Sony A7r III with Canon 1.2 lenses - Aperture error - 1.3
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Old 05-04-2018   #1
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Default Sony A7r III with Canon 1.2 lenses - Aperture error - 1.3

Have been using my Metabones Adaptor with the a7R III for Canon EF glasses.
However, I notice that with both the 50/1.2L and 85/1.2L II, both lenses only open up to f1.3, and not f1.2.
I am curious as to why that may be? Is it Metabones problem? Canon's? It obviously does not matter to the images, but I am curious why that may be the case. Anyone?


The lens is fully open but aperture is 1.3 not 1.2.... Anybody has the same problem?

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Old 05-04-2018   #2
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Default Re: Sony A7r III with Canon 1.2 lenses - Aperture error - 1.3

Metabones covers this in their FAQ available here: Metabones®

Quote:
Originally Posted by Metabones
Why does the camera body display f/1.3 when I use the EF 85/1.2L wide open?
Different cameras may display aperture values differently.

Some cameras display the apertures as F1, F1.1, F1.3, F1.4, F1.6, F1.7, F2 and so on, but a Canon camera body displays the exact same apertures as 1.0, 1.1, 1.2, 1.4, 1.6, 1.8, 2.0 and so on.

They are the exact same apertures, but different companies choose to round them and display them differently. Mathematically speaking you multiply each f-number by 1.122462 to get the next f-number 1/3 stops down. The actual f-stop sequence, rounded to 2 decimal places, would then be 1.00, 1.12, 1.26, 1.41, 1.59, 1.78, 2.00.
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Old 05-05-2018   #3
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Default Re: Sony A7r III with Canon 1.2 lenses - Aperture error - 1.3

yes, it must be it!!!
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Old 05-06-2018   #4
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Default Re: Sony A7r III with Canon 1.2 lenses - Aperture error - 1.3

`


Some companies do NOT round the max open
aperture, some do, and the readout of those
that do can also be affected by whether you
choose 1/2 or 1/3 EV steps for your controls.

Also it's sometimes just the way the exif data
comes thru. I have non-adapted lenses that
sometimes read either higher or lower.

Add to the mix that the lens barrel markings
are usually optimistically rounded, while the
data transmission might NOT be so, and the
verdict is don't let it bug you

IOW a lens marked as 24-105 f/2.8 may very
well really be a 25.5-101 f/2.95 in it's actual
physical measure [ignoring the T-stop here].
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Old 05-06-2018   #5
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Default Re: Sony A7r III with Canon 1.2 lenses - Aperture error - 1.3

I have a Tokina 17 mm "f/3.5" ATX non-pro model lens that acts as if the exposure difference between wide open as opposed to being stopped down to the next major stop (f/4) is closer to 1/2 than 1/3 stop.


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