Missed Focus, DOF and Dinara Safina

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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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?

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.

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.

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!

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.

Thanks Bob - posted before I read your reply.

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Originally Posted by Bob

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

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

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Originally Posted by Bob

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

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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?

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Originally Posted by Bob

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

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Not sure what you mean by this.

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Originally Posted by Bob

lso, using a faster shutter speed could help.

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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.

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Originally Posted by canoli

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?

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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! :)

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


<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:p></o:p>


<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:p></o:p>


<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:p></o:p>


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


<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:p></o:p>
<p class="MsoNormal" style="margin: 0in 0in 10pt;"]<o:p><span style="font-family: Calibri; font-size: small;"]</o:p>

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

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Originally Posted by Sean Setters

But in tennis, the subjects typically move toward you, away from you, and side to side.
<div style="CLEAR: both"]</div>

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<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]Thatis very true, but an object coming towards/away fromyou is easier to track than one moving side to side. <o:p></o:p>


<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]So how fast is the subject moving whenyou take the exposure / focus readings?<span style="mso-spacerun: yes;"] If the subject is moving slowand is at a far distance (DOF will aid focus) then NON servo will work fine or better- 50 to 100 ms to take the focus/exposure. <o:p></o:p>


<span style="font-family: 'Verdana','sans-serif'; color: black; font-size: 11pt;"]When you are panning, unless you use the assist focus points, you will probably not get a super sharp image, as shown in the above examples. In these examples, the multi focus points would have given a sharper photo. Yes, you may need to switch between single / multi focus points quickly and some cameras allow you to do this. But the example shown is what we are discussing. You can also use the AF-on switch.

HI Bob,

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Originally Posted by Bob

<span style="font-family: 'Verdana','sans-serif'; color: #000000; font-size: 11pt;"]Thatis very true, but an object coming towards/away fromyou is easier to track than one moving side to side.

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I think you got it all mixed up here, anything that comes at you is very difficultto track and I don't care if you're using Canon, 40D, 50D,1D Mark III or Nikon D3, D300, I shoot a long side with guys that use those cameras and hear their complains all the time. As good as auto focus performance of theses camera gets, the AF results are not consistent if the subject comes at you. My experience is that if you shoot moving subject, always use AI Servo and practice on the subject that you're interested, and I mean practice a lot because not all moving subjects move the same. Birds move differentlyfrom tennis players.

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Originally Posted by Sinh Nhut Nguyen

HI Bob,

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Originally Posted by Bob

<span style="font-family: 'Verdana','sans-serif'; color: #000000; font-size: 11pt;"]Thatis very true, but an object coming towards/away fromyou is easier to track than one moving side to side.

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I think you got it all mixed up here, anything that comes at you is very difficultto track and I don't care if you're using Canon, 40D, 50D,1D Mark III or Nikon D3, D300, I shoot a long side with guys that use those cameras and hear their complains all the time. As good as auto focus performance of theses camera gets, the AF results are not consistent if the subject comes at you. My experience is that if you shoot moving subject, always use AI Servo and practice on the subject that you're interested, and I mean practice a lot because not all moving subjects move the same. Birds move differentlyfrom tennis players.
<div style="CLEAR: both"]</div>

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<p class="MsoNormal" style="margin: 0in 0in 0pt;"]<span style="font-size: small;"]<span style="font-family: Times New Roman;"]I think your definition of tracking and mine are different. <span style="mso-spacerun: yes;"]
<p class="MsoNormal" style="margin: 0in 0in 0pt;"]<o:p><span style="font-family: Times New Roman; font-size: small;"]</o:p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"]<span style="font-family: Times New Roman; font-size: small;"]Tracking as I&rsquo;m describing it, and the point of this thread, is the photographer following the subject with the selected focus point(s) &ndash; tracking the subject movement, NOT the servo circuit keeping the object in focus.
<p class="MsoNormal" style="margin: 0in 0in 0pt;"]<o:p><span style="font-family: Times New Roman; font-size: small;"]</o:p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"]<span style="font-family: Times New Roman; font-size: small;"]The difficultyfor the photographer tracking a subject that is moving side to side required more angular camera movement than a subject coming straight towards you.
<p class="MsoNormal" style="margin: 0in 0in 0pt;"]<o:p><span style="font-family: Times New Roman; font-size: small;"]</o:p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"]<span style="font-family: Times New Roman; font-size: small;"]So, I think you maybe confused when you make the statement that an object coming straight towards you requires more camera movement (is more difficult) vs. one that is going side to side.

have to agree - in my limited experience, side to side is much easier to track than toward/away.


As far as quickly switching between AF points during a tennis rally, I think that's probably unrealistic. Between rallies, sure, but while the rally is in progress? If that's the goal then I think I'd rather have a Leica and just learn to focus manually all the time. I really don't enjoy being dependent on AF anyway. Unfortunately today's DSLRs aren't geared toward MF at all, esp the APS-C bodies...


A few months back I posted a new thread asking for input on the Katz Eye Optics (split-prism focusing screens for various DSLRs) and the product (and the thread) was so popular it didn't even generate one reply. Ha! Oh well, not much call for MF out there apparently.


Anyway, whatever the case may be, I think I'll try Servo mode again, but this time I'll enable all nine points and let the 40D do its thing. Hold the shutter button down halfway, follow the subject, and snap bursts of shots. I'm hoping if I drift a little - when the center point slips off the subject - an adjacent AF point will pick up the focus. I'm not entirely sure it works that way, but I'll give it a try.

Canoli,


I too am a first year DSLR owner/shooter, keep this in mind, I am not an expert.


I have been primarily shooting my daughter playing soccer, so I have an understanding of what you are trying to do. The one thing I noticed in your post is that you are still using the shutter button to set focus. Most of the pros and semi-pros I have read or spoken with separate the focus from the shutter button, specifically to make it easier to track and focus on a target that is moving. I did this with my 30D (custom function 4 set to option 3 if I remember correctly, read your manual), and it took a little time to get used to it but once I did the results I got were much improved.


My set up is basically, move the "focus" button to the AE lock under my thumb, use AI Servo, center focus point only, High speed continuous shooting, and set the rest for appropriate exposure. I track my target with the center focus point, and AI servo adjusts the focus plane if the target is closer or further away. I found that I am much more comfortable "tracking" this way, and I feel more confident that I will get the shot when I pull the trigger.


Good luck and happy shooting,


David

Thanks David -


I've come across this suggestion before, but had totally forgotten it - thanks for the reminder, and your explanation. So a half-press on the shutter button doesn't activate focus but it still meters, right? You keep your thumb on the AF button (or the AE if you switched) and track the kids that way...interesting...I wish I'd asked for help before I went to the Open!


I read a post from a bird photog and he said the method you described really improved his keeper rate. I'm going to try it next time out.


So do you shoot this way all the time, or only for sports?


And do you always select the center point? What happens when the center point slips off your target, do the other AF points become active? I guess they wouldn't if you selected Center Point AF, but what if you didn't select any, and just let the cam decide? Do you ever work that way?


Thanks again for your response.

Sorry for the delayed response, it's been really crazy at work this week.


I pretty much leave the focus on the back button all the time now. However, that custom function has several options, option 3 is best when you are using AI Servo, but option 1 works a little better with one shot focus. I often leave the custom function on option 3 even when I'm not using AI Servo, it still seems to work. I am so used to "focusing" with my thumb that I don't even think about it anymore.


On the focus point, probably 95% of the time I use the center point. The other 5% I am trying to focus on something off-center and I don't want to recompose so I try to find a focus point that is close to the subject. I always use the center point for any type of action shots. I don't think the xxD series has the capability to automatically shift focus points, at least I have never seen my 30D do this. I know the 1 series has this and I think the new 7D will as well.


Give it a try, it will be a little frustrating the first time or two, but with a some patience and practice I think you will like it.





David

I've been working with this back button focus method and I'm starting to like it - it's becoming a habit. But I have noticed something in PP that I don't like - maybe you can correct me if I'm missing something.


The only image-editing program that shows the AF points for the 40D, including the activated AF point, is DPP. But with back button focus, although you can call up the grid of AF points, they're all in black. It doesn't show which one activated, like it will for images captured in shutter focus, by highlighting it in red. (unless I'm doing something wrong) It's a real bummer for me because that's all I ever really use DPP for, to remind me which AF point I used...


Any DPP users out there that also back button focus?