[Leica] Infinity focus tip

[Jim Brick <jim@brick.org>]

At 11:30 PM 12/16/97 -0500, you wrote:
>Alf:
>
>Perhap this is just personal voodoo, but it has been my observation that
>with many wide angle lenses there is an infinity focus softness that is
>greatly reduced by not focusing there. I have seen this with Nikkor 24mm
>and 20mm, Canon EF 24mm and the 28mm Rokkor for the CLE. Is short, better
>infinity focus is achieved shooting at f5.6 or f8 when the lens is not
>focused at infinity but at about 15ft, with the infinity marker aligned
>with the f4 mark on the DOF scale.
>
>Am I nuts?
>
>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