Strange settings when using auto ISO

[gwinegarden]

I was just looking at some photos that I took recently and found some of the picture very noisy.  When I looked at the metadata, the settings were a bit strange.

I was using a t5i with the Canon 55-250 IS STM lens.  The camera was set to Apeture priority @ f11 and Auto ISO.  An example of the settings, on the noisy photos, was 1/400 with ISO 6400!!  This seems odd.  I can see why it might pick that ISO at 1/400 but why choose that speed?  The others had similar settings.

On other photos, all seemed more correct e.g. 1/100 @ ISO 320 & 1/160 @400.

To me, the issue is that the camera is selecting too high a shutter speed, at certain times.  I do not know if Auti ISO has anything to do with it.

Any thoughts would be, greatly, appreciated.

[gwinegarden]

Possibly, but that would be counter=productive as the lens is IS. But, stuff happens.

[ebiggs1]

I do say, "The camera will do exactly what you ask it to do." And I think it applies to your case as my friend pointed out you have chosen to let the camera control two of the necessary settings for proper exposure. The only thing you told the camera is it can not change the aperture. You said, camera select whatever ISO or SS you want to.  It did exactly that!

I came from a time where a photographer had to set everything.  This background has me using little of the 'auto' features. One of my favorite modes is Av. However, I almost never use auto ISO. It is my least favorite auto setting.  I want to know where the ISO is all the time.

[ebiggs1]

"I can see why it might pick that ISO at 1/400 but why choose that speed?"

Along with setting an upper or lower ISO limit, you need to also set limits on SS, fastest and slowest. What camera are you using?  Did I miss that? Some cameras allow you to set the minimum shutter speed automatically based on the focal length of the lens. The camera uses the reciprocal rule to do this. 

It's good to know the limitations of auto ISO. For example, there is a risk of creating overexposed images, or underexposed, as the camera would not be able to drop or increase the ISO enough.

[gwinegarden]

I was using a T5i which does not have SS limits.

I might have noticed, in the viewfinder, but if I see 1/400 @f11 I would not. normally, look at the ISO.

To me, the main question is why it selected 1/400 @f11.  That, of course, cause the high ISO.  

Was it due to the focal length of the lens?  Doesn't make sense, to me, especially, as the lens is IS. 

Is my sensor nuts?  Maybe, but was checked out a year ago. 

Does auto ISO cause strange behavior?

Anyway, I don't often use auto so I will stay away from now on unless, absolutely, necessary.

Thanks

[ebiggs1]

"Was it due to the focal length of the lens?"

It could be. I don't have a T5i to try.  Check your manual.

"Doesn't make sense, to me, especially, as the lens is IS."

The fact the lens has IS, has no factor in this issue. What lens were you using?

I personally don't like auto ISO but most (all) of my pro friends that shoot for the Kansas basketball games all use it.  They are telling me I need to use it, too.  I think it is pretty common in all of professional sports anymore.  I don't see, at this point in my life, any good reason for me to use auto ISO. 

[gwinegarden]

I did some research.  Canon does use the focal length to determine SS and does not consider IS. 

[Waddizzle]

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@gwinegarden wrote:

I did some research.  Canon does use the focal length to determine SS and does not consider IS. 

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Correct!  Not every lens has IS, so having IS does not factor into the behavior.  

BTW, we still do not really know what exactly you are doing.  For example, we do not know what focal length you are using, how much available there it, how far away is your subject, etc.

[ebiggs1]

"...we still do not really know what exactly you are doing."

The more info you supply the more accurate the solution will be.

[gwinegarden]

My research gave me the answer.  But, I do not understand why the camera does not take IS into consideration.

Oh well.  Once burned.

[kvbarkley]

If the info is given to the camera - does DPP tell you whether IS was used? - it can be three states: No Lens IS, IS present but off and IS present but ON. It is probably easier to ignore IS, since that gives you a more conservative answer. After all, how many stops do you allow for IS? 2? 3? 4? There are many IS's and they all have different abilities.

Remember to, that IS came after the invention of the EF lens, and before digital. The whole point was to make it as invisible to the camera as possible.