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Archive 2014 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?

  
 
Michaelparris
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p.1 #1 · p.1 #1 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


Just curious.....


Jul 02, 2014 at 11:25 PM
Pixel Perfect
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p.1 #2 · p.1 #2 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


Michaelparris wrote:
Just curious.....


Well you see it depends on how Canon rounds the numbers and if the 1.2 is actually a 1.19 or a 1.26 lens. If you calculate 1/2 stops and 1/3 stops starting at f/1.0 you can end up with 1.19 which is rounded to 1.2 or 1.26 which should be rounded to 1.3 but some liberties are taken. Sony might be reading actual aperture and rounding correctly.



Jul 02, 2014 at 11:41 PM
Michaelparris
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p.1 #3 · p.1 #3 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


Forgot to mention FD w/ EF mount


Jul 03, 2014 at 12:17 AM
Constable
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p.1 #4 · p.1 #4 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


Pixel Perfect has it nailed.
The Sony displays f-stops in 1/3 stops i.e.either f/1.1 and f/1.3 instead of 1/2 stops as on the Canon i.e. f/1.2. The actual aperture is the same and the lense is wide open.

Ed



Jul 03, 2014 at 12:31 AM
Gochugogi
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p.1 #5 · p.1 #5 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


I seem to recall the EF to FD adapter having glass in it to increase the flange distance? If so, greater distance plus additional optics mean less light at the image plane.


Jul 03, 2014 at 04:48 AM
ZoneV
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p.1 #6 · p.1 #6 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


Does the EF mount has an EF chip? There are programmable adapters, you could programm every f-stop number you want (and the adapter has in its list). So probably you could programm f/1.0 as well - but with no positive effect on the picture.


Jul 03, 2014 at 05:10 AM
kezeka
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p.1 #7 · p.1 #7 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


Constable wrote:
Pixel Perfect has it nailed.
The Sony displays f-stops in 1/3 stops i.e.either f/1.1 and f/1.3 instead of 1/2 stops as on the Canon i.e. f/1.2. The actual aperture is the same and the lense is wide open.

Ed


1) The sensor would measure T-stop not F-stop in the method you are ascribing to Sony's aperture detection system. You are describing transmissivity itself - not the f-stop calculations for it.
2) As far as I know, cameras read whatever a chip tells it.
3) Sounds like a camera chip in this case needs to be reprogrammed.
4) 1/3 stop and 1/2 stop do not include f/1.3. F/1.3 is a QUARTER STOP. f/1.2 is both a 1/2 stop and a 1/3 stop.








Jul 03, 2014 at 09:26 AM
Pixel Perfect
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p.1 #8 · p.1 #8 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


That 1/3 table entry for AV = 0.7 (should be 0.666) stop is rounded incorrectly. f/1.26 is 2/3 stops slower than f/1.0. You cannot get f/1.2 in 1/3 stops. In 1/3 stops the table should read

f/1.0, f/1.12, f/1.26, f/1.41, f/1.59, f/1.78 which rounded would be f/1.0, f/1.1, f/1.3, f/1.4, f/1.6, f/1.8 for the first several.

Yes a stop 3/4 slower would also round to f/1.3 as it's f/1.297, but you cannot round f/1.26 to f/1.2

Best to leave the table to two decimal places.



Jul 03, 2014 at 07:39 PM
Mike Sowsun
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p.1 #9 · p.1 #9 · Fd 85 1.2 only reads 1.3 on my a7....anyone know why?


Canon FD lenses can't report an f/stop, so what ever you are seeing has nothing to do with the lens itself. Canon FD lenses are strictly mechanical and there is no way to know electronically what the f/stop is.

It sounds like you have a Canon FD 85mm 1.2 that has been converted to an EF mount. You must also have an AF chip either on the EF mount or on the EF to Sony adapter.

Most AF chips that are not programmable report f/1.4 and those that are programmable can be set to almost anything. The fact that yours says f/1.3 must mean that it is programmable.

I used to have an FL 55mm f/1.2 with a programmable AF chip set to 55mm and f/1.2 My Canon 7D set to 1/3 stops would show it as f/1.2 Maybe the Sony a7 works differently and rounds it up to 1.3?

Here is a photo with the EXIF intact...




Jul 04, 2014 at 11:37 PM





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