Manual Exposure with Auto ISO

Learn a fantastic exposure technique for action photography. What is floating ISO? How do you use it? When do you use it?

Updated:
November 26, 2023

Remember when you were stuck at a certain ISO value until you finished your current roll of film?

Me neither – I’m not that old.

What if I told you there is a really great technique you can use for action photography that combines manual mode with auto-ISO that will give you great exposures while you keep control of your shutter speed and aperture?

I call it the ‘floating ISO’ exposure mode. I probably didn’t make that up, but can’t remember where I heard it first.

What Is Floating ISO?

It’s a pretty simple technique

  • Set your camera to manual exposure mode (stay with me, it’s not scary – I promise)
  • Set your camera to auto-iso

That’s it.

How Does Floating ISO Work?

If you’re familiar with photography you will know that there are three things that impact the exposure of a photograph. Shutter Speed, Aperture and ISO.

(Yes, I know ISO technically doesn’t impact exposure, but let’s keep it simple)

The Theory

By setting the shutter speed and aperture manually you can retain complete control over how your photos look – and by setting the ISO to be set by your camera, you don’t have to worry (to a degree) how your settings will effect the overall exposure of your photo.

To recap:

  • Aperture affects depth of field (blurry backgrounds)
  • Shutter speed affects how much motion is in the photo (usually the aim in ‘none’)

By manually setting these two variables manually you have complete control over how they affect the look of your photos.

By activating auto ISO the camera will compensate for your aperture and shutter speed settings to ensure your exposure is good.

Perfect!

Well, yes – but there are a few things you still need to think about that we’ll discuss in a bit.

Screenshot of the Auto ISO settings on a Nikon camera
The Auto ISO menu on a Nikon D7500

Setting Auto ISO Correctly

Making sure your Auto ISO settings are appropriate is crucial to making this technique work.

Most cameras will allow you to set a maximum ISO value to use. If you set this too low then you will find that you get a lot of dark photos. Let your ISO roam free and set it to a decently high value (I usually set mine to ISO 12,500 or 25,000).

But what about the noise? I hear you cry!

If you use appropriate settings for your shutter speed and aperture (read on) – you don’t need to worry about your ISO being higher than it needs to be. Remember: A noisy but sharp shot is better than a clean but blurry one!

Conversely, you also need to make sure you don’t set the minimum ISO too high – there is really no reason to set it to anything above the minimum value. This will usually be somewhere between ISO 64 and ISO 200 depending on your camera.

In The Field

So how does this work in the field?

Your camera will hopefully have two command dials. In manual exposure mode, rotating one of them will adjust the shutter speed, rotating the other will adjust aperture.

You have control over those two things with the twist of two fingers

Now you just need to know what settings to use, and when – which is a little out of scope for this article, but as a guide:

Choose the aperture that will give you the depth of field that you’re after. Small numbers (f/1.8, f/4, etc) for blurry backgrounds, bigger numbers for more things in focus.

Then choose the lowest shutter speed that will stop whatever is moving in your photos. Slower number (1/60, 1/100, etc) for slow moving scenes, fast numbers (1/1000, 1/8000, etc) for fast moving scenes.

As you change what you are pointing your camera at, use the two dials to quickly change settings to whatever is appropriate.

When To Use The Floating ISO Technique

Floating ISO is useful for any situation where controlling the aperture and shutter speed are important. Personally, I use it for most situations except tripod based landscape photography.

Once you get used to checking in that you have the appropriate shutter speed and aperture set for the scene you’re looking at, letting the floating ISO take care of the exposure

Birds & Wildlife

Birds and Wildlife are a great use case for floating ISO. When chasing animals around, shutter speed is often very important to get right.

  • Set your aperture to a low number (f/2.8, f/4.0, etc) so your backgrounds are blurry and your subject stands out.
  • Set your shutter speed to a value that will make sure there is no motion blur in your photo.
  • Let auto-iso take care of the correct exposure.

For example:

You might be tracking a bird of prey through the sky with a your shutter speed set to 1/4000 of a second and your lens set to f/4.0 to ensure sharp shots. Suddenly it lands on a branch next to it’s partner and you want to capture both.

Using the floating ISO technique you can quickly drop your shutter speed down to 1/500 and up your aperture to f8 to ensure both birds are sharp. Auto-ISO will then make sure the exposure is still correct for those settings. Perfect.

Photo of a Pink Robin on a branch
Setting the camera to f/5.6 at 1/400s allowed the camera to set the ISO to 5000 for the correct exposure

Macro

When shooting macro out in the field there is often a lot going on and you need to be able to react quickly.

  • Set your aperture that will give you the depth of field that you need. The closer you get to your subject, the more careful you need to be with this.
  • Set your shutter speed high enough to stop any motion.
  • Let auto-iso take care of the exposure

For example:

See a bee hovering above a flower? You’re going to need a fairly fast shutter speed and medium aperture to get a sharp shot with enough depth of field to get the important bits sharp. Set your shutter to 1/800 and aperture to f/9 by rotating your command dials. Auto ISO will keep the exposure correct.

Then you see a beetle sitting motionless on a leaf. You don’t need as high of a shutter speed by will want a higher aperture so you can get in really close and keep the depth of field reasonable. You can quickly flick the command dials to set 1/250 and f/16. Auto ISO will take care of the exposure to compensate the change.

Photo of a damselfly on a twig
Manually setting f/10 and 1/400s allowed for appropriate depth of field and a shutter speed to stop camera shake (taken handheld). The camera chose ISO 640 to get the exposure correct.

Sport and Other Action

Sports photography is just like nature photography when it comes to using floating ISO – the same principles apply

Same with chasing your kids around the park

Or chasing your dog down the street

Street & Event

Manual mode with auto-iso is also useful for street and event photography. Manual mode allows you to set the creative elements of the exposure that you need and auto-iso will take care of the exposure.

Just take care not to combine wide open apertures, slow shutter speeds and bright scenes (as discussed below) or you could run into some trouble with auto-iso not being able to get low enough for the correct exposure.

When Not To Use Floating ISO

The floating ISO technique is fantastic for action photography, however it doesn’t work in all situations.

If you need to keep noise levels as low as possible, floating ISO might not be the best choice as you will want to manually set it to the lowest value you can.

Landscapes

When taking landscapes you will (usually) want to keep your iso at the lowest value possible. You will likely be on a tripod and longer shutter speeds aren’t generally a concern. Here you will want to manually choose your ISO value to make sure it’s as low as possible.

Almost all of my landscape photography is done in aperture priority with a manually set iso (and a ‘floating shutter speed’), or full manual mode.

Manual Exposure,Auto ISO
Keeping ISO low and controlling the f-stop is more important than manually setting shutter speed for landscapes on a tripod

When Using Flash

You can use the floating ISO technique when using a flash, but it gets a little more complicated as the camera now has two ways of controlling the exposure. Increase the flash intensity? or increase the ISO?

If you’re comfortable with setting the flash intensity manually (adjusting for whatever the scene needs) – then go right ahead and experiment with auto-iso.

Other

I’m sure there are other situations where using this technique isn’t ideal – if you know of any – please let me know in the comments section (or on the contact us page if you prefer)

Considerations

Although the technique works very well – there are still a few things you need to think about when using the floating ISO technique

Exposure Extremes

Using auto ISO isn’t a magic bullet – the combination of shutter speed, aperture and ISO still need to suit the lighting conditions you are in. For example, if you are shooting indoors and set your shutter to 1/8000 and your aperture to f22… your ISO will probably hit it’s maximum and you’ll still end up with a dark image.

Make sure you keep your eye on what ISO your camera is using and if it getting to levels close to maximum or minimum values then you may need to reconsider your manual settings.

Avoiding Noisy Photos

Similar to thinking about exposure extremes – you should also think about how the complete combination of shutter speed, aperture and ISO will affect the noise levels in your photos.

As with any exposure mode – you still need to think about how your settings will affect the look of your photo, including noise.

Thinking about and setting sensible values for your shutter speed and aperture will make sure the ISO value to get the correct exposure remains as low as possible (always desirable).

Do remember though, with modern noise reduction software, noise isn’t nearly the problem it used to be.

Topaz Photo AI

Conclusion

Auto ISO is great!

It does take a little getting used to. You need to think about your shutter speed and aperture settings to make sure you’re getting the shot you want…. But you should be doing that regardless of your exposure technique.

Floating ISO isn’t perfect for every photography situation, but it allows you to carefully control your shutter speed and aperture – which in turn controls the ‘look’ of your shot – without you needing to worry too much about if your photo will turn out too bright or dark.

Give it a go – see if you like it (not everyone will) – then let us know what you think in the comments section below.