Seiko shutter mamiya sekor 80mm f2.8 30th to 500th range. Tested at all speeds at f22 and f2.8. Mamiya afd iii with leaf aptus 65s. Metered with gossen ultraspot 2 flash meter 4 and I camera matrix meter. Deviations are in stops (ExIN). 30th at f22 +.22. at 500th at f2.8 is was +.17 a 30th at 2.8 was .01%+ a 500th @ f22 (smallest the lens gets) +.27 So the difference at a 500th from f2.8 to f22 is +.1 so even if you extrapolate that out to f45 which is 2 more stops you get to a difference of .13 (a gain of .03 stops) stops from 2.8 to 45. or f45@ a 500th would be +.273 stops.
On Apr 2, 2014 4:11 AM, "karl shah-jenner" <shahjen@xxxxxxxxxxxx> wrote:
Funny but not what im talking about and that shutter looks nothing like a
modern copal. And im not talking about what you are talking about. Im
saying this. As the shutter design fails and exposure isnt accurate. That
over exposure because of the closeness of the iris is equal failure across
the entire frame. The failure will not result in an uneven exposure just an
inaccurate exposure.
agreed, it's really a lens or vigneting issue if there's uneven exposure across a frame as the shape of an iris has little or nothing to do with exposure across a frame for a leaf shutter (focal plane of course is a very different animal). cat's eye, slit, star, blinking eye, rotary, window blind - propeller - none of them should affect the exposure from center to edge (well, maybe the propeller).
Andy linked:
http://www.davidhazy.org/andpph/2014-pix/2014-mechanical-shutters-1.jpg
which looks kinda like a more modern shutter illustrated here:
http://www.kern-photo.com/2013/01/why-leaf-shutter-lenses-matter/
In Andy's, I can't see the scale and am presuming it's in similar time intervals, if this is the case then at the smallest aperture the exposure is open from the first shot.. or all 18 frames. 18/18
wide open is only open for 4/18 intervals. that's 2/9ths of the exposure .. meaning the first frame aperture was open 4.5 times longer than wide open exposure.. that's not at all to say it got 4.5 times more exposure, as the incremental exposures also added to the overall exposure - but I am not in the frame of mind at the moment to throw myself at complex calculations to determine the total difference. I would guess it would be more than 1/10th of a stop difference though.
