Micro Four Thirds Focal Reducer Shootout

Started Feb 20, 2014 | Discussions thread
OP brian Senior Member • Posts: 1,206
Re: Shootout Part 2: Hotspotting

SiFu wrote:

Hello Brian!

Thank you for your answer - unfortunately I am a bit language handicapped and not sure I understood correctly; in other words, are you measuring the distance from the iris blades of the lens to the image sensor in the camera as it would be with the lens mounted on the camera?



Not quite.  You're measuring the distance between the *image* of the iris blades (as viewed from the rear of the lens) and the image plane.

When you look through the back of the lens at the iris blades you aren't looking directly at the blades, unless there is no glass after the stop - which can happen with some telephoto lenses etc..  The powered lens elements in the back of the lens change the apparent location and size of the iris diaphragm.  This is why what you are seeing is an image of the iris, not the iris itself.

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Brian Caldwell

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