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Vignetting in Super16


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#1 Eugene Lehnert

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Posted 03 February 2011 - 03:26 PM

I recently had my SBM Bolex converted to Super16 by JKCamera and he did a fantastic job. I'm getting some vignetting when I use my old 10mm RX Switar lens. Do 10mm lenses exist that cover the Super16 area better than my Switar?
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#2 Jean-Louis Seguin

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Posted 03 February 2011 - 03:37 PM

The 10mm switar is not known to vignette. There is a slight fall-off in density in the extreme corners no intrusion normally.
If you have one of the preset 10mm Switars with a black filter retaining ring at the front, try removing the ring.

I can't really recommend other lenses because none of them are designed for the Bolex reflex system.

Cheers,
Jean-Louis
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#3 Todd Pinder

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Posted 03 February 2011 - 09:38 PM

I can't really recommend other lenses because none of them are designed for the Bolex reflex system.

Cheers,
Jean-Louis

Is it possible to collimate or adjust the back focus of any non RX c mount lens into one suitable for Bolex RX
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#4 Dom Jaeger

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Posted 03 February 2011 - 10:44 PM

RX lenses were designed to include the prism in their optical pathway, and account for the abberations introduced. Changing the back focus on non-RX lenses won't solve that issue. Stopping the lens down several stops is effective, and the abberations are less pronounced on longer focal lengths.

There was a long thread on 10mm vignetting in Super 16 a while back:

http://www.cinematog...showtopic=37152

but Jean-Louis probably just covered it in one post!
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#5 Todd Pinder

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Posted 03 February 2011 - 11:03 PM

RX lenses were designed to include the prism in their optical pathway, and account for the abberations introduced. Changing the back focus on non-RX lenses won't solve that issue. Stopping the lens down several stops is effective, and the abberations are less pronounced on longer focal lengths.

There was a long thread on 10mm vignetting in Super 16 a while back:

http://www.cinematog...showtopic=37152

but Jean-Louis probably just covered it in one post!

Thanks for digging up that post! Cheers!
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#6 Eugene Lehnert

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Posted 09 February 2011 - 10:54 AM

I seem to have a lot of vignetting in my image. Nothing on a 16mm lens but the corners of the 10mm are very dark.
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#7 Jean-Louis Seguin

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Posted 09 February 2011 - 01:32 PM

Hi Eugene,

Have you actually shot any footage with the 10mm Switar?

It could be just an issue with the groundglass screen.

I've seen this in some cases were the groundglass surface has been polished up.

It changes the light diffusing characteristic of the screen and can lead to what looks like a hot spot in the center with fall-off at the corners.

Screens like this react differently to different lenses depending their optical characteristics such as exit pupil location and diameter.

The image looks fine at the film plane.

Only a film test will confirm for sure what is happening.

If you're still looking for an alternate wide lens with abundant coverage for super-16, I can recommend the Kinoptik 9mm f/1.5.

It will however have the usual loss of sharpness used wide open on a Bolex RX. Stopping down to f/2.8 will greatly improve the image.

Cheers,
Jean-Louis
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#8 Eugene Lehnert

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Posted 11 February 2011 - 10:32 AM

Yeah I shot some footage with it. I'll have to check that black ring you spoke about. Maybe it's on there and causing a problem.
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