Re: [Leica] Infinity focus tip

[Thomas Kachadurian <kach@freeway.net>]

At 12:06 AM 12/17/97 -0800, you wrote:

Jim:

So perhaps my practice is just making the most of DOF. Thanks.

Chuck Westphal of Canon explained to me that longer lenses with flourite
and other rare earth glass are made to focus past infinity because the
glass can expand in very warm situations, shifting the focus points. I'm
not sure I buy it.

Tom


>
>After reading some of the WA voodoo stuff, it dawned on me that I learned
>something at Brooks that I involuntarily do. I never ever focus a lens at
>infinity. I was taught, at Brooks, that there is no such thing as infinity.
>And, of course, there isn't. If you think about it, infinity is not one
>mile, not 100 miles, not a million miles, it's forever away from you.
>Otherwise it wouldn't be infinity. Now we all know that focus extends 1/3
>in front of and 2/3 behind the subject. So if your lens is set at infinity,
>your focus is 1/3 in front of infinity and 2/3 behind infinity. Not very
>logical. So I was taught to ALWAYS, when focusing on far away subjects
>(distant landscapes, etc.) take the lens to the infinity stop, then
>back-off a little. This puts a lens' depth of field into a real world (as
>opposed to imaginary world) perspective.
>
>Some lenses, especially when using extenders, focus past (yes past)
>infinity. That's a real oxymoron. Past infinity. Only Steven Hawking knows
>about this. Anyway, this is usually with very long lenses where you can
>actually focus on that distant mountain, or the moon. In this case, you can
>focus where you want so that your depth of field will take care of what you
>want it to take care of (it's late.)
>
>Jim
>
>