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Re: [OM] Play in Frank's OM 2.8/8mm - fussy buyer

Subject: Re: [OM] Play in Frank's OM 2.8/8mm - fussy buyer
From: "David Brown" <keswick@xxxxxxxxxxx>
Date: Thu, 4 Jun 1998 18:28:56 +0100
Hello Helmut - I have just tried your "test" on about 10 different Zuiko
lenses. Most, as you say, have absolutely no movement at all. 

One lens has a very small movement (I presume we are talking side to side
movement - there is no movement away from the mount) and my 8mm fisheye
lens has a little more - I would guess quite a bit less than one degree but
certainly more than any other lens.

Does this help at all?

David

----------
> From: Helmut Dersch <der@xxxxxxxxxxxxxxxx>
> To: olympus@xxxxxxxxxxxxxxx
> Subject: [OM] Play in Frank's OM 2.8/8mm - fussy buyer
> Date: 04 June 1998 15:34
> 
> 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
> 
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