On 2/22/2017 3:01 PM, Mike Gordon via olympus wrote:
Metric Variable Moose writes:
<<When making the below shots, I measured the distance from focal plane marked on the
camera to the point I carefully manually focused on. Just a rough measurement, but I think
accurate within a mm or so, two at most - 155 <<mm
<<Then I checked the EXIF - 180 mm.
<<I have no information why the difference. Could be the accuracy is "x% ±30 mm",
which is quite OK, except at really short distances. Or the lens may report that it has hit closest focus,
and the camera assumes that is the <<published 180 mm, as opposed to what this particular lens is
doing.
<<Just a reminder that not all is as reported in this wonderful digital world.
<<Keep your wits about you. :-)
I strongly suspect it is just the lower accuracy/precision as a consequence of
using stepper motor counts to estimate focusing distance to report in exif.
The error is greatest at near and long focusing distances.
I think that's generally true. But at closest distance, I suspect it's just using the spec. - as likely to be more
accurate than a stepper count. I looked at a few closest shots, including with CU-diopters, and all say 180 mm. Either
stepper count repeatability is really, really good, or it's a default value.
Panny doesn't even bother unless they have changed there ways, which I really
don't like at all.
It would be nice to have in EXIF, but perhaps none is better than inaccurate. It may be that their different hardware,
and perhaps lens firmware, won't allow the body firmware to do a useful job of estimating distance. From out here, it's
a black box problem. Both brands of lens work in all major functions v. close to identically, through the interface, but
we have no idea how similar they are inside.
As I found with a tripod mounted comparison of a complex, 3D subject, even with the same lens and AF settings as similar
as possible, a GX7 and E-M5 found slightly different focus depths. Just a tiny difference, 1 or 2, maybe even 3 mm, out
of maybe three meters, but with obvious focal plane differences at 100%.
How Far Is Moose
--
What if the Hokey Pokey *IS* what it's all about?
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