Auto Focus question: Lens vrs Camera

the_manchine

Just curious, how much influence does either the lens or the camera have on the speed and accuracy of the auto-focus?

I know that different lenses are driven by different motors - USM / HSM etc... and this had a direct influence, but at what point does the camera matter?

DaireQuinlan

depends on the camera and lens really :-)

Camera wise I'd say AF is pretty much a solved problem at this stage. Any modern AF camera uses multiple AF points and contrast detection to nail the AF. My Nikon F4 was their first pro AF body, and the AF is pretty appalling on it. Hunts for focus lock a lot in challenging conditions. The F5 or the newer digital bodies have considerably improved focus capability. The AF can also be quite slow on longer lenses with the old Nikon screw connection. Luckily they were thinking ahead and AFS lenses (which weren't in the nikon line up when the F4 was released) all work correctly and focus quietly and surprisingly quickly.

Lens wise its all up in the air. There's the physical characteristics of the lens itself (ie USM/HSM/AFS or screwmount) which dictates how fast they actually physically can move the lens elements around, but there's also the aperture to consider which affects how accurate the sensor in the camera is going to be. A 70-200 f2.8 zoom is always going to lock focus much more quickly and more accurately than an equivalent focal length zoom that has a variable aperture from f4.5-f5.6 for example. f5.6 is normally the limit specified for AF modules to lock focus with any degree of accuracy, and a lot of cheap consumer zooms hit that at their long end, making focus in dim light in particular troublesome.

ThOnda

for PENTAX users it depended only on camera, because their lenses didn't have motors. However Pentax released first two lenses with ultrasonic motors this year.
So if you go PENTAX way, the newer camera, the faster autofocus. With the same image quality. And for older lenses - The better is coordination between your eye and hand, the faster human-focus you have :-)

OT: Some say that reading magazines like PLAYBOY enhances coordination between eye and hand...

Sebzy

In the Olympus camp just about every body only has 3 focus points and all the pro lenses have fast motors this causes issues in very low light and when tracking very fast objects such small birds.

I'm waiting to see how fat the new supersonic wave drive motors will preform on the new bodies.

DaireQuinlan

ThOnda wrote:

OT: Some say that reading magazines like PLAYBOY enhances coordination between eye and hand...

I normally focus with my LEFT hand though

the_manchine

So what affects the sensitivity of the AF points in the camera?

Fair enough that the quality of the light reaching the is down to the lens, as it the actual mechanics of moving the glass (servos and whatnot), but the decision about where position everything and the speed that the decision is taken at must be down to the camera.

What I'm getting at here is that the general consensus is that it's better to put your hard earned cash into good glass (which I agree with), but past a certain point do you start to get limited? Kinda like putting a Ferrari engine into a Fiesta?

DaireQuinlan

the_manchine wrote:

So what affects the sensitivity of the AF points in the camera?

Fair enough that the quality of the light reaching the is down to the lens, as it the actual mechanics of moving the glass (servos and whatnot), but the decision about where position everything and the speed that the decision is taken at must be down to the camera.

What I'm getting at here is that the general consensus is that it's better to put your hard earned cash into good glass (which I agree with), but past a certain point do you start to get limited? Kinda like putting a Ferrari engine into a Fiesta?

I would imagine that the actual mechanics and sensitivity of the AF sensors on modern day cameras are all pretty much identical, and all pretty good. If you get into complicated AF modes like movement tracking across multiple AF points and what not I'd say you'd see a continuum of capability ranging from the cheaper consumer cameras to the pro level bodies, but from the point of view of a single AF point I'd say all cameras are equally as capable.