Canon AI Servo - Focus and Recompose

[Ken Kovak]

In this thread Artie talks about using AI Servo when handholding to achieve and keep focus when the camera or the subject moves around: http://birdphotographers.net/forums/...ad.php?t=18369

Well perhaps I am being dense but I cannot figure out how to accomplish this on my Canon 40D. Right now I have the CFs set up so the I use the AF-ON button on the back of the camera to get focus and use the shutter button for exposure and shutter actuation. However, when I go to recompose the focus moves to a new point. If I take my thumb off the AF-ON button it seems like the camera stops trying to acjieve focus even when I am set on AI Servo.

Or can the 40D not do this?

Can anyone set me straight?

Thanks
Ken

[Dug Threewitt]

I think you are doing it correctly. You follow focus and let your thumb off to recompose. Then just shoot. By taking your thumb off, it's like shooting in one-shot. If you are following a BIF, you'd keep your thumb on the focus button the entire time, even while shooting. I just switched to shooting like this and can never go back. Don't know if that helps, but good luck.

[Kerry Perkins]

Thank you for this post. I was just getting ready to ask a similar question, i.e., what AF method do most folks use for bird photography? It seems that using AI Servo in conjunction with the AF-ON button gives you the best of both worlds and actually functions like one-shot when you take your finger off of the AF-ON button. I was getting frustrated by not being able to recompose a shot when using AI Servo, but this seems to be the hot ticket.

[Alfred Forns]

Kerry for static subjects you can also move the AF points around !!

[Jason Franke]

It seems to me, after readings Art's posts, that the 45-point grid of the EOS-1 series bodies has enough density to keep the subject under more than one AF point. My understanding is that the camera should then track it regardless of which focus point it moves under, so long as it doesn't leave all of the points. I.e. focus is gained using the center point, then as the camera continues to track the subject with the rest of the points keeping the distance/focus right.

With the 40D you often don't have the density of AF points to always keep the subject under an AF point, nor the ability to control how rapidly the camera goes looking for something else to focus on when things move out from under a point. So when the center point moves off the subject, if the subject isn't already under another point, the camera goes of looking for something to focus on. If you can keep the subject under several focus points (or select a focus point and keep the subject under it) you should be able to keep AI-Servo active and the subject in focus, similar to how I'm understanding Art is doing things.

As for Kevin's question about what AF method I use. I use AI-Servo coupled with either the shutter release or the * button to activate it (I use a 40D w/ a grip so I have the AF-on and Exposure lock buttons reversed (good going Canon with the lack of an AF-On button on the new grip)), depending on what I'm doing. I find tracking small fast birds for any length of time is rather difficult when using a rear button to activate the AF. But I have the two custom modes programmed in a C1 and C2 with that being the only difference so I can rapidly switch between them, when shooting if I need to make a change.

[Jim Neiger]

Another way to accomplish this is to set the AF-ON or * buton to AF lock. Then you can focus with the shutter button halway pressed, lock the focus with the * or AF-On button, recompose, and shoot, all why remaining in AI Servo and focusing using your index finger on the shutter button. I've found it is better for me to focus with my index finger instead of my thumb because my index finger is more co-ordinated than my thumb. I also found it uncomfortable to have to press two buttons to shoot (* to focus and shutter to shoot). Using the my index finger for focus helps when bumping the focus. See my thread on bumbing the focus for BIF for more info.

[Kerry Perkins]

One more question (well, for now...) - the manual says that I should use auto-AF point selection but I have read that it is best to use only the center point. I am referring to using AI-Servo mode and the manual's description of the camera switching to different points if the subject moves away from the center. This is most critical for BIF, of course, and that is what I am trying to get a handle on. My primary body is a 50D.

Thanks!

[Jim Neiger]

One more question (well, for now...) - the manual says that I should use auto-AF point selection but I have read that it is best to use only the center point. I am referring to using AI-Servo mode and the manual's description of the camera switching to different points if the subject moves away from the center. This is most critical for BIF, of course, and that is what I am trying to get a handle on. My primary body is a 50D.

Thanks!

I use center point only. This gives me the most control when photographing BIF.

[Kerry Perkins]

Thanks Jim. That's what I have been doing but got a little confused by reading the manual. :o A great feature of DPP is the ability to see where the AF points were at the time of capture. It seems that the bird can be pretty far away from the center point and still be tracked, but this is not always the case in my experience. I do have the custom setting for AF set to "give up" if focus is not achieved, as the tele lenses can get way out of focus while searching.

[Jim Neiger]

Thanks Jim. That's what I have been doing but got a little confused by reading the manual. :o A great feature of DPP is the ability to see where the AF points were at the time of capture. It seems that the bird can be pretty far away from the center point and still be tracked, but this is not always the case in my experience. I do have the custom setting for AF set to "give up" if focus is not achieved, as the tele lenses can get way out of focus while searching.

When the center point hits the sky it will stop focusing after a short delay. Sometimes the bird will remain in the focal plain and the shot will still be sharp.

[Kerry Perkins]

Thanks Jim. You are the master at this!

[Jonathan Michael Ashton]

In this thread Artie talks about using AI Servo when handholding to achieve and keep focus when the camera or the subject moves around: http://birdphotographers.net/forums/...ad.php?t=18369

Well perhaps I am being dense but I cannot figure out how to accomplish this on my Canon 40D. Right now I have the CFs set up so the I use the AF-ON button on the back of the camera to get focus and use the shutter button for exposure and shutter actuation. However, when I go to recompose the focus moves to a new point. If I take my thumb off the AF-ON button it seems like the camera stops trying to acjieve focus even when I am set on AI Servo.

Or can the 40D not do this?

Can anyone set me straight?

Thanks
Ken

Hi Ken,
I asked a similar question and V Jason Franke kindly offered this advice, it is related to the 50D but I suspect it will be the same on the 40D:I think you're looking for C.Fn IV-1 Shutter button/AF-ON button, set to "1: Metering + AF Start/ AF stop". If you want to keep using the * button instead of the AF-ON button, set C.Fn IV-2 AF-ON/AE lock button switch to 1 as well.
I think this is what you are looking for

Jon

[Roger Clark]

I do do not use the AF-on button. I move the AF point around to track the animal in the best composition using AI servo mode. I've been ding it this way for years with 10D, 20D, 30D, 40D, 1DII and 5DII bodies for both birds in flight as well as general animal action. I feel this way I don't lose any time trying to recompose and freeze in the heat of action. With moving the focus point, I can keep a good composition (easier on the 1D bodies) follow the action, and image at will. I try and keep an AF point on the eyes.

I have an article about AF focus tracking at:
http://www.clarkvision.com/photoinfo...with.autofocus

Roger