Bob55 Loc: Valhalla NY

I have a Canon Mark 4 with back button focus, using the AF-ON button. For the second time while shooting, my camera has gone out of focus AFTER I pressed the BBF button. The first time that happened I called the technicians at Canon who helped me reset the focus. That clearly did not resolve my problem. Can any of you fellow hogs think of anything else I can do to resolve my problem, short of resetting my entire camera? I would hate to lose all my special settings. By the way, I was in manual, indoors and using a speed light. Thanks in advance for any help you can give me. Bob

martinfisherphoto Loc: Lake Placid Florida

Indoors using flash (how dark was it) might mean your lens was hunting for focus. No mention if you have a Single Focus point selected and if the focus point was pointing into a dark area or in different area than last focused on. Are you letting the camera select the area to focus on?? Lots of variables. If your camera has lost focus only 2 times since using I would not even give it a second thought..

Bill_de Loc: US

Nikon users have that issue sometimes when they set the back button to focus, but neglect to stop the shutter release from also trying to focus. Your camera may have a setting for what the shutter release does when you press it.

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AndyH Loc: Massachusetts and New Hampshire

I don't know how this works on Canons, but on my Nikons, I use continuous focus, then set and release the BBF button (AF/AE on Nikons), which holds the focus on the original focus point. Holding down the button or hitting it again refocuses. Letting it go allows the focus to remain on the original point. I expect Canon has something similar.

Andy

AndyH Loc: Massachusetts and New Hampshire

This is also possible. You need to set BBF so that the shutter release doesn't have the same effect.

Bob55 Loc: Valhalla NY

Thanks to those who replied. I will check to see that the shutter button is disabled, although I think it is. Bob

AndyH Loc: Massachusetts and New Hampshire

I've been reminded by another member that on the later Nikons, the button is not AF-AL, but "AF-ON". Nice catch, thanks.

Andy

jeep_daddy Loc: Prescott AZ

You need to go back into custom settings and take autofocus off of the shutter button. The shutter button should only start looking at exposure and not autofocus.

And please don't refer to your camera as a Canon Mark 4 because there are 2 different Mark 4's. It's either a 5D Mark IV or it's a 1D Mark IV. It's not a Canon Mark 4.

Bob55 Loc: Valhalla NY

It's a 5D Mark 4. I'll check the settings, thanks.

Bob55 Loc: Valhalla NY

I think you solved my problem. Thanks again for your advice.

jeep_daddy Loc: Prescott AZ

I figured it was a 5D Mark IV but it's always best to be concise when asking for help. I have that camera and I have a 7D Mark II and both of the custom settings work the same way. On the 5D 4 you can use the touch screen to change custom settings. Did you know that you can set 2 bbf buttons? I have one set for whatever current focus points I choose to use and I can change them any time I like, (usually a single focus point) and the other I have set up for AI Servo focus, and 9 focus points and Case 2 focus settings. This way I can switch to that button any time I want to get BIF (Birds In Flight).....

amfoto1 Loc: San Jose, Calif. USA

By default, all the Canon with the rear "AF-On" button are set to activate autofocus BOTH when you press that button OR when you halfway press the shutter release button.

In order to set up BBF, you actually have to disable autofocus from the shutter release button. Otherwise, in some focus modes (Ai Servo for sure, Ai Focus maybe) if you "focus and recompose", the camera will want to re-focus the wrong place.

To "remove" autofocus from the shutter release button, navigate to the "button & dial customization" screen and then to the shutter release button....

There you will see three choices: "AF", "Meter" and "AE Lock". By default it's on "AF". Change it to "Meter" and then press the "Set" button and exit from the menu. Done! Now the autofocus will ONLY work when you press the AF-On button with your thumb.

Use this in conjunction with Single Point, manually selected for the greatest control over where they camera & lens focus. You can use it with either Ai Servo or One Shot mode. In Ai Servo, you can start and stop the autofocus by pressing or releasing the AF-On button. In One Shot mode you activate autofocus by pressing the button and as soon as focus is achieved, autofocus stops, locks and gives you "focus confirmation". If you or your subject move, you have to lift off the AF-On button and reapply it to make the camera re-focus.

Some zoom lenses are "varifocal" designs which don't maintain focus when zoomed to a different focal length setting. With that type of zoom, if you are pressing the AF-On button in AI Servo (continuous focus/moving subject) mode the camera will automatically correct focus. But if you are using One Shot (stationary subject) mode you have to remember to lift your thumb off the button, then re-apply it to cause the camera and lens to re-focus. I don't have a list of varifocal zooms, so you might want to test your lenses. Generally varifocal are less complex and lower cost to produce, so I'd expect more entry-level lenses to be that type. "Parfocal" zooms are those that maintain focus while being zoomed. I'd generally expect more premium lenses to be that type.

One of the primary reasons to use BBF is to be able to leave the camera in AI Servo mode for use with most subjects... both moving and stationary. There's little need for One Shot at all, when using BBF. After focus is achieved, with BBF you can "lock focus" yourself any time you wish simply by lifting pressure off the button.

The other way common way to have "focus issues" is when using too many AF points. Generally speaking, the fewer active AF points, the better. "Single Point" is best, but of course is more work for you keeping the AF point right where you want the camera & lens to focus. It also may require changing the selected point at times. With faster moving and erratically moving subjects, "Expansion" points may be needed. With this you still select the single "starting" AF point.... but the camera can switch to one of the adjacent points if it detects that the subject is no longer under the selected point. Some Canon have two types of Expansion: 4-point and 8-point. The difference is that 4-point allows the camera to use the points immediately above and below, right and left of the user selected one. 8-point allows those plus the four "corner" or diagonally located points.... all 8 points surrounding any given point, to "help", if needed.

Many of the more recent Canon also have one or more forms of "Zone" focusing. This again uses multiple points, anywhere from 9 to 15 in each zone on most cameras, except now it leaves it up to the camera to choose both the "starting" AF point and to switch to the others in the zone, if needed. The user cannot make the camera start AF with a particular point. In fact, this is sort of like a scaled down version of All Points/Auto Selection, which leaves it entirely up to the camera to decide which of it's AF points to use. This automation might choose to focus upon something different than you wanted. It will usually choose whatever is closest and covered by one (or more) of the AF points in the camera's array. In your case, the camera can choose among all 61 points.

raymondh Loc: Walker, MI

"After focus is achieved, with BBF you can "lock focus" yourself any time you wish simply by lifting pressure off the button."

To clarify, are we locking focus on the location the subject is at or the subject itself? If a basketball player moves down the court should the button be held down or released?

AndyH Loc: Massachusetts and New Hampshire

I'm a Nikon guy, but in that system you hold down the button to maintain focus on a moving subject. Release it to lock the focus at the distance where you first focused. I would imagine that Canon works the same way.

Andy

Bob55 Loc: Valhalla NY

Thanks for this. If I keep my finger on the BB while in AI Servo wouldn't that work without using a second Bob Beck?