[OM] Re: Sigma lens

[Chuck Norcutt]

It can be very difficult to determine what camera mount a specific lens 
was built for just from looking at a low grade photo on ebay.  But this 
one is easy.  I don't know what camera it's for but it's definitely not 
an OM lens.  Notice the brass/gold contacts around the lens flange. 
These are electrical contacts for an autofocus lens which also has an 
electrically controlled diaphragm.  OM camera and lenses are manual 
focus and the diaphragm is mechanically actuated from a lever just 
inside the body's lens mount flange.  OM shutters may be electronically 
timed depending on model but the OM-1 and OM-3 have mechanical shutters 
as well.  That why, when you adapt OM or other lenses to your E510 you 
won't have any automation.  No automatic aperture control and no auto 
focus.  These things didn't exist in 1973.

Chuck Norcutt

Matthew Granger wrote:
> Does this look like an OM mount lens?
> 
> http://cgi.ebay.com.au/Camera-Lense-Sigma-Zoom-1-4-5-6-7-UC-100-300_W0QQitemZ160176076913QQihZ006QQcategoryZ707QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
>

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