Question on 5D III / 1D X Auto ISO

In Auto ISO mode you can select a minimum shutter speed like 1/60 or 1/250, etc. There is an AUTO setting as well. I can find no description of how the AUTO setting works. What rules does it use. Does anyone know how it works or where to find a good description? I've search up and down both manuals with little luck. Help would be appreciated.

Auto Minimum SS would just be equivalent to no minimum SS being set.

Auto implies that the longest allowed exposure time is about 1/focal length. So it's not like having no limit at all, I'd say.

Then there is no way to set "no minimum shutter speed" as there will always be a 1/FL minimum...Interesting. Auto is as close to "no minimum SS" as you can get.

Since Auto will start raising the ISO long before you reach 1 second, which is the longest fixed time you can select, I think the 1 second setting is closer to no limit at all.

So with the 5D3 and a 500mm lens(for example) and enough light so that ISO doesn't max out, Auto will actually produce a faster SS than 1/250 minimum would. Nice to know.

I haven't tried to see exactly what happens, but I guess we'll have to bring our long lenses and teleconverters out to find out!

swldstn wrote in post #16891783
In Auto ISO mode you can select a minimum shutter speed like 1/60 or 1/250, etc. There is an AUTO setting as well. I can find no description of how the AUTO setting works. What rules does it use. Does anyone know how it works or where to find a good description? I've search up and down both manuals with little luck. Help would be appreciated.

If you care about shutter speeds, it might be better to just shoot in Tv mode with auto-ISO. You then have access to EC as well. When I used that mode at the last two sporting events, the 5D3 floated the ISO much more than it touched the aperture. The aperture on my 70-200 stayed at f2.8 to f3.2, but the ISO shifted between 8000 and my set max. It is as close to nearly a perfect auto-ISO mechanism for what I shoot without the 1DX's capabilities/settings that the 5D3 doesn't have.

apersson850 wrote in post #16892597
I haven't tried to see exactly what happens, but I guess we'll have to bring our long lenses and teleconverters out to find out!

Please let me know the results.

Where, in what manual, does it says Min. Shutter Speed set to Auto is a 1/f rule? I can't find a statement other than Auto is "Auto". Heck that means it can do what ever it wants with no explanation IMO.

swldstn wrote in post #16893849
Where, in what manual, does it says Min. Shutter Speed set to Auto is a 1/f rule? I can't find a statement other than Auto is "Auto". Heck that means it can do what ever it wants with no explanation IMO.

That info does not appear in the manual. It was probably stated elsewhere in an article by a Canon spokesman such as Chuck Westfall.

apersson850 wrote in post #16892194
Auto implies that the longest allowed exposure time is about 1/focal length. So it's not like having no limit at all, I'd say.

IIRC, this is how it works in "auto". I remember reading it somewhere when I first got a 5d3

The user's manual is indeed good to read, but sometimes knowledge can be acquired simply by using the camera and observing the behavior.