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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: Richard Schätzl <Richard.Schaetzl@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, 05 Jun 1998 18:32:03 +0200
Helmut Dersch wrote:

> 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)

As discused earlyer, some, minimal, lose is inevadeable at this point.

> but rather the connection
> of the lensmount to the rest of the lens. 

The conection between the chrome lensmount and the black part of the
lens mount should not have any lose or play at all.

> 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. 

I checked my lenses and nearly all have no optical perceptible play or
lose, especialy my long lenses are firm (even if the 200mm/4.0 Zuiko
needs a regrease). The ony lens with a barely noticeable twist or play,
is my old 50mm/1.8 Zuiko, but the focusing is smooth, firm and without
any grinding focusing noise.

> whereas
> Frank's (or now my) fisheye freely moves at least 1 degree.

Sounds much.

> and
> I know, that _any_ play in precison optical devices means
> bad news. 

Every mechanical device needs a certain play to work.

> 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.

To check this, you could focus the lens near to your ear and check for
grinding noises. There should be no play with turning the focusing ring.
You should not feel any "bumps" or changeing resistance during turning.
You should not be able to "bend" the lens barrel extended (do not aply
force!).

> 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.

There is a difference if you can twist the helicoil of the barrel (no
tilt), or bend the lens barrel and get a tilt.

> 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?

There is a device, which prevents the three rings of the helicoil to
twist against each other, this could have some play (no problem) or it
could have come loose (needs adjustment).

My 2 cents

Richard



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