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Re: [OM] Changing lens mount

Subject: Re: [OM] Changing lens mount
From: "Jeff Keller" <om-list@xxxxxxxxxxx>
Date: Sun, 5 Dec 2010 09:16:45 -0800
Badly built may not mean poorly machined. It may just be a case of taking
their "standard design" and putting different locking tabs etc on it. The
thickness could be way off as in the pictures I linked. Both were sold as
Nikon to EOS adapters, and sort of worked, but the generic Chinese adapter
was way off on its thickness.

A soft corner could be caused by the adapter bayonet being the wrong depth.
When the lens is mounted on the camera the lens could tilt down until the
bayonet tabs finally caught the mounting flange. Many DSLRs have a prism
housing that hangs out over the lens. It may not be obvious the lens isn't
being held in the correct position.

Keep in mind that there are millions of tiny anonymous manufacturers in
China. Antifreeze in foodstuffs, toxic medicines: a lack of knowledge, a
desire for a quick profit, no due diligence, anonymously produced can cause
dramatic failures.

Jeff Keller

-----Original Message-----
From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx] 
Sent: Sunday, December 05, 2010 6:08 AM
To: Olympus Camera Discussion
Subject: Re: [OM] Changing lens mount

I'm still having difficulty accepting this except in the case of 
extraordinarily badly built adapters.  To put a corner out of focus the 
two faces of the adapter would have to be out of parallel by a 
ridiculously large amount by even the loosest standards of machining.

To illustrate the point consider the notion of "depth of focus" as 
opposed to "depth of field".  Depth of field equates to near and far 
focus points in front of the lens.  The term depth of focus used to be 
used synonymous with depth of field but as it is now used equates to the 
position of the image plane of those near and far points on the image 
side of the lens.

Now consider your wide angle lens.  As an example I'll give you a 24/2.8 
focused at 15 meters (my guess at the distance to the porch as used in 
the test shots at 16:9).  Using typical 35mm parameters for depth of 
field at f/8 the near focus point is at 1.9 meters and the far focus 
point is at infinity.  On the image side of the lens the depth of focus 
is 0.54mm or 0.022".  To cause notable differences in focus in one 
corner of the lens the two faces of the adapter would have to be out of 
parallel by so much as to probably be visible to the eye let alone a 
micrometer.  Even wide open and focused only at one meter the depth of 
focus is still 0.003".

I have three cheap ebay OM to EOS adapters.  They work just fine except 
that two of them won't mount a couple of my non-Zuiko OM mount lenses 
although all Zuikos mount just fine.  I've seen no problems with 
infinity focus and, although I haven't put a micrometer to them there is 
certainly no visually obvious difference in parallelism of the two 
mounting faces.

Are you sure the FM forum correspondents aren't shills for CameraQuest?
:-)

Chuck Norcutt




On 12/4/2010 11:51 PM, usher99@xxxxxxx wrote:
> Perhaps stating the obvious but WA's are particularly
> susceptible to adapter issues.  Have seen several examples on FM alt
> lens forum whereby
> one side of an image was not sharp due to an uneven adapter.  Never have
> seen a complaint about a Cameraquest one, though may be overkill for
> many applications.
> Mike
>
>
>
> Looks like significantly more than 0.002" in the case of the 16-9.net
> test:
> http://www.16-9.net/lens_tests/15mm_2/sigma1224vnikon15f.html
>
> picture of adapters:
> http://www.16-9.net/lens_tests/nikon_adaptors.jpg
>
> Jeff Keller
>
>
>
>
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