Autofocus Demands

So I ran into an interesting issue that I figured the know-it-alls from on high would be able to figure out... I previously was using my SL1 on my 70-200 for the long reach second camera with my 5D2 on the general use end with the 24-70. Now that I have a shiny new 5D4, I am wondering which is actually more demanding on the autofocus to nail focus - long end or short end? Which would you put the older 9 point autofocus system on versus the latest and greatest?

If it were me I'd just put whatever lens/focal length you think will be used the most on the newer camera. If they get used the same amount then I'd think that the narrower DOF of a longer lens would make focus more critical.

I haven't had focus speed/accuracy issues since I sold my 5Dc. Well, discounting the 6D in AI-Servo. Pretty much any modern camera with any modern lens attached should do a good job of AF. Of course, extremes exist.

Bassat wrote in post #18617276
Well, discounting the 6D in AI-Servo.

The 6D has no problems with AI Servo.

At least mine doesn't. I guess I got the only 6D with a focus system that works quite well for moving subjects. How lucky I am.

saea501 wrote in post #18617340
The 6D has no problems with AI Servo.

At least mine doesn't. I guess I got the only 6D with a focus system that works quite well for moving subjects. How lucky I am.

I used a 6D side by side with a 1D4. The 6D can't compete. Traded 1D4 for an 80D. Ditto.

I would think that speed of focus depends on what ranges your focusing. If you need to select full range with your 70-200mm to focus, then it will take longer to focus from far end to something close by. Likewise for 24-70mm. I think the main consideration is whether you want to use the SL1 for reach with the longer end of the 200mm or don't need the reach and want more focus points from the 5D4.

davesrose wrote in post #18617461
I would think that speed of focus depends on what ranges your focusing. If you need to select full range with your 70-200mm to focus, then it will take longer to focus from far end to something close by. Likewise for 24-70mm. I think the main consideration is whether you want to use the SL1 for reach with the longer end of the 200mm or don't need the reach and want more focus points from the 5D4.

Well, before I got the 5d4, I assumed that the AF performance across my gear was par. The lenses would perform the same in terms of focus accuracy/capability whether on the little rebel or the 5D2 negating the framing difference of the two cameras (ie if I took a picture of something 15 ft away and just crop the 5D2 picture to get the same image as the SL1).

Now, on a recent shoot, I was to take pictures of a child running towards me across a bridge with her balloons billowing behind her, I went from 200mm when she started out (~150 ft) down to near 35mm (running past me ~ 5 ft away). So I had to have both cameras at the ready. In terms of criticality of nailing the focus on a running child, would the 5D4 or 5D2 be on the wide end or the long end?

I put the 70-200 on the 5D2 since I thought at the time that the distance differential between shots would be less severe on the AF keeping up (5 ft of change from 150 ft away would not cause the focus to shift much since % change in focus distance was less). I still ended up with significantly more keepers on the 5D4 than the 5D2. Just trying to rationalize whether I made a mistake or did the right thing in my setup.

I went from a 5Dc (which had the same AF as the 5D2) to a 5D3 (which has similar AF to the 5D4). I did some manual focusing with the 5Dc because of the limited AF points and the less sensitive low light capability. Again, I think the main deal with AF speed (in daylight) is more to do with how much focus pull it’s having to do (example being wildlife, where you might switch focus from something far, to close, to far again). Personally, I prefer the 5D3/5D4’s use of more AF points. I got a 7D2 for a crop since it has more AF points and an interface like the 5D3. I know some people have said they don’t use the 7D2 as much if going with a 5D4, as the extra resolution is more tolerant of cropping.

Extra AF points helps with normal focal lengths where I can select a particular point I want to focus on. It also helps with telephoto: in your example of a kid running up to the camera, a camera with 61 AF points has more spread for AF tracking and keeping points on the kid.