Ok, I am the fussy buyer. Thanks a lot for all comments which
show that this "problem" is not uncommon. Still, I am not convinced
that it really is harmless. Let me explain my worries.
First, I would like to clarify what I am talking about.
The loose lensmount I was referring to is _not_ the connnection
to the camera body (which indeed might be related to the
particular body I was using) but rather the connection
of the lensmount to the rest of the lens. To check that for your
own lens you should hold the lensmount (without attached body)
in one hand and the front of the lens (e.g. the filter mount)
in the other hand. Then, without excerting any force, try
to twist the lens. None of my other lenses (a 17 year old
1.8/50mm, and two 14 year old vivitar zooms, where I had
to block the zooming mechanism) show _any_ play, whereas
Frank's (or now my) fisheye freely moves at least 1 degree.
I am not a professional photographer, not even a serious
amateur (I will use the fisheye for VR), but I have quite
some experience in working in optics research labs, and
I know, that _any_ play in precison optical devices means
bad news. Of course, the rotation itself does not influence
image quality at all (most lenses, not only fisheyes, are
symmetrical against rotations). However, the play may hint
to some more serious problem: The rear mount and front elements
of a lens slide against each other by means of some guiding
mechanism (e.g. rails) to enable focusing. The play I observed
may (in worst case) mean that these rails are worn out.
The fisheye lens may be prone to that, since the rather heavy
lensbody cannot be supported on a tripod. This, in turn,
tilts the lens relative to the mount, which causes
image distortions. A tilt cannot be observed with the
naked eye on the current lens, but it is undoubtedly real, if
the sliding mechanism has this problem, and it will
quickly get worse.
Any sliding mechanism can be expected to wear at some
stage (although not exactly in a like-new lens). A good design
should provide some adjustments for that case, or
should allow the exchange of the sliding parts.
Let me therefore specify my questions: Is that
possible with the 8mm OM, and how involved is it? And
are there more (harmless) possible reasons for this play?
Thanks, and best regards
Helmut Dersch
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|