Question about auto iso & min shutter speed

ajax_andy

ajax_andy

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I've just been having a play around with the 5D MKIII and tried setting up the auto iso to be max 6400 and min shutter speed 1/60.

However when testing it and with the camera in AV and auto ISO it selected ISO 12800 and shutter speed 1/20. Any idea why?

I've never used auto iso before as like to be in control of what settings are being used, but could see the benefit if I could get it to work without the worry of it selecting a too high iso or too low shutter speed
 
Phil Young said:
The scene must have been pretty dark...

Your body is most likely upping the ISO to it's highest native before finally resorting to lowering the shutter speed.
Click to expand...

Yep, this is what my 1DIII would do (although up to 3200)

1/60s min speed limitation is pretty strange. If I need auto iso I am probably shooting a moving target in a dim setting, so I'd want 1/200s or more. Anyway changing ISO yourself is not so bad. Maybe it works better with Tv mode?
 
ajax_andy said:
I've just been having a play around with the 5D MKIII and tried setting up the auto iso to be max 6400 and min shutter speed 1/60.

However when testing it and with the camera in AV and auto ISO it selected ISO 12800 and shutter speed 1/20. Any idea why?
Click to expand...

Safety Shift is on? You set it in the custom functions somewhere I think.
 
It looks like you have Safety Shift on, have a look at page 317 in your manual for the description of what it does and how to set it. I had a few problems with it when I first got the camera and it wasn't until I disabled it that I got the exposures right.
 
Thanks for the info guys! I'll take a look at the safety shift thing and change it so it works as planned.

As for the shutter speed of 1/60 I was just testing how it worked and seeing if it threw up any unexpected issues... the chosen shutter speed was just a random one and yes it was in a dark room... I chose to test it in those conditions as wanted to see how it coped :)
 
I checked the safety shift and it was set to 'off' so I'm not sure why it's going outside the set parameters... any ideas anyone?

Also I noticed sometimes it was upping the ISO to say 5000 but with a shutter speed of 1/200... any idea why it would up the ISO instead of dropping the shutter speed? Or is the stop difference between ISO 4000 and 1/125 (this was the set min ss) too great and so it had to up the ISO over changing the SS?
 
dave_bass5 said:
It states in the manual that shutter speed will go below the minimum set, if the camera cant get the correct exposure.
Its nothing to do with safety shift (as you have discovered) and perfectly normal.
Click to expand...

Yeah I guess that makes sense... think I just need to set the upper ISO limit higher as even if I went to full manual mode it's not like I can cheat the system and somehow get a properly exposed image using different settings to what the camera is selecting. :)
 
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