Using Auto ISO: when, how and why on earth would you do such a thing?

More and more, with wildlife photography I find myself using auto-ISO setting in order to maintain a fast enough shutter speed to either stop my subject OR to stop camera/lens movement when using a telephoto lens, both in order to get sharper images. It is also quite useful when needing to shoot quickly. I find, when a subject moves from low light to bright light, this method is VERY helpful as well.

In my workshops and surveys I’ve done over the years, one of the MOST OFTEN asked questions has to do with making a sharp image and what settings to use. Some of the questions I get are:

Choosing the correct everything (shutter speed, aperture, ISO) when there isn’t much time to do so.
What camera settings to use shooting in manual mode.
Pressure to get camera settings correct.
Getting blurry photos because the settings were wrong
How to avoid screwing up the camera settings if in the field without much time to experiment > leading to a blurry shot

The REASONS for what is causing the blurry image is likely either:

Too slow of a shutter speed
Camera movement

Or a combination of both.

Well, there’s no “Silver bullet” to these issues, but I have one solution that works pretty darn well to get a sharp, well-exposed image nearly every time. I don’t always use this solution, but I do use it a lot whenever the action is happening fast, especially when shooting wildlife or adventure, some aerial photography – even street photography. Anytime I find myself in the heat of the moment and don’t have (or don’t want to take) the time to switch settings. The MAIN object is to get a sharp image no matter what! Because a blurry image is useless.

I NEVER use this method for landscapes, night-sky, portraits, macro, long daytime exposures, anytime I’m not in a hurry and anytime where I’m being creative with depth of field or motion.

The short answer is: Use the Manual Exposure setting. Then manually set your shutter speed and your aperture (see below for what to set it at) BUT, set the ISO to “A” for Auto.

The settings should be:

Set shutter speed to 2.5 X of the longest focal length of the lens you are using. (eg: if a 100-400mm, select 1/1000th second — 400 x 2.5 = 1000. If using a 24-105mm select 1/320th — 105 x 2.4 = 262… round it up to 320. NOTE: Set it even faster if your subject a speed demon– i.e. jumping bear or birds in flight use 1/2000th. OR set it faster if your shooting platform is a rocking boat, or gyrating helicopter. WHY? With the shutter speed set up for 2.5x focal length (or more), this SHOULD avoid any camera shake and make for a sharper image. Use your judgment for what’s best in your particular situation.

Set the aperture near or at F/8. This is an arbitrary aperture, but typically gives just a little bit of depth of field as opposed to the aperture being wide open. Also, it is oftentimes within a lens’ “sweet spot” for sharpness. Use your judgment for what’s best in your particular situation.

Put the ISO to “A” for Auto.
Camera settings on LCD back of camera set for Manual exposure with ISO set to AUTO.
OPTION — use Auto Exposure Bracketing. See below.CAVEAT: Remember, the camera’s meter is programmed to give you a “normal”, medium-gray exposure. So, if you’re shooting on white snow, you’ll need to use “exposure compensation” so the snow is not underexposed.
BULLET-PROOF THE EXPOSURE: The final setting to change (as an option) in order to guarantee you’ll get a “proper, medium-gray” exposure each time, is to set your camera to “bracket” the exposure. Canon calls it “AEB — Auto Exposure Bracketing”. I typically set AEB to do three bracketed exposures (you can set it for 5 or even 7). I set the three “AEB” exposures to be: Normal Exposure, 1-stop overexposed, 1 stop underexposed. (This AEB also can be moved using exposure compensation.) I set the motor drive to shoot many frames per second so these three go off in rapid succession. Contrary to how the logic SHOULD work for this process, for each under and overexposure made in AEB, the camera will alter the shutter speed by 1-stop (instead of the ISO). So best to increase this shutter speed by one-top faster than the original setting.

Camera settings on LCD back of camera to show where to find AEB on Canon.

ONE LAST THING: To be sure I get a sharp image, Whether I’m shooting in AEB or not, I also shoot at least three frames of the same image, in rapid sequence. This way, if I pushed too hard on the shutter for the first frame (causing the camera to shake), it’s likely the second and third frames will be sharper.

I believe this will help you create sharper, more well-exposed images when you don’t have the time to adjust the settings yourself.