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
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