In article <4nlli5$rfe@newsstand.cit.cornell.edu>, d_ruether@hotmail.com says...
>In article <319D1A99.30DA@magna.com.au>, kelvinl@magna.com.au says...
>>I've recently been looking for a second hand 180 or 200mm lens for my
>>nikon to do concert photography. I've found a nice second hand 180mm
>>f2.8 (Nikkor AIS), but it focuses past infinity. The salesman said
>>that's normal for a lens of that age. Should I believe him, or stay
>>away from the lens? Does that mean it's been bashed around by some
>>photojournalist in its past?

>........................................................ALL Nikkor
>ED-glass lenses are built to focus beyond infinity (since ED glass
>contracts/expands more with temperature than other glasses, and as
>a result, causes a shift in lens focal length [and barrel length
>needed for infinity focus]).

And mirror lenses also focus beyond infinity because of mirror shape
change with temperature - though teles without mirrors or special
glass generally are NOT designed to focus beyond infinity.....
Hope This Helps