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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 22 Dec 2012 (Saturday) 20:27
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Technical Question on EF 100mm f/2.8 L IS USM Macro

 
Al ­ Heline
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Dec 22, 2012 20:27 |  #1

I noticed something this evening that I do not recall having seen before. On my EF 100mm f/2.8 L IS USM Macro lens, the focus has to be course focused before the 'real' auto focus will home in on the subject. I have tried it at several different distances, with and without IS being turned on, always with the same results. My other lenses, Canon and otherwise, will jump from close-in to infinity and back again, but the 100mm doesn't budge until you at least manually bring it into course focus before causing a half shutter button action. If IS is turned on, you can hear the IS working, but the USM doesn't budge. Once you somewhat bring it into course focus (i.e. you can loosely define edges of the item), the USM will kick in and give tack sharp shots. Since I do not use this lens every day, and suffer from severe CRS (Can't Remember DooDoo), I don't remember this happening before.  :o

Anyone out there with a 100 that can clue me in on whether I am just having a senior moment (and all is working correctly) or am I seeing a problem with my 'baby'?

For info, the contacts are clean, battery fully charged, lens cap off, AF 'ON' at Center Point in spot focus, etc. She is mounted on a 60D, and not in LIVE mode.


Al
Canon 60D Meike gripped / Canon S5 IS - Canon EFS 17-55mm f/2.8, Canon EF 100mm f/2.8 L IS USM, Canon EFS 18-135mm F/3.5-5.6, Tamron SP 70-300mm F/4-5.6, 430 EX Speedlight

  
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lar55
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Dec 22, 2012 20:48 |  #2

Same body, different macro lens, but maybe relevant: check Custom Function C.Fn III-1 "Lens drive when AF impossible". I had this on (1) Stop Focus Search, to keep a different lens from 'hunting', but with the macro lens it had to be (0) Continue Focus Search or it would sometimes do exactly what you said - refuse to autofocus until I manually focused closer.




  
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Al ­ Heline
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Dec 23, 2012 08:24 |  #3

lar55 wrote in post #15398197 (external link)
Same body, different macro lens, but maybe relevant: check Custom Function C.Fn III-1 "Lens drive when AF impossible". I had this on (1) Stop Focus Search, to keep a different lens from 'hunting', but with the macro lens it had to be (0) Continue Focus Search or it would sometimes do exactly what you said - refuse to autofocus until I manually focused closer.


That is exactly what it was. Thank you. Now, I will have to get my head wrapped around that concept. Something seems to be a little backwards...'If it is not in focus, don't even try' ??? I'll have to think about that one.

Thanks again.


Al
Canon 60D Meike gripped / Canon S5 IS - Canon EFS 17-55mm f/2.8, Canon EF 100mm f/2.8 L IS USM, Canon EFS 18-135mm F/3.5-5.6, Tamron SP 70-300mm F/4-5.6, 430 EX Speedlight

  
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lar55
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Dec 23, 2012 09:44 |  #4

It's not that it isn't in focus. The problem is that it is so far out of focus that the AF system can't tell which way to go - in or out. At that point, the camera can either give up trying to focus, or tell the lens to try a random direction and see if it gets better (and if not, try the other way). That's what the custom control is for - it tells the camera whether to give up or keep trying.

This should probably only happen with lenses that have a very wide focus range (macros), and only when the focus is very far off. If it is happening when the focus doesn't have far to go, something else could be wrong.




  
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Technical Question on EF 100mm f/2.8 L IS USM Macro
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