Effective aperture in 135mm f8 lens.

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JohnyM
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Joined: Tue Dec 24, 2013 7:02 am

Effective aperture in 135mm f8 lens.

Post by JohnyM »

What's gonna be an effective aperture in Agfa Repromaster, large format reproduction lens? 135mm f/8 @ 1:1 and f/8
What calculation should be used? Is the aperture measured at infinity or rather at working magnification (1:1)?

Charles Krebs
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Post by Charles Krebs »

The rated aperture should be as if "inifinity". So the effective aperture would be:

f (m+1)
8 (1+1) =16

This is accurate only if it is a symmetrical lens where:
entrance pupil size= exit pupil size.

This is generally the case with graphic arts lenses of this type. Hold it out at arms length and look into the front, an then the back. The aperture should appear the same size. If it is obviously different sizes, let us know and we can dig up the relationships that take papillary magnification factors into consideration.

JohnyM
Posts: 463
Joined: Tue Dec 24, 2013 7:02 am

Post by JohnyM »

It indeed seems to be symmetrical. Thanks for help Charles.
I wonder if the lens is worthy the metalwork required to adapt it to bellows (it have no screwmount at all, as it was mounted on large format repro machine). I was thinking of it as LWD up to 1:1 lens, but small aperture is quite scary for my a6000 aps-c sensor.

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