How bad is it to use Auto ISO?

I almost always 99.99% of the time shoot in Av. But for an upcoming trip to California which will include whale watching I am planning on using Tv mode and setting the ISO to auto. In this way I can maintain a proper shutter speed in changing conditions(clouds moving through the area, etc) to freeze motion.

Is this how most people use Auto ISO in conjunction with Tv mode? Any suggestions?

I personally use auto ISO when I am shooting manual in widely changing lighting conditions. I shoot a lot of BMX race photos and must use a higher shutter speed but still need an aperture that is not wide open. Unless you shoot every rider in one position on the track, the shots are often in shade for one shot and sun in the next. This is where Auto ISO is great, where you need an auto mode but AV and TV are not good enough.

In my opinion, if you can get the shots without using manual, auto ISO is rarely needed. Auto ISO is to give you an automatic mode where you can set both aperture and shutter speed at the same time before making the shot. Best for rapid action, where you don't have time to make changes to your settings between shots.

My experience with TV mode using Auto ISO is that the camera will not change the ISO until it can't use a lower aperture setting. To clarify what I am saying, say your settings are ISO 1000 with a 1/500 shutter and the camera picks an aperture of 4.5. Put the camera in TV and Auto ISO, it will pick a wide open aperture (for example 2.8) and use a lower ISO (200 for example.) Then if it gets cloudy, the aperture will stay at 2.8 and the ISO may move up to 800 (for example) Those numbers are not accurate, just using them for example. My point is, in my experience Auto ISO will not be increased until the aperture is opened up. Unless you wish to shoot wide open when it gets darker, auto ISO is limited in use.

Mr_ipsum wrote in post #17669981
I almost always 99.99% of the time shoot in Av. But for an upcoming trip to California which will include whale watching I am planning on using Tv mode and setting the ISO to auto. In this way I can maintain a proper shutter speed in changing conditions(clouds moving through the area, etc) to freeze motion.

Is this how most people use Auto ISO in conjunction with Tv mode? Any suggestions?

Like Nogo, I often use auto ISO in manual mode, so I can set the shutter speed and aperture as I wish, and let the ISO float.

Auto ISO in Tv mode is a whole new concept to me. You would be asking the camera to make the aperture/ISO decision. How would it decide? I just had a look. With my 100L/2.8, it just keeps the aperture at or close to 2.8 and varies the ISO until it hits minimum ISO. At brighter conditions, it holds the ISO at minimum and varies the aperture.

Hmm, I would stick to using M with auto ISO.

Mr_ipsum wrote in post #17669981
I .
Is this how most people use Auto ISO in conjunction with Tv mode? Any suggestions?

Exactly

I personally never use auto ISO but if you set it to usable ones I don't see how it can ever be bad.

maverick75 wrote in post #17670050
I personally never use auto ISO but if you set it to usable ones I don't see how it can ever be bad.

Cameras have unusable ISO settings?

I use it in manual, as others have said: when lighting conditions will change a bit (but I want to maintain the aperture/ss values chosen). I don't set a wide range of ISO's though, currently I believe it's set to 100-800. Most if not all cameras can handle that range with little noticeable degradation to IQ.

GeoKras1989 wrote in post #17670078
Cameras have unusable ISO settings?

Well, my 5D2 can go above ISO 1600, but I almost never use it above that. Maybe 3200 in a pinch, but it looks pretty bad, so as to be "unusable" for prints at decent sizes, like 13x19" and bigger. Other people may have different ideas of what is acceptable to them.

In any case, on a camera like the 5D2, where I often try to optimize the exposure to maximize dynamic range, auto-ISO is a no-no. On something like a 1Dx where you have flat DR from ISO100-800, using auto-ISO all the time is a no-brainer. It depends on the camera used really.

As for photographing whales, expect to use really fast shutter speeds, auto ISO may not even be necessary as you'll certainly be shooting at high ISO all the time anyway.

I use auto ISO a vast majority of the time. If you understand how to read your meter and how to use exposure compensation there is quite literally no downside IMO.

I shoot a lot in M with auto ISO, it offers a great flexibility with this little dose of automation that makes things easier. I wish though I could exposure compensation in M mode this way, I know it's doable on other brands.

Another feature I'd like is the possibility to link Auto ISO and shutter speed or aperture, like setting the threshold where the ISO starts to raised (like keep a minimum speed of 1/200s or a minimum aperture of f/5.6). It's also possible on other brands

Anyhow, it's just to make things easier, I can live without it (I currently do!)

I suggest that you shoot a series like this with Auto ISO & see how accurate it really is: Post #47

Auto iso in manual mode makes some sense in certain applications, but I would never use it in AV or TV mode as you are giving the camera control over two variables. If your exposure were off because of meter bias do you fix the iso or the other variable?

I rarely ever use auto ISO, and prefer TV when shooting family photos. I set ISO low enough to give me the shutter speeds and apertures that I want.
The only time I Use auto ISO is when lighting is rapidly changing, like a trip to the circus.

Surely if you using Auto ISO in M mode then you are not actually shooting in Manual mode but Auto Iso mode as the camera will try and AUTOMATICALLY compensate for exposure errors by adjusting the ISO. IMHO Manual mode should mean everything is adjusted and controlled by the operator.

However a small problem I see using Auto ISO in M mode is the ability to do exposure compensation as easily as you can in Av or Tv modes. Based on the OP purpose for using Auto ISO in M mode is that they want to set the Aperture and Shutter speed manually and leave them set and the ISO will adjust automatically to account for small variations in the lighting - I assume the Auto ISO will be adjusted to centre the needle which negates any required exposure compensation. Of course there may be some cameras available that do include EC when shooting in M but my experience is based on the consumer/amateur level equipment such as the EOS 550D. Alternatively what happens if in M mode one adjusts the settings for the needle to be off-centre by the desire EC amount, will the Auto ISO remember this and adjust accordingly on each subsequent shot ?