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Old September 19th, 2006, 08:07 PM   #1
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Use of BCX as a condenser

I'm using a bi-convex lens as a condenser in my adapter and it's proved more effective than a plano-convex in my device.

Is anyone else using a BCX?

I'm not asking for any other reason than curiosity... my apparatus is working very well and I have no intention of changing my condensor. I just find it odd that I seem to be the only one getting better results with a BCX, rather than a PCX.

I also have to admit that this doesn't make much sense from an optics standpoint, but I'm not going to argue with reality. With the spacing I'm using (can't get closer to the GG than about a centimeter due to structural constraints), a PCX just doesn't work as well.
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Old September 20th, 2006, 10:59 AM   #2
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That sound interesting.

Can you post some stills.
Hows about vignetting in the corner or chromatic aberration?

Daniel
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Old September 21st, 2006, 06:15 PM   #3
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As far as I can tell there's no chromatic aberration and the vignetting isn't really noticeable in (at least in the test footage I've taken so far, which has been in shady areas).

These were all taken late in the day and the shadows make it a little difficult to discern vignetting, but the last one is a clear shot of the sky, which shows the left edge as slightly darker... this is mainly a mirror alignment issue.

These screens are all straight from the camera - no color correction.

http://www.particleproducing.com/images/o35-1.jpg
http://www.particleproducing.com/images/o35-7.jpg
http://www.particleproducing.com/images/o35-10.jpg
http://www.particleproducing.com/images/o35-11.jpg
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Old September 21st, 2006, 06:52 PM   #4
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What I tend to look at is a piece of paper. If you can read the font across the whole page in sharpness - left to right and top and bottom , then you are good to go. Sometimes the PCX or the BCX lens is sharpest in the middle and tends to gets soft as it goes outwards.
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Old September 21st, 2006, 10:08 PM   #5
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That's a great idea... I'll do a test like that the next chance I get.
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Old September 22nd, 2006, 12:55 AM   #6
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Justin.

My own first non-flip adaptor setup used a generic 50mm 2" telescope eyepiece for Tasco scopes, part number SW5042. I remounted the glass in a custom adaptor for a PD150.

Although it only had an effective exit pupil diameter of 44mm it was enough to zoom through to the motion picture sized frame.

I had to couple it very very close to the camera as the magnification power was very strong. The focal distance range was about 12 to 18mm from front of the combined lens assembly.

This eyepiece consisted of a doublet and a third separate single element. In this reversed arrangement, the single element became a condenser element. It was as is with your adaptor, a BCX style lens, one face very curved the other only slightly.

If you get any barrel or pincushion distortion, you may be able to adjust that out by varying the distances between the camcorder and lens, in combination with lens and groundglass.

You may find you have to also move the macro (close-up lens) if you are using one, closer or furthur away in a third combination as well.

Edge softness you may not be able to do much about. the furthur away from the camcorder or the less zoomed in you are, the worse it may become. As posted, your images look fine.

You should simply go ahead and enjoy working with it as is to build user skills for a while before you make any furthur modifications.

Are you using a Canon GL1 (XM1) or PD150/VX2000 for those images?
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Old September 22nd, 2006, 02:27 PM   #7
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I am pretty happy with it right now... I have another GG on order that I want to try, but other than that I'm perfectly content to shoot with it as is. I've gone through a number of condenser lenses and two GG's so far (not counting the one on order), and I think I have something now that looks pretty good.

Actually, the biggest problem I'm having with it is the mirrors shifting slightly from vibration. I'll put lock nuts in it when I get the chance.

Those images (no cc) look washed out on my laptop, but they were shot with an XL2 with a 28mm FD mount lens connected to the camera as a relay.

I don't believe there's noticeable distortion. When I have a 28mm lens on front as the prime I notice the image pin-cusions a little, but I think that's the because of the prime, not the adapter. A 40mm lens (which I think is close to normal field of view with a frame close to academy aperture) doesn't seem to yield any distortion.

Here's another screen I took today. The lighting was better so you can get a better idea of the quality. Still haven't done the "writing test".
http://www.particleproducing.com/images/o35-12.jpg
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Last edited by Justine Haupt; September 22nd, 2006 at 06:38 PM.
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