Verzeichnung

[hofsethpaul]

Fisheye lenses are supposed to project a 3D scene into a 2d plane in a particular way. This entails unvoidable bending of straight lines.Wide angles should just distort perpsective, making closer objects larger.With digital recording rather than film, manufacturers can save money or prioritize correcting other optical faults, skip this quality measure and use cheaper electronic correction rather than making precise optics.

In my limited understanding of optics, wide angles have a physical disadvantage in having to project light onto a plane which will decrease light intensity by the cosine of the angle to the plane of the incoming light just like any dimension projected at an angle. Although there are optical tricks to reduce this geometrical vignetting.

Years ago I used the Zeiss Hologon on my M3 with its standard "verlauffilter" ( concentrically graduated shades that compensated perfectly for the light loss by darkening from the centre and outwards). That lens had straight lines, but gave remarkably "distorted" pererspective. Eventually I gave up using it as I did not perceive it as as sharp and contrasty enough all over the field.

Fisheyes can be straightened by a "defish" program. I agreed with the Danish programmer to help provide a profile of my Minolta-Leitz fisheye for his library, this entailed making several snaps of the same scene (at fixed angles of 12 degrees apart). After an unsuccesful attempt at doing this freehand ,my variable panorotator tripod head managed the required exactness, Too much time consuming work to post examples here, but if you want straight lines from your fisheye I recommend using his library where most available fisheyes are listed.

p.