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K 8.4/2.8 Fish-Eye

General Description

For a long time it was thought that this lens existed only as a prototype, but in early 2004 one lens was offered for auction at Yahoo Japan. The lens appears to be essentially identical to the prototype "smc PENTAX BIRDS-EYE 1:2.8 8.4 mm", but it carries the name "smc PENTAX FISH-EYE 1:2.8 8.4 mm". The lens shown for auction did not have the rubber ring between the aperture ring and the mount (visible on the prototype lens), but I think that it was because it had fallen off and not due to a production redesign.

Something very interesting about this lens is that it lacks a focusing ring! But at this short focal length, the depth of field is so huge, so no wonder...

The optical diagram and size information comes from this paper. Apparently the lens was designe by Satoru for Asahi Optical and is sepecified in Japanese patent JP60-153018.

Product Information
Exact Namesmc PENTAX FISH-EYE 1:2.8 8.4 mm
Years of ProductionPhotokina 1982
Availabilityonce in a lifetime
Catalog Numberunknown
Sold with Hood
Sold with Caseunknown

Technical Specifications

Optical Formula10 elements in 7 groups
Aperture Rangef/2.8 ~ f/11
Number of Aperture Bladesunknown
Minimum Focusing Distancelens has no focusing ring
Maximum Magnificationdepends on the lens-to-subject distance
Special Featuresfish-eye lens
Front-Filter Threadno
Gelatine-Filter Holderyes
Maximum Diameter81.6 mm
Length139.7 mm
Special Featuresmanual diaphragm
Fitting Hood(s)unknown
Fitting Case(s)unknown