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Re: [OM] E-M1 focus testing

Subject: Re: [OM] E-M1 focus testing
From: Moose <olymoose@xxxxxxxxx>
Date: Fri, 29 Jul 2016 20:54:59 -0700
On 7/29/2016 7:48 PM, Don Holbrook wrote:
After using the TG-4 for stacking, I decided to try the EM-1 for comparison. 
Only certain lenses will focus stack, and others will only bracket.  I made 
three shots:  60 macro stack, 60 macro bracket w/CS6 stack, and 14-150 bracket 
w/CS6 stack to see any differences.  All three are unedited jpegs.  Comments 
can only help!

http://zone-10.com/tope2/main.php?g2_itemId=20466

http://zone-10.com/tope2/main.php?g2_itemId=20468

http://zone-10.com/tope2/main.php?g2_itemId=20470

No big, obvious differences. But you need to use a tripod for careful comparison; changes in subject size and/or orientation make it hard to see subtle differences.

What settings did you use? It looks like the stacks weren't deep enough to catch the back part of the cluster (which may or may not be what you want.)

Aperture and the Focus Differential setting interact in a way I didn't expect. Some of my early shots had an odd quality where the sharpness got greater, lesser, greater, and so on, with focal distance. I did some searching and reading.

It seems that the way it works is that Focus Differential setting tells the camera how much sharpness variation you are willing to accept with depth. The camera knows the DoF for the lens and aperture setting, and spaces the stack accordingly.

If I set for 10 shots and aperture @ f2, those shots will be very closely spaced and the total focal depth of the stack will be relatively shallow. If I change the aperture to f11, the stack will be much deeper. Or, if I need the lens speed, I can leave it open and increase the number of shots in the stack.

My current default settings are:

1.  Number of shots = 12
This is simple. The shot buffer fills up at about 12-13. The first 12 in a stack are always taken very quickly. Any more, and those over 12 come very much slower. Fine on a tripod, a pain handheld. (If I don't wait for the buffer to clear, the first shots in the next stack also go slow.)

2.  Aperture = f5.6 or f8
Again, simple; these are generally the best IQ apertures for µ4/3 lenses, at least in my experience. As I am stacking for DoF, there's no point in using smaller apertures that balance lens sharpness against diffraction. Anything larger makes the stack shallower and may have less than the best IQ of which the lens is capable.

3. Focus Differential = 1.
I definitely saw focal differences that annoyed me with depth at three. One, with the above other settings, has been giving me results I like. Two might be OK.

Another caveat. The stack starts at the current focus distance and works its way farther away until it has taken the set number of shots. With subjects like flowers, insects, etc., its really easy to miss a bit or two that are closer to the camera than where the lens is focused, resulting in a wonderful image, but for a couple of prominent bits that are softer - right up front. So I've taken to focusing, then moving the camera back just a little before pushing the release the rest of the way. This has been working well for me.

This is true for the E-M5 II, and I imagine the E-M1. The TG-4 works differently, at least for in-camera stacks, apparently evaluating the whole frame to determine closest part of the subject.

{Moose}

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