> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Talbot
> Sent: Sunday, February 25, 2001 12:35 PM
> To: [EMAIL PROTECTED]
> Subject: Re: EOS EF 20-35 with extension tubes
>
>
> 1. DOF is indeed not the same as DOF ;o)
>
> 2. Wide aperture on ANY lens reduces DOField but decreases DOFocus.
>
> 3. Just as with DOField, DOFocus is a function of magnigication (is
> it not?) rather than focal length per se.
You're probably right here. My point was that a 12mm extension tube on a
20mm lens will probably leave you with no usable focusing range.
I don't have a 12mm tube, but I do have a "mini optical bench" (actually an
odd bracket thing I picked up at a camera show years ago). I mounted my EOS
1N and placed my 21-35 in front of it with the lens flange 12mm from the
camera flange. At 21mm, focusing range was from 1/2 inch (at infinity) to
1/4 inch (at .5 meters) from the front front lens element. Interesting, but
not very practical.
Chuck Skinner
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