by definition zoom lenses hold focus while zooming. If they don't they arent zooms, they are varifocal which are rare, not common. Im sure there are some cheapo zooms that don't hold focus properly but I would call those attempted zooms falling to varifocal not on purpose.
-- J.C. O'Connell (mailto:[email protected]) Join the CD PLAYER & DISC Discussions : http://tech.groups.yahoo.com/group/cdplayers/ http://launch.groups.yahoo.com/group/cdsound/ -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Dario Bonazza Sent: Saturday, July 17, 2010 5:44 PM To: Pentax-Discuss Mail List Subject: Re: 2 touch? What do you prefer? J.C. O'Connell wrote: >I tend to like 2 touch zooms over 1 touch > because sometimes in zooming a 1 touch you may accidentally alter the >focus when you don't want to. I like to focus at the longest end of >the zoom range and then adjust the zoom setting for the > composition last. Provided it stays focused. A true zoom should keep focus as you change its focal length. That can be achieved by some kind(s) of optical/mechanical compensation for focus shift. On the other hand, a generic varifocal lens is not required to do that. However, many so-called zooms are varifocals, with some extent of focus shift throughout their focal length range. One of the reasons for making 1-touch zooms was allowing/forcing the photographer to perform the required compensation for the focus shift of the varifocal lens. For that reason, 1-touch zooms were so much in fashion in the pre-AF era. With AF cameras, that problem is less important, as focusing is performed after selecting the focal length. Dario -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
