> Say you have a small object (about the size of a postage stamp)
> that you are trying to photograph at high resolution. You can
> get it all in focus using a large aperture setting (say, 14) but
> it comes out sort of blurry/noisy. When you use a small aperture
> setting (say, 4) you can get really sharp details, but the depth
> of field is so narrow, that in 3/4 view you can only get a part
> of the object in focus.

Then something is wrong with your lens.  Depth of field is much
greater at large f/stops than at smaller ones (up to a point --
at very small f/stops, say f/64 or f/128, I believe diffraction
effects reduce quality; these f/stops are usually only on view
camera lenses; hmmm, aperture opening on small sensor cameras at
large f/stops, may be small enough for this effect to occur -- I
just don't know).

For a fixed lighting situation, as you increase the f/stop the
shutter speed will decrease to keep constant illumination at the
focal plane.  Maybe it's not a lens artifact that you are seeing
but motion blur (camera or object or both) due to a slow shutter
speed when you select a large f/stop.

My recommended procedure for macro photography (cameras using
bellows systems are ignored to keep instructions managable)...

Mount the camera body on a tripod.  It's easier if you can mount
the camera to a micro-adjusting platform then mount the platform
to the tripod.  This allows you to move the camera & lens fore
and aft without refocusing (which changes magnification).

Put a macro lens on your SLR (film or digital, physics of light
doesn't care).  Set desired magnification on lens.

Rough position the object so that it is nearly in focus.  Move
camera/lens forwards & backwards until desired focus point is
sharp.  If specific magnification is immaterial, use focus ring
on lens plus camera/lens movement to achieve sharp focus.

If object is flat, ensure that object surface is perpendicular
to the lens axis.  Remember that your lens' "plane of focus" (*)
may be slightly curved, either concave or convex.  Macro lenses
are usually pretty good in this regard.

Optionally, use camera's depth of field preview to ensure that
all that you want sharp is actually sharp.

Use largest f/stop consistent with reasonable shutter speed for
given lighting conditions.  If shutter speed goes down too much,
add more light (or pray).  Normally, mirror slap may cause some
blurring between 1/30 down to 1/2 (varies by model).  Use mirror
lock up function if available.  Use a cable release or self-timer.


> Of course, you can move the camera back, but then you don't get
> the high resolution.

A nit pick, but I'd say you would get the same resolution but at
a lower magnification.

						Lee

(*) not sure if this is the correct term, I mean the plane formed
    from all the sharpest focus points over the angle of coverage
    of the object field in front of the lens.

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist