Having some back focus in AF-C

MolitorPhotography

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Ive only had my D7100 for a couple months now, and for the most part I'm very happy with it. I am having an issue when using AF-C on an approaching subject (a running toddler) I'm getting about 10% or less success rate and im not sure if it's me, the camera or the lens. My 50mm 1.8G is basically glued on so that is the only lens I have noticed this problem on or even attempted an AF-C shot. For all shots in question I use single point, manual AF selection. I read on another forum that the AF speed of the lens could affect the accuracy of the continuous AF. Does anyone think if I put on a 24-70 2.8 or 300mm 2.8 I would get better results? (I'd have to borrow or rent one of these lenses) Or does someone have any other thoughts on how I might increase my success ratio in AF-C? I included a recent shot showing the issue
 

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Braineack

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That's always the most difficult subject for AF.

what zone system are you using and what aperture are you shooting at?
 

Derrel

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" single point, manual AF selection."

That I would submit, is not the best choice for action work...you're artificially limiting (as in crippling) the camera's ability to do its best job at predictive AF...instead of bringing in multiple data points, you're deliberately limiting the AF system. Try a multi-point AF strategy, I am almost certain you will find it gives better results. 9,11,21 point AF is what I have had best luck with when my subjects are moving. I shoot in AF-C a lot (99% of the time, actually). Different cameras have different multiple point counts, not all have 9 and 11 or 9 or 11. I'm not a fan of using all 51 points.

Admittedly though, the 50/1.8 AF-S is a surprisingly SLOW lens in focus speed for an AF-S lens...it's known to be slow...and compared to the 70-200 VR or 300/2.8 AF-S Mk II, it is slow. But, it's not horrifically slow, but the older 50 1.8 screw-drive focuses faster...I have both, and the G-series 50/1.8 just seems slower than one would expect. I think this might be favoring accuracy and precision, for wide-aperture work. Over the last decade, the 50mm lens has become a favorite of beginning professionals who use it wide-open, or nearly so, at CLOSE distances, as a portrait lens. It's become a very strong trend, and I think there might be a bit of design bias in there favoring high-precision focus, more so than the "speed" focus of older 50's. According to testers who have compared both the 50/1.4 G series model and the 50/1.8 G, the more-expensive f/1.4 model is deemed extremely slow-focusing, but I have not shot that lens, but I've read that multiple times from sources I trust.

But I would ditch the single-point, smack-dab in the middle focusing...a lot of time, with a 50mm lens, that center AF point can be right on the belly area of a person, and on something like a smooth T-shirt, that's really not a very good AF target...adding more AF points gives the computer more data points, and can speed up focusing, especially predictive AF.

In the menus, AF-C also has parameters you can set, giving priority to Release, or to Focus, or a combination of the two. If you favor "Release", that tells the camera to blast away more freely, even if the focus is not dead-dead-dead on; if you're using f/11, there's not nearly the same need to focus critically as if shooting at f/2, and beyond 20 feet with f/11, who cares...you can be off five feet, and DOF will cover it.
 
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BillM

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What are your results with a static subject ?

What were your aperture and shutter setting for the attached photo ? For a close shot like that shot at f1.8 your dof is going to be about an inch or two at the most.

Her left arm is trailing a little behind her and it is in focus. So if this happens with every shot I'd set AF- Fine Tune to a -2 and see how it looks.
 
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MolitorPhotography

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That shot was ISO 250 / f3.2 / 1/800 ( its nice to have 1.8, but I tend not to shoot below 2.8 for sharpness and chroma reasons)
Thanks for all the pointers Derrel and Bill. I took the kiddos outside and did some more shots with both my 50mm 1.8G and 35mm 1.8G using d9 and d21 AF and just looking at the shots in cam, it appears I got a zero hit rate on about 60 shots, all slightly back focused.

-"a lot of time, with a 50mm lens, that center AF point can be right on the belly area of a person" I only shoot on the center point maybe 25% of the time. Im pretty good at moving that thing around the 11 cross types :)

Focus is spot on when shooting AF-S, or even AF-C on a mostly stationary target, but so far not so good on the approaching target. I do portraits 95% of the time but My 11 year old is starting her softball season and was hoping to get more action shots.

I checked my AF priority and it is set to focus instead of release, those seem to be the only 2 options for me. Ill have to look in to the AF Fine tune, but will that affect the AF-S mode? I also have a setting called "focus tracking with lock on" (menu a3 for me) I'll have to look at my manual for that but I think it has more to do with how easily the AF system moves from a focus lock to continuous servo while in AF-C.
Thanks again for the help and pointers
 

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"a zero hit rate on about 60 shots, all slightly back focused"

Wow...that is absolutely horrifically poor performance...
 
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"a zero hit rate on about 60 shots, all slightly back focused"

Wow...that is absolutely horrifically poor performance...

Thats what I thought! Ive been hoping it was something attributable to me or the lens. I'm going to borrow a 300mm 2.8 for one of my daughters softball games so if that doesnt prove better ill be upset. I really dont want it to be a body issue
 

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Try the af fine tune and then shoot static and moving targets again.
 
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MolitorPhotography

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Here was a shot I took today in AF-C on a stationary subject. Focus was spot on as usual. I'm working on figuring out ho to fine tune my AF. Tomorrow is busy so we'll see if I can mess with it some more
 

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bribrius

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so much for all the 51 points and that "better" sensor eh? Why people buy canon. :biggrinangelA:
 

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"a zero hit rate on about 60 shots, all slightly back focused"

Wow...that is absolutely horrifically poor performance...
no doubt. My 7100 is at least good for 1 in 10 in AF......well, unless it is in dim light then you might as well forget about it and use manual focus (which i actually do a large portion of the time) as it just hopelessly misses shots. Pathetic really. since i often use manual and manual lenses it doesn't phase me as much anymore. I usually keep it on single when on af. Otherwise it would often lock on to what i dont want it too. Nature of the beast. sometimes in continous it just really goes right to ****. like it is guessing. "Is this what you want to focus? or maybe this? is that in focus? i can't tell. i think it is in focus" like really pathetic, worse in dim or weird light. Occasionally it does okay? Really, though, often in contiuous it is like it is guessing. i don't even bother with it much anymore i just shoot single manual or manual lenses. it starts messing up i dont waste my time with it and just flip over to manual.
 
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bribrius

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Ive only had my D7100 for a couple months now, and for the most part I'm very happy with it. I am having an issue when using AF-C on an approaching subject (a running toddler) I'm getting about 10% or less success rate and im not sure if it's me, the camera or the lens. My 50mm 1.8G is basically glued on so that is the only lens I have noticed this problem on or even attempted an AF-C shot. For all shots in question I use single point, manual AF selection. I read on another forum that the AF speed of the lens could affect the accuracy of the continuous AF. Does anyone think if I put on a 24-70 2.8 or 300mm 2.8 I would get better results? (I'd have to borrow or rent one of these lenses) Or does someone have any other thoughts on how I might increase my success ratio in AF-C? I included a recent shot showing the issue
it's the light. Daylight, does pretty good. Anything odd, it doesn't know what to do. i shot a photo of my daughter under a street lamp last year with mine. TEN tries. well lit, but by the street lamp. TEN tries. Even on single manual. drop the box right on her. It wouldnt focus right. Went home, checked the camera info in post. It has the square straight on her for the focus point in all of them. Not one is in focus. went through my photos before that, i watch my photos since. Checked the recorded focus points. All i have come to a conclusion it is the any dim, or weird lighting. But daytime or studio lighting, well lit, normal light source, usually it will lock right on (usually). Since i shoot a lot in dim light, i have my share of experience swearing at mine. It is a good camera though, just with its limitation. I can go through all kinds of my photos, and have ones that are dead on locked for the focus point itself but the focus is way off. But then show another in a friendly light source where it locked right on.
 
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MolitorPhotography

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Ive only had my D7100 for a couple months now, and for the most part I'm very happy with it. I am having an issue when using AF-C on an approaching subject (a running toddler) I'm getting about 10% or less success rate and im not sure if it's me, the camera or the lens. My 50mm 1.8G is basically glued on so that is the only lens I have noticed this problem on or even attempted an AF-C shot. For all shots in question I use single point, manual AF selection. I read on another forum that the AF speed of the lens could affect the accuracy of the continuous AF. Does anyone think if I put on a 24-70 2.8 or 300mm 2.8 I would get better results? (I'd have to borrow or rent one of these lenses) Or does someone have any other thoughts on how I might increase my success ratio in AF-C? I included a recent shot showing the issue
it's the light. Daylight, does pretty good. Anything odd, it doesn't know what to do. i shot a photo of my daughter under a street lamp last year with mine. TEN tries. well lit, but by the street lamp. TEN tries. Even on single manual. drop the box right on her. It wouldnt focus right. Went home, checked the camera info in post. It has the square straight on her for the focus point in all of them. Not one is in focus. went through my photos before that, i watch my photos since. Checked the recorded focus points. All i have come to a conclusion it is the any dim, or weird lighting. But daytime or studio lighting, well lit, normal light source, usually it will lock right on (usually). Since i shoot a lot in dim light, i have my share of experience swearing at mine. It is a good camera though, just with its limitation. I can go through all kinds of my photos, and have ones that are dead on locked for the focus point itself but the focus is way off. But then show another in a friendly light source where it locked right on.

Interesting. I have not had any issues regardless of lighting unless I'm shooting an approaching subject in AF-C. The light I shot in today was good, mid-day, overcast light. And still no hits on a moving target. Once she stopped... Spot on.
 

bribrius

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Ive only had my D7100 for a couple months now, and for the most part I'm very happy with it. I am having an issue when using AF-C on an approaching subject (a running toddler) I'm getting about 10% or less success rate and im not sure if it's me, the camera or the lens. My 50mm 1.8G is basically glued on so that is the only lens I have noticed this problem on or even attempted an AF-C shot. For all shots in question I use single point, manual AF selection. I read on another forum that the AF speed of the lens could affect the accuracy of the continuous AF. Does anyone think if I put on a 24-70 2.8 or 300mm 2.8 I would get better results? (I'd have to borrow or rent one of these lenses) Or does someone have any other thoughts on how I might increase my success ratio in AF-C? I included a recent shot showing the issue
it's the light. Daylight, does pretty good. Anything odd, it doesn't know what to do. i shot a photo of my daughter under a street lamp last year with mine. TEN tries. well lit, but by the street lamp. TEN tries. Even on single manual. drop the box right on her. It wouldnt focus right. Went home, checked the camera info in post. It has the square straight on her for the focus point in all of them. Not one is in focus. went through my photos before that, i watch my photos since. Checked the recorded focus points. All i have come to a conclusion it is the any dim, or weird lighting. But daytime or studio lighting, well lit, normal light source, usually it will lock right on (usually). Since i shoot a lot in dim light, i have my share of experience swearing at mine. It is a good camera though, just with its limitation. I can go through all kinds of my photos, and have ones that are dead on locked for the focus point itself but the focus is way off. But then show another in a friendly light source where it locked right on.

Interesting. I have not had any issues regardless of lighting unless I'm shooting an approaching subject in AF-C. The light I shot in today was good, mid-day, overcast light. And still no hits on a moving target. Once she stopped... Spot on.
Did you have it in live view? I never use live view. Everything slows down in live view. Dont ask me why, it just does.
 

bribrius

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and your subject is back lit. Which messes with it. The camera is searching for the highest closest contrast. It is stupid. That may or may not be your subject. It gets confused easily. You could also try the 3d tracking. I would at the least, pull your exif and start looking through (do you have software that will show you the focus points in exif data?) to figure it out. So you can work around it in the future.
 

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