70-180 Vario Apo Elmarit

[Chan <janpo@tm.net.my>]

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