The problem:
I use Zeiss Contax lens (e.g., contax 50mm 1.4) adapted to Canon 5DIII.
Since there is no electric aperture control. a normal process for using lens
is as follows for taking a photo with f8.
1. adjust camera aperture setting to f 8.0
2. set Av mode.
3. adjust lens aperture to f 1.4 and then focus and then AE lock.
4. while in the AE *lock mode, adjust the aperture to 8.0.
5. click the shutter button.
It's inconvenient to use AE lock and then adjust the aperture to the
desired aperture.
What I want is pre-adjust the lens aperture to the desired aperture
say f8.0. And focus use the LCD live screen. So I don't need
the step of AE lock and re-adjustment of the lens aperture.
The problem of this is that it will have over exposure.
The reason is that at Av mode, the camera assume that my lens
aperture during focusing is max aperture (f1.4) and at time of taking
the photo, the camera will be able to automatically adjust the camera
setting value of f8.0. So the calculation of exposure is based on the above
assumption, and metering is done at (focus time f1.4)
and auto compensate the final aperture(f8.0). With my above procedure,
the metering is actually done at f8.0, give the camera a wrong
impression that the light it obtained at f1.4 (not f8.0), so in order to have enough
exposure for f8.0, the exposure time needs to be increased. Therefore the result
of the calculation will be over exposed.
The work around for solve this problem is :
set the camera aperture value as lens max aperture(f 1.4 in this case),
but adjust real lens aperture to a desired value, say f8.0.
So the final exposure will be correct (as it will not compensate for
the difference of the 1.4 vs 8.0. Because, camera thought the light
it get is already at max aperture(and final aperture is also max 1.4).
But the issue of the work around is that the EXIF data recorded for the photo will always
be f1.4. But the photo is actually taken at f8.0.
The solution:
Magic lantern add a function so that the exposure will be calculated
as if the aperture setting on the camera is lens' max aperture. But
the recording of the EXIF, will still use the camera aperture setting.
Thanks
I use Zeiss Contax lens (e.g., contax 50mm 1.4) adapted to Canon 5DIII.
Since there is no electric aperture control. a normal process for using lens
is as follows for taking a photo with f8.
1. adjust camera aperture setting to f 8.0
2. set Av mode.
3. adjust lens aperture to f 1.4 and then focus and then AE lock.
4. while in the AE *lock mode, adjust the aperture to 8.0.
5. click the shutter button.
It's inconvenient to use AE lock and then adjust the aperture to the
desired aperture.
What I want is pre-adjust the lens aperture to the desired aperture
say f8.0. And focus use the LCD live screen. So I don't need
the step of AE lock and re-adjustment of the lens aperture.
The problem of this is that it will have over exposure.
The reason is that at Av mode, the camera assume that my lens
aperture during focusing is max aperture (f1.4) and at time of taking
the photo, the camera will be able to automatically adjust the camera
setting value of f8.0. So the calculation of exposure is based on the above
assumption, and metering is done at (focus time f1.4)
and auto compensate the final aperture(f8.0). With my above procedure,
the metering is actually done at f8.0, give the camera a wrong
impression that the light it obtained at f1.4 (not f8.0), so in order to have enough
exposure for f8.0, the exposure time needs to be increased. Therefore the result
of the calculation will be over exposed.
The work around for solve this problem is :
set the camera aperture value as lens max aperture(f 1.4 in this case),
but adjust real lens aperture to a desired value, say f8.0.
So the final exposure will be correct (as it will not compensate for
the difference of the 1.4 vs 8.0. Because, camera thought the light
it get is already at max aperture(and final aperture is also max 1.4).
But the issue of the work around is that the EXIF data recorded for the photo will always
be f1.4. But the photo is actually taken at f8.0.
The solution:
Magic lantern add a function so that the exposure will be calculated
as if the aperture setting on the camera is lens' max aperture. But
the recording of the EXIF, will still use the camera aperture setting.
Thanks