ViewFinder Photography Forum

General discussion - our photography living room. Talk about aesthetics, philosophy, share your photos - get inspired by your peers! Moderated by another view and walterick.
ViewFinder Forum Guidelines >>
Introduce Yourself! >> Gatherings and Photo Field Trips >>
Results 1 to 3 of 3
  1. #1
    Faugh a' ballagh Sean Dempsey's Avatar
    Join Date
    Mar 2004

    Canon USM lenses... experiences with them?

    I underestimated the USM lenses until I got the 17-40L. The USM on this focuses at a blinding speed, and is dead silent. I was shocked at how fast it focused. So I have some questions.

    First, do all USM lenses focus this fast? Or does the 17-40 focal length have something to do with it's ability to focus so fast. OR, is that a function of the L series lens? Also, do the non-L lenses with USM focus just as fast?

    I am pretty much wanting to eventually end up with all L and USM lesnes... but I want to see if the USM speed is the same in all of them, or just certain ones. If you have experience with any of the above things, please post.

    A good craftsman never blames his tools.

  2. #2
    Erstwhile Vagabond armed with camera Lionheart's Avatar
    Join Date
    Feb 2004

    AF speed-my understanding of it with regards to USM

    A large part of it is the short focal length,(probably-17-40 is a decidedly short range) but most of the USM "L" lenses that are f4 or faster will focus much faster than their consumer USM counterparts. A lot of it has to do with the fact that more light is available for the sensors to lock focus. I'm not sure if engineering has anything to do with it, but it might well be that they're engineered to be faster as well. I know that on my old 1D and 1V, the central 5-7 sensors are cross-basis sensors only with lenses that are f4 or faster (or was f5.6?), and for lenses that are slower aperture than this, only the central sensor is cross basis, to reduce focus fishing according to the manuals that came with the cameras. Makes sense to me, since at f4 and faster, more light is available for a cross basis sensor to function properly, and f5.6 and smaller, the screen starts to get pretty dark even in bright daylight.
    I don't see really any focus speed difference on my consumer level 20mm f2.8, 50mm f1.4, 85mm f1.8 lenses versus my f2.8 "L" zooms, but I do recall that the 100-400 f4-5.6 L was noticeably slower to lock focus than any of my other lenses. The 28-135 f3.5 USM was plenty quick as I recall. I've read reviews on the 85 f1.2 as being slow to focus, and that is an L USM lens. Might be the focal length in some cases, might be engineering in some.
    Last edited by Lionheart; 04-25-2004 at 08:31 AM.
    Seek the Son and the shadows fall behind you.

    slowly inching to 2000

    Mac's Rule, Windblows drools
    Friends don't let Friends use WindBlows XPee
    <img src="">Lionheart O'Canon Feel Free to Help

  3. #3
    Member Lemming51's Avatar
    Join Date
    Apr 2002
    Springfield, IL, USA


    There is a difference between "ring-USM" which is used in the L lenses and the mid-level consumer zooms (EF 20-35 f/3.5-4.5, EF 24-85 f/3.5-4.5, EF 28-105 f/3.5-4.5, EF 28-135 f/3.5-5.6, EF 70-300 f/4.5-5.6 DO, and EF 100-300 f/4.5-5.6) and the "micro-USM" which is used in the entry-level consumer zooms (EF 28-90, EF 28-105 f/4-5.6, EF 75-300, EF 75-300 IS).

    Ring-USM moves the focus elements directly, without reduction gearing, and is used on internal focus elements which are smaller/lighter making AF faster. In "micro-USM" lenses the motors drive reduction gearing (a la conventional af motors) and the focus elements are the larger/heavier front group.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. must I only use canon EF lenses on EOS7e?
    By rsmith55 in forum Help Files
    Replies: 2
    Last Post: 03-08-2004, 12:20 PM
  2. Press Release: 3 New Canon Digital ELPH Cameras
    By Photo-John in forum Camera News & Rumors
    Replies: 0
    Last Post: 02-09-2004, 05:25 PM
  3. Press Release: Canon PowerShot A75 and PowerShot A310
    By Photo-John in forum Camera News & Rumors
    Replies: 0
    Last Post: 02-09-2004, 03:14 PM
  4. Press Release: 8 Megapixel Canon PowerShot Pro1
    By Photo-John in forum Camera News & Rumors
    Replies: 0
    Last Post: 02-09-2004, 02:55 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts