Why Auto ISO and Minimum Shutter Speed Will Change the Way You Shoot

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In the last 10 years, manufacturers have introduced a new level of control to cameras: auto ISO plus the option to set a minimum shutter speed. If you’ve never tried using your camera with this setup, you may want to give it a go, as it could completely change how you shoot.

Here’s a quick summary of how it works. Say you’re shooting informal portraits on location at golden hour. The light is slowly fading, and choosing aperture priority mode, you know you want an aperture of f/1.8, but are happy for the camera to decide shutter speed and ISO. However, you don’t want the camera to set the shutter speed so slow that your subject’s movements become blurred or your shots become soft due to camera shake. By setting your camera to auto ISO and choosing a minimum shutter speed of 1/125th of a second, you can let the camera do the work and focus instead on interacting with your models, safe in the knowledge that the camera won’t let any blur creep into your shots.

As the light fades, the camera reduces the shutter speed. Once it drops as slow as 1/125th of a second, the camera starts increasing ISO. Strongly backlit subjects and snowy scenes still require careful attention, but with improvements in metering coupled with displays on mirrorless cameras that give ever increasingly accurate indications of exposure, letting the camera do all the heavy lifting is getting easier and easier.

Auto ISO lends itself well to certain shooting scenarios, and it’s one that photographers use frequently when shooting candidly, such as street photography or at weddings. Personally, I’ve recently started to use it a lot when photographing casually with friends, as it allows me to shoot without having to give a lot of thought to how I want my camera set up.

Better Sensors, Less Grain, Greater Trust

In the past, the amount of noise introduced into an image by increasing the gain (i.e., turning up the ISO) meant that giving your camera free rein over the ISO was a risk, as image integrity could easily be compromised. Recently, however, better sensors and improved processing software have meant that grain is less of a concern, and this gives greater freedom. The camera can make more decisions, allowing you to shoot in a more relaxed mode. If you’re particularly worried about noise, many cameras now allow you to set a maximum ISO where the minimum shutter speed is overridden in the event that light levels drop so low that you hit your ISO ceiling. Personally, I’d always prefer to get a sharp, noisy image rather than a blurred one, but other photographers find this useful.

Who Got There First?

Intrigued, I started digging into camera history, but discovering exactly when this feature was introduced proved a bit of a challenge. The Canon 1D Mark IV and original iteration of Canon 7D seem to have been the first Canons to feature auto ISO, but it wasn’t until more than two years later in 2011 that the Canon 1D X and the 5D Mark III allowed you to also determine the minimum shutter speed. Nikon, by comparison, seems to have been a little ahead of the game, introducing an on/off “ISO Sensitivity auto control” with a minimum shutter speed in the D3 and D300 in 2007, though adjusting the settings still required a bit of menu digging. However, the pioneer might be Sony’s a100, released in the middle of 2006, giving users auto ISO but no minimum shutter speed. If you know differently, please let me know in the comments. (For some reason, this quirk of digital camera history appeals to the giant nerd in me.)

In sifting through old forums, one thing that amused me was how many angry people were complaining that there was a mode called “manual” even though the camera was determining your exposure. If there’s one thing you can be sure of about the photography community, it’s that people are easily outraged.

Liberate Your Fingers and Mind

Having shot in manual for so many (read “too many”) years, stepping into my Sony a7 III’s automated features has been liberating, allowing me to use my camera more casually and shoot friends and family in a more candid manner. My recently discovered “toggle autoexposure lock” is now assigned to a customizable button, giving me even greater flexibility in shifting conditions, and I’m keen to see how this can transfer to other scenarios. No doubt, many readers will find it ridiculous that I’ve only just made this discovery, but I know that many photographers operate on a “if it ain’t broke, don’t fix it” mentality and are resistant to changing how they use their cameras. If that’s you, I can relate.

When shooting parkour events, my default has been to shoot manually somewhere between f/4 and f/5.6 with a shutter speed somewhere above 1/1,000th of a second, tweaking my exposure by changing my ISO. I’ve since switched to shooting in manual but with my ISO on auto, locking the exposure using my toggle button where necessary, and tweaking with the exposure compensation dial — and yes, as you might recall, that’s a dial that I once had absolutely no use for.

Know the Limitations

It’s good to know the limitations of this camera functionality. For example, if you are shooting in manual mode with auto ISO and using slower shutter speeds or wider apertures in sunny conditions, there is a risk of creating overexposed images as the camera would not be able to drop the ISO low enough. Similarly, auto ISO does not lend itself well to shooting with strobes, as the camera will meter for the ambient light and not give you the control that you require.

It’s also worth noting that if you’re shooting in aperture priority and find yourself constantly using the exposure lock and exposure compensation dials, it might be worth shooting fully manual. I’m fortunate not to have to do this, as changing the ISO on my a7 III still feels fiddly, despite being four months in.

The Takeaways

Perhaps the takeaway here is twofold: firstly, if you’ve not tried auto ISO, give it a go. It passed me by for too many years. Secondly, technology isn’t everything, but occasionally, something new comes along that makes shooting easier. Gear won’t make you a better photographer, but if you’re taking shots that you would otherwise have missed, it probably gives you the chance to become one.

by Andy Day