Here’s a relatively new Canon feature in mid-range and upper-end EOS DSLRs that I think flies a bit under the radar for many photographers. But every time I use it, I’m grateful that we have it as an option. I’m speaking of Canon’s “AE Lock with Hold” feature, which is an option within the camera’s Custom Controls (in the Custom Functions menu) on the following cameras:

EOS-1D X Mark II; EOS-1D X
EOS 5DS; EOS 5DS R
EOS 5D Mark IV; EOS 5D Mark III
EOS 6D Mark II; EOS 6D
EOS 7D Mark II
EOS 80D; EOS 70D
A review of conventional AE Lock
To understand why this can be a significant addition to a camera’s exposure control, it may be helpful to review how ordinary AE Lock on EOS DSLRs has traditionally worked (this “standard” version of AE Lock remains the factory default for every EOS DSLR camera, past and present).

A press of the rear AE Lock button (marked with an asterisk icon — Canon’s symbol for AE Lock operation) in P, Tv, or Av mode will lock in place the exposure settings for whatever lighting the camera is reading at that moment. The idea, of course, is to allow the shooter to now recompose a shot, without exposure changing if the camera reads different brightness values in a scene. An obvious example might be focusing upon a person’s face in a portrait, locking exposure on their face, and then moving the camera so that the final scene has them off center.

When exposure is locked, an asterisk icon appears at the bottom display in the viewfinder to alert the photographer that AE Lock is active.

Standard, traditional AE Lock has the following characteristics… some helpful and some, frankly, annoying to various photographers:

• AE Lock is tied to the camera’s meter timer. Simply stated, with most EOS DSLRs, the meter is activated by pressing the shutter button halfway down or by pressing the rear AE lock button. If no other button is pressed, the meter goes off after six seconds. If a picture is taken and the shooter lifts his or her finger off the shutter button, the meter goes off immediately after the shot is taken (with most Rebel models) or after two seconds (with other EOS DSLRs).
• When the meter timer turns the camera’s meter off, you lose any previous AE Lock setting.
• To maintain an AE Lock reading after a shot is taken, you must either continually hold in the AE Lock button or be sure to put your finger halfway down on the shutter button within two seconds after a picture is taken. Otherwise, the meter timer turns off the meter and, again, any AE Lock reading is lost.
• To intentionally turn off an AE Lock reading with Canon’s traditional AE Lock system, you don’t simply press the AE Lock button a second time — that just takes a new reading of whatever you’re now viewing. Instead, you have to either be sure not to press any other buttons and wait six seconds for the meter timer to extinguish the meter system, or turn the camera off and then back on again.

So until recently, AE Lock was easy to lose after taking more than one or two pictures at a time. And if you took a quick AE Lock reading and decided you didn’t want it after all, you had to go through a bit of a procedure to deactivate it. What should be a smooth and seamless process sometimes seemed a bit more like “work” than it probably should have, at least to me.

The new option: AE Lock with Hold
This was first launched as an option within the Custom Controls on the EOS 5D Mark III and EOS-1D X models. Since then, it’s also found its way into the more affordable EOS 6D and EOS 70D models. It works the same way in each of these cameras. It’s indicated on the menus by the same asterisk icon, but now with an upper-case letter “H” adjacent to it.

1. AE Lock with Hold is different from Canon’s conventional AE Lock operation. You still press a button (either the rear AE Lock button with the asterisk icon or one of several others… more on that in a moment), and exposure is locked at whatever values are in place at the moment. Here’s how it differs from conventional AE Lock: A locked exposure is no longer tied to the two-second or six-second “meter timer.” Instead, it’s linked to the camera’s Auto Power Off timer — which keeps the camera awake for anywhere from one to 30 minutes after a picture is taken. The benefit is that there’s no need to work to keep exposure locked after any number of pictures are taken. By turning Auto Power Off completely off (in the camera’s Set-up Menu), you can keep a locked reading in place until you turn the entire camera off.
2. You can deactivate any locked exposure reading by just pressing the AE Lock button a second time. Unlike conventional AE Lock, which would take a new AEL reading with a second button push, AE Lock with Hold means you can cancel a reading at any time without having to turn the camera off and then back on.

This is an AE Lock function that many shooters will find more intuitive and simpler to activate, particularly when you want to take a reading, lock it in place and then be free to take a series of pictures of a scene or subject using the same exposure, but without concern about keeping the reading locked.

Activating AE Lock with Hold
The Custom Controls menu, within the camera’s Custom Functions menu, allows you to reprogram different controls on the camera to change their functions. The EOS 70D, for instance, allows users to activate AE Lock with Hold via any of the following buttons:

• AE Lock button
• AF-ON button
• Depth-of-field preview button
• Lens AF-Stop button (on certain Canon super-telephoto lenses only)

High-end models like the EOS 5D Mark III and EOS-1D X add the options of the Multi-function (M-Fn) button and M-Fn 2 button on the EOS-1D X.

Because the new AE Lock with Hold can be activated by any of several buttons, it’s theoretically possible for a shooter to have conventional Canon AE Lock operation via one button (for instance, the normal rear AE Lock button), and the AE Lock with Hold active when another button is pressed (such as the adjacent AF-ON button or the depth-of-field preview button).

Using AE Lock with Hold
Always a terrific way to combine the speed of auto exposure with precision, AE Lock with Hold works great in a mode like Tv or Av, when combined with Spot or Partial metering. It’s now easy to lock exposure on any particular part of a scene, recompose and shoot as many shots as you want with the same exposure setting. If necessary, Exposure Compensation can be easily dialed in for those times when a Spot or Partial meter reading was taken from a light or dark-toned subject or part of the scene.

Sometimes when shooting quickly, you may want to take several fast pictures of a particular scene with a precise, locked-in reading — and then, quickly move on to something else. Again, AE Lock with Hold becomes an asset here. A reading stays in place for as many pictures as you initially want to shoot. Then, just press the button a second time to clear it and you’re back to ordinary auto exposure with continuous metering.

One caution: as you’re getting used to AE Lock with Hold, remember that it won’t just go away a couple of seconds after your last picture was taken. If you use it for a particular series of pictures, put the camera down and then pick it back up a few moments later to photograph a new scene. AE Lock with Hold will still be active and that reading may not be right for whatever the new scene is. A quick press of whatever button you’ve set to use AE Lock with Hold will clear it, so get into the habit of doing that when you’re finished with any particular locked-in reading.

A few general notes about Auto Exposure Lock
Regardless of whether you prefer the new AE Lock with Hold or Canon’s traditional approach to AE Lock, there are a few things to remember about how it’s handled in the EOS System. These can be helpful in quickly getting to the exposure settings you want, especially for more experienced shooters who are looking for fine exposure control.

AE Lock always occurs when Evaluative metering is combined with One-Shot AF
Well, almost always. Even if you never press the AE Lock button, whenever you lock focus in One-Shot AF (the round green LED illuminates at the bottom of the viewfinder), you’ve also locked exposure if Evaluative metering is active.

Want to see this? Lock focus, hold your finger halfway down on whichever button you used to activate AF, and move the camera around — the speed and aperture displays in the viewfinder won’t change, even if the lighting does. And, there’s no asterisk icon in the finder to indicate exposure is locked. Just be aware that it is.

If you want or need exposure to remain continuously active even if focus is locked in One-Shot AF, there are several things you can do:

• Switch to back-button AF; focus on your subject with One-Shot AF and then pull your thumb off the back button. Exposure will now revert to continuous adjustment in any auto exposure mode (Av, Tv, or P), and focus won’t change if you’ve removed it from the shutter button.
• Switch to Center-weighted, Partial or Spot metering. Exposure is not locked when any of these are combined with either conventional AE Lock or the new AE Lock with Hold.
• Switch to AI Servo AF — although if you’re shooting stationary subjects, it’ll work far better via back-button AF (press rear button to focus, pull your thumb off the back button to stop focus). Exposure will continually adjust as the shutter button is pressed halfway down, without locking as it would in One-Shot AF. If you really need to activate focus via the shutter button, another option to avoid locking exposure with Evaluative metering would be to use AI Servo AF and commit one of the back buttons to focus lock (“AF-OFF”), via the Custom Controls menu.

AE Lock can be combined with Manual exposure mode on newer EOS cameras
Recent EOS models, such as the EOS Rebel T4i and T5i or EOS 70D, and so on also allow AE Lock to function even in Manual mode. You’re entitled to wonder why because in Manual, the speed and aperture are (by definition) already locked in place.

With newer EOS models, if you aim at a certain part of a scene in Manual mode and activate AE Lock, the analog meter scale in the viewfinder now continually updates to show you how different any current lighting is versus what you locked-in for exposure. Exposure isn’t changing, of course, but you get an easy reference as to the difference between highlights, mid-tones and shadows.

You could take a reading off the highlight side of a subject’s face, for instance, and then see at a glance how much darker the shadows were before a shot is taken. Again, this really becomes an asset if you’re using Partial or Spot metering.

Keep in mind that many older EOS models, including popular cameras like the EOS 7D and so on, cannot use AE Lock when in Manual exposure mode.

AE Lock can be combined with E-TTL flash
Just remember that it’s locking ambient exposure only and not flash (Canon offers FEL — Flash Exposure Lock — as a means of locking-in Flash exposure, but that’s a separate function; be careful not to confuse the two). Conventional Canon AEL, or AE Lock with Hold, can be especially helpful in daylight fill-flash situations. The same large asterisk icon appears in the finder, even with a Speedlite mounted, to indicate that ambient exposure has been locked with AE Lock.

Summary
AE Lock is a feature that can make auto exposure even more practical in everyday shooting situations for the critical DSLR photographer. But the new capabilities and simplified operation of the AE Lock with Hold feature on newer EOS DSLRs can make auto exposure arguably even more suited for some situations and really give the experienced user a great option to turn to when he or she wants that combination of speed and control. I’ve really come to like and lean on AE Lock with Hold, and I strongly suggest that any EOS shooter who’s ventured away from Green Zone operation give it a try and become familiar with it.