On 11/13/2015 9:53 AM, Chuck Norcutt wrote:
Just a guess on my part but I think with focus stacking that the camera is changing the focus distance thus the need
for the Pro lenses. I think with focus bracketing the user is changing focus distance.
That's not the way I read it. And I hope it's not true. When stacking focus manually, one wants carefully graduated
subject or focal distances, to assure that the required DoF accuracy is maintained. The classic way to shoot them is
using a focusing rail with rulings allowing precise distances between shots, rather than changing lens focus. With
randomly spaced shots, the distance between any given two may be greater than DoF "spec." I don't see how one could have
much accuracy in manually setting focal distance with the unmarked, fly-by-wire focus rings on the µ4/3 lenses I have.
I might be totally wrong but that's the only reason I can think of for the lens
differentiation.
I can think of another reason, although I have no way of knowing if I'm right. Focus stacking software for "real"
computers has to be able to work without knowing the subject and/or focal distance of the images it is stacking. I
believe it works first by re-sampling to get all the sizes matching, then by finding areas with the best focus. to "mask
and match". That's very computationally intensive, requiring lots of CPU power and fast memory.
To do that in-camera sounds impossible, or at least impractical in the time it would take. To do it in-camera, I would
want to know the exact focal distance of the central image, the surrounding ones, the precise aperture, focal length,
DoF, etc. and if possible the focal distance at all the other focus points. With all that information given, the task of
mix and matching a fixed number of eight images at precisely fixed increments of focal distance becomes far less
computationally intensive.
Assuming something like that, perhaps those few lenses are the only ones that have the required precision/accuracy of
reporting and/or being set to, sufficiently accurate focal distances. When invoked on web images from Oly cameras
Jeffrey's Exif Viewer says, "Warning: Olympus camera focus-distance data is often erroneous." I have on occasion thought
that to be true of some images I've taken where it seems that the EXIF focal distance just can't be right. Perhaps these
are the only lenses for which that isn't true to the extent that they are suitable for the current capability of the
firmware?
Speculative Moose
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What if the Hokey Pokey *IS* what it's all about?
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