Manual Focus Question

Discussion in 'Digital Photography' started by supergrandma, Sep 28, 2009.

  1. supergrandma macrumors member

    Joined:
    Sep 27, 2005
    #1
    I recently purchased my first lens with a "real" manual focusing ring (Canon EF 85mm f/1.8 USM). Question: when I manually focus, I can turn the ring past the minimum/maximum markings on the distance window (no focusing occurs before the minimum focus distance or after infinity, of course). Is this action normal, and will it damage the focusing mechanism?
     
  2. SLC Flyfishing Suspended

    SLC Flyfishing

    Joined:
    Nov 19, 2007
    Location:
    Portland, OR
    #2
    It won't damage the lens, you can rotate the ring a full 180 degrees or more (not sure why you'd want to if it's not doing anything).

    If it was going to damage the lens, they'd make it so you couldn't turn it any further and give you a warning in the manual.

    SLC
     
  3. supergrandma thread starter macrumors member

    Joined:
    Sep 27, 2005
    #3
    Thanks. It just kind of freaked me out when the focus ring turned past infinity. I'd hate to ruin a $350 lens after only a day.
     
  4. SLC Flyfishing Suspended

    SLC Flyfishing

    Joined:
    Nov 19, 2007
    Location:
    Portland, OR
    #4
    Nope you're good, I did the same thing to a lens of mine, only my lens was $1900.00
     
  5. Nicolasdec macrumors 65816

    Nicolasdec

    Joined:
    Dec 7, 2006
    Location:
    São Paulo
  6. Ruahrc macrumors 65816

    Joined:
    Jun 9, 2009
    #6
    It's something to do with the way most modern lens' optical formulas are designed and implemented. It is possible to focus beyond infinity with these optical formulas, and it does not harm the lens.
     
  7. LittleCanonKid macrumors 6502

    Joined:
    Oct 22, 2008
    #7
    He's referring to the physical turning of the ring past any sort of focus distance. Full-time manual focus lenses allow you to do this (that I know of). Quite a difference from the non-USM/FTM lenses, eh?
     
  8. Ruahrc macrumors 65816

    Joined:
    Jun 9, 2009
    #8
    I'm aware of that- I was just pointing out that not only does the ring turn beyond "infinity", the lens will actually focus beyond infinity as well. There are multiple reasons for this but for example many zoom lenses are varifocal, or the cushion is put in to account for thermal expansion in different environments or manufacturing tolerances. This is important to realize because if you are looking for maximum focal distance from the lens cranking the ring all the way to the stop probably isn't going to work.

    http://www.panoramas.dk/technics/focus.html

    Ruahrc
     

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