This is a record of using a Kyocera CONTAX G mount 28mm f/2.8 lens converted by AVENON to Leica M mount with a Leica M digital camera.

Table of contents

The company that converted this lens, Avenon Koki (hereafter referred to as Avenon), no longer exists, but in the past it has released original Leica L39 screw mount lenses, including the AVENON-SUPER-WIDE 21mm, AVENON 28mm, and pinhole lenses.
Avenon has been offering a service to convert CONTAX-G mount lenses to M mount to work with the Leica M camera rangefinder. This lens is one of the converted lenses.
Before I got the black Biogon 28mm lens in the photo, I had a champagne gold version, which I sold when I got the black one.
The helicoid converted to manual focus is very smooth and there is no problem at all in focusing.
The aperture ring stops with a nice click at each click stop just like the original.
The aperture blades are the same as the original 6 blades.
It is unclear whether it is due to the old design or the lens coating, but depending on the position of the sunlight, color casts may occur in the periphery and fringing may appear around trees.

The change in minimum focusing distance (0.5m > 0.8m) is thought to be due to the fact that the lens was modified at a time when film cameras were in their heyday and mirrorless cameras were not available, so there was no point in extending the lens to a point where it would not work with the Leica M-type rangefinder. The reason for not being able to get as close as the 0.7m rangefinder-linked limit of the Leica M may have been a concern about parallax at 0.7m, or a concern about insufficient focusing accuracy at close-up.

Lens features and specification
AF lens for CONTAX G converted to Leica M mount (distance meter linked) by Avenon.
Unlike the total lens barrel replacement method of Ms-optics (Miyazaki Kogaku), this converted lens features the replacement of only the mount part with the Leica L39 rangefinder mount while maintaining the original lens barrel.
The minimum focusing distance was changed from the original 0.5m to 0.8m.

focal length(mm)28
Maximum aperture2.8
Minimum aperture16
Lens configuration5groups 8elements
Minimum distance(m)0.8Linked to Leica M camera rangefinder from 0.8m to infinity
Lens length(mm)31.2Distance from lens tip to lens mount.
Lens max diameter(mm)57.7
Filter diameter(mm)46
Weight(g)194222g(Total weight of L-M adapter, hood, filters, and lens)
Diagram of Biogon 28mm lens for CONTAX G (scanned and traced from the lens manual)
Champagne gold BIOGON-G 28mm



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