AI Servo & Focus Point & BBF
Sep 20, 2014 11:40:38 #
I have a Canon 60D, understand AI Servo for moving subjects and also use back button focusing. I always use single point autofocus. I have searched the archives and can't find if it is ok to use only a single point autofocus with AI Servo and when using AI Servo, do i continue to hold down the back button for autofocus. Have seen related subjects but nothing that addresses both the autofocus point, back button autofocus and AI Servo. Just one of those nagging questions that I can't find the answer to. Any comments or help is appreciated.
Sep 20, 2014 12:10:43 #
Yes i have wondered the same thing, I have a canon 7d. I think from what I have heard, you should use evualuative focusing or the camera will work too hard to try and focus on that spot focusing and it wont get the focus that your trying to achieve...but I am not sure...so I will like to hear what others recommend. :)
Sep 20, 2014 12:45:07 #
Yes, you must keep the BB pushed in order to servo focus and it will be using the center focus only - as the best on a 60D - the 7D has options ..."evaluative" is a metering mode not an AF mode ...
Sep 20, 2014 12:45:27 #
This is something I am working thru also, I also have the 60d. One thing I noticed is that when in AI servo, when you push the BB to focus it does not beep to let you know you have focus and the only focus point that is active is the center point. From my understanding you must start on the center focus point but as you continue to hold the BB down and the subject moves to the other focus point those points will pick it up. But you must start with the center point. Hope this makes cents.
Sep 20, 2014 12:59:23 #
amfoto1
Loc: San Jose, Calif. USA
It is fine to use Single Point/Manual Selection when using BBF and AI Servo. In fact, it's ideal to do so, though it is more work for you, maintaining the AF point right on target.
If you have your camera set up for BBF... Then, yes, when tracking a moving subject, you need to maintain continuous pressure on the AF-On button so that the camera continues to focus on and track with the subject. (Alternatively, if not using BBF, you need to keep the shutter release button half-pressed continuously.)
In fact, if the subject passes behind an obstruction momentarily, you can briefly lift off pressure to prevent the camera from accidentally re-focusing onto the obstruction, and then reapply pressure to the button pick up focusing on the subject again after it clears the obstruction (think of photographing a car driving past, with axis a telephone pole between you and the car at one point along the panning axis, for example).
Again, you do need to maintain the single, active AF point right on the subject, where you want the camera to focus.
Both the 60D and the 7D have all "cross-type" AF points, so all the points are pretty darned sensitive and might be used. However, the center one is even better when using an f2.8 or larger aperture lens, so can be superior in some situations.
Sorry, but there is no such thing as "evaluative focus" on a 7D (or any other Canon camera model). They have Evaluative Metering, but that's a completely different subject and for all practical purposes has nothing to do with focusing. (One exception... if doing Spot Metering, which is only possible on these cameras at the very center of the image area, so you must only use the center AF point in order to do both non-AE Lock Spot Metering and AI Servo focusing at the same time.)
Both 60D and 7D have three focusing modes: One Shot, AI Servo and AI Focus.
I recommend to not use either camera's AI Focus setting at all. This is actually not a focus mode... In this setting the camera is supposed to decide for you whether or not the subject is moving, then switch to use the correct mode: One Shot or AI Servo. I have found it sometimes choose wrong... and that it causes a slight delay while the camera is "thinking about" whether or not the subject is moving. AI Focus is sort of snapshooter or point-n-shoot mode... In fact, Canon's more advanced, pro-oriented models don't even have AI Focus mode... they only offer One Shot and AI Servo.
AI Servo, for moving subjects, acquires focus and then tracks the subject, updating focus x number of times per second and trying to predict where the subject will be when a shot is taken. Because it never stops and locks, there is no Focus Confirmation possible. Think about it... Focus is continuous, so there's actually nothing to confirm! If Focus Confirmation were made to work in AI Servo... you'd get a continuous "beeeeeeeeeeeeeeeeeeep" as long as you held down the button and maintained focus! Or if you turned the beep off, the green LED would remain lit continuously. What good does that do?
If using BBF, it's possible to make AI Servo your default AF mode, making AI Focus largely unnecessary. This is because you can manually start and stop the AF with BBF. So, for example, you can use "focus and recompose" techniques, which is not possible with AI Servo if not using BBF. The only downside to using AI Servo, which will work with either stationary or moving subjects now that you are using BBF, is the lack of Focus Confirmation... Instead you have to learn to trust the camera and yourself, and that's something that does happen in time and with practice.
One Shot is the other "actual" AF mode... For stationary subjects it acquires focus, then stops and locks, and gives you Focus Confirmation: the green LED in the viewfinder lights up... and the audible "beep" sounds, if you have it enabled. This can be reassuring and One Shot might be better when possible, for greatest accuracy. But if you or the subject or both move, if the distance to the subject changes at all, you must fully lift pressure (whether using BBF or still using the shutter button to control AF) and reapply, to cause the camera to refocus. Otherwise, focus will be off. I have the "beep" enabled on my cameras, mainly to warn me if I accidentally leave my camera in One Shot mode and then start shooting moving subjects! (I never cease to be amazed how many peoples' cameras I hear merrily beeping away throughout sporting events... most of their hundreds or even thousands of shots are going to miss focus! They really should read their damned owners manuals! Instead they'll probably blame the gear in online forums, go out and buy a "better" camera and/or lens trying to solve the "problem".)
AI Servo focus mode also can be very useful with a lot of zoom lenses... Many of which today are "varifocal" designs. This means they don't maintain focus when zoomed to a different focal length. I.e., they need to be re-focused after any changes in focal length. Varifocal zooms are simpler and less expensive to build, less difficult to keep in calibration than "parfocal" zooms, that do maintain focus when zoomed.
Because AF is so good, many zooms today are varifocal design. So long as you are using AI Servo, the camera will maintain focus even when you zoom a varifocal design lens, so no worries whether or not your zoom is varifocal or parfocal. If using One Shot, you need to know if your zoom is varifocal, because if it is you need to consciously re-focus any time you change the focal length setting of the zoom.
You also can use BBF with All Points/Auto Selection AF pattern in all Canon cameras. However, this mode leaves a lot up to chance, that the camera will choose to focus on a point that you're okay with. Usually the camera will focus on the closest object covered by an AF point. In AI Servo, it might be "attracted" to movement (or "distracted" by movement). In general, you'll have more missed focus shots leaving it up to the camera to choose, rather than skillfully using a single point that's fully under your control.
Not on 60D, but on 7D there are three more AF pattern choices, in addition to Single Point and All Points. 7D also offers Expansion Points, Zone Focus, and Spot Focus. (All five focus pattern choices can be enabled or disabled in the menu of the camera, in case you don't see one or in case you don't want one to even be offered.)
7D has 19 AF points (as opposed to 9 in 60D)... It's additional AF Patterns operate as follows...
Expansion Points, you select one point as a starting point, just like in Single Point, but setting this allows the camera to use the adjacent 4 points - one to each side and one above and below that "starting" point - if the subject strays (or you allow it to stray) from the first point.
Zone Focus is sort of like a smaller version of All Points... You choose a region of the image area with up to nine active AF points (it may be less in some areas of the AF point array), but the camera is allowed to auto select any point or points within that group of active points. Any of them can be the starting point and the camera can automatically jump to any of them if it thinks it needs to.
Both Expansion Points and Zone Focus can be useful with erratic moving and fast moving subjects that are difficult to track. You likely won't have as high a percentage of accurately focused shots, since there's some chance the camera will be fooled into focusing with the wrong AF point, but it might improve your odds with hard to track subjects. I would only use Zone Focus with a fairly distant and/or very plain background, such as birds against the sky (but not if they are flying close to a treeline).
Spot Focus is a high precision form of Single Point... using a smaller AF point. I call it a "Bird In Trees" mode, since it's helpful when trying to focus on something beyond a tangle of branches. In Spot Focus, AF is a little bit slower than in standard Single Point, so it might not work well for rapidly moving subjects. But I do know folks who use it successfully with long lenses to photograph butterflies.
To summarize...
Back Button Focusing can be used with either One Shot (stationary subject) or AI Servo (moving subject) focusing modes. In fact, it makes AI Servo more generally useful.
One Shot and AI Servo both can be used with any of the AF Focus Pattern choices, which on all Canon cameras are Single Point and All Points, and on 7D are also Expansion Points, Zone Focus and Spot Focus, for a total of five. (Note: 1D series cameras have some other Focus Pattern choices... 5D Mark III has six, in addition to what 7D offers it has a second type of Expansion pattern. And 7D Mark II is getting a total of seven, with the same five as original 7D, but now two Expansion and two Zone pattern choices.)
EDIT: 13 or so years ago, when I first switched to Canon I bought two EOS-3s and an Elan 7E film cameras (EOS-33 in other parts of the world, I think. It was an extremely quiet model, ideal for weddings and some wildlife.) Those all had Eye Control, which I tried hard to make work for the first several months... with marginal results. Then I learned about BBF and started using it instead... and my results skyrocketed. I now use a pair of 7Ds for most of my action shooting (and a 5DII for some other stuff) and get around 97-98% in focus with them. Before I primarily used 10D, 30D, 50D... the last have very similar to 60D's AF system. With them I got upwards of 95% of shots acceptably in focus, using BBF most of the time.
It does take practice to get a high percentage of in-focus shots. I know when I haven't been shooting action for a while, my first time or two out I don't do as well. But the more you do it, the more it becomes second nature with BBF, which puts you in more full control of where the camera focuses, and the more you learn to know and trust how your camera responds, the better you will be at it.
No one is perfect, though... so don't fret over some misses. Just take more shots and keep practicing! (Note: There are other factors effecting AF performance too... Such as lenses: those with larger aperture and USM drive lenses are generally the fastest and most accurate focusing... And such as lighting conditions, low light will make the camera struggle, as can "weird" lighting such as fluorescent. Even filters on lenses can have a negative effect on AF, while lens hoods might help.)
Also, BBF on 7D is actually already set up for you (not sure about 60D, but pretty sure it's the same). By default, both the shutter button and the AF-On button start and run AF. To set up "true BBF" on 7D (and probably 60D), you actually remove the AF function from the shutter release button, leaving it only on the AF-On button.
One other thing... on most Canon cameras you can simply use the AF-On button for BBF... or optionally can swap the functions of the AF-On and * (AE Lock) buttons, so that * activates and runs AF instead. I choose to do the latter for several reasons. One was that the older Canon models (and/or the vertical grips for them) didn't have the AF-On button, so the * button had to be used for BBF, and that's what I'm used to doing. Another is that the * button is larger and more prominent, plus falls more right under my thumb. I focus every single shot, but only occasionally use AE Lock, so it makes more sense to me to use the more prominent button for the most frequently used function. Also, this puts BBF AF right next to the other thumb operated AF-related button... the one that's pressed to allow AF point selection. This swap of AF-On and * button function is purely optional, though.
If you have your camera set up for BBF... Then, yes, when tracking a moving subject, you need to maintain continuous pressure on the AF-On button so that the camera continues to focus on and track with the subject. (Alternatively, if not using BBF, you need to keep the shutter release button half-pressed continuously.)
In fact, if the subject passes behind an obstruction momentarily, you can briefly lift off pressure to prevent the camera from accidentally re-focusing onto the obstruction, and then reapply pressure to the button pick up focusing on the subject again after it clears the obstruction (think of photographing a car driving past, with axis a telephone pole between you and the car at one point along the panning axis, for example).
Again, you do need to maintain the single, active AF point right on the subject, where you want the camera to focus.
Both the 60D and the 7D have all "cross-type" AF points, so all the points are pretty darned sensitive and might be used. However, the center one is even better when using an f2.8 or larger aperture lens, so can be superior in some situations.
Sorry, but there is no such thing as "evaluative focus" on a 7D (or any other Canon camera model). They have Evaluative Metering, but that's a completely different subject and for all practical purposes has nothing to do with focusing. (One exception... if doing Spot Metering, which is only possible on these cameras at the very center of the image area, so you must only use the center AF point in order to do both non-AE Lock Spot Metering and AI Servo focusing at the same time.)
Both 60D and 7D have three focusing modes: One Shot, AI Servo and AI Focus.
I recommend to not use either camera's AI Focus setting at all. This is actually not a focus mode... In this setting the camera is supposed to decide for you whether or not the subject is moving, then switch to use the correct mode: One Shot or AI Servo. I have found it sometimes choose wrong... and that it causes a slight delay while the camera is "thinking about" whether or not the subject is moving. AI Focus is sort of snapshooter or point-n-shoot mode... In fact, Canon's more advanced, pro-oriented models don't even have AI Focus mode... they only offer One Shot and AI Servo.
AI Servo, for moving subjects, acquires focus and then tracks the subject, updating focus x number of times per second and trying to predict where the subject will be when a shot is taken. Because it never stops and locks, there is no Focus Confirmation possible. Think about it... Focus is continuous, so there's actually nothing to confirm! If Focus Confirmation were made to work in AI Servo... you'd get a continuous "beeeeeeeeeeeeeeeeeeep" as long as you held down the button and maintained focus! Or if you turned the beep off, the green LED would remain lit continuously. What good does that do?
If using BBF, it's possible to make AI Servo your default AF mode, making AI Focus largely unnecessary. This is because you can manually start and stop the AF with BBF. So, for example, you can use "focus and recompose" techniques, which is not possible with AI Servo if not using BBF. The only downside to using AI Servo, which will work with either stationary or moving subjects now that you are using BBF, is the lack of Focus Confirmation... Instead you have to learn to trust the camera and yourself, and that's something that does happen in time and with practice.
One Shot is the other "actual" AF mode... For stationary subjects it acquires focus, then stops and locks, and gives you Focus Confirmation: the green LED in the viewfinder lights up... and the audible "beep" sounds, if you have it enabled. This can be reassuring and One Shot might be better when possible, for greatest accuracy. But if you or the subject or both move, if the distance to the subject changes at all, you must fully lift pressure (whether using BBF or still using the shutter button to control AF) and reapply, to cause the camera to refocus. Otherwise, focus will be off. I have the "beep" enabled on my cameras, mainly to warn me if I accidentally leave my camera in One Shot mode and then start shooting moving subjects! (I never cease to be amazed how many peoples' cameras I hear merrily beeping away throughout sporting events... most of their hundreds or even thousands of shots are going to miss focus! They really should read their damned owners manuals! Instead they'll probably blame the gear in online forums, go out and buy a "better" camera and/or lens trying to solve the "problem".)
AI Servo focus mode also can be very useful with a lot of zoom lenses... Many of which today are "varifocal" designs. This means they don't maintain focus when zoomed to a different focal length. I.e., they need to be re-focused after any changes in focal length. Varifocal zooms are simpler and less expensive to build, less difficult to keep in calibration than "parfocal" zooms, that do maintain focus when zoomed.
Because AF is so good, many zooms today are varifocal design. So long as you are using AI Servo, the camera will maintain focus even when you zoom a varifocal design lens, so no worries whether or not your zoom is varifocal or parfocal. If using One Shot, you need to know if your zoom is varifocal, because if it is you need to consciously re-focus any time you change the focal length setting of the zoom.
You also can use BBF with All Points/Auto Selection AF pattern in all Canon cameras. However, this mode leaves a lot up to chance, that the camera will choose to focus on a point that you're okay with. Usually the camera will focus on the closest object covered by an AF point. In AI Servo, it might be "attracted" to movement (or "distracted" by movement). In general, you'll have more missed focus shots leaving it up to the camera to choose, rather than skillfully using a single point that's fully under your control.
Not on 60D, but on 7D there are three more AF pattern choices, in addition to Single Point and All Points. 7D also offers Expansion Points, Zone Focus, and Spot Focus. (All five focus pattern choices can be enabled or disabled in the menu of the camera, in case you don't see one or in case you don't want one to even be offered.)
7D has 19 AF points (as opposed to 9 in 60D)... It's additional AF Patterns operate as follows...
Expansion Points, you select one point as a starting point, just like in Single Point, but setting this allows the camera to use the adjacent 4 points - one to each side and one above and below that "starting" point - if the subject strays (or you allow it to stray) from the first point.
Zone Focus is sort of like a smaller version of All Points... You choose a region of the image area with up to nine active AF points (it may be less in some areas of the AF point array), but the camera is allowed to auto select any point or points within that group of active points. Any of them can be the starting point and the camera can automatically jump to any of them if it thinks it needs to.
Both Expansion Points and Zone Focus can be useful with erratic moving and fast moving subjects that are difficult to track. You likely won't have as high a percentage of accurately focused shots, since there's some chance the camera will be fooled into focusing with the wrong AF point, but it might improve your odds with hard to track subjects. I would only use Zone Focus with a fairly distant and/or very plain background, such as birds against the sky (but not if they are flying close to a treeline).
Spot Focus is a high precision form of Single Point... using a smaller AF point. I call it a "Bird In Trees" mode, since it's helpful when trying to focus on something beyond a tangle of branches. In Spot Focus, AF is a little bit slower than in standard Single Point, so it might not work well for rapidly moving subjects. But I do know folks who use it successfully with long lenses to photograph butterflies.
To summarize...
Back Button Focusing can be used with either One Shot (stationary subject) or AI Servo (moving subject) focusing modes. In fact, it makes AI Servo more generally useful.
One Shot and AI Servo both can be used with any of the AF Focus Pattern choices, which on all Canon cameras are Single Point and All Points, and on 7D are also Expansion Points, Zone Focus and Spot Focus, for a total of five. (Note: 1D series cameras have some other Focus Pattern choices... 5D Mark III has six, in addition to what 7D offers it has a second type of Expansion pattern. And 7D Mark II is getting a total of seven, with the same five as original 7D, but now two Expansion and two Zone pattern choices.)
EDIT: 13 or so years ago, when I first switched to Canon I bought two EOS-3s and an Elan 7E film cameras (EOS-33 in other parts of the world, I think. It was an extremely quiet model, ideal for weddings and some wildlife.) Those all had Eye Control, which I tried hard to make work for the first several months... with marginal results. Then I learned about BBF and started using it instead... and my results skyrocketed. I now use a pair of 7Ds for most of my action shooting (and a 5DII for some other stuff) and get around 97-98% in focus with them. Before I primarily used 10D, 30D, 50D... the last have very similar to 60D's AF system. With them I got upwards of 95% of shots acceptably in focus, using BBF most of the time.
It does take practice to get a high percentage of in-focus shots. I know when I haven't been shooting action for a while, my first time or two out I don't do as well. But the more you do it, the more it becomes second nature with BBF, which puts you in more full control of where the camera focuses, and the more you learn to know and trust how your camera responds, the better you will be at it.
No one is perfect, though... so don't fret over some misses. Just take more shots and keep practicing! (Note: There are other factors effecting AF performance too... Such as lenses: those with larger aperture and USM drive lenses are generally the fastest and most accurate focusing... And such as lighting conditions, low light will make the camera struggle, as can "weird" lighting such as fluorescent. Even filters on lenses can have a negative effect on AF, while lens hoods might help.)
Also, BBF on 7D is actually already set up for you (not sure about 60D, but pretty sure it's the same). By default, both the shutter button and the AF-On button start and run AF. To set up "true BBF" on 7D (and probably 60D), you actually remove the AF function from the shutter release button, leaving it only on the AF-On button.
One other thing... on most Canon cameras you can simply use the AF-On button for BBF... or optionally can swap the functions of the AF-On and * (AE Lock) buttons, so that * activates and runs AF instead. I choose to do the latter for several reasons. One was that the older Canon models (and/or the vertical grips for them) didn't have the AF-On button, so the * button had to be used for BBF, and that's what I'm used to doing. Another is that the * button is larger and more prominent, plus falls more right under my thumb. I focus every single shot, but only occasionally use AE Lock, so it makes more sense to me to use the more prominent button for the most frequently used function. Also, this puts BBF AF right next to the other thumb operated AF-related button... the one that's pressed to allow AF point selection. This swap of AF-On and * button function is purely optional, though.
Sep 20, 2014 16:32:58 #
Oops. Sorry I got mixed up with the metering and focus...so much to learn still...
Sep 21, 2014 12:29:30 #
7D man here..Thank you SO much for such good info on BBF.I learnt
more from this than I did from the Canon Book. I have one
question...in LIVE VIEW when I press the AF-ON button my
screen goes blank to focus..then I have to press the shutter
button.to take the picture does that sound right to you.
Thanks for UHH..
more from this than I did from the Canon Book. I have one
question...in LIVE VIEW when I press the AF-ON button my
screen goes blank to focus..then I have to press the shutter
button.to take the picture does that sound right to you.
Thanks for UHH..
Sep 21, 2014 13:04:23 #
sidney wrote:
7D man here..Thank you SO much for such good info on BBF.I learnt
more from this than I did from the Canon Book. I have one
question...in LIVE VIEW when I press the AF-ON button my
screen goes blank to focus..then I have to press the shutter
button.to take the picture does that sound right to you.
Thanks for UHH..
more from this than I did from the Canon Book. I have one
question...in LIVE VIEW when I press the AF-ON button my
screen goes blank to focus..then I have to press the shutter
button.to take the picture does that sound right to you.
Thanks for UHH..
Yes, it is working properly. One of the reasons I don't use live view. To get good tracking use your viewfinder, it is much easier.
Jim D
Sep 21, 2014 13:23:31 #
[quote=amfoto1]It is fine to use Single Point/Manual Selection when using BBF and AI Servo. In fact, it's ideal to do so, though it is more work for you, maintaining the AF point right on target. [quote]
amfoto1,
All good information but this pretty much says it all, for the 60D. Even though the photo quality is equivalent to the 7D the 7D has so many other features. The lack of focus points is going to make something like a BIF difficult at best. I owned a 6D and got rid of it for this reason.
Jim D
amfoto1,
All good information but this pretty much says it all, for the 60D. Even though the photo quality is equivalent to the 7D the 7D has so many other features. The lack of focus points is going to make something like a BIF difficult at best. I owned a 6D and got rid of it for this reason.
Jim D
Sep 21, 2014 19:45:03 #
Sep 22, 2014 20:34:22 #
Sep 23, 2014 08:44:19 #
As the original poster, want to thank all those that replied, especially amfoto1 for such a complete explanation. Finally got an answer to a question I have had ever since i have been using my 60D
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