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.
--
What if the Hokey Pokey *IS* what it's all about?
--
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