Ok, it looks like I got hold of the wrong end of the stick. The green
button mode should just stop it down to the aperture set on the lens,
take the reading and then calculate appropriately.
I'm sure I have had errors when using this method in the past but when
I went to test it just now (*ist-D with FA43 and M50/1.4) it worked
perfectly across the range.
All I can think of is that perhaps the camera is taking the reading
before the lens has fully stopped down. This would account for over-
exposure, but if under-exposure is occurring then I'm right out of
ideas. Or idle speculation as the case may be.
Paul
On 05/04/2009, at 11:43 AM, Godfrey DiGiorgi wrote:
The issue could be related to the way the diaphragm mechanism works
in interaction with the body's iris actuation mechanism, but the
linearity or non-linearity of the iris regulation mechanism doesn't
matter. When a K or M-series lens is on the camera and the camera is
in manual exposure mode, it stops the lens down accurately to the
setting on the aperture ring. I tested for that with a hand held
meter ... proper exposure is achieved with every apert...@time
setting when using a K or M-series lens in Manual exposure mode and
the meter reading is taken from the external meter.
Lenses like the FA77/1.8 work fine in manual metering mode when used
normally (lens locked on the A setting, aperture set by the body
controls) but show the same metering issues as K and M series lenses
when the aperture ring is used to set the lens opening and the green
button stop down metering is used. I tested that too.
The mechanical aperture follow-cam sensor of old would allow full
aperture metering with these lenses, but it doesn't affect how the
iris regulation mechanism works or how this metering mode functions.
Godfrey
--
PDML Pentax-Discuss Mail List
[email protected]
http://pdml.net/mailman/listinfo/pdml_pdml.net
to UNSUBSCRIBE from the PDML, please visit the link directly above and follow
the directions.
