Canon 50mm autofocus

grapejapegrapejape Registered Users Posts: 57 Big grins
edited December 9, 2009 in Cameras
I just obtained a Canon 50mm f1.4. The lens is great, and focus very quickly in "one shot" autofocus mode. However, when I select AI Servo, it continually hunts and is very noisy compared to my 28-135mm lens. The 28-135 is extremely quiet in both one shot and AI servo autofocus modes (but not as fast as the 50mm in one shot mode).

Perhaps this new lens is just a different beast. Anyone care to comment?

- Jason

Comments

  • ziggy53ziggy53 Super Moderators Posts: 24,079 moderator
    edited December 8, 2009
    Both the Canon EF 28-135mm, f3.5-f5.6 IS USM and the EF 50mm, f1.4 USM have USM motors, but the 50mm, f1.4 has a "Micro Motor" USM where the 28-135mm has a "Ring-type" USM. The ring-type is much quiter.

    The 50mm should not be hunting terribly unless there is nothing on which to lock focus, like trying to focus a bare wall. Even in that case, the bare wall, the addition of a flash with an AF assist light, or the ST-E2 transmitter, should allow rapid focus in even very low light and low contrast subjects.

    FYI, the EF 50mm f/1.2 L USM has ring-type USM and would be very quiet as well.
    ziggy53
    Moderator of the Cameras and Accessories forums
  • grapejapegrapejape Registered Users Posts: 57 Big grins
    edited December 9, 2009
    It focuses very quickly and effectively in "one shot", it's just noisy in "AI Servo" mode. I'll play around with it some more. It seems to slightly "hunt" when I focus on objects, barely moving back and forth. The object never goes in and of focus to my eye, but I can hear the mechanism moving around.

    FWIW the f1.2 would cost a small fortune - likely 50% of everything I own once the divorce was settled.


    - Jason
  • ziggy53ziggy53 Super Moderators Posts: 24,079 moderator
    edited December 9, 2009
    grapejape wrote:
    It focuses very quickly and effectively in "one shot", it's just noisy in "AI Servo" mode. I'll play around with it some more. It seems to slightly "hunt" when I focus on objects, barely moving back and forth. The object never goes in and of focus to my eye, but I can hear the mechanism moving around.

    FWIW the f1.2 would cost a small fortune - likely 50% of everything I own once the divorce was settled.


    - Jason

    In AI-Servo mode the AF is expecting a moving subject and it constantly samples. You should not normally use it for stationary subjects. More than likely the slight movement of hand-holding the camera is causing the slight AF adjustments. Single-shot AF is appropriate for stationary subject matter.

    http://photonotes.org/other/ai-servo.html
    ziggy53
    Moderator of the Cameras and Accessories forums
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