>> The 200/4, however does not lose
>> any light, due to its IF construction,
>> and remains an f/4 lens at 1:1
> Sorry, but due to the extension involved,
> it loses slightly over a stop of light at
> 1:1 (Moose says 1 1/3 stops).
Yep, rear focus and internal focus lenses
do lose light at minimum focus. Not as
much as the old-type move everything lenses,
but it's detectable. I've got a 105mm/f2
(rear focus) and 180mm/f2.8 (internal focus)
on my desk here, a quick check indicates that
the both loose around 1/3 a stop at minimum
focus.
For comparison an old 300mm/f4.5 AI-S I used
to own lost around 2/3 stop.
Unless you're using a hand-held meter, don't
worry about it. Even 1-1/3 stops is much less
light than you loose when the sun goes down.
It is kinda fun to obsess about such things
though, isn't it?
-Don
