When to use Auto-ISO

I received an email this week asking about auto ISO, and whether or not this was the appropriate way of shooting wildlife given the advancements in our cameras as of late. 

This. Is. A. Great. Question. 

Auto ISO has been available in our cameras for some time now. When it was first released, I flat out hated it. I refused to ever use it. This had nothing to do with me not wanting to relinquish control as much as it had to do with the fact that it always seemed to pick the worst darn ISO setting possible! However, as our technology as advanced, my opinion of auto ISO has shifted and do find it to be useful in very specific types of situations. 

With today’s modern cameras, there is no reason that you should be afraid of shooting as high as 12,800 ISO. I do all the time. In fact, I routinely push things on up to 20,000 ISO and above. This isn’t just with the Nikon Z9. I use the Sony A1 and the Canon R3, as well.

In general, the more megapixels you have the worse your low light capabilities are going to be. This is why Nikon and Canon’s flagship pro level camera bodies that cost nearly $7k have historically been in the sub 20 megapixel range. And this is why noise is ALWAYS worse on crop sensor cameras vs full frame cameras (you have to fit the same amount of megapixels onto a smaller sensor). 

But, this is not the year 2010 – which I find is where a lot of photographer’s understanding of their camera’s low light and ISO capabilities tend to be stuck at. In today’s world, save for the most basic of consumer level DSLR camera bodies, everyone’s cameras are going to handle 6400 ISO without issue. 

Of course, when we talk about high ISO and why you should or should not go past a certain point, we are really talking about noise in our photographs. And I am here to tell you that 99% of the noise you see in your photographs has nothing to do with your ISO. Instead, its sloppy exposure settings. 

But let’s move back to the original question about auto ISO.

The primary reason most professionals shied away from it for years was because our cameras tended to opt for the highest possible ISO setting when there was absolute no reason for it.  And when 6400 ISO was a really high ISO setting, it was just easier to remove the variable of the auto ISO so as to ensure your exposures are exactly as you set them. The fact of the matter is that when it comes to ISO, you want to lowest possible setting you can use at any given time. The closer you are to your camera's native ISO, the more dynamic range and color depth you will have. The one exception to this rule is Nikon's D5 which actually has better dynamic range at higher ISOs. 

Any time we introduce something “auto” on the camera, be it auto ISO, aperture priority, or shutter priority, we introduce variables into the equation. 

Take a bear for instance. If my bear only makes up 25% of my composition, that means that 75% of the frame is something else. That something else will probably be a different tone of light than my bear, it might be brighter, or it might be darker. When we use auto anything, our cameras are making judgement calls based on dominant tones of light in the composition. So, we set an exposure compensation in this instance so that our camera renders the scene correctly. 

But what happens if the bear walks closer? What happens if the bear becomes 75% of the composition? Now the dominant tone has changed, and our auto settings will adjust accordingly. We, in turn, then have to respond by changing the exposure compensation again – which often requires a test shot or two to confirm a proper exposure on the histogram as well. 

Whether our bear is 25% of the frame or 75% of the frame, the light itself hasn’t changed, however. This is why most professional photographers preach the wonders of manual exposure. As long as the light itself doesn’t change, then you can set it and forget about it until something major does change. The variables are removed. You have consistency in your exposure. You create predictability. And you have the same proper exposure as the bear moves about her world - regardless of how close or far away she is. 

At this point, if your reading closely, you have probably noticed that I am saying two different things. The first is that I like auto ISO in modern cameras. The second is that I don’t like auto anything. Seem incongruous yet? 

In 90% of the situations I find myself in, I shoot manual everything. Manual aperture. Manual shutter. Manual ISO. Even manual white balance. Manual. 

More often than not, light changes constantly. Highlights and shadows. Clouds sailing overhead. Birds flying between bright and dark backgrounds. Moose threading their way through the dappled lighting of a forest. The list goes on.

But then there is the other percentage of time that is made up of situations where nothing is really changing except time. As the day progresses, the light simply get’s lower or brighter. There are no shadows to contend with. There are no highlights. The light is even. Diffused. Relatively flat. And the only changes happen subtly with the progression of the sun. These days are called overcast.

In overcast light, you know that you will want anywhere between +.7 and +2.7 stops of light added to your base exposure to compensate for the general lack of light.

Overcast lighting is about the easiest type of light that anyone can find and photograph animals in. We generally do not compose large and sweeping environmental portraits in this. We keep the sky out. We come in tight. We create portraits of our subjects and call it done. And it’s in these extremely simplistic lighting scenarios where slowly but surely there is a gradual change of light happening, we find that auto-ISO works fabulously.

When I am on a boat in Panama during the rainy season, for instance, photographing monkeys and sloths and snail kites, on an overcast day I am going to most likely set my camera to auto-ISO. Save for the earliest and latest of hours, when I need to add even more light to compensate for the blah, I know I can dial in my shutter speed and aperture manually, set my ISO to auto, and then add some measure of exposure compensation to that in order to push my histogram as far to the right as possible.

Honestly, it’s this last bit about pushing the histogram that is really the primary reason I would even consider using auto-ISO. Of course, I can always do this manually. But when the light is low, when I am using extremely high ISO settings, exposing as far to the right as possible is how we reduce the amount of noise captured in our photographs. And setting our ISO to auto and dialing in some measure of positive exposure compensation ensures I don’t get complacent as the light subtly changes.

But then again, since the light is so even and flat and slow to change, it’s really not that big of a mental challenge to simply keep an eye on my histogram.

In the days of DSLR photography, I found myself using auto-ISO on overcast days with considerable regularity.

However, with today’s mirrorless cameras and their subsequent electronic viewfinders that display things like live histograms, I no longer have to take the time to create test shots from time to time and check the exposure on the back of the camera by pulling up that histogram. Now-a-days, the histogram is always displayed in my viewfinder. And so, I have even less of a need to consider using auto-ISO in these situations.

ACTIONS

Consider using auto-ISO if you are still shooting with a DSLR camera and have to regularly take test shots and check the histogram on the back of the camera. On overcast days, this can help with the slow and steady change of light during situations when high ISO settings are mandatory. But if you are photographing with a mirrorless camera and have the ability to work with the live histogram in your viewfinder, there is really no need to ever introduce variables like auto-ISO into your field workflow.