On 3/9/2017 2:18 AM, Moose wrote:
On 3/8/2017 2:11 PM, Mike Gordon via olympus wrote:
. . . It is also an interesting conjecture that the exit pupil distance to the sensor matters more for lens
performance even with MFT lenses due to the thick sensor stack.
I have noticed indications to lead me to suspect that extension isn't always best. I wanted a close-up adapter for the
Panny 14-140on GM5 in my light/casual kit. So I did some not too formal testing. (corrected)
<http://www.moosemystic.net/Gallery/tech/Close-Up_Lens_Tube/C-U_on_14-140.htm>
The results were clear. The lens itself, at the long end and closest focus is not good in the center, and gets worse
from there. The Minolta No1. has nice magnification, but is otherwise the same. It was unfair to try the MCON P-02, as
it is 47 mm thread and the lens is 58 mm; just too small. In fact, if a theme emerged, it was that bigger is better.
The Minolta and B-Macro are both 55 mm, but the Minolta is also 55 on the front. The B-Macro is quite a bit larger.
So, that's fine, but the B-Macro is relatively big and heavy, for this little kit. So I did another test, to see how
extension tubes would compare. (corrected) <http://www.moosemystic.net/Gallery/tech/Close-Up_Lens_Tube/14-140mag.htm>
The 16 mm tube was close in magnification. Here, the casual nature of my testing caught me. It's obvious that in
putting a box on the table in front of a tripod mounted camera, I didn't get them quite parallel. Still, the lens is
quite a bit better than tube in the center and both right corners, about even, lower left and a little worse, upper
left. Could be some decentering in the lens, pretty common when you look this close, but I think it's mostly simple
sloppiness of technique in a test never intended to be posted. Assuming that's true, the lens is quite a bit better
than the tube. The lens is in the kit.
I was chatting with Ctein the other day, about too many topics in a brief meeting, and mentioned this suspicion. He
was the one who thought the fine balance between exit pupil/angle and sensor stack thickness might be a factor.
Thought experiment; shoot, as Jim and Rick have been doing, through glass, at an angle. What's the difference between
stretched clear wrap, 1/8" glass and 1/2" glass? Assuming the same refraction index, the first air-glass boundary
changes the direction of the rays, the second changes it back, but laterally displaced. The thicker the 'stack', the
greater the displacement. It seems to me that a thick stack would be more sensitive to moving the lens body than a
thinner one.
I have only seen the exit pupil distance mentioned as a known important variable when using lenses designed for
different sensor stack thickness- . . .
Putting an extension tube on a MFT lens may be fine but would anticipate some
issues with lenses with floating elements.
All of the primes I have, but the lens cap lenses, focus internally, not by movement as a unit, so all have what
amount to floating elements, and change FL in order to focus. And all the zooms are vari-focal, changing FL changes
focus. We aren't in unit focusing MF lens land any more, Dorothy. :-)
Re Link Moose
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What if the Hokey Pokey *IS* what it's all about?
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