My less than scientific experience is that f5.6 is the dividing line.
The Zuiko 400mm f6.3 and 600mm f6.5 are easy to use with the right
focusing screen. The Tamron 400mm f4 is easy to use with every focusing
screen I happened to have in the camera. When the 400mm f4 is used with
a 1.4x the resulting 560mm f5.6 seems to be easy to focus but my tripod
is pretty marginal for that combination. The f8 and slower mirror lenses
take special attention to focus.
Interestingly I don't remember vibration being a problem with the Zuiko
600mm. Perhaps the longer length reduces the resonant frequency or I was
doing something different. Definitely need to spend more time testing
;^)
I've almost given up trying to focus a mirror lens without a varimagni
finder. Too many missed shots. But I'm going to play with finder screens
again ... hopefully soon.
I've been carrying a 300mm f4.5 with me daily for the last couple weeks
... just in case. I take the 400mm f4 with when I go over to the bay
lands to relax. It's been a long time since I used it but the 200mm f5
seemed easy enough to hand hold and focus. In summary the 400mm f4 is my
favorite long tele for when I'm going after tele shots. The 300mm f4.5
is small enough, easy to use, and gives good results, that I often carry
... just in case. Of course the focal length difference is more
noticeable than the max aperture.
I found that a 1-8 screen works very well with long mirror tele's but
later found it didn't work well with slow wide angle zooms. I probably
didn't have a 2-4 but did have a 2-13 when I carried a half a dozen
screens with me over to the baylands for some testing. The archives six
months ago or so would have a record of my posted results. I'm going to
repeat that effort again. Probably have to spend nearly the whole day
swapping screens and lenses. Before I didn't take pictures for making
comparisons. Just spent two or three hours building impressions on
focusing ease. I'm going to try to get results on film.
-jeff
>>>A moose that trolls asked ...
F4.0 is less than half a stop faster than f4.5. Does it really make a
big difference? Are you using a 1 series or 2 series screen?
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