Just a splash or, the perils of auto ISO

[Chrisclick]

The following three shots, although technically not great, show what can happen when choosing Auto ISO while shooting in manual mode. The practice of 'floating' the ISO on cameras that provide the option, can be a wonderful time saver for sports and wildlife photography. However, like all things photographic, there is a compromise.

I discovered this for the first time just last month. I had been enjoying the benefit of my new 'trick' with ISO when I took this series of 3 shots in less than 1 second. I would never have thought that the camera would choose to change the ISO during three consecutive shots taken so rapidly.

As you can see, the 2nd and 3rd shots are at ISO 125, while the 1st shot is at ISO 100 and is noticeably darker.

I live and learn.............

1/1250, f/5.6, ISO 100
Myna Bath 1 by Chrisclick, on Flickr

1/1250, f/5.6, ISO 125
Myna Bath 2 by Chrisclick, on Flickr

1/1250, f/5.6, ISO 125
Myna Bath 3 by Chrisclick, on Flickr

[Mike Buckley]

Considering that the scene is different in all three photos, I would expect different exposures when using Auto ISO. Only one of your exposures was different. The difference is only 1/4 stop, which is easy to change during post-processing, especially if you shot raw files and your software has an exposure tool. Even so, after making that adjustment, I would expect the first photo to still look darker because more of the scene is in shadow (the bird, the bird's reflection and water).

[John 2]

Mike's explanation holds good Chris but thanks for the heads up. It would never have occurred to me.

[NorthernFocus]

What you just learned you likely already knew had you given it consideration. The "auto" part of auto ISO is just like in any other auto mode, the camera is adjusting exposure. That's what is programmed to do. Typically when one shoots in manual mode there is a desire to control exposure. As soon as you switch to any version of auto exposure, you've surrendered that control to the camera and you get what it gives you.

[chauncey]

Appreciate the heads-up...have often wondered about use in real world.
I do wonder about the criteria in which it selects "proper ISO".

Keeping the same settings in different scenes and allowing the ISO to float would prove interesting.

[Mike Buckley]

have often wondered about use in real world.

I use Auto ISO about 99% of the time that I'm not using a tripod. However, I rarely shoot scenes that I want exposed the same way in every capture such as I would want in the OP's situation. I wouldn't use it in that situation.

I do wonder about the criteria in which it selects "proper ISO".

It's not that it is selecting the "proper ISO;" the camera is using the meter to select the "proper exposure." If you have configured Auto ISO in combination with Aperture Priority, the camera will adjust the shutter speed first in accordance with your Auto ISO configuration. If adjusting the shutter speed doesn't achieve the "proper exposure," the camera will then adjust the ISO to achieve "proper exposure." If you have configured Auto ISO in combination with manual metering, the camera will only adjust the ISO to achieve "proper exposure."

[NorthernFocus]

...Keeping the same settings in different scenes and allowing the ISO to float would prove interesting.

No more interesting than any other auto exposure mode. What is more interesting is using it in conjunction with what Mike explained whereby one can place limits on how far either aperture or shutter change and then ISO takes over as needed to achieve exposure.

[Mike Buckley]

one can place limits on how far either aperture or shutter change and then ISO takes over as needed to achieve exposure.

Auto ISO doesn't allow you to place a limit on how much the aperture will change. When you're using Aperture Priority, the aperture will normally not change because that is the one setting the user is controlling. The aperture will change in that situation only as a last resort if the proper exposure can't be achieved first by automatically changing the shutter and then by automatically changing the ISO value.

Auto ISO can be configured with Shutter Priority, in which case the aperture will automatically change but there is no way to limit the amount of change (at least not on a Nikon camera). Even so, I've never understood why anyone would use Auto ISO when also using Shutter Priority. That's because using Shutter Priority is usually used to ensure that a particular shutter speed being used is fast enough. When configuring Auto ISO in a modern camera, one of the settings is the minimum shutter speed to be used. So, I don't understand why anyone would use Auto ISO to control the minimum shutter speed when it is already being controlled using the Shutter Priority setting.

[Shadowman]

ISO 100-125 is still in the safe zone although you can still get a bit of noise in some dark tones or shadow areas, nothing that cannot be edited and sometimes something you might not even bother correcting.

[NorthernFocus]

Auto ISO doesn't allow you to place a limit on how much the aperture will change...

Sure it does. As you eloquently explained

[Mike Buckley]

Sure it does. As you eloquently explained

Ouch! (sort of)

[IzzieK]

Last night on a beauty event we went to, I had another opportunity to use Auto ISO again because the venue that was supposed to be held at the stadium ended up being held in a basement of the county building. I thought I'd used Auto WB too but I changed my mind and stuck to Daylight WB instead because of the horrible lighting conditions (Flourescent). I can freely change my aperture Mike, as I had wanted but I preferred to use the widest to blur the horrible backdrop too so I had only two simple setting to change and that was the SS and the EC.