7D AF spot problem

[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