Thanks for the link. I have these instructions somewhere (since I have
a bigIS adapter) but I have yet to use it let alone program it.
I spent a little time with the instructions and have concluded there is
no magic there. The part about shooting in AV mode really has nothing
to do with AV per se. It's all about allowing the chip report maximum
aperture of the lens vs shooting aperture to be recorded by the camera.
What it does imply to me is that the camera really isn't concerned about
actual exposure parameters at the time of an exposure reading and
exposure lock. It must simply be recording an Exposure Value (EV) which
will later be interpreted in light of the aperture it's told is in use.
There are three cases given:
Mode A, Mode B and what I'll call Mode AV for lack of any other name.
Mode A and Mode B are done in manual mode and exist for the sake of
recording actual shooting aperture to the EXIF. Both allow metering and
focusing at full aperture but require the lens to be manually stopped
down to the desired aperture prior to exposure. In both cases the
camera has to be advised of the desired aperture. The difference
between Mode A and B here is that in Mode A you set the camera to the
desired aperture before the exposure measurement and in Mode B you do it
afterward. Both methods store an EV and interpret that EV at the time
of exposure in light of what the body believes the aperture to be.
Now to Mode AV. What we think of as AV mode is not happening here.
Mode AV with respect to this adapter is just a trigger to accept the
exposure measurement in stopped down metering mode rather than the wide
open metering of Modes A and B and subsequent exposure lock. What gets
written to EXIF is whatever aperture has been set on the camera. This
is no different from Modes A and B except that for Mode AV you are
advised to set the maximum aperture of the lens on the camera body so
that that value is written to the EXIF. Presumably just a means of
identifying the lens.
If there are exposure problems between a particular MF lens's
characteristics and the camera body's metering system none of this will
straighten that out. You will still need to understand the particular
characteristics of each lens and apply appropriate exposure
compensation. If your "AV mode" on the adapter is giving you perfect
exposures just count yourself lucky that stop down metering is working well.
Chuck Norcutt
On 5/8/2012 4:18 PM, Joel Wilcox wrote:
> On Tue, May 8, 2012, at 03:42 PM, Chuck Norcutt wrote:
>> OK, I hear you but:
>> 1) why does that work and
>> 2) how did you figure that out
>
> I was afraid you would ask #1 and I'm going to punt on that.
>
> For #2, I was going to say read the manual:
>
> http://emfphoto.com/forum/index.php?topic=3.0
>
> The part that helped me was under "Shooting and not recording exposure
> aperture setting."
>
> Joel W.
>
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