7d intermittent focus problem

foxbodychris wrote in post #16806227
Thanks and BTW how do you like the 400mm 5.6? I am in the process of getting one

It's a fantastic lens. Although once you start using it, you'll want longer lol. It's typically a sunny day lens unless you can ramp up the ISO and be happy about it. Can't go below 1/400th or it's serious camera shake if you're skinny like me. I just lean it on a fence. One person told me that I needed a bean bag with it, and it's not till now that I know why. Otherwise there's not a lot better for IQ and speed.

Paulstw wrote in post #16806208
C.Fn III -1 – AI Servo tracking sensitivity
I set this to fast on my 1D3 as soon as I got it. Never misses focus - The advice is to set it slow, however, I set it to how fast my subject changes direction. If it's too slow it won't poll for AF before the next shot and your subject might have moved out of the plane of focus. That's why I just have it on fast.

This is almost totally wrong.

This custom setting does not alter the rate at which the camera's AF 'polls'. It alters the speed at which the camera will switch from one object to another. If you're tracking a BiF and your focus point slips off the bird then the camera will be tempted to focus on the background. With this set to 'fast' it will switch to the background immediately. If it's set to 'Slow' it will wait a while before switching, giving you a chance to re-acquire the bird.

Paulstw wrote in post #16806208
I wished there was the wealth of information on the 7D AF system as there is for the 1D3.

I have learned a lot by looking (and listening) to Ruby Winston on YouTube.
His presentations at B&H are very informative.

hollis_f wrote in post #16806327
This is almost totally wrong.

This custom setting does not alter the rate at which the camera's AF 'polls'. It alters the speed at which the camera will switch from one object to another. If you're tracking a BiF and your focus point slips off the bird then the camera will be tempted to focus on the background. With this set to 'fast' it will switch to the background immediately. If it's set to 'Slow' it will wait a while before switching, giving you a chance to re-acquire the bird.

For me Fast works perfectly in all situations. Slow isn't the be all and end all of all advice that's given. I might have it wrong in the wording but all I know is that it works perfectly for me. I never miss now.

foxbodychris wrote in post #16806222
I'll give it try next time I am out shooting birds

Thanks for the info. yeah I have it set up as you stated other than #1, I have mine on -1 which is slow. I am going to try all these ideas stated here and see what happens

I have had mine set between slow and the middle. This is just based on conversations years ago but I'll give it a shot at fast and one step down this summer.

You'll find that it depends a lot on how well you ,the photographer, can keep the focus point on the target. Only experimentation and keeping track of your hit count will answer the question for sure.

I do know that recently I was shooting an event and an intruding subject crossed in front of my desired target. I have C.Fn III-1 set to slow, but in the half-second my view was blocked, the camera jumped to the closer subject; it was too late to let go of the AF-ON button by the time I realized what was happening. And yes, I had C.Fn. III-3 set to Continuous; it made no difference because the target was completely obscured. In my case, even "slow" was too fast to prevent the camera from jumping focus.

So trial, error, and correction are really the only way to solve an AF issue. It does help to thoroughly understand how your camera AF system works, though, because it will save you a lot of twiddling that doesn't help.

Thanks for the feedback. I don't have too many issues but I'm always willing to try something new just to keep things interesting. I must admit I'm not too thrilled with another target crossing and the AF jumping which is why I kept it in that between slow and the middle. I normally don't have this issue birding.

I set this up a after the first month and have been shooting this way ever since. I usually recommend this to people as a staring point.

CF III.1 - AI Servo Sensitivity - set to 1 up from slow.


CF III.2 - AI Servo 1st/2nd img prio - set to 0 AF/Tracking


CF III.3 - AI Servo AF Tracking method - set to 1 Continuous Track priority


CF III.4 - Lens Drive when AF impossible - Focus search off

My early tests to see how it tracked and ignored backgrounds. AF sensitivity - set to 1 up from slow.


This shot not PP.

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If that's typical of the shots you get, I'd say you are tracking pretty well in the field.

I did a bunch of tests that day but won't post them. I'm pretty happy with my keeper rate. If I'm OOF it is usually me.

For the record Trying to track a BIF with trees in the BG is pretty much a fail on many cameras. Anyone would do well to get that type of shot. Maybe too many shades of brown. In the viewfinder and in the pants on checking the shots.

Thanks everyone. I just thought of something that may or not pertain to the issue I am having. Lets say for example I was trying to take a picture of a bee hovering over a bush (which I was trying to do). It happened a lot that when I was in expansion or single point AF I was having issues with the AF locking on and off the subject so the subject was going in and OOF. If I switched to spot af it would stay locked more but was harder to keep on subject.
So reading through all this and my own theory is that I think I may need to use spot AF on small birds or subjects with a lot of background distractions and the other 2 for larger subjects.
So if using spot AF will it just focus on that single point where the sensor is or will it still af the whole subject??

I did not realize you picked something so easy to shoot. A bee hovering over a bush? Not That is a tough subject to shoot. Those darned things are small, don't stay in one place for very long and don't fly in predictable patterns. If you can get 4 out of 8 shots you should be teaching us

I had a similar issue but it ended up being a faulty 50mm f/1.8

Spot AF, like single point, uses the point you selected as the primary focus point; if it slips off the target, the AF will behave according to the settings you have selected as far as trying to re-focus. Only the expanded points or the area selection modes will try to put another point on the target; single point and spot will not.