsistent in maintaining focus through a zoom. The picture would go out of focus while zooming out and then back into focus so I was somewhat limited in what framing I could zoom out to on the GG. I think I got used to zooming, autofocusing, setting to manual focus, and then zooming out while the camera would go out of focus for a moment and then back into focus and leave it there. It worked for me perfectly probably 95% of the time (Aesthetically I dont like using sharpness in the custom preset settings, but it can be even more difficult to focus when it is off, found that out the hard way). I generally dont like using manual focus on prosumer cameras when you need it to be very accurate since the screen isnt really high enough resolution to tell when things are in focus.

Chromatic abberation generally is much more noticeable in places of high contrast (especially edges of bright objects). It looks like there is abberation in your video around the bright icons on the computer screen, but that sort of thing is much less noticeable when most of the screen is out of focus. Blurriness hides abberation pretty well.
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