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Canon 50mm 1.8 STM

  • 21-05-2018 3:43pm
    #1
    awec
    Administrators Posts: 54,059 Admin ✭✭✭✭✭


    Is it just me lacking the skills, or does the autofocus on this lens really struggle at high apertures?

    I am really struggling to get it to focus on what I want. It hunts like crazy sometimes.


Comments

  • #2
    ED E
    Registered Users, Registered Users 2 Posts: 36,169 ✭✭✭✭ED E


    The AF motor is in the lens but the AF sensing is in body.

    I'm assuming by higher you mean larger fstop, up there your DoF should be very large so its the "easiest" to focus. At 1.8 its more work to get the points sharp.

    Are you using LiveView perhaps? In LV mode the shutter is up so the normal AF components are blocked so its using the sensor to digitally focus instead. This is weaker and needs a lot of light, something you dont have as much of at say F22.


  • #3
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators Posts: 50,039 CMod ✭✭✭✭magicbastarder


    ED E wrote: »
    I'm assuming by higher you mean larger fstop, up there your DoF should be very large so its the "easiest" to focus. At 1.8 its more work to get the points sharp.
    surely the lens autofocuses wide open though? i've never noticed a lens stepping down to complete autofocus.
    i would wonder whether the aperture issue is a red herring?


  • #4
    ED E
    Registered Users, Registered Users 2 Posts: 36,169 ✭✭✭✭ED E


    magicbastarder wrote: »
    surely the lens autofocuses wide open though? i've never noticed a lens stepping down to complete autofocus.

    Doesnt change it, operates through it.
    magicbastarder wrote: »
    i would wonder whether the aperture issue is a red herring?

    Maybe if its real AF, definitely not if its fake AF via LiveView.


  • #5
    awec
    Administrators Posts: 54,059 Admin ✭✭✭✭✭awec


    I mean it struggles to autofocus at f1.8. I never seem to be able to get it to focus on exactly what I want without going to manual.


  • #6
    delly
    Moderators, Home & Garden Moderators, Recreation & Hobbies Moderators Posts: 7,715 Mod ✭✭✭✭delly


    awec wrote: »
    I mean it struggles to autofocus at f1.8. I never seem to be able to get it to focus on exactly what I want without going to manual.

    Is it specifically very low light? When using it in low light I don't usually have a problem, but there are occasions when I will pick one of the focal points rather than using all. I'll then half press to fix focus on the brightest part of the subject.


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  • #7
    wonski
    Registered Users, Registered Users 2 Posts: 13,685 ✭✭✭✭wonski


    Which AF mode are you using? Trty single point and see if there is an improvement. I am not using Canon, but had issues with Nikon lenses doing same thing...


  • #8
    ED E
    Registered Users, Registered Users 2 Posts: 36,169 ✭✭✭✭ED E


    ^This.


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