7D AF speed?

[pwnage101]

My understanding is that the Canon 7D has "fast" AF as opposed to, say, the 5DII or 50D. What exactly does this mean? Does any given lens actually operate physically faster or is the focusing sensor just more photosensitive allowing it to hunt less? I always thought canon uses fixed-speed built-in motors for their lenses, as opposed to Nikon's AF(-D) vs. AF-S (in which case a body with a faster AF motor would focus a screw-drive lens faster).

On the same note, are people's complaint about the 5DII focusing the result of an insensitive AF sensor?

Does Nikon's camera lineup also have different levels of "AF speed" ? Before these questions arose in my head I was sure that any given AF-S lens would focus identically on all Nikon cameras, but I never considered the fact that focusing sensors and algorithms differ (or do they NOT?).

I don't plan on buying a camera anytime soon; these are just fun things to know

[Dave Humphries]

Hi Troy,

Causing trouble again, eh?
I dunno, what we gonna do with you?

Seriously, interesting ideas.

My initial thoughts on Nikon AF-S lenses, the only ones I know, are;

I wonder if there is a fixed speed for their USM motor and drive train which results, for lenses with wider or smaller "focus arcs", in them taking more or less time to traverse from one end to the other?

Need to measure degrees of (manual) focus ring rotation from infinity to closest on each lens, then time them from one end to other and see if there is a correlation.

Other things that'll affect speed, particularly with body drives I expect is battery charge state and whether a grip (with extra battery) is attached.

Some speed issues will be due to camera "thinking time", which as we know, often extends in poor light.

Need a Canonite with a lens and two bodies to reveal whether a given lens is any different between bodies.

Cheers,

[rpcrowe]

I conducted a very unscientific experiment with my older D60 (not 60D) camera and my newer (but, still a couple of generations old) 40D and my 70-200mm f/4L IS lens.

The 40D seems like it focuses faster than my 30D but, the 40D is not known for its fast focus like the new 7D. However, this seems to confirm (albeit unscientifically) that one camera might focus faster than another.

[pwnage101]

I conducted a very unscientific experiment with my older D60 (not 60D) camera and my newer (but, still a couple of generations old) 40D and my 70-200mm f/4L IS lens.

The 40D seems like it focuses faster than my 30D but, the 40D is not known for its fast focus like the new 7D. However, this seems to confirm (albeit unscientifically) that one camera might focus faster than another.

when you say faster, are you referring to the time it takes to crank the lens from infinity to near and back? or does the 40d just hunt less and give you the focus lock earlier?

if it is the former, what can possibly be the cause? an electric motor can operate faster with higher voltage, but why would canon limit the voltage in their cheaper cameras? i suppose it is either a battery issue or a marketing technique.

[rpcrowe]

The 40D just hunts less and seems like it locks on earlier. I don't believe that it has anything to do with voltage, but is simply the focusing capability of the newer camera. The 40D incorporates a newer AF sensor with 9 AF cross points... The 7D has even more points and an entirely newly designed auto focus sensor. I am sure that the 7D is much better than the 40D....

Here are some comments on the 7D focusing system from photographers who have used the 40D...

http://photography-on-the.net/forum/...d.php?t=772150

I like the idea of having certain groupings of A/F points that can be activated. I would use the grouping towards the top of the frame for sports photography since I like to get the faces of the players in focus above anything else...