Autofocus expectations vs. reality

I am curious what people expect out of their autofocus system. I recently read someone's comment somewhere that mentioned a "focusing on a twig issue when shooting birds" and it got me wondering.

The camera doesn't really know what you are photographing, so when you point the camera (any camera) and whatever lens at a subject and it is out of focus, the AF system (on full auto) is going to adjust focus until the sensors come into contact with something that is in focus, right? So if the first thing that the camera arrives at in focus is a twig that is in front of a bird, then why would I be surprised at this result if I did not tell the camera where to focus? I guess I am trying to decipher what the problem could be other than the person expected the camera to magically know what was expected to be in focus and focused on something else instead. I always use some kind of point selection (of various sizes on my 5D3) to get the camera to focus where I want it to. If I have the camera on full auto for focus, then I am making a choice that the camera should do its best to decide what should be in focused based on the data it is getting.

Am I missing something? What do people expect from their AF system?

-K

Some folks think their cameras are intuitive like that.

For the price, my 5DIII should be, but alas.

Some also shoot a scene that's half sky, in full auto, and wonder why the subject is dark.

The closest you come would be the iTR system on the 1DX, which is capable of focus tracking a specific color, or a face, if it can find one where you start aiming your initial AF point.

But otherwise, there is an enormous lack of knowledge among people who use DSLR cameras.

Agreed with apersson850 on the 1DX AF system.

When I shoot portraits with AI Servo with auto-point selection, iTR will try to select the focus point on the eyes of the subject, even technically the nose is nearer to the camera.

Bravo and well put. I use AF on my 6D because, of the focus options available on it, AF is usually the best. I am considering a 3rd party split image screen for MF to get me back to the shooting style I have used with MF film cameras for decades. In MF (including rangefinder), I like having confirmation of what I have focused on (bird and not the twig) and not having to refocus every shot or use a cumbersome AF lock.

kurt765 wrote in post #16301530
.....So if the first thing that the camera arrives at in focus is a twig that is in front of a bird, then why would I be surprised at this result if I did not tell the camera where to focus?

The most extreme end of this scale is the new user in Full Auto, with the camera focusing on thing in front of their subject. The other end of the scale is someone using single point spot AF to focus through the branches at a subject beyond.

I haven't tried iTR for portraits in the traditional style, but I have tried it on runners in a competition, and it worked pretty well, keeping the focus points at or near the head of the competitors.

One legitimate issue might be that the actual focus points extend beyond the boxes in the viewfinder. Aim a little square at an eye and the cross hair may pick up the nose/ear/lips. Another legitimate issue might be that the focusing point needs decent contrast to work effectively. Aim the focusing point at someone's cheek and the camera may decide to focus on an eye/nose/ear.

These things are obvious when you know how the system works but may be a surprising/confusing to the uninitiated or intellectually challenged.

mccamli wrote in post #16301829
One legitimate issue might be that the actual focus points extend beyond the boxes in the viewfinder. Aim a little square at an eye and the cross hair may pick up the nose/ear/lips. Another legitimate issue might be that the focusing point needs decent contrast to work effectively. Aim the focusing point at someone's cheek and the camera may decide to focus on an eye/nose/ear.

These things are obvious when you know how the system works but may be a surprising/confusing to the uninitiated or intellectually challenged.

Seriously?

A bit elite, are we?

Oops, fair point! Not really what I meant. I need to be more csreful what I type before I've fully woken up!
I'll have another crack and probably get this wrong too...how about less technically sophisticated (if that even means anything). People who don't much care for technical details or take things at face value.

Intellectually challenged works for me. Some people really are stupid. I call them stupid because they don't even try to inform themselves or they ask then basically say "nevermind" when you explain and they conclude that it requires some effort of thought - something they had no intention of supplying. Stupid and lazy. People like that do exist.

I'm stupid and lazy about some things too.

Come on...that just elitist nonsense. We are in a camera forum because we crave that stuff. I wouldn't say the average photographer (regardless of IQ) is always going to go searching for that stuff. That doesn't mean they are lazy, devoid if tech savvy, and just stupid.

For example, unless you browse these forums a lot, you probably have no idea that the AF points don't quite correlate to the actual AF boxes. I don't remember reading anything in the manual about the contrast based AF and how it works. I wouldn't discredit anyone that didn't know that stuff and think they were just lazy or unintelligent.

Not everyone needs to know the science behind the art to make beautiful art.

Gregg.Siam wrote in post #16302982
Come on...that just elitist nonsense. We are in a camera forum because we crave that stuff. I wouldn't say the average photographer (regardless of IQ) is always going to go searching for that stuff. That doesn't mean they are lazy, devoid if tech savvy, and just stupid.

For example, unless you browse these forums a lot, you probably have no idea that the AF points don't quite correlate to the actual AF boxes. I don't remember reading anything in the manual about the contrast based AF and how it works. I wouldn't discredit anyone that didn't know that stuff and think they were just lazy or unintelligent.

Not everyone needs to know the science behind the art to make beautiful art.

Read the whole post, don't just skim. Mere ignorance of something isn't the same as lazy stupidity. What you describe is the former, not the latter.

Gregg.Siam wrote in post #16302982
Come on...that just elitist nonsense. We are in a camera forum because we crave that stuff. I wouldn't say the average photographer (regardless of IQ) is always going to go searching for that stuff. That doesn't mean they are lazy, devoid if tech savvy, and just stupid.

Regardless, they're all valid reasons why autofocus expectations might not match reality...

mccamli wrote in post #16301829
One legitimate issue might be that the actual focus points extend beyond the boxes in the viewfinder.

http://blogs.stonestep​s.ca/showpost.aspx?pid​=54