Re: Optics question (not alt)

From: Tom Ferguson ^lt;[email protected]>
Date: 03/10/05-09:17:13 AM Z
Message-id: <>

I'm wondering if Dan has confused the size of the image versus the size
of the circle of illumination (as a lens is stopped down).

For all practical purposes, the size of a focused image doesn't change
as you alter f/stops. The size/appearance of significantly "out of
focus" areas can change slightly. That is why it is best to changes
shutter speed or lights if you intend to stack files for density range
expansion. But, the in focus stuff stays the same, F/2 or F/32.

What does change "big time" on many lenses is the circle of
illumination. That is important to view camera users. As most lenses
are stopped down, they throw a larger circle of light. Nothing in the
circle get larger. You just get more area around the edges added to the
circle. In a fixed system (DSLR, SLR) this is just wasted light. It
hits the black areas inside the mirror box and does nothing. In a view
camera it allows more movements at F/64 than you can get at F/5.6.

Tom Ferguson
Received on Thu Mar 10 09:17:38 2005

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