IS vs USM - is it worth the money?

Started Feb 21, 2013 | Questions thread
Don Daugherty
Contributing MemberPosts: 641
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Re: Focus tracking an L lenses
In reply to Chris R-UK, Feb 23, 2013

If we define tracking as the ability to maintain focus on a subject moving in, around and out of the focal plane then I think the focus speed of the lens can actually impact some aspects of tracking.

Chris R-UK wrote:

John_A_G wrote:

[snip]

The 55-250 is a very nice consumer grade zoom - a great bargain and good quality. But you are deluding yourself in thinking it's on par or in any way better than the L. ESPECIALLY when it comes to continuous focus. The L isn't just quicker to ACQUIRE it will track better too.

I don't disagree that the 70-200 f4L will focus faster (since it has a USM ring motor) but that is the first time that I have heard it suggested that an L lens will track better as well.

Surely focus tracking is a function of the body not the lens. In what way will an L ‚Äčlens‚Äč track better than a non-L lens.

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Chris R

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