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COOKE 20-100 Zoom on RedOne HELP


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#1 Sam King

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Posted 14 November 2010 - 08:53 AM

Hi,

I have a Cooke 20-100 Zoom lens on my RED. At the widest end I get vignetting only down the right side of screen. Shooting wide open at most lengths also has blur only on the right side of the screen. When I stop down to 5.6 the blur goes away.

Would this be an issue with the lens or with the RED? I'm uncertain of how old this lens is and whether that could be a contributing factor.

Any help with this would be much appreciated!

Cheers,

Sam
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#2 Sherman Johnson

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Posted 14 November 2010 - 11:39 AM

Hi Sam,

The Cooke 20-100 was introduced in 1971 and does not fully cover Super-35 (roughly the size of the Red's sensor).

- Sherman
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#3 Markus Rave

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Posted 14 November 2010 - 11:56 AM

I had the same lens and there was never an issue with vignetting. At that time there was no 4.5k widescreen area, so I donĀ“t know about that. But with 4k no problem. Is the lens clean on the collimator? Could be a problem there. 20mm should cover S35 if I recall. There will be an issue going wider though. I had a standard prime lens set form Zeiss and the 16mm showed vignetting and the 24mm did not.
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#4 Stephen Williams

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Posted 14 November 2010 - 01:32 PM

Hi,

I have used one for S35 film, it was necessary to take off the fitted matte on the front of the lens. I suspect the lens mount on your camera is not exactly in the middle of the sensor.

Stephen
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#5 Sherman Johnson

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Posted 14 November 2010 - 01:45 PM

I stand corrected...
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#6 Dom Jaeger

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Posted 14 November 2010 - 06:25 PM

A quick way to check would be to mount the zoom upside-down (if the mount allows). If the vignetting remains on the right side, I would concur with Stephen that the camera mount is probably not correctly centred. Alternatively, mount a lens that you know will vignette and see if the porthole is off-centre.
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#7 Stephen Williams

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Posted 15 November 2010 - 02:40 PM

A quick way to check would be to mount the zoom upside-down (if the mount allows). If the vignetting remains on the right side, I would concur with Stephen that the camera mount is probably not correctly centred. Alternatively, mount a lens that you know will vignette and see if the porthole is off-centre.



All the ones I have used have been off, some more than others....
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#8 Dom Jaeger

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Posted 15 November 2010 - 08:10 PM

All the ones I have used have been off, some more than others....


Good grief, really? So as well as possible edge shadows every zoom would track off to one side. What dinky cameras.
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#9 Sam King

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Posted 16 November 2010 - 07:58 AM

Thanks for all your replies so far.

Stephen, so apart from weird vignetting, have you had that blur on one side of the screen too? Do you think it's the camera? The primes seem fine. But my zoom, yeesh!

What have you done to correct it?

Sam
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#10 Stephen Williams

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Posted 16 November 2010 - 02:46 PM

Thanks for all your replies so far.

Stephen, so apart from weird vignetting, have you had that blur on one side of the screen too? Do you think it's the camera? The primes seem fine. But my zoom, yeesh!

What have you done to correct it?

Sam


S35 is at the absolute limit for most cine zooms, everything must be spot on to work properly, most primes have a bigger image circle so it's less of an issue.

Using a film camera is the quick fix I usually do, failing that check out a few bodies & take the one that works best or just use primes, it's just one of those little issues that many people just ignore & accept. I do know a few cameras that have been sent back to the factory.
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#11 John Sprung

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Posted 16 November 2010 - 03:30 PM

The primes seem fine. But my zoom, yeesh!


Based on that, the next step should be to find a good lens shop, and get your zoom properly tuned up. Where are you, perhaps someone will have a local recommendation.




-- J.S.
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