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[OM] Re: Fisheye confusion

Subject: [OM] Re: Fisheye confusion
From: Jim Brokaw <j.l.brokaw@xxxxxxxxx>
Date: Mon, 14 Nov 2005 23:00:49 -0800
on 11/14/05 9:03 PM, Dan Mitchell at danmitchell@xxxxxxxx wrote:

> Poking around on the bay for fisheye lenses, I find one place selling
> two different things:
> 
> item 7563223184 is a 8mm/f3.5, which is what I'd expect a fisheye to be.
> 
> but what, then, is item 7563223339 ? It's apparently 16mm/2.8 fisheye
> -- but how can that also be a fisheye if the 8mm lens was? Is fisheye
> just "not rectilinear"? And also the auctions claim that the 16mm one
> has a 180 degree FOV, and also that the 8mm one has a 180 degree FOV.
> I'm confused -- what's going on here?
> 
> -- dan

Two different 180-degree views. The 8mm fisheye typically shows a fully
circular image, usually about 23mm diameter to fit across the frame of the
film. The corners outside the circle are blank or black and have no image in
them.

The 16mm fisheye makes a larger circle, then crops out the 24 x 36mm full
frame from the circle, just fitting it across the circle, so that the
diagonal from one corner to the opposite corner touches the edges of the
circle. This means that -across the diagonal of the rectangular frame- there
is a 180-degree view. Horizontally or vertically it is somewhat less than
180-degrees, and there is the circular image 'distortion' in any areas but
the horizontal and vertical center axises (damm, pendants, what is the
plural of that word...!?). So effectively the 16mm fisheye would create a
circular image of about 43mm diameter if you have the film to fit it... I've
never tried it but I suppose if you had an OM to Hassleblad adapter it might
be interesting.
-- 

Jim Brokaw
OM-'s of all sorts, and no OM-oney...




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