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Angenioux 25-250 mm Lens Focus


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#1 Gary Robinson

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Posted 17 January 2009 - 06:07 PM

Hi Guys,
I have Angenioux 25-250mm lenses on both my Arri 2b, and BL2. I haven't shot with the BL2 yet, but I noticed that on my BL2 only, when I zoom in and focus, I lose focus when I pull out to 25. Any ideas on why this is happening?

Thanks,
Gary Robinson
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#2 Frank Cook

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Posted 17 January 2009 - 07:47 PM

Have you checked the flange depth and ground glass on the BL2? With your Angenieux zoom at 250mm the is a less depth of field at the subject and more depth of field with the lens at 25mm, but at the film plane, it is opposite. At the film plane, the depth of focus is much more shallow with the lens set at 25mm than at 250mm! Check your flange depth and ground glass. If it was the lens, it would cause the same problem with both cameras.

Hope this helps - it should be cheap to check and fix.

Edited by Frank Cook, 17 January 2009 - 07:49 PM.

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#3 Gary Robinson

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Posted 17 January 2009 - 11:32 PM

Thanks Frank,
I'll look into it.

Have you checked the flange depth and ground glass on the BL2? With your Angenieux zoom at 250mm the is a less depth of field at the subject and more depth of field with the lens at 25mm, but at the film plane, it is opposite. At the film plane, the depth of focus is much more shallow with the lens set at 25mm than at 250mm! Check your flange depth and ground glass. If it was the lens, it would cause the same problem with both cameras.

Hope this helps - it should be cheap to check and fix.


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#4 Delorme Jean-Marie

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Posted 27 January 2009 - 03:03 AM

notice also that the focus of a zoom is never linear but in an "s" shape
if your focus reference is at the midel you'll be off focus at beguining and end of the lens.
if the mark matches the end you may be way out at the beguining.

if the eye focus matches the mesurement focus mark focus on the neg the ground glass will be good.
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