Depth of field preview

[P3D Paul S. Boyer <boyer@xxxxxxxxxxxxx>]

Lincoln Kamm wrote: "I noticed a camera for sale (not stereo), in a
catalog, it said it has a
depth of field preview.  Does any one know how that works?  Also,
would it
probably be a bad idea to get an slr that has auto focus, considering
I will
always be shooting two shots with it for stereo?"

Ther depth of field preview alllows one to stop down before taking
the shot, so that you can view the improved depth of field which
results from a smaller aperture.  Obviously, the view one previews is
much darker than wide open.  This would be OK for table-top shots,
but it takes time, and in practice I find it of limited utility
(personal opinion).

Your guess about auto-focus is very much to the point.  It is better
to focus, shoot, then shift with the confidence that the focus is not
going to change between stereo pairs.  Also, you'll save battery
life.
Some auto-focus cameras allow the user to manual focus, but make sure
that this means REALLY manual focus.  Using my Minolta and my 100-mm
macro, I am able to do true manual focus, where my hand actually
rotates the focus ring and makes the adjustment under my own muscular
power.  One of my longer lenses has a manual setting, but the
servo-motor does the work, which takes too much time, and chews up
battery life.

The two most critical technical factors in photography are exposure
and focus.  I find that even auto-exposure often requires human
override, and focus is best done by the human *unless*:
1. You are too slow, and expect to be shooting moving sports or
wildlife;
2. Your eyes are going bad and you cannot focus;
3. All the good equipment seems to be auto-focus;
4. You wish to impress your friends with expensive equipment.

Auto-focus is over-sold and over-bought, IMHO.
--Paul S. Boyer   <boyer@xxxxxxxxxxxxx>


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