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Re: [OM] WTFocus Stacking`

Subject: Re: [OM] WTFocus Stacking`
From: "Wayne Harridge" <wayne.harridge@xxxxxxxxxxxxxxxxxxx>
Date: Sun, 17 Jul 2022 10:25:31 +1000
I've read through that DP Review thread several times and from what I 

* The focus differential you set for FS is not a fixed value but is modified by 
the camera depending on aperture (and presumably focal length)
* The focus differential you set for FB is a fixed value and is not modified by 
the camera depending on either aperture or focal length

Is this correct?  I found the posters explanation somewhat confusing.


> -----Original Message-----
> From: olympus <olympus-
> bounces+wayne.harridge=structuregraphs.com@xxxxxxxxxxxxxxxxx> On
> Behalf Of Martin Walters
> Sent: Sunday, 17 July 2022 12:44 AM
> To: olympus@xxxxxxxxxxxxxxxxx
> Subject: Re: [OM] WTFocus Stacking`
> 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? 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?
> 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!!!!!
> So, the difference between using f/2.8 and f/11 at a focus differential of 3 
> is
> the total depth of field covered.  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.
> 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)."
> Martin
> On 2022-07-01 8:14 a.m., Piers Hemy wrote:
> > There is a just released useful video presentation of both stacking
> > and bracketing, with explanation of both modes, and clarification of
> > the different presentation in the menus of OM-1 and OM-D
> >
> > https://friedmanarchives.blogspot.com/2022/06/focus-stacking-on-sony-o
> > lympus-and.html
> >
> > He goes on to cover S and F cameras too, as if anyone would want to use
> them, as well as merging stacks in PS with links to cover Helicon Focus.
> >
> > Although it's on Gary Friedman's site, the video is Tony Phillips' work.
> >
> > Piers
> >
> > -----Original Message-----
> > From: olympus<olympus-
> bounces+piers.hemy=gmail.com@xxxxxxxxxxxxxxxxx>
> > On Behalf Of Moose
> > Sent: 27 June 2022 21:48
> > To:olympus@xxxxxxxxxxxxxxxxx
> > Subject: Re: [OM] WTFocus Stacking`
> >
> > On 6/27/2022 11:07 AM, DZDub wrote:
> >> On Mon, Jun 27, 2022 at 12:09 AM Moose<olymoose@xxxxxxxxx>  wrote:
> >>
> >>> On my E-M II:
> >>>
> >>> Focus stacking          = Off (i.e. Focus Bracketing = On, as set on the
> >>> prior screen.)
> >>> Set number of shots  = 31
> >>> Set focus differential  =  1
> >>> Charge Time              = 0
> >>> --------
> >>> Focus stacking          = On (as an option within Focus Bracketing)
> >>> Set number of shots  = 11
> >>> Set focus differential  =  1
> >>> Charge Time              = 0
> >>>
> >> This makes sense to me now.  Thanks for sticking with me.
> > Excellent! My pleasure, literally.
> >
> >>    I've even gotten
> >> it to work, and it's extremely fast compared to focus stacking, which
> >> makes me think the 15 seconds or so that it takes to do an in-camera
> >> focus stack is mainly spent on processing rather than exposing.
> > Yup. If you watch the EVF/LCD during the process, you can see when
> > shooting stops and processing begins. On my E-M1 II, shots are quick,
> writing out ORFs and JPEGs and then processing is almost all of the time.
> >
> >>> You mention backgrounds more than once. That's not what I'm looking
> >>> for with stack/bracketing. I'm looking for deeper DoF than one shot
> >>> can provide. Yes, the background matters, but that's a separate
> >>> issue to me, dealt with differently.
> >> Two sides to a coin to me, although I suppose I think about
> >> backgrounds more because I'm generally unwilling to spend a lot of
> >> time on backgrounds in post.  I generally bracket (the old fashioned
> >> way) from f5.6 to f11 to see where I get the best compromise of DoF and
> good background.
> > Chuck and the other DoF mavens claim(ed) that f5.6 is optimal for a
> > 4/3" sensor. My experience and testing disagree, but
> > f11 does get into visible loss of detail/sharpness.
> >
> > I suspect that part of the disagreement 'tween the tables and practice
> > may be that demosaicing the Bayer array data loses detail. Ctein
> > estimates that loss at 50%. I've certainly seen it. Shoot on a tripod, 
> > regular
> and HR. Downsample the HR file to the size of the straight shot. The result
> has much better, clearer fine detail.
> >
> > In my Bracketing practice, part of the process of leafing through the
> > stack to determine which frames to merge is looking at the background.
> >
> >> I guess I'm saying they are never really separated for me.
> >>
> >> One of the jobs of the stacking soft/firmware is to align the frames.
> >> The second is to adjust for focus breathing making frames slightly
> >> different sizes. All before actually merging focus.
> >>
> >> Focus breathing may be one of the criteria for choosing which lenses
> >> are compatible with in-camera FS
> > Notice that the Stacked JPEG is larger than the individual shots.
> > There's a frame when shooting FS to show the tighter AoV. Dealing with
> focus breathing?
> >
> >> I assumed it was something more proprietorial than focus breathing per
> se.
> > I did say "may be" and "one of the criteria". 😁
> >
> >> Not all mZ lenses seem to work, which suggests design is a key.
> > It's all clear as mud to me. None of the non-macro primes are included, only
> zooms, the macros and 8mm fishy.
> >
> >> Do you happen to know if any Panny m43 lenses will focus bracket on an
> Oly camera?
> > Random grab - Panny 25/1.7 works fine. I suspect they all do. Bracketing is
> much less fussy than Stacking.
> >
> > Testing, Testing Moose
> >
> --
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