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Old Saturday 18th June 2011, 01:18   #1
John In Ireland
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Canon 100-400 AF range

The Canon 100-400 has two AF focus range settings. 1.8m and 6.5m. I have it constantly set at 1.8m. I can't figure out why anyone would want to use the 6.5mtr setting or even why it is there. Am I missing something here?
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Old Saturday 18th June 2011, 02:36   #2
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When you are shooting distant birds (and particularly birds in flight), it can speed up focusing if you use the 6.5m setting. In that setting, the lens never tries to rack all the way in while trying to find focus. I'm often shooting dragonflies and butterflies in addition to birds which tend to be close, so I rarely use the focus limiter (6.5m) setting.
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Old Saturday 18th June 2011, 05:57   #3
Tony_79
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I always use focus limiter while shooting birds in flight. It makes focusing much faster.
Sometimes it is impossible to catch those fast birds without focus limiter.
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Old Saturday 18th June 2011, 07:41   #4
Roy C
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Quote:
Originally Posted by John In Ireland View Post
The Canon 100-400 has two AF focus range settings. 1.8m and 6.5m. I have it constantly set at 1.8m. I can't figure out why anyone would want to use the 6.5mtr setting or even why it is there. Am I missing something here?
Using focus limiters can significantly speed-up AF on most Telephotos John.
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Old Saturday 18th June 2011, 09:15   #5
Keith Reeder
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The posts above amply describe the upside of focus limiters, but there's a downside.

It's very easy to forget that you've got the focus limiter set: then, when that Bee Eater lands on a branch ten feet away from you in glorious evening sunlight, and you forget to switch back to the shorter setting, every one of those images will be OOF.

It's happened to me more often than I care to admit to. To be honest, while the focus limiter works exactly as advertised, I avoid it on my lens.

I'm also not good at estimating distance, and I sometimes doubt that a given BIF is actually more than 6.5m away, which is distracting.
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Old Saturday 18th June 2011, 09:24   #6
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as said it does make a big diffrence in AF speed iv lost shots simply because iv been set on the full focus range .
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Old Saturday 18th June 2011, 09:38   #7
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When using the 300/2.8 + 2x I almost always had a focus limiter set, it made a huge difference to AF speed - when something came inside of the focus distance then using back button focusing was the saving grace for me. I could switch to full time manual just by releasing the back button and did so an many occasions - mind you manual focussing is a lot easier done if on a tripod (which I almost always was when using the 2x).
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Old Saturday 18th June 2011, 10:04   #8
Keith Reeder
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It's sometimes better to prefocus at or around the longer focal length, then you've got the best of both worlds.

Doesn't work in every situation, but then neither does the focus limiter.
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Old Saturday 18th June 2011, 12:12   #9
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Fully with Keith on this one. Mine is always on the 6.5 M setting as thats a more normal working distance for me. I too have been caught out however. Such is the excitement when something comes closer than 6.5m and you cant lock on focus you tend to forget why and often end up loosing the shot altogether.
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