[OM] 16mm fisheye on E-1

[Bernard Frangoulis]

I am trying to understand what the field of view 
of a 15 or 16mm fullframe fisheye (such as the 
Olympus or Sigma ones) would be on a 4/3 body.

I found this site for explanations and formulas:
http://www.photo.net/learn/fov/index.html

So... the 4/3 sensor effective size is 17.3 * 
13.0mm 
(http://www.wrotniak.net/photo/oly-e/e1-rev.html#SENSOR), 
i.e. a 21.6mm diagonal.

So the FOV of a full-frame fisheye 15mm lens would be:
4 * arcsin(21.6/(15*4)) = 84°
i.e. the FOV of a 24mm rectilinear lens in 35mm 
terms, and not of a 30mm which we would obtain by 
simply multiplying the focal length by 2.

For a 16mm:
79°
i.e. a FOV between a 24 (84°) and a 28mm (75°) rectilinear lens in 35mm terms.

Whereas for a rectilinear 14mm:
2 * arctan(21.6/(14*2)) = 75°
i.e. a 28mm lens in 35mm terms: this time 
(rectilinear lens) we can multiply the focal 
length by 2.

So, maybe a Zuiko 16mm, or a Sigma 15 or 16mm, or 
a Zenitar 16mm, wouldn't be useless on an E-1?

Bernard
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