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This question discusses the iris placed in camera body and this question does not reveal too much details about external iris.

I recall from scattered information that I have read that iris placed in front of front lens has some application. For example, hobbyists owning objectives without internal aperture make external aperture stop.

I also recall a compact film camera having an external iris.

My questions:

  • what cameras used external iris? Compact ones in particular
  • what is the good source to read about placing iris in front of lenses? I searched the webs for quite long but found nothing significant
  • When you say "in front" do you mean between the lens and the subject, or between the body and the lens? – Caleb Apr 13 '16 at 14:26
  • @caleb: between lenses and subject. – Euri Pinhollow Apr 13 '16 at 14:29
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See textbook “Optics The Technique of Definition” by Arthur Cox 1945. Excerpts from: The fact that different parts of the lens of the glass is used when the stop is in front of the lens, from that that is used when the stop is ---- the aberrations are different ------ this is the utmost importance in establishing a lens constriction that will give good definition and holds whether the is simple or complicated as to construction.

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In answer to your question about specific cameras, the only models I can recall seeing with an external aperture in front of the lens are a few of the oldest Kodak Autographics and Kodak Vest Pocket Cameras from approximately 1913-15 that featured a 'meniscus achromat' lens.. Here's an example of some..

When I first saw these, I assumed the front element had simply fallen out, as they were simple lenses and not apparently constructed as well as the more famous lenses. It didn't make sense that the aperture was exposed to the elements, but upon inspection you'll see they're designed this way, with sturdy fixed circular apertures, much like Waterhouse stops.

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The older (50's-60's) large format Schneider Symmars that are "convertible" fit this description when used with the front group removed.

My 135/235 isn't wonderful used as a 235 with the front group removed, but it's not awful either, at least by f16.

Suspect there are other convertibles (Cooke?) that this is also true for.

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The MS SuperTriplet Perar 24mm F4 and MS SuperTriplet Perar 28mm F4 were objectives which I tried to recall. They are M-mount objectives not tied to a specific camera. Photographs suggests the iris is in front.

Here is an article which says it straightly.

MS SuperTriplet Perar 24mm F4

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I have a commercial Canon lens, 125 mm, f/2.6 with dual counter-rotating irises in front of the lens glass. It came from a 35 mm high-speed x-ray cine camera, Canon #XI 125 mm, no. 78928.

It has a focal distance back through the lens of just over 8 inches, and it is a beast weighing 2 pounds.

I cannot find out any info about it other than I have said. At f/8 the iris is 5/8" wide; at f/2.5 it is 2".

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