Wow, all that made my head hurt. Confusing, possibly impenetrable comments on
exposure with chipped adapter, suddenly
interleaved with focus confirmation/accuracy comments.
I think this post of Chuck's comes closest to showing the problem understanding
Av behavior everyone seems to be having.
First, those who can't understand why it would make any difference to the
exposure system whether greater or lesser
light coming through the lens was due to aperture, filters or simple ambient
light would be right - are right in
principle - except for one camera exposure system problem that chipped adapters
solve.
Second, Chuck is simply wrong in assuming that exposure non-linearity should
persist with a chipped adapter.
Third, getting the right aperture in the EXIF, while nice, isn't the most
important reason for having the adapter tell
the camera the maximum aperture of the lens.
The issue is that the exposure sensing cells in the viewfinder housing, peering
at the viewfinder screen, at angles, are
affected by the maximum aperture of the lens. I could speculate as to the
combination of reasons, but the point is that
it is simply so. (Does not, of course apply to live view.)
Way back in 2006, I did this simple test of exposure with manual adapter with
50/1.4 attached.
<http://www.moosemystic.net/Gallery/tech/300D/300Dexp.jpg>
Note that Manual exposure is largely consistent across aperture, slight
differences probably due to imperfect diaphragm
precision.
Then note that Auto exposure is quite inconsistent at large apertures, settling
down at smaller ones. I believe this is
the effect that Oly was concerned about in use of OM lenses on the E-1,
although the details of their system will give
different incorrect results than Canon's.
THUS - These exposure systems are dependent on knowing the full aperture of any
lens in order to calculate the correct
exposure!
SO - When a chipped adapter reports the correct maximum aperture of the lens,
the exposure system works correctly.
THEN - Exposure tracks correctly throughout the aperture range.
-------------------------------------------------------------------------------
This aspect of a chipped adapter is the most important to me. Shooting with
Sigma 600/8, it often took me several trials
with chimping to get exposure correct. I even had to go to Manual because the
correction is greater than the range of EV
adjustment.
With the Big-IS adapter, and I would think, any others that are working, I
usually get correct auto exposure first shot.
At least with Big-IS and Canons, once the correct max aperture is set, one may
set the Av the actual shooting setting of
the lens. This has no effect whatsoever on the actual exposure, per "First",
above. But it does record that aperture in
the EXIF, which is useful to me.
Full Aperture Moose
On 5/8/2012 12:42 PM, Chuck Norcutt wrote:
> OK, I hear you but:
> 1) why does that work and
> 2) how did you figure that out
>
> It seems to me that, with the camera set to f/2.8 but the lens set at,
> say, f/5.6 the camera would sense the ambient lighting at two stops less
> than the actual. But, believing the camera is measuring at f/2.8 it
> would underexpose on the shutter speed.
>
> That apparently doesn't happen. What's wrong with my thinking? Is it
> that the camera sees only the stopped down reading at the time of
> exposure and makes a correct exposure because of it. If so, what's the
> relevance of telling the camera the maximum aperture?
--
What if the Hokey Pokey *IS* what it's all about?
--
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