What is a Custom Mode?
A Custom mode is a camera setting that allows the photographer to instantly recall a saved camera setup configuration by simply turning the top dial (or via a button press and dial turn on the 1-Series models) to one of the designated "C" modes. Most of us have go-to, most-used camera settings for at least one photography scenario and spending a few minutes to program a custom mode for this use can be a great time-saver and a move that can even save the day if those settings are needed immediately.
Canon's mid and high-end EOS DSLR cameras have between one and three Custom ("C") modes available. For example, some EOS **D models (the EOS 70D and EOS 60D) have one Custom mode and the EOS 6D Mark II and EOS 80D have two. Canon's high-end models, including the EOS 7D Mark II, EOS 5Ds, EOS 5Ds R, EOS 5D Mark III and EOS 1D X, have three "C" modes. This feature has typically been omitted from the lower-end Rebel (***D and ****D) series cameras.
How to Configure a Custom Shooting Mode
Configuring a "C" mode is very easy. Simply adjust all of your camera settings as desired for the "C" mode being programmed and then find and select the "Custom shooting mode" menu option located in the "Tools" tab. Next, select "Register settings". If more than one "C" mode is available on your camera, the mode number desired must then be selected. Done. That's it. That "C" mode is programmed.
Two other "Custom shooting mode" menu options are available. The first is "Clear settings". I don't recall ever using this one. I simply program over the top of an already configured "C" mode if I want to make a change and haven't felt a need to clean up any no-longer-needed "C" mode.
The other available option is "Change Auto update set". While a "C" mode is being used, camera settings can be changed. When "Change Auto update set" is set to "Enabled", any camera setting changes made while in a "C" mode are saved to the respective "C" mode. The camera will retain the new settings even after being powered off. When this option is set to "Disabled", the camera will revert back to the originally programmed settings when the camera powers off. My cameras all have this feature set to "Enabled". "Enabled" requires a little more attention to the as-last-configured settings when beginning to shoot, but ... I found "Disabled" to be somewhat maddening and requiring even more constant attention.
Bryan's Custom Mode Settings
I am generally using camera models with three Custom modes and I have a standard configuration that I use on all of my cameras. Being configured identically means that it doesn't matter which camera I am using, I know which Custom mode to use when the configured-for situation presents itself. That configuration and the thought process behind it as follows:
Custom Mode 1: Landscape and Still Life Photography
I am very frequently shooting landscape and still life subjects from a tripod and my typical settings for such photography are programmed into "C1". My selected exposure mode is "M". I generally leave the aperture set to f/8-f/11 (full frame) or f/8 (APS-C) to plan for as much depth of field as I can get without compromising sharpness (due to diffraction). The shutter speed I need varies widely when I'm in "C1" mode. It is usually set to whatever shutter speed I last used and usually needs to be set for the current situation, accomplished by simply rolling the top dial. My "C1" ISO is set to 100 for the least noise possible.
In "C1", I have One Shot AF mode selected along with a single AF point. Key for ultimate image sharpness is that mirror lockup and the 2-sec self-timer are selected (I often use the mirror lockup and 1-sec timer combination made available in the 5Ds R). With the mirror automatically raising a second or two before the shutter release, all vibrations, including those caused by my shutter release button press, subside before image capture begins.
I usually have Long Exposure Noise Reduction enabled in "C1".
While "C" modes are great for setup speed, my "C1" needs are not usually happening fast. Still, having this configuration readily available saves me a lot of setup time. Convenience has a lot of value.
Custom Mode 2: Action Photography
The action photography I do, especially including sports action, has general overarching camera setting requirements that lend themselves perfectly to a "C" mode.
My most-used standard camera mode is "M" (Manual) and this is also what I have "C2" programmed for. I use "M" mode for about 97% of my photography with "Av" (Aperture Priority) mode picking up most of the remaining mode use (most often when shooting under rapidly changing light levels when I have little concern for shutter speed). My "C2" is programmed for manual exposure settings that include a wide-open aperture, an action-stopping 1/1600 shutter speed and Auto ISO. If light levels are constant, I usually change the ISO to a specific setting at the venue.
My "C2" is configured for AI Servo AF with a single AF point selected along with the surrounding points assisting and the camera's highest speed burst drive mode selected. With AI Servo selected, the higher end cameras have a set of focus performance parameters that can be adjusted and I typically leave the default, Case 1, selected for these. If shooting under very low light (such as an indoor gym), I select a slower/longer shutter speed, accepting some modest motion blur in some situations for a lower/cleaner ISO settings to be used.
Having an action mode ready for immediately use has great benefits that include being able to properly photograph a suddenly-fast-moving subject that was near motionless just moments before.
Custom Mode 3: Wildlife Photography
I formerly used "C3" to store situationally-dependent camera settings, programming this mode as-needed at each event venue with this strategy working well. Also, I formerly used "C2" for photographing wildlife along with sports action and this strategy also worked well. But, I eventually decided that I wanted slightly different AI Servo focus parameters for wildlife photography and decided that using "C3" to store my most-often-used wildlife settings made sense. I usually have enough to think about in the field and this preset reduced the need to remember one more setting change.
Basically, my "C3" is programmed identically to my "C2" with the exception that Case 4 is selected as my set of AI Servo AF Parameters. AF Case 4 better accommodates erratically moving subjects and has for me produced a better AI Servo AF experience for this type of photography than Case 1, optimized for more-general-purpose needs. I should note that, because I am most often using a single AF point with the surrounding AF points in assist mode (not using the AF point auto switching feature), AF Case 6 should produce identical results to AF Case 4. And, AF Case 3, with an even slightly higher tracking sensitivity, stands to be another good AF Case option for wildlife photography.
Basically, I program the camera for "C2" and "C3" at the same time. Then, with "C3" selected on the mode dial and "Change Auto update set" enabled, change the AF case to 4. Done.
You are using your camera's custom modes, right?
The variation of camera setup needs between photographers can be dramatic and your setting needs are likely not the same as mine. But, you likely have some most-encountered scenarios that could be covered by custom modes. Determine what those needs are and program your custom modes to best cover them. They will be available for instant recall and you will be less-likely to forget a setting change needed in those situations.
If your camera's "C" mode is not your most-frequently-used camera mode setting, give some thought to making one that.