Lucas Rijnders wrote: > Op Wed, 27 Sep 2006 16:07:19 +0200 schreef Adam Maas <[EMAIL PROTECTED]>: > > >>Lucas Rijnders wrote: > > >>>Anything on backward/forward compatibility of the USM and the old AF >>>system? Did your rep explain the AF/MF switch on the lenses? > > >>The AF/MF switch on the lens will work just like it does on Canon USM or >>Nikon AF-S lenses. It's not exactly unique. Does exactly what it looks >>like it will do (Allows you to turn off AF on the lens). > > > I am not familiar with Canon or Nikon lenses. Could you explain what the > point is, given that you can turn off AF in the body, and that USM (at > least the Canon variant) allows manual focus in AF mode? > > Genuinly interested,
Note that not all USM lenses allow full-time manual focusing. Micro-motor USM lenses (all low-end Canon USM lenses as well as the Nikkor 18-55 and 55-200) do not allow it, except for the 50 f1.4 USM which is clutched like a DA lens (the 50 is only micro-motor USM for size reasons, ring-type would make it notably bigger). The switch on the lens disengages AF in the lens directly, and tells the body that it's been done (ensuring nothing bad happens to the motor). It's also much more conveniently located than the on-body switch typically. Note that while USM allows MF override, in AF-S mode it works just like the clutched DA/D-FA lenses, you need to let it lock first then override. -Adam -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
