Autofocusing query

Hey all,

Recently I acquired a 24-105 L F4... And now I wish I didn.t... Mainly because I can't go back to buying standard lenses after seeing the quality of this lens. I also had a thread recently about buying a 70-200, well I ended up getting the Non IS F4 version.

Now, I've noticed a difference in focusing which I was hoping to get your input on. Now, if I select AF on the 24-105 and hold down the shutter half way it INSTANTLY locks on and it's ready to shoot. However, if I do this with the 70-200 it takes 1-2 seconds. Sometimes it will slowly put itself out of focus and slowly back into focus to "lock on" to a subject.

I tried on a bright sunny day and the 24-105 locked on straight away every single time, so I set it to 100mm and it still locked on perfectly, then I set my 70-200 to 100m and it would sometimes take seconds to focus correctly, and when it says its focused on a still object... sometimes it still comes out blurry as if it'd out of focus... However at 200mm it's very, very accurate in focusing (but still slow).

So, my question is, what's the difference? Why does one focus incredibly fast but the other one is slow? Someone mentioned aperture etc but they're both F4 and both used on sunny days for the test (within 3 minutes). I'd like to work it out because I've already missed a few shots due to the slow focusing so I'd like to avoid buying a lens like this in future (although it's perfect at longer distances)

You've got me stumped. The 70-200 has the exact same ring type USM motor in it as the 24-105. Are you trying to focus on high contrast subject matter and still having difficulties?

The camera and lens each have their focus tolerances, I wonder if maybe they are off opposite directions causing the focusing system to not work properly.

Dave

Hi, my experience of the 70-200 is that it locks focus instantly. There's usually no need to wait between "half press" and "full press" of the shutter button. The only things that cause hunting are darkness and focusing distance below 1.2/3 meters (whichever is selected). To me it seems as either you're trying to focus below minimum focusing distance, or there's something wrong with your lens.

Thanks for the replies. The object I was locking onto was roughly 10 metres away. I'm thinking maybe the object could have been too small, but then again the 24-105 had absolutely no trouble. I mucked around with the other setting 1-infinity or 3-infinity but it made no difference. I also tested on a very bright bird in a tree and it took ages to lock on, yet again the 24-105 was instant. I was thinking the focusing may be a trade off of the lens barrel not moving, but judging by what you've both said it sounds like a lens fault. I'll do some more testing tomorrow.

One thing I am very impressed with though is that the lens barrel doesn't move, unlike the 24-105 which moves with your zooming and is prone to lens creep.

Quote:

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Originally Posted by Squidy

Hey all,

Recently I acquired a 24-105 L F4... And now I wish I didn.t... Mainly because I can't go back to buying standard lenses after seeing the quality of this lens. I also had a thread recently about buying a 70-200, well I ended up getting the Non IS F4 version.

Now, I've noticed a difference in focusing which I was hoping to get your input on. Now, if I select AF on the 24-105 and hold down the shutter half way it INSTANTLY locks on and it's ready to shoot. However, if I do this with the 70-200 it takes 1-2 seconds. Sometimes it will slowly put itself out of focus and slowly back into focus to "lock on" to a subject.

I tried on a bright sunny day and the 24-105 locked on straight away every single time, so I set it to 100mm and it still locked on perfectly, then I set my 70-200 to 100m and it would sometimes take seconds to focus correctly, and when it says its focused on a still object... sometimes it still comes out blurry as if it'd out of focus... However at 200mm it's very, very accurate in focusing (but still slow).

So, my question is, what's the difference? Why does one focus incredibly fast but the other one is slow? Someone mentioned aperture etc but they're both F4 and both used on sunny days for the test (within 3 minutes). I'd like to work it out because I've already missed a few shots due to the slow focusing so I'd like to avoid buying a lens like this in future (although it's perfect at longer distances)

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Warranty repair is in the offing if you can.

"The Canon EF 70-200mm f/4 L USM Lens focuses very fast, very quietly and very accurately thanks to Canon's excellent Ring USM (Ultrasonic Motor). " from Bryon's review.

So, this morning I tested again. The 24-105 locked on instantly, the 70-200 is focusing much faster, but still has considerable lag on the same object as compared to the 24-105. It's much quicker, but it still focuses out then in a bit whereas the 24-105 just goes "beep" and its into place already.