Godfrey DiGiorgi wrote:
The issue could [ ... ]
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.
Do you have to do that with FA lenses? I've always been under the
impression that they would transfer the actual aperture value
electronically when the ring was used, which should mean you could
always do full aperture metering even without the mechanical coupling...
- Toralf
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
On Apr 4, 2009, at 6:19 PM, Paul Ewins wrote:
AFAIK the diaphragm on the K & M lenses works differently to those on
the A, F & FA lenses. One is quite linear in action, the other more
of a curve. If the metering can't tell the difference between the two
then one will be accurate across the range and the other will be
accurate wide open and get increasingly innaccurate as you stop down.
I believe this is the essence of JCO's lengthy aperture simulator
(stimulator?) crusade as that was the missing link that made both
systems work on the same camera.
So a 77/1.8 will work fine in manual mode but a K85/1.8 or M85/2 will
need you meter at full aperture and then count the number of stops
from wide open as you stop down and adjust exposure accordingly
(easier to do than say). On a SMCT 85/1.8 you simply set the lens to
manual and stop it down and meter. And I'm not sure what happens on
the M42 lenses that had the two pin system for the ES and ESII.
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