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Author Topic: Location of Aperture  (Read 6230 times)  bookmark this topic!
KeithB
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Location of Aperture
« on: August 20, 2008, 01:28:32 PM »

Bob:
After reading your exposure article, I have a question.

Are there any limitations/advantages as to where in the lens you place the aperture iris?

I know that you can't place it in front of the lens since that will just get you a small piece of the image, not a general darkening - as those with too long of a lens hood can attest to.

ISTR that there were some view type cameras that had the aperature as part of the shutter - the shutter would just open to the required aperture - but I may be all wet.
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Bob Atkins
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Re: Location of Aperture
« Reply #1 on: August 21, 2008, 11:31:37 AM »

The aperture location is part of the optical design of the lens and its position is dictated by the position and nature of the individual lens elements. You can't just put it anywhere.

There are lenses with the aperture as part of the shutter, but in those lenses (leaf shutter lenses), the shutter is located somewhere in the middle of the lens (i.e. between the lens elements).

You can use a front aperture in some circumstances, such as with a simple, long telephto lens.  A classic example is a telescope, where you can place an aperture over the front of the lens in order control the effective aperture (f-stop).
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KeithB
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Re: Location of Aperture
« Reply #2 on: August 21, 2008, 12:54:44 PM »

I was thinking more along the lines of whether there is a virtual image where you put the aperture or is it at the exact opposite of a virtual image - whatever that would be called.  I would think it would go about the same place as the IS element.  The place in the lens where the light is necked down, but completely defocused - if that is the right term.
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