@KWL58 wrote:
Just bought the 300mm f/4 lens, it seems to take along time focusing. I am using the lens on my 70d. I didn't notice any focusing concerns when reading reviews. Does anyone know if this is an issue with this lense or did I get a problem lens? Thanks Kate
Just to me sure which lens we're talking about... did you buy a new lens or a used one?
If new, it must be the EF 300/4L IS USM. That's the only version being sold new today.
If you bought used, there's at least a possibility that you got the older non-IS model (that was discontinued about 18 years ago). And if it happens to be that earlier version, our answers to your questions might be different.
I have the current, IS version, same as ebiggs. It's very fast focusing and reliable on my 7D cameras (whose AF system is similar to your 70D's). In fact, that lens is actually pretty good on my 5D Mark II too (which isn't known for it's speedy AF system).
I also have the EF 70-200/2.8L IS USM (first version, not the Mark II) and the EF 70-200/4L IS USM. I very often use the 300/4 and one or the other of the 70-200s alongside each other... and I notice very little difference between them, with respect to AF speed and performance.
There are a number things that might effect AF speed.
First thing I'd do with either a new or used lens would be clean the gold, electronic contacts on the rear of the lens, just to be sure there is nothing on them that might be slowing or interrupting the communication between the camera and lens. JUst use a few drops of isopropyl (rubbing) alcohol to dampen a clean, lint free rag and use that to wipe those contacts. Often this is all that's needed, even some little finger oil on the contacts might cause problems. You might also inspect the corresponding "pins" just inside the front of the camera, too. Those are spring loaded and should pop back up easily, when lightly pressed down. (Be careful to keep off the lens' optics and don't touch the mirror inside the front of the camera. Don't use anything abrassive on the contacts either.They're gold plated to insure good flow of current and prevent oxidization. Anything abrassive might damage the gold plating.)
What focus set up do you have on the camera? For stationary subjects, you should normally be using One Shot mode. For moving subjects, you should be using AI Servo. In any case, hopefully you aren't using AI Focus (which isn't realy a focus mode at all). AI Focus may work a bit slower than the other two modes.
The 70D also has three focusing pattern choices: All Points/Auto Selection, Single Point/Manual Selection and Zone Focus/Auto Selection. Normally I'd use Single Point to have the most control over where the camera and lens focus.
In addition, there are several focus fine-tuning "tweaks" possible in the 70D's menu.
First, there is Custom Function II - 1, "Tracking Sensitivity" which governs how quickly the AF in AI Servo mode will jump from one subject to another at a different distance.... Many users like to turn this down slighlty... to -1 or -2. In particular this may help while becoming familiar with the new lens. If you turn this setting up high (+1 or +2) the camera and lens will focus onto other objects at other distances much more quickly and might appear to be struggling to achieve focus. Again, this is only in AI Servo focus mode.
Next, Custom Function II - 2 "Acceleration/deceleration tracking" also pertains to AI Servo mode. Set to +1 or +2 to better focus on subjects that start, stop or change speed erratically. However, by making the AF system more sensitive to movement with these higher settings, it can cause somewhat less focus stability, which might appear as if the lens were struggling to focus.
Custom Functions II - 3 and II - 4 are "First image priority" and "Second/subsequent image priority", respectively. Use these to tell the camera what's more important to you: Do you prefer the camera to release the shutter as quickly as possible, even if the subject isn't quite in focus? Or, is it okay for the camera to shoot a little slower, but be more certain of achieving accurate focus? If biased toward the latter, the camera and lens may seem to focus more slowly.
There are other possibilities, but one I think you really should check is Custom Function II - 9 "Orientation linked AF point". When this is enabled, you can set up different AF point selections (and even different AF focus patterns) that the camera will switch between automatically, whether you are holding the camera in horizontal (landscape) or vertical (portrait) orientation. When this is enabled, you have to go to each orientation and set up something... Leaving it un-set, I've found the camera can act strangely. Also, it's important to be aware that there are actually three possible orientations: horiz./landscape, vert./portrait with the camera grip at the top and vert./portrait with the grip at the bottom. It's important to set up all three, or strange things can happen!
Actually I've found with the same feature on my 7D's that even when set up correctly, it often causes a slight focusing delay, possibly while the camera is sensing its orientation and changing the setup according to the settings I've made. It can be useful in certain situations, but most of the time I just leave C.Fn II - 9 disabled.
Yes, this lens has a focus limiter and you need to have that set appropriately for your subject's distance. If incorrrect the lens will struggle to focus. Normally you'll want to set it to "1.5M to infinity". That allows the lens to focus across it's full range. Sometimes when you want the lens to focus faster and are only working with more distant subjects, you might want to set it to "3m to infinity"... however be sure the lens is focused beyond 3m (about 10 ft) before you try to autofocus it. And be aware that if your subject comes closer than 3m (~10 ft.) the lens will be unable to focus.
I agree too, that some of the vibrations you are feeling might be the IS working... assuming yours is the curent IS version of the lens, of course.
Finally, what about the lighting where you are shooting and your subject's tonalities? Good light and a contrasty subject are the most ideal for camera and lens to focus upon quickly and accurately. Poor light and contrast can cause them to struggle and function consderably more slowly.
All the above... and probably some other things I'm forgetting... might effect autofocus speed and performance. Sure, it's possible you got a faulty lens... Even if it's brand new. But IMO it's far more likely that something is simply set wrong or in a way that slows down the lens' AF performance. It should be quite fast. Hope this helps solve the problem!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & EXPOSUREMANAGER
As they say.
