Thanks, Moose, for the clarifications. I couldn't find any real detail
for FS on the 5-II, likely because it's an older camera. Looking at the
stacked photos again, it seems that I did focus on the nearest point,
probably because I was not using the smallest focus rectangle.
It's clear, however, that the focus in the second photo in each of my FS
sequences moves towards the camera (and goes out of focus). After that,
the next photo reverts to the initial focus. Subsequent photos show the
focus gradually moving away from the camera.
Yes, focus bracketing would probably be better, but I don't have any
software to do that. I see that Wayne has identified a couple of
freeware options, which I may try.
Martin
On 2022-07-16 4:03 p.m., Moose wrote:
On 7/16/2022 7:44 AM, Martin Walters wrote:
I'm late to the focus stacking (FS) discussion. I finally decided to
try FS with my E-M5-2 and the 12-100. Works fine, at least on a tripod.
First: my dumb question.
As FS moves both towards and away from the camera, where should I set
the initial focus point?
You seem to be confusing recent posts about FS on later cameras, in
the M1 series, with your E-M5 II. They work differently. The E-M5 II
does not do the closer/further dance of the later ones. They also
handle up to 13 slices, a clue to the limitations of 8.
As I wanted to shoot things several inches deep, such as big Dahlias,
I set up a still life target and did some experimentation. My results
agree with this DPR post. It was as a result that I stopped trying to
use FS and went to Focus Bracketing, merging later, in post. I just
wasn't getting what I wanted with FS - as a fussy pixel peeper.
I chose a point somewhere near the middle of the subject (an
echinacea flower, which has at least 2 cm depth). The eight frames
did cover the full flower. So, while this worked fine, would it be
better to start at the nearest point in focus?
With your camera, start with the closest point. If using FB, with
large numbers of slices, focus a little closer than closest point.
Other than when testing, I work sans tripod. I focus on closest point
using small point AF, then lean back a little bit, before pressing the
button all the way.
The is purely empirical, as a result of missing too many actual
closest points. I also only use Focus Differential of one. As the DPR
post says, setting of 3 may be ideal - on a tripod. Standing in a
narrow, dirt path through a rice paddy, while on the way to something
else, thus with limited time, shooting an insect that will soon move,
and in other similar situations, I'm shooting with a long FL, often
400 mm, hand held. There's no way I don't sway fore and aft, if only a
tiny bit. By using the lowest Focus Differential, I greatly increase
the chances of covering the whole depth thoroughly.
Here's four examples, using that technique, with an E-M5 II.
<http://galleries.moosemystic.net/MooseFoto/index.php?gallery=Olympus_List/Stacks>
It works! I'll add some more, as I think of it.
Second:
Here's a DPReview post offering an explanation of how FS works,
particularly as it relates to lens aperture/DOF and the focus
differential setting. Quite interesting. In my case, I did not see
any lack of focus anywhere in the stacked version, with using F/4. I
did not try F/8 or something like that, though a single shot at F/8
was not sufficient to have the entire flower in focus.
https://www.dpreview.com/forums/thread/4392236
"Ran an experiment last night to find out what is really going on
with the focus stacking in my EM-1 ii. I was under the mistaken
belief that the focus differential setting was unaffected by the
aperture setting. WRONG. I was under the impression that one would
not get soft focus in the composite image when using a high focus
differential setting as long as one also used a large f stop. WRONG.
So, what I was actually looking for was the minimum aperture I should
use at each focus differential setting within the Focus Stacking
feature. IOW, I expected that maybe at a focus differential of 1,
you could use f/2.8, but at a focus differential of 5 or 7 or
9...somewhere f/2.8 would fail to cover the gaps between the 8 shots
the focus stacking feature takes. I wanted to know at what point
f/2.8 fails to cover the gaps. I wanted to know the same for f/4 and
f/5.6 and f/8. Turns out I was asking the wrong question.
Here's what I found. At f/2.8, the highest focus differential one can
use and not have soft spots between the frames and in the final jpeg
is 3. A f/4, the highest focus differential one can use is 3. At
f/5.6, the highest focus differential is 3. At f/8, 3. At f/11, 3.
Noticing a trend here? But wait, higher f stops mean greater depth
of field, right? Why aren't the higher f stops covering the gaps?
Because as you increase your f stop number, the camera increases the
space between the shots!!!!!
Yup! Exactly what I found to be true (and posted here, ages ago). It's
as though their engineers determined the minimum CoC required for
"sharp" and adjusted slice separation with aperture to deliver that.
So, the difference between using f/2.8 and f/11 at a focus
differential of 3 is the total depth of field covered.
Exactly so. For a deep subject, set a small aperture. The right choice
for an in-camera FS with only 8 slices. Unfortunately, they carried
the idea over into FB.
Remember, though, that 4/3 sensors start to suffer diffraction
softening by f11. I wouldn't go past f8. According to the old rules,
even f8 is into diffraction limiting, but practice says it ain't so.
If you go to a focus differential of 4, you will start to see some
minor soft spots in the final product. Go to a focus differential of
5 and the soft spots interspersed become more apparent. The higher
you go on the focus differential scale, the larger and more apparent
the soft spots get...regardless of aperture. What the aperture does
is increase or decrease the total depth of field.
I thought of them as "waves of focus".
So, it finally dawned on me that what Olympus seems to be doing here
is relating the coverage as much to the number of shots stacked, as
with aperture. It may well be that stacking 8 shots works well with a
focus differential of 3 or less. If you want to use a focus
differential of 4, you'd better stack at least 9 frames . If you want
to use a focus differential of 5, better stack 10 shots. If you want
to use a focus differential of 2, you may only need to stack 7
shots. As I don't have a good focus stacking software, I was not
able to test this theory. The EM-1 does do focus bracketing up to 999
frames. I'm guessing that is overkill even when you set the focus
differential to 10.
Bottom line...I did the testing and now I know. For in-camera focus
stacking, the magic focus differential is 3. Use the aperture to
adjust the total depth of field. If you can't get enough depth of
field even with a high aperture...then you need to switch to focus
bracketing and take a lot more frames, which allows you to use a
higher focus differential and still not get soft spots (I call them
spots, but they are really more like strips).
One other note, the place to aim your focus when using the focus
stacking feature is at 1/5th of the total distance from the close
edge you want in focus. So, you want your total depth of field to be
5 inches, focus 1 inch deep from the close edge of that 5 inches
you've targeted (4 inches from the back edge)."
Maybe for FS, with its limited number of slices. For real world, FB,
hand held, with E=M5 II, focus on the nearest point.
--
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