Auto ISO setting when using a zoomlens of 70-200mm

I use a Canon MkIII with the Canon lens 70-200mm f/2.8.
In the camera settings I limited the ISO value to max. 6400.

Now, when shooting with this equipment in low light, whatever ISO value I manually choose the system (body or lens) changes the ISO automatically, in this case, to 6400.

I'm used to change manually the ISO value to the available light environment, here it was 1200 ISO. This automatically change to 6400 ISO brings a lot of noise in the image.

How does this happen?

How can I correct this setting?

Watch other settings. If it is enough exposure it should give not very noisy images with this sensor @6400.
May be your camera set to under expose.

Set your Auto ISO Limit to 6400. Shoot in full MANUAL MODE but with exposure compensation enabled if needed.

Me, I'm a BIF'r.. I also use BBF.. I also use a 1.4 ex on my 100-400 mk ii lens and found my sweet spot to be f9.

So: On a day with plenty of light I will set for 1/1000 and use EC if the sky varies. It has to be really low light to get 6400... Usually for kingfisher or hummers in the leaves....

Let us know.

CD

Which camera are you talking about? There's more in the model name than just "Mark III". The behavior of more or less automatic ISO is different in different models.

I use a 90D.. Same as on a t7i set up as on a t7i. I don't ever use AV. I find that many people don't understand that using AUTO ISO also involves using your brain a lot to get around the subtleties of Exposure Compensation. You learn

Yes it sounds like the he is overriding the AUTO ISO with a fixed ISO.

Sorry, I was referring to the thread starter. He doesn't say which camera he's using. There are at least three totally different models with the suffix Mark III today.