Canon USM vs Non-USM Accuracy

Discussion in 'Canon' started by Edward Holt, May 22, 2006.

  1. Edward Holt

    Edward Holt Guest

    I'm not sure if this got past my ISPs Usenet service so apologies if you've
    seen my question already.

    I've got a Canon 50mm f1.8 mk2 and a 28mm f2.8 which are both non-USM.
    I seem to have hit and a miss focusing accuracy with them.

    I've also got a 20mm f2.8 which is a USM and have no problems with the

    Are the non-USM focusing lenses less accurate than the USM versions?

    I'm thinking of replacing the 50mm and the 28mm with the bigger aperture and
    more expensive USM focal length equivalents.
    Edward Holt, May 22, 2006
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  2. Edward Holt

    Alex Guest


    I get the same hit & Miss with my 50mm f/1.8, but put it down the the wide
    aperture and very low depth of field. In fact it only really happens to me
    when the subject I am focusing on has low light AND low colour contrast i.e.
    it cant determine where the focal point is.

    Apart from that I think its brilliant. Maybe USM is quick enough to find
    the focal point and stop the mechanism before it overshoots back out of
    focus like on the MKII.

    Alex, May 22, 2006
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  3. Edward Holt

    aaJoe Guest

    What's the price difference generally between the USM and non-USM in a
    50, 85 or 105 lens? Is it huge?
    aaJoe, May 23, 2006
  4. Edward Holt

    Edward Holt Guest

    It's not huge - but when I looked at buying a 50mm f1.4 USM I noticed that I
    could buy a 50mm f1.8 mk2 AND a 28mm f2.8 for less than it.

    As I didn't need f1.4 over f1.8 and coming from an era when manual focus was
    the norm, I thought that two lenses would make more sense. I think that USM
    lenses focus faster, but I'm not bothered about focus speed as my shots are
    primarily landscape. My autofocus option on the camera is set to One Shot AF
    using only the centre autofocus point to focus then recompose.

    I have found that the Auto Focus/Manual Focus switch on my copy of the 50mm
    f1.8 mk2 is poor quality leaving me in doubt most of the time what mode I'm

    wasn't aware of any focusing issues - hence the questions here.
    Edward Holt, May 23, 2006
  5. Edward Holt

    henryp Guest

    According to Canon USA, the USM technology means faster and quieter AF
    operation but should have no impact on the lens' optical performance.

    Henry Posner
    B&H Photo-Video, Inc.
    henryp, May 24, 2006
  6. snips focusing issuses USM vs non USM
    i have a old 28mm to 80mm non USM lence and a 75mm to 300mm USM lence
    niether seem to be probomatic with regards to auto focus.

    the 50mm is a older desgine possibly a evolution which might explain
    your issues?

    by poor quality do you mean loose? not the case here, the switch is
    fairly stiff but we're not comparing like with like. my lences are close
    on 10 years i'd guess.

    Roger Merriman, May 30, 2006
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