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Re: [OM] WTFocus Stacking`

Subject: Re: [OM] WTFocus Stacking`
From: "Wayne Harridge" <wayne.harridge@xxxxxxxxxxxxxxxxxxx>
Date: Sun, 17 Jul 2022 10:09:40 +1000
There are some beautiful examples in that group Moose!


> -----Original Message-----
> From: olympus <olympus-
> bounces+wayne.harridge=structuregraphs.com@xxxxxxxxxxxxxxxxx> On
> Behalf Of Moose
> Sent: Sunday, 17 July 2022 6:03 AM
> To: olympus@xxxxxxxxxxxxxxxxx
> Subject: Re: [OM] WTFocus Stacking`
> 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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