Pairing Auto ISO with Manual exposure mode on a Canon EOS 80D, used for this experience, creates a fast workflow where you’ve absolute control over exposure and can – almost – select the combinations of aperture and speed you prefer.
Although previous cameras as the EOS 50D or the EOS 600D offered some form of Auto ISO, there are some limitations of use that never made them appeal to me. It’s only with modern cameras, since the EOS 7D, that Auto ISO is a more versatile function, and the only one, as far as I know, that allows you to do something that is impossible when using the camera in “regular” Manual mode. It’s both an important feature and, for me, used to “regular” Manual mode, a curiosity.
When using Aperture or Speed Priority mode, you control the amount of exposure by compensating one of the values, following an indication on a scale in the viewfinder – and an icon with +/- appears on the LCD and viewfinder, close to that scale. In Manual mode the icon indicating that exposure compensation is active never appears, simply because you are responsible for adjusting directly both the aperture value or exposure length. The scale is still there to guide you, but the camera does not adjust automatically one of the parameters when you adjust the other, as it does in Av and Tv.
Auto ISO can be used in P, Tv, Av and Manual mode. It offers different options and possibilities in each mode and users should define which works best for them, after being aware of the advantages and pitfalls of each. Personally, because I tend to work in Manual mode all the time, I feel that Manual mode plus Auto ISO work best, as I still have absolute control over exposure, although now I can introduce exposure compensation in a new way. But before I go ahead and explain it, let’s look briefly at how Aperture Priority (Av) and Speed Priority (Tv) modes work with Auto ISO. I leave aside the Program mode, which does not offer, from my point of view, the same versatility as the other three.
In Speed Priority (Tv) mode the user sets the speed, the camera picks the aperture and then adjusts the ISO speed within the parameters defined in the Auto ISO selection in the menu. As long as the exposure falls within the ISO range defined the camera keeps the aperture the same. When it cannot offer a “correct exposure” it will change the aperture. If it cannot expose correctly, the aperture value blinks, to warn the user.
In Aperture Priority mode (Av) mode the user chooses the aperture wanted and the camera adjusts the speed and ISO. When it cannot offer a “correct exposure” the exposure length is changed. Here, as it happens many times in normal use of Aperture Priority, the problem is that if you’re not careful you can finish with such a slow speed that your images will be blurred.
Canon introduced a safety feature that works both in P and Av. The Minimum Shutter speed function has two options, Auto and Manual. In Auto it is possible to adjust, through a scale, if the shutter speed tends to a higher or lower value, knowing that the camera will continue to try to maintain a shutter speed of at least 1 stop above the reciprocal of the focal length, changing ISO to maintain this as long as possible. In Manual mode it is possible to select the lowest shutter speed one wants the camera to use in Av or P. The camera will only go below that value after it has raised ISO to the highest ISO chosen under the Auto ISO range.
Although I do think that each different mode has applications, I prefer the Manual mode with Auto ISO, which gives the user the responsibility of selecting both aperture and exposure length – something I always preach is essential for absolute control and is my preferred method of work. Associated to Auto ISO it allows users to select the aperture they want and still keep/choose a minimum safe shutter, while the camera adjusts ISO.
Working this way, one discovers that the icon of exposure compensation appears in Manual mode… when you press the SET button (on my camera, you may have defined another button), to indicate that ISO is being changed. In fact, in this mode you’ve a fast and reliable way to compensate exposure, using the scale, to get your images lighter or darker: you adjust the ISO.
One interesting aspect of using Auto ISO with Manual exposure mode – in Canon DSLRs – is that the exposure lock button, which usually “locks” exposure, now serves as a way to know the difference between the locked exposure and the value metered when you move the camera. This works in a similar way to cameras like the old Canon T90 SLR, which allowed the user to spotmeter a series of sections of the image in the viewfinder and memorize them for the system to compute the final exposure. Here it will give you, rapidly, an idea of the difference in lighting, through the scale, of different areas of your image.
Although there may be some problems if you’re dealing with extreme values of ISO, the combination of Auto ISO and Manual mode opens some interesting possibilities, like having series of images with very similar exposure, even if you change from shadow to light areas, or being able to keep the same value of speed and aperture in a series of images, if you need/want to. I believe that besides creating a seamless workflow under different lighting conditions, this opens some creative options as well, that should be explored. So do pick your camera, get out of your comfort zone and explore the possibilities.
Another good thing about Auto ISO and modern sensors is that you can rely on the results – as long as you don’t get into extreme values of ISO – for a series of photographs. I tried recently, with the EOS 80D, to use higher values of ISO than I would dream of using before for my photographs of flowers, and was happy to find I could go up to 800 ISO with confidence. This time I chose Auto ISO and for a three hour session at a park I trusted it completely: the results show you can trust the system. Although, because the light was good, most images taken fall within the 400 ISO – and have no problems of noise in the shadows, many are at values of 800 ISO and above, up to 2000 ISO. I am quite happy with the results, and you can see a series of the images from the day, blown up, on my article “The Last Colours of Summer”, published at Medium.
Using Auto ISO with Manual exposure mode for this series of photographs reveals how well the system works, allowing for fast adjustments, but still giving you full control over exposure, something I really appreciate. Especially when working with backlit subjects as is the case in some images, the combination of features makes for a workflow that got me convinced. Auto ISO is, no doubt, a new tool in my bag.
One limitation – not that it worries me, really – of Auto ISO is that it cannot use the extended ISO present in Canon cameras. Another aspect to be aware of is that while it is possible to use flash with Auto ISO, it works quite differently, at least on Canon DSLRs, so this is something that need another approach. The highest ISO is 400 on M, Tv and Av, while in Program the camera goes to 1600 ISO, as soon as you move your flash from the forward position, to use it bounced.
One good thing about Auto ISO, is that it also works for video, although there are some limitations in terms of shutter speeds and ISO usable. Program, Tv and Av are available, but here I find that Manual exposure mode is, again, the way to go. Although you’ve no absolute control over ISO, the fact that you may define aperture and shutter speed and let the camera take care of exposure, makes it easier to adapt to light changes, especially if you’re moving. Try it and you’ll be amazed.