PaulaBrady Loc: Havre, Mt

Hi everyone- I usually focus and recompose my shots ( will try back focus button someday) but my camera isn't holding the focus when I recompose. I have turned my camera off, removed battery And my back focus button isn't on ( I don't believe anyway) I have a Canon Markii. Any ideas out there? Much appreciated.

ecobin Loc: Paoli, PA

You need to keep the shutter release button depressed half way when recomposing otherwise it will refocus. Make sure that you're not releasing the button.

arousey Loc: Morrison, Colorago

do try the back button focus…it is only a short learning curve but once you get it you'll probably never want to go back.

http://www.learn.usa.canon.com/resources/articles/2011/backbutton_af_article.shtml

mwsilvers Loc: Central New Jersey

First, there are a few Mark II cameras, as in the Idx Mark II, the iD Mark II, the 5D Mark II and the 7D Mark II, there are also several Mark II lenses. Which equipment are you referring to? Secondly since you are not using back button focus, I assume you know that you must hold the shutter button 1/2 way down, as was mentioned above, to lock focus. If you don't recompose is your subject in sharp focus or are you saying that it doesn't lock focus or that it doesn't achieve focus in the first place. Off the top of my head a couple of things occur to me. Do you have the AF switch on the lens you are using switched on? Did you disable AF on the shutter button? Are you sure that you are not in AI Servo mode which constantly refocuses? You need to be in One Shot. If none of these suggestions helps, we will need more specific information on how you've set up and are using the camera.

PaulaBrady Loc: Havre, Mt

Thank you, I'm not releasing the shutter button. I'm shooting the way I have been for 4 years. In thinking a setting is wrong.

mwsilvers Loc: Central New Jersey

Are you sure that you are in One Shot and not AI Servo mode?

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Back button is always on unless you have redefined it's application in the custom menu. You can, and probably should, disable focus on your shutter button. That is causing you problems. Even if you keep the shutter pressed halfway, there is still the chance that you wil accidentally reacquire focus.

Also consider that there may be a slight distance issue when you move the camera to recompose - if you are using short distances to your subject, and you are using large apertures, that could contribute some focus error.

PaulaBrady Loc: Havre, Mt

Embarrassed to say I was in AI servo mode. Thank you all for your help. I really appreciate it.

MtnMan Loc: ID

Nikon has several focus settings. AF-A or AF-C would do this. Don't know if your camera has counterpart.

(Edit: from the post above where this went I guess that is AI Servo mode!)

Tjohn Loc: Inverness, FL formerly Arivaca, AZ

Use the back focus button today.

camerapapi Loc: Miami, Fl.

I can only tell you this, most AF problems are the result of improper camera operation involving the operator.

amfoto1 Loc: San Jose, Calif. USA

First of all "Canon MkII" doesn't tell us very much. Over the years Canon has produced something like a dozen different Mark II models. There have more recently been or currently are 1D Mark II, 1Ds Mark II, 5D Mark II, 7D Mark II and 1DX Mark II digital models alone. There also are Mark II lenses... lots of them! There are even some Mark II accessories such as teleconverters and macro extension rings. There is likely soon going to be a 6D Mark II and probably eventually a 5Ds Mark II and 5Ds-R Mark II. "Mark II" simply indicates it's the first upgrade to an earlier model.

Without knowing exactly what model camera you are using, it's a little hard to advise.

However, "camera not holding focus" is rarely a problem with the camera itself and won't be solved by turning the camera off or removing the battery.

The problem is most likely you, the user, not understanding how the AF system works and not using it correctly. So, stop blaming the gear. It's probably working the way it's supposed to. Look to yourself, how you have the camera set up and are using it. Chances are, that will solve your problem (and should be eliminated as the cause first, before starting to suspect any actual fault in the gear).

Very likely, you have the camera set to the wrong focus mode. Canon cameras have two or three (depending upon the exact model): One Shot, AI Servo and AI Focus.

One Shot (FYI, Nikon calls it "AF-S" or "single" shot focus) is for use with stationary subjects, not moving ones. One Shot achieves focus, stops, locks and gives you Focus Confirmation. If the subject moves or you move, you need to re-focus by releasing the button and re-applying pressure to make the camera and lens re-focus. If the subject (or you, or both) continues to move, One Shot is the wrong mode because it stops and locks, and a moment later the moving subject is again out of focus. You mention the problem occurs when you use a "focus and recompose" technique. If not using BBF (back button focusing), you must use One Shot with that technique, or there will be focus errors.

AI Servo (which Nikon calls "AF-C" or "continuous" focus) is for use with moving subjects. It never stops and locks. Focus is continuously updated and corrected, as the subject or you or both move. In other words, it tracks movement as long as you maintain pressure on the button. Because it never stops and locks, Focus Confirmation isn't possible and doesn't occur with AI Servo. You also cannot use AI Servo when using a focus and recompose technique (unless you are also using BBF). Doing so will cause focus errors.

AI Focus is found on many, but not all Canon cameras (1D-series don't have it). This is not really a separate focus mode at all.... It's automation that's supposed to detect whether or not the subject is moving and then decide for you which of the two modes - One Shot or AI Servo - to use. Sometimes it works. Sometimes it doesn't. It might be a bit of a hint that the most pro-oriented models don't even have AI Focus. I tried it many years ago with my film Canon and found that it was slower and just plain chose incorrectly too much, so I stopped using it. Newer cameras might do it better, but I really don't need AI Focus and haven't tried them.

AI Servo actually can be used with both moving and stationary subjects. However, for some techniques such as focus and recompose or to dodge obstacles that momentarily come between you and the subject, Back Button Focusing is needed. BBF allows AI Servo to be used as your default mode (though you also can switch back and use One Shot with BBF at any time, too). BBF gives the user more control over when and where the camera and lens focus... but this also requires more work on the part of the user.

Depending upon what model camera you have, BBF is set up differently. Earlier models, it was a matter of reassigning it (usually to the */AE-Lock button). Later models with the "AF On" button, it's already enabled at that button by default, and just a matter of un-assigning AF from the shutter release button. And, depending upon model, sometimes there is the option to assign BBF to the * (AE-Lock) button, instead.... swapping the function of AE-Lock over to the AF On button.

It takes a little practice to use BBF, but soon becomes second nature. It really puts the photographer more in full control of when and where the camera and lens focus.... And when done right can greatly reduce missed focus problems. To do "focus and recompose" with AI Servo and BBF.... it's simply a matter of putting the AF point over the subject, pressing the button to achieve focus, then lifting pressure off the button so that focus remains there, and then recompose (moving the AF sensor away from the subject). If you didn't use BBF this way, after you recompose AI Servo would cause the lens to re-focus onto whatever the AF point is now covering.



Correct... if using One Shot. Incorrect... if using AI Servo. Hard to say if it will work right or not... if using AI Focus.

But wait, there's more...

The focus pattern you select also can make a noticeable difference. All Canon have at least two patterns: Single Point/Manually Selected and All Points/Auto Selection. Some models have more, such as: Spot Focus (High Precision Single Point), Expansion, Zone and more. Single Point is best to use as much as possible. This way, there's little chance of error so long as you do your part and keep the AF point right where you want the camera and lens to focus. On many Canon, the center AF point is enhanced to be more sensitive and responsive, so can be the best one to choose. But if light is adequate and the subject has good contrast, the other AF points can work quite well, too.

Any of the multi-point AF patterns are trickier to use. They are usually best used with a moving subject against a relatively plain, and distant background... such as a bird flying by with only the sky behind it.

Multi-point patterns such as All Points and Zone allow focus to start with any of the active AF points in the pattern. Expansion (some cameras have several types) is different.... it starts with one point that's chosen by the photographer, but then can switch to adjacent points if necessary, such as when tracking a difficult moving subject.

Multi-point patterns risk the camera focusing somewhere you don't want. They will usually focus on whatever is closest and covered by one of the active AF points. Some of the more sports-oriented camera models are optimized to lock onto movement.

And, different cameras are more or less capable, tailored to their primary "purpose". For example, the 6D has a fairly simple 11-point AF system. The center point is an enhanced, dual axis type that's able to focus in very low light, a good match for that camera's very good high ISO/low light shooting capabilities. But, it's a relatively "entry level" full frame model, so the other 10 AF points are simpler single axis type that aren't as capable in low light or as fast in good light, so it's probably not the best choice for action photography and multi-point AF.

Conversely, the 7D-series and 1D-series Canon all use a discrete chip to run their AF system, separate from the imaging sensor. This makes them very fast focusing, quicker to lock on and more capable of tracking movement. (Note: they also have dual image processors for continuous shooting rates, as well as larger buffers to be able to take more shots before they need to slow or pause to clear the memory.) AFAIK, all other Canon models share AF system functions through the same processor that handles images. Newer models of these with faster processors, the difference might not be all that noticeable except in the most demanding situations.

Besides the above considerations, the lens being used can make significant difference in several ways.

One is the lens aperture. Larger aperture lens, f2.8 and faster, deliver more light to the AF sensors and can make for better AF performance. Also, most Canon models have one or more AF sensors that are further enhanced when f2.8 or faster lenses are used. You'll have to check your camera manual, to see which, if any, of these it has.

Zoom lenses are another factor. Many modern auto focus zooms are a "varifocal" design. This means that when you zoom the lens, when you change the focal length, focus is not maintained. So, if using One Shot focus mode with a varifocal zoom, you MUST remember to re-focus after any change in focal length, even if neither you nor the subject moved. (Note: "Parfocal" zooms maintain focus when zoomed... but are more complex, harder to get and keep calibrated, can be larger and heavier... and are usually more expensive.) Conversely, AI Servo focus mode will rapidly and automatically correct for any loss of focus when a varifocal zoom's focal length is changed.

Lens focus drive systems make a difference, too. More entry-level lenses typically use a micro motor that's slower and noisier. Canon also offers quite a few STM or "Stepper Motor" focus drive lenses, that cost a little more but are faster, quieter and smoother (better for video, too). Or, a third type Canon offers, USM or "Ultrasonic Motor" is often at least 2X faster than STM. For fast moving subjects, USM is best (though most are not as good for video). Third party lens manufacturers make micro motor and USM-type lenses, but AFAIK none are making STM-type.

Also, Canon micro motor lenses (no "STM" or "USM" markings on them) MUST NOT be manually overridden, without first turning off the AF at the switch. That will damage the focus system of those lenses. Both STM and USM lenses have "Full Time Manual" focus... you can override them at any time, with the AF system still engaged, without concern of damage. For example, this might be used to deliberately de-focus a lens, so that autofocus is redone.

Some Canon lenses are slower focusing by design, even if they use higher performance USM focus drive.... especially macro lenses and lenses with very large apertures, both of which have very shallow depth of field potential, where focus has to be extra precise. So these lenses use a "long throw" focus design that puts emphasis on higher precision, at the cost of some speed.

There also can be other things that are often mistaken for focus problems... such as "protection" filters that cause soft images or too-slow shutter speeds (especially with non-stabilized lenses) that result in camera-shake blur.

Ultimately, AF performance is a combination of factors: camera, lens, ambient lighting conditions and subject contrast, plus the knowledge, techniques and skill of photographers themselves.

Of course, there can be faults with lenses and cameras, too,... It's not always the photographer's fault and we can't entirely rule out some failure or flaw in the system. However, I bet that far, far more often than not it's "user error".

For more info about Canon AF systems, I recommend watching a series of three approx. half-hour videos beginning with this one: https://vimeo.com/36931479

Those videos are a bit old now, refer to earlier camera models... but the general info is still good and quite useful understanding the AF system and how to get it to work as best possible for you.

mwsilvers Loc: Central New Jersey

I suggested that the OP may have been in AI Servo several posts back and upon checking, he confirmed it and indicated he was embarrassed by it.

GENorkus Loc: Washington Twp, Michigan

What kind, year, and size lens? Several older tele-zooms used to creep as they aged.

tdekany Loc: Oregon

Please read the other posts? This seems to happen with every post. As a matter of fact, just read the post above yours