Re: 70-180 Vario Apo Elmarit

[Jim Brick <jim@brick.org>]

At 09:42 PM 11/5/97 -0800, you wrote:
>Given that the subject matter and time factor permit, a user of this lens 
>would prudently focus on the subject at the 180mm setting and then shift 
>the zoom to the appropriate focal length for recomposition. Is there any 
>risk of the focussed point being shifted in this process? Do the laws of 
>mechanics apply to have caused some shift, albeit being minor, but enough 
>to degrade the final image when projected on a screen in the case of a 
>transparency or a fully-blown 30X40 print? Would I be expecting an answer 
>that any possible variable in this case is so negligible that it cannot 
>be detected with normal vision and I should not lose any sleep on it? I 
>would indeed for the money I had to pay for this lens!
>
>Paul Chan
>

The 70-180 Vario Apo Elmarit is not a zoom lens. It is a variable focal
length lens. I don't have the instructions immediately handy but I believe
you should set the focal length first, then focus at that focal length. I
do not believe it is guaranteed to hold focus when changing focal lengths.
I certainly would not trust it to hold focus. For me, with any lens in
almost any situation, focus is the thing you do just immediately before
releasing the shutter. I'll double check later when I find my book.

Jim