7D AF spot problem

[Richard Lane]

No wind.


One thing seems strange to me : spot AF is very sensitive, but in this case, if it had missed, something just behind or beside would be sharp, no ? . If you check the balconly, it's quite sharp but it's not in the same plan (much more in front).
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Yes, it does seem strange. HDNitehawk had some good suggestions, to help identify the problem.


Tripod to eliminate camera motion, stationary subject to eliminate subject motion, and try2 different lenses if you have them. Also try to get squared to same plane as your subject, as opposed to shooting on an angle.


Please forgive me if I am over simplifying this, since I don't know your level of experience with Canon, but if you are in One shot mode, then make sure that the red square is lined up on your target and then press the shutter button half-way to achieve focus lock. You should then hear the beep and then press the shutter button the rest of the way to take the photo.


Just remember, it is more important where focus lock was initiated, and not where the red square ends up, as occurs in re-composition.

[conropl]

Just remember, it is more important where focus lock was initiated, and not where the red square ends up, as occurs in re-composition.
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Rich:


This is kind of the discussion we got into about a week ago in the "post your best bird shoots" post. You were nice enough to try and help me out, and I said I would post some examples. I have not had a lot of time to do so, but this post seems to be addressing the same issue... so here is what I have found.


All shots below were with taken with a 7D, 100-400L @ 400mm and f/7.1


My problem has been when trying to focus when the background is cluttered (or has better contrasting feature as compared to the subject). In my case I was trying to shot Sand Cranes in a cornfield.


What seems to be happening is the spot size is bigger than the square, and it tends to focus on the higher contrast background. This is true even at wide open aperture... I closed it down some just in hopes that I could get a better DOF so I could focus on the body and get a sharp eye. (did not work to good though).


The shots below were not intended to be great pictures. I was just trying to figure out the AF problems in a difficult situation.


This first shot was in "One-Shot" mode and "Spot Focus". The focus point was confirmed to be centered on the head of the bird in the middle. It is totally out of focus. In this case the camera was well supported, and I pushed the shutterbutton half way a dozen times and got focus confirmation but was always out of focus.


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Next I switched to AI-Servo with Spot Focus. This next shot was AI Servo and the spot was centered on the head. However, I had to move the spot back and forth over the head until it would final register the head as the focal point only for an instant, and then I would quick take a quick picture to get something half way decent. Still difficult to get a good focus, and it is fleeting.Also, the bokeh is horrible.


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At this point I pointed at the base of the neck and could get it to focus pretty easily... so this next one is focused on the base of the neck (spot smaller than subject). Still horrible bokeh.


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Since the bokeh was so distracting, I then spent some time blurring the back ground in post processing. This helped, but still not great (see next one)


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To give you an idea of the lens ability without the distracting background confusing the AF - below is the same lens, but the background is nice blue water and the spot was just under the eye (but the head was covering most of it).


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I must say, I do not usually have a problem with AF, but the spot needs to be smaller than the subject (which means getting close). If the spot is larger than the subject, then the background and type of background can effect the focus a lot. Also, AI-Servo does help in cluttered background situation, but it is hit and miss and does not hold focus long.


Sorry for the long post. If anyone has a good idea on how to set up a shot better to overcome these problems in corn fields... I am open.


Pat

[Fast Glass]

Man, I liking manual focus even better now![:P] Well, at least I don't feel like I'm missing as much as I thought.


John.

[Richard Lane]

Just remember, it is more important where focus lock was initiated, and not where the red square ends up, as occurs in re-composition.
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Rich


My problem has been when trying to focus when the background is cluttered (or has better contrasting feature as compared to the subject). In my case I was trying to shot Sand Cranes in a cornfield.


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<span style="font-size: small;"]This is a difficult situation, but I can assure you that the 7D is capable of getting these shots!


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What seems to be happening is the spot size is bigger than the square, and it tends to focus on the higher contrast background. This is true even at wide open aperture... I closed it down some just in hopes that I could get a better DOF so I could focus on the body and get a sharp eye. (did not work to good though).


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<span style="font-size: small;"]I understand you are using spot focus in order to get around the branches in the foreground and this may be an acceptable use, and if it was working for you then I would say stick with it, however since it's not working then I say lets change it up.


<span style="font-size: small;"]The spot AF sensor does not have to be bigger than the object that it is focusing on. The spot auto focus point just has to be smaller than any obstructions in the foreground which may block it's acquisition of your subject.


<span style="font-size: small;"]If the AF sensor point is half on your subject and half on the background, then it will lock on the closest point to the sensor. All that the "smaller spot" sensor point is doing is making it more difficult for you to lock onto your subject, and it is also making it easier for the small square to fall off of your target and grab onto the background.


<span style="font-size: small;"]The spot sensor point is actually larger than it appears in the view finder and the single point sensor is actually smaller than it appears in the VF. All of the AF sensors should lock in on the closet point and not the background.


<span style="font-size: small;"]"One thing that I did notice was that you and Tapazan were both using a Spot Focus Point with One Shot."


<span style="font-size: small;"] If you use one shot, with "spot" focus point, and press and hold down the shutter button in high speed burst mode, and you miss your target, then you will miss every shot after that. This occurs because the AF will lock-in on something in "one shot mode" so if you grab the background by accident for the first shot, then every other shot following the initial one will be focused on the background so "every shot will be OOF." You should try this at home.


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<span style="font-size: small;"]The shots below were not intended to be great pictures. I was just trying to figure out the AF problems in a difficult situation.


This first shot was in "One-Shot" mode and "Spot Focus". The focus point was confirmed to be centered on the head of the bird in the middle. It is totally out of focus. In this case the camera was well supported, and I pushed the shutterbutton half way a dozen times and got focus confirmation but was always out of focus.


[img]/resized-image.ashx/__size/800x1200/__key/CommunityServer-Components-UserFiles/00-00-00-66-81/8124_2800_centered-on-head_29002800_one_2D00_shot_2900_.JPG[/img]


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<span><span style="font-size: x-small;"]Next I switched to AI-Servo with Spot Focus. This next shot was AI Servo and the spot was centered on the head. However, I had to move the spot back and forth over the head until it would final register the head as the focal point only for an instant, and then I would quick take a quick picture to get something half way decent. Still difficult to get a good focus, and it is fleeting.Also, the bokeh is horrible.





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<span style="font-size: small;"]The reason that you had some success with the AI Servo mode was because since AF was not locked, your "small Spot" sensor point would sometimes grab the background and sometimes grab your subject, since AI Servo does not lock in on one or the other. AI Servo is constantly trying to lock onto and track something, so sometimes you're getting lucky. Therefore, when you use burst mode under these conditions some will be in focus and some won't.


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At this point I pointed at the base of the neck and could get it to focus pretty easily... so this next one is focused on the base of the neck (spot smaller than subject). Still horrible bokeh.


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<span style="font-size: small;"]Remember that the AF red square does not have to be smaller than the subject, as long as it hits your subject and not the foreground. The spot AF is good for shooting in between a soccer net, face-mask on a helmet, or in between branches like you're doing, but if your subject is moving or is very far away, then it just makes it more difficult to hit your target.


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To give you an idea of the lens ability without the distracting background confusing the AF - below is the same lens, but the background is nice blue water and the spot was just under the eye (but the head was covering most of it).





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<span style="font-size: small;"]Excellent shot that is also very sharp!


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Also, AI-Servo does help in cluttered background situation, but it is hit and miss and does not hold focus long.


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<span style="font-size: small;"]As stated above, AI Servo will constantly search for the nearest AF point that is captured on the AF sensor, so sometimes you will get your subject and sometimes you will get the background, especially if your AF point and your subject are moving, which is occurring in this case. However, if set up properly with other custom functions, then you should definitely nail most of your shots.


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[Richard Lane]

I didn't want to lose what I wrote, so I thought I would just summarize it here:


Use AI Servo


Use single point focus, unless "spot" is absolutely necessary.


Neuro had also mentioned AF point expansion and Zone AF (especially for a clear sky background) which are also very useful, depending on the shooting situation and we should definitely delve further into those settings as well.


If you set the AF-ON button to focus and meter, and detach all Auto focusing from the Shutter button, then you will "also" be able to use AI Servo to achieve AF with the AF-ON button, and then just let go of the AF-On button, and fire away in burst mode for stationary subjects. This way there is no risk of moving the AF point off of your target. If you then re-press the AF-On button for focusing, then it will begin to reacquire focus or start tracking your subject if it takes off.


There are a lot of nice Custom AF and optional settings on the 7D, and I will be glad to go over my settings with the both of you in the next day or so.


Tabazan, this certainly doesn't mean that your camera is working properly, as that still has to be determined.


Have a good night,


Rich

[Tabazan]

So, finally one could say that Spot AF must only be safely used in macro or tripod+safe background ?


In the case of landscapes, the risk is then that the red square validates the focus but the camera takes another point.


@ John


I agree :-)

[neuroanatomist]

So, finally one could say that Spot AF must only be safely used in macro or tripod+safe background ?


In the case of landscapes, the risk is then that the red square validates the focus but the camera takes another point.

I would not say that, no. I use Spot AF for static shots of wildlife and birds, where it's very useful for geting a focus lock on an animal/bird surrounded by branches, for example. Honestly, I don't really think we've gotten to the root of the issue here.

[Richard Lane]

So, finally one could say that Spot AF must only be safely used in macro or tripod+safe background ?

As you mentioned; Spot AF is excellent for Macro and tripods, but it is also good for taking shots handheld of peoples eyes through a facemask in a helmet, of an animal in a cage, through a fence, or branches. If you use "one shot" for stationary objects in this situation then make sure you focus-lock and press the shutter button in single mode and then press again and again (while taking your finger off the shutter button completely in between shots), while each time trying to focus-lock on your subject. If you do use burst mode (High speed frame rate) and the first shot is in focus then the rest of the burst will be in focus. If you use burst mode and the first shot is out of focus, then every shot in that burst will be out of focus.


If the object that you are focusing on is far away, and very small (like the birds head above) and moving slightly, and the background is large and diffuse,and the the lens is not held perfectly still, or is not on a monopod or tripod, then the spot AF and photographer may have a hard time focusing on the subject and the spot AF will have an easier time focusing on a large diffuse background.


I never have my camera on spot, until there is a need to switch it to spot.


I just wanted to reiterate that spot AF works great in the proper setting if you need pinpoint accuracy, then you shouldn't hesitate to use it at all. I tried it in the house last night with One Shot and stationary objects and every shot was in focus. So, test it out.

In the case of landscapes, the risk is then that the red square validates the focus but the camera takes another point.

There should be no risk if the red square validates the point (the only risk is using the very small spot AF point on a very small subject with a large background, because you will have a greater chance of hitting a large background then a small target/subject. So, check in the LCD under magnification to see if you got the shot.


If the red square validated the focus, but the subject is out of focus then this means that you locked on the background while pressing the shutter half-way and then just before you pressed the shutter the rest of the way, you then moved the "very tiny spot AF" red square onto your target to ensure proper composition, and you then pressed the shutter button the rest of the way to capture the photo, however your focus-lock occurred on the background before the shutter press. The camera will not pick another AF point, unless you're in 19 pt. Auto Select Focus (where you allow the camera to pick the AF point for you.), Zone AF (where you pick the zone and the camera picks the point), or AF expansion (where you pick the point location and the camera provides 4 near assist points), Full Automatic mode (green square), or CA mode.


There are some other instances when the Camera will use another AF point then the one that you selected, like in AI Servo where you pick the AF starting point and as you're subject moves across your view finder, the camera will pick and use all of the available AF sensors automatically for tracking purposes.


If you're camera is doing anything else differently then there is either something wrong, or we have to tweak your user settings.


Rich

[neuroanatomist]

If the object that you are focusing on is far away, and very small (like the birds head above) and moving slightly, and the background is large and diffuse,and the the lens is not held perfectly still, or is not on a monopod or tripod, then the spot AF and photographer may have a hard time focusing on the subject and the spot AF will have an easier time focusing on a large diffuse background.

This is a common scenario for me - bird surrounded by branches, with the 100-400mm lens at 400mm handheld on my 7D. My settings are Spot AF and spot metering, and I prefer to use an off-center AF point for composition reasons. Here's where back-button AF really helps. The sequence of events goes: center subject in frame, half-press shutter to spot meter (also starts the lens' IS going) and press AE Lock, recompose with selected AF point over subject, press AF-ON to focus, press shutter. All of these were shot using Spot AF:

[Richard Lane]

Neuro, Great Shots and examples of how it should work, when you lock AF correctly. You have wonderful technique and your shots are relatively clear of a foreground mess. I hope that I didn't imply that shots of this nature (pun intended) are unattainable with Spot AF and a confusing foreground and/or background, except for the fact that it makes it more challenging.


Additionally, one user was focusing on a twig which the spot AF is supposed to get around, and the other user was focusing on a birds narrow head in a convoluted, low contrast corn field (not the easiest shooting conditions), so if they're slightly off, then they're OOF.


I believe that the users are not locking AF properly and/or there settings are off, since there are so many confusing choices (quite understandable) and I think that it is a common problem throughout the internet, and one that can be easily rectified with some discussion and practice.


Certainly, we can't be sure at this point if one of the cameras is malfunctioning, however, the OP did mention that he sent his camera to Canon and it checked out fine and he will do further tests on it like HDNitehawk had suggested.


Stay tuned folks!


I will be away from my computer until this evening.


Rich