This page is currently a copy of a diary article from 17 September 2017. It is intended to
develop.
It's been nearly two years since Olympus came out with firmware support
for Focus stacking, and I have yet
to completely make friends with it. Every time I
use it, I have to go back to the instruction manual and read what little it can tell me.
What Olympus calls focus bracketing, where the camera takes up to 999 (!) images with
marginally different focus settings, starting at the closest. The default is an equally
unrealistic 99 images.
What Olympus calls focus stacking, where the camera takes exactly 8 images, starting at
the mid-range and moving first closer and then further away. After taking the photos,
they are merged into a JPEG image
covering about 90% of width and height. It also saves the original images in the format
specified in the camera settings (in my case raw) and also in JPEG, whether you ask for
it or not. The merged JPEG image is in addition to the other 8, so in my case I get a
total of 17 images. The result is like this, first the JPEG image, and then the same
photos processed with DxO Optics “Pro” and
merged with external software:
Kim Holst summarizes the in the following image (click to get full size):
The distance moved is controlled by a value that Olympus calls “focus step”, a number
between 1 and 10 that has some relationship to the size of the step. The larger the number,
the larger the step. Apart from that, there is no reliable information. Some say that the
size of the step also depends on
the depth of field, and some say
that step 1 means a step of exactly the depth of field, so that for any two images the near
limit of the second image is the far limit of the first image. That doesn't make sense to
me for two reasons: first, that would make the larger steps far too large, and secondly
“depth of field” is a matter of opinion: how unsharp can something be? In addition, it
doesn't line up with my inaccurate observations. One thing is clear from observation is
that the step is not constant: it gets larger with focus distances.
In each case, the camera uses the electronic shutter. This places severe (and undocumented)
restrictions on the shutter speed with flash: 1/8 s maximum for the Mark I, and 1/50 s for
the Mark II. The camera will happily shoot at higher speeds, giving images like these (E-M1
Mark II, 1/250 and 1/60 s):
When using flash, you can extend the time between shots to allow the flash to recharge.
There's no feedback from the flash, of course, so if you choose it too short, you'll get
uneven exposure.
Setting the parameters
There's nothing obvious about where to find the settings for focus stacking. They're in the
camera 2 menu, under Bracketing.
Resources
Here's a list of other pages with information on this topic:
