Missed Focus, DOF and Dinara Safina

[canoli]

I wonder if you'll be surprised the way I was, looking at this shot. The 1st one is a 100% crop and the other 2 include the focus points (from DPP) and a DOF calculator with the specs, one using 0.035mm as the CoC and one using the Pixel Pitch of the 40D.


I wanted Dinara Safina's face but got the back wall instead. That wall is approx. 10 feet behind her, yet the shot is close to being acceptably sharp. Of course definitions of "acceptably" vary, but regardless, wouldn't you think her face would be way out of focus, considering how far away the focus point is? (disregard the motion blur in her arms, hands, racket - it was intentional)


I ask because I have shots where I really nailed the focus, right on the player's face, and the difference, while obvious, isn't exactly "night n day." I'm surprised. I thought missing focus by 10 feet, with a DOF of (at most) 4 feet would show a very blurry subject.


[from the U.S. Open, Thursday 9/3/09, Louis Armstrong Stadium - 40D 70-200 2.8 IS, 1/640 @ f/4.0 ISO 100 hand held. Shooting distance approx. 40 feet, focal length 145mm.]


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[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.29.05/DOF_5F00_.35CoC.jpg[/img]


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[Rodger]

Did you use AI Servo for autofocus or one shot? If you used one shot, would it be possible that you focused on her face then recomposed a little?

[Wes]

Just my thoughts but if you used one shot and she was still in the plane of focus then I would expect her to still be in pretty good focus. If using AI Servo I would expect the focus to sift to the back wall unless you took the shot as soon as focus was locked.

[Bob]

So why do you think you missed the focus point for her face?


Looks like you were using center focus point only, vs. letting the camera select the focus point of the closest object.


You could have used the the center plus the expanded focus selection.


Also, using a faster shutter speed could help.

[canoli]

ah, good question you guys, I didn't consider the focus mode. It was Servo (Hi-Speed Continuous as well). I have 6 images all created at 11:35:57am, and two of them show the center point touching her body. In these shots her face is definitely sharper than the one I posted, but it's not a dramatic difference.


I'm sure I was attempting to follow the play, trying to keep the center point over her face. I was hoping at 145mm @ f/4, about 40 feet away, the DOF would be at least a foot or two (quite frankly I was just guessing).


Lately I've just been winging it with Servo mode (first-year photographer here). I figured the U.S. Open would be a good chance to try it out. Theoretically I know what it does, but without a confirmation of focus - no light, no beep - I'm not sure I could ever swear I got the shot until I saw it later in post. Is that just the way it is?


Or to put it another way, if you really had to get the shot - of a fast-moving subject (athlete) - would you completely avoid AI Servo mode and stick with One-Shot? (assume 40D or better, L glass, good light, hand held, etc.)


Thanks for your input!

[Wes]

AIservo for sports is the way to go. Just got to remember to keep following the subject especially if shooting in burst. Takes lots of practice.

[canoli]

Thanks Bob - posted before I read your reply.

So why do you think you missed the focus point for her face?

just poor technique I guess, not quick enough ("undeveloped" technique I should say). I hope eventually I'll get better...!

Looks like you were using center focus point only, vs. letting the camera select the focus point of the closest object.

Yes, I rarely use all the AF points simultaneously, and never with a moving subject. I believe I give up too much control that way. Unless I'm shooting at infinity I always have one of the AF points selected. Maybe that's my problem here? Should I use Servo but "let the camera decide" what AF point to use? Could that be the secret to using Servo mode, the correct way to use it?

You could have used the the center plus the expanded focus selection.

Not sure what you mean by this.

lso, using a faster shutter speed could help.

I like the look of some motion blur on the swing - the racket, the arms, etc. 1/640 seems to be a good compromise for that. But I also shot plenty at much higher speeds as well.

[Rodger]

always have one of the AF points selected. Maybe that's my problem here? Should I use Servo but "let the camera decide" what AF point to use? Could that be the secret to using Servo mode, the correct way to use it?

nope typically (in my experience) center point and AI Servo is the way to go. Unless the 40D has strong focus points other than the center. But I find on my 20D I get the best results when shooting sports on AI Servo with AF center point selected. Then I track the subject and crop to my liking in post. Tracking is difficult and I've blown plenty of shots because of poor technique. Don't worry, you'll get it down soon enough!

[Bob]

<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]Canoli,<o></o>


<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]If you ask 10 people for an opinion you will get 11 answers. <o></o>


<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]AI servo is NOT the best option if the subject is moving side to side. AI servo is best if the object is moving towards or away from you.<o></o>


<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]You stated you did not understand my comment about assist focus points. Your camera may not have this option, but this option allows the focusing system to transfer the object toan adjacent focus points when you cannot follow theobject with the selected focus point.<o></o>


<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]<o></o>


<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]Since your subject was alone, the automatic focus point selection would have given you a better focus fromyour moving (side to side as view from the camera's position) subject.<o></o>
<p class="MsoNormal" style="margin: 0in 0in 10pt;"]<o><span style="font-family: Calibri; font-size: small;"]</o>

[Sean Setters]

But in tennis, the subjects typically move toward you, away from you, and side to side.