On 4/17/2004 12:10 PM SofaKing spake thus:

OK.

Yes; it increases the depth of field of the projected image in exactly the
same way as with a camera taking a picture. Smaller aperture = greater depth
of field = more latitude in misfocusing.

Just what was described above: increased overall sharpness.

Nope.

Only that what grain is visible will be more sharply in focus. That could be
good or bad, depending.

Nope; you're apparently thinking of reciprocity failure characteristics. I
don't think this becomes a problem with photo paper until your exposures are
into the range of several minutes or more.

No, all the image focus is in the negative, your enlarger will not make focus
where there is none.  Oft time a grain focuser is used to focus on the grain of
the negative which has nothing to do with image focus.  If you missed focus at
the camera stage you will not get it back of come close at the printing stage.
In the darkroom all you can do focuse the negative to sharpness and let the
image fall where it will.

values (f5.6).

Every lens has a "sweet spot".  It is usually mid way between max and min
apature, maybe 5.6 or 8.  Enlarging lenses are flat focus lenses in that they
project a flat negative image onto a flat piece of paper, unlike camera
lenses..  All the DOF the image has in in the negative, closing the apature
will not increase image DOF.  It will lengthen exposure time which is a good
thing.  I personally like exposures of more than 30 seconds and if burning or
dodging is involved I will stop down as much as possible to insure enough time
for burning or dodging.

_________________
Ready, Fire, AIM.
Bruce
Brooklyn, N.Y.

Your questions are very good. Some of  the replies are not.

Small aperature will increase depth of field, but not enough to overcome
poor initial focus.

What are the

None, as to the resulting image.

You are loosing sharpness because of optical defraction when you use your
lens much below f8.0.  This a matter of light itself, not lens design or
construction. The only way a close comparision would not clearly show this
for you would be if you were using a very low quality lens or were out of
focus.

No.

tone

No.  If you want longer print times, which can be useful, use a lower output
bulb or insert neutral density filtration above the negative, and [assuming
35mm printing with a 50mm lens] keep the lens aperature in the 5.6 - 8.0
range.

Use f/5,6 to f/ 8,0, no smaller. That is the optimum aperture for most
enlarging lenses.

Stopping down any lens reduces optical abberations, increases depth of
field, depth of focus, contrast and resolution, but only to a point.
After that point, resolution, contrast, and "sharpness" degrades due to
diffraction.  Most lenses, enlarger or taking, obtain the "best"
balance between the improvements gained by stopping down and the
degradation due to diffraction 2 to 3 stops down from wide open.

Most b&w papers perform best in the 10 to 60 second range.  With longer
exposures, they begin to suffer from reciprocity failure -- loose
speed, change contrast -- just like film does with exposures longer
than they were designed for.

To obtain critical focus, buy a grain magnifying focusers.  It needn't
be an expensive one.  (I use a 20 year old Patterson that I bought new
for about $20 and it works just fine.)  After composing and focusing
wide open, stop down to your printing aperture and check the focus to
be sure there has been no focus shift.  Most modern Plasmat type
enlarging lenses, that is, 6 elements in 4 groups, don't suffer from
this, but cheaper lenses with less elements are more apt to.