Hi Eric -
Three thoughts come to mind - first that DOF is the range of "apparent"
or "acceptable" sharpness, but parts of the subject that are not right
at the focal plane will still be slightly out of focus. Not an issue in
many genres of photography but in macro, where the detail is crucial, it
becomes more noticeable.
Second - at f22 diffraction will degrade sharpness. See
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
for formation overload on diffraction.
Third - shooting from 20 to 30 feet away means shooting through some
degree of haze, dust, and thermal distortion in the atmosphere. Not an
issue in many kinds of photography but possibly enough to affect macro
results (obviously depends on conditions at the time.)
_ Mark
On 4/11/2015 8:23 AM, Eric Weir wrote:
Mark’s post about stack focusing brought to mind a problem I encountered the other
day. I was shooting wildflowers at Arabia Mountain, just outside Atlanta. (One of
several stone outcrops, with unique ecosystems, that occur here in Georgia.) I was
using my DA 50-200 with the camera on a tripod with aperture set at f/22. My target
was plots of wildflowers 3’ to 5’ in diameter, each with a mixture of species, some
“normal" sized and upright, others tiny and growing closed to the ground. I was
20’ to 30’ from the target.
I assumed that if I was focused at infinity everything within the target would
be in focus. I was also trusting autofocus to give me good focus. I was very
disappointed. The larger plants and flowers were reasonably sharp, though
nothing like what Mark showed us yesterday. But the tiny close to the ground
wildflowers were fuzzy. In the case I’m thinking of the tiny flowers were in a
strip 4” to 6” wide immediately in front of the larger plants.
Any thoughts about why I got this result?
------------------------------------------------------------------------------------------
Eric Weir
Decatur, GA USA
[email protected]
"Imagining the other is a powerful antidote to fanaticism and hatred."
- Amos Oz
------------------------------------------------------------------------------------------
Eric Weir
Decatur, GA USA
[email protected]
"What does it mean...that the world is so beautiful?"
- Mary Oliver
---
This email is free from viruses and malware because avast! Antivirus protection
is active.
http://www.avast.com
--
PDML Pentax-Discuss Mail List
[email protected]
http://pdml.net/mailman/listinfo/pdml_pdml.net
to UNSUBSCRIBE from the PDML, please visit the link directly above and follow
the directions.
