flare cutting diaphragm?

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what's this i hear about some canon lenses having a flare cutting diaphragm? what exactly does this do and what lenses have it?

-- Jeff Nakayama (moonduck22@hotmail.com), January 15, 2002

Answers

It's a rectangular doodad behind the front element that moves as you zoom. I saw one in the EF 20-35 3.5-4.5 USM. I think some of the other wide angle zooms have it too (EF 24-85 3.5-4.5 USM?).

-- Puppy Face (doggieface@aol.com), January 15, 2002.

The 24-85 does not have one.

-- Isaac Sibson (isibson@hotmail.com), January 15, 2002.

actually, i got the idea from the b&h catalogue that said the 24-85 had one...

-- Jeff Nakayama (moonduck22@hotmail.com), January 15, 2002.

Things might be clearer if you got your idea from Photozone instead:
http://www.photozone.de/canonFAQ.htm#3Q5c

-- Julian Loke (elan7e-owner@yahoogroups.com), January 15, 2002.

Before posting my above reply, I did in fact check my 24-85, and it does not have one.

On the 20-35 USM, it can be seen at the top and bottom of the lens, where there is masking which corresponds to the top and bottom of the frame. This is not present on the 24-85 USM.

-- Isaac Sibson (isibson@hotmail.com), January 15, 2002.



Maybe the FCD is in a place that you cannot see?
The block diagram at the Canon Camera museum seems to indicate the presence of two diaphragms: one has to be the aperture diaphragm; the other is probably the FCD.

-- Julian Loke (elan7e-owner@yahoogroups.com), January 15, 2002.

maybe the FCD is circular on the 24-85? the only time i have ever seen a lens with a rectangular thing in it was in the wide angles. we need an expert opinion on this...

-- Jeff Nakayama (moonduck22@hotmail.com), January 15, 2002.

Indeed. This is interesting. I'm quite prepared to be corrected. As jeff says, we need an expert opinion.....Bob?

-- Isaac Sibson (isibson@hotmail.com), January 16, 2002.

The new 100mm 2.8 macro USM has it.

-- Willie Ju (wju@mediaone.net), January 17, 2002.

Bob??

-- Jeff Nakayama (moonduck22@hotmail.com), January 22, 2002.


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