Auto ISO in 7D Av mode

Roy C

Roy C

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Just been playing around with auto ISO on the 7D. What is interesting to me when in AV mode is just how does the Camera calculate what shutter speed to use?
I understood that it would be equal to the focal length you are using but this is clearly not the case. as an example this is what I consistently got when playing around with a few lenses:

420mm focal length = 1/640 to 1/800 sec
200mm focal length = 1/250 to 1/320 sec
70mm focal length = 1/100 - 1/125 sec

This is just about 1/FL x crop factor of the Camera which is interesting.
 
I'm also using auto ISO on the 7D most of the time, however I shoot in Manual and keep a careful eye on the iso, used it a lot on Safari recently with excellent results.
Wish my 1Ds 3 had it!!
 
George said:
I'm also using auto ISO on the 7D most of the time, however I shoot in Manual and keep a careful eye on the iso, used it a lot on Safari recently with excellent results.
Wish my 1Ds 3 had it!!
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The problem with using auto ISO in manual George is that you cannot use any exposure compensation can you?
 
Roy C said:
The problem with using auto ISO in manual George is that you cannot use any exposure compensation can you?
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Yes, Roy, you are probably correct, however I'd just correct it in post processing.
I haven't found it a problem, however, and the ability to know I'm getting the DOF and shutter speed I want outweighs that.
 
arad85 said:
I believe it does.... but I could be wrong :)
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Yea, there was a thread about this some time ago, I seem to remember, and the consensus was that you used the 1.4 (or 2x) for the shutter speed setting, although to be honest I try and up the Tv a bit more than that to be on the safe side, if poss.....

That is when using an extender, of course...sorry!!
 
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George said:
Yes, Roy, you are probably correct, however I'd just correct it in post processing.
I haven't found it a problem, however, and the ability to know I'm getting the DOF and shutter speed I want outweighs that.
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I prefer the ability to be able to set aperture, shutter speed and exposure compensation something you cannot do with Auto ISO on the 7D.
I my experience letting the Camera expose how it wants and relying on correcting this in processing is a receipt for disaster - if you under expose and push in processing you create noise and if you over expose you run the risk of blowing the highlights and losing detail that will not be able to recoverable. Each to their own though I guess George - whatever works for you is the best for you.
 
George said:
Yea, there was a thread about this some time ago, I seem to remember, and the consensus was that you used the 1.4 (or 2x) for the shutter speed setting, although to be honest I try and up the Tv a bit more than that to be on the safe side, if poss.....

That is when using an extender, of course...sorry!!
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Hmm, you have completely lost me there George!!!! unless you are saying that a tc adds to the focal length which in turn determines which shutter speed is used, which is ,of course, obvious.
My query was what is the exact calculation it uses to determine the shutter speed in auto ISO?
 
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Roy C said:
Hmm, you have completely lost me there George!!!!
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Yes, sorry, I meant to say that your original comments were correct, and of course it also applies when using an extender as well, just ignore it and I'll go back to sleep!!:lol::lol:
 
Roy C said:
I prefer the ability to be able to set aperture, shutter speed and exposure compensation something you cannot do with Auto ISO on the 7D.
I my experience letting the Camera expose how it wants and relying on correcting this in processing is a receipt for disaster - if you under expose and push in processing you create noise and if you over expose you run the risk of blowing the highlights and losing detail that will not be able to recoverable. Each to their own though I guess George - whatever works for you is the best for you.
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I accept what you say, but I must say that having taken a couple of thousand shots recently, I've not found a problem, but I do keep an eye on the iso and adjust shutter/aperture accordingly, wherever possible.
 
I've sometimes found that using Av mode + auto ISO leads to shutter speeds which are only just hand-holdable in the evenings. In auto ISO mine doesn't seem to want to go above 5000... I have the ISO expansion set to 'on', but I've yet to see the camera choose 12800 by itself!
 
Cyprino said:
I've sometimes found that using Av mode + auto ISO leads to shutter speeds which are only just hand-holdable in the evenings. In auto ISO mine doesn't seem to want to go above 5000... I have the ISO expansion set to 'on', but I've yet to see the camera choose 12800 by itself!
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Hmm, interesting, just tried it with mine and you are right, my iso won't go above 3200.

I also thought that you could limit the upper end, but on a quick flash through the custom functions I can't seem to find that.
 
micloi said:
I think that the post implied that you cannot use compensation in M mode
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That's the way I read it too. I think Canon are missing the "nearly M" mode where you can set aperture and shutter speed and let the camera work out what ISO is needed.
 
arad85 said:
That's the way I read it too. I think Canon are missing the "nearly M" mode where you can set aperture and shutter speed and let the camera work out what ISO is needed.
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That's what Auto ISO does, camera in M, set the shutter and aperture yourself and the camera sets the ISO. Obviously by the very nature of Auto ISO you can't add any compensation as changing the aperture or shutter the ISO would just get changed.
 
George said:
Hmm, interesting, just tried it with mine and you are right, my iso won't go above 3200.

I also thought that you could limit the upper end, but on a quick flash through the custom functions I can't seem to find that.
Click to expand...

Anybody else checked the upper limit of iso in auto setting?
 
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