Olympus-OM
[Top] [All Lists]

Re: [OM] 21mm f 3.5 and B+W SLIM C-POL

Subject: Re: [OM] 21mm f 3.5 and B+W SLIM C-POL
From: "Paul Farrar" <farrar@xxxxxxxxxxxx>
Date: Tue, 7 Mar 2000 09:19:07 -0600 (CST)
> 
> In a message dated 00-03-06 22:10:14 EST, you write:
> 
> > 3.  Open the back and carefully look through the film gate and wide open
> >  diaphragm, especially at the corners.  If you line up the corner and edges
> >  of the film gate with the diaphragm you should not see any blockage from
> >  the lens ring on the front of the lens (or in this case the filter ring).
> >  Any blockage is likely vignetting.  The amount of vignetting (severity) can
> >  be estimated by how much of the aperture area is blocked.
> >  4.  If any vignetting is seen, then gradually stop down until it is gone.
> >  This is the widest aperture without vignetting and will also give you an
> >  idea of how severe it is.
> 
> I was going to suggest this test but John beat me to it. If you look through 
> the corners of the film opening with the back of the camera and shutter open, 
> and directing the camera and lens at a bright light, it is either a no or 
> no-go situation.  I haven't had any vignetting with my Pentax 49mm wide angle 
> linear or the Minolta 49mm wide angle circular polarizer.
> 
> Warren

I find it easier to look from the front. Tilt the camera diagonally to see the
corner of the film gate. Continue tilting as the corner disappears. If the
filter encroaches on the lit area before the corner disappears, you have
vignetting.

Reverse telephoto wide angles can have less than cos^4 falloff because
they bend the light more on axis as it gets to the diaphragm. They still
have the fall off due to the rectilinear projection. The Olympus 8mm
is an equal area fisheye, rather than a classic fisheye, so it should
ideally have no projection falloff.

Paul

< 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 >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz