CONTAX G BIOGON T* 28mm(AVENON)

Kyocera CONTAX G mount BIOGON 28mm review and photo examples.

Table of contents

Photo example
CONTAX G1 +FUJIFILM TREBI100C
Film scanning was done with a Minolta DiMAGE Scan Multi PRO.

Leica M-P +Lens mount changed from CONTAX G to Leica M mount with AVENON.

SONY α7SII

Review
The BIOGON 28mm lens for the Kyocera/Contax G series is a wide-angle lens released at the same time as the CONTAX G1.
It has a nearly symmetrical lens construction with three elements in the front group and four elements in the rear group, which is unique to rangefinder cameras, where the rear lens element is hidden in the film chamber. Because of its wide-angle focal length of 28mm, the lens was rarely out of focus on film, even when shooting with the Contax G1’s AF system, as long as the lens was slightly stopped down.
With a 35mm full-size digital camera, there is often no problem, but depending on the lighting conditions, color casts may occur in the periphery or purple fringing may appear around trees, although it is unclear whether this is due to the older design or the lens coating.
For cameras with APS-C size sensors, the focal length of 42mm is a semi-standard focal length, making the lens easy to use. It is easy to use and does not have the negative effects of the 35mm full-size sensor mentioned above.
This lens was also planned to be converted to M mount when I got rid of my CONTAX G1/G1, but I obtained a used CONTAX G 28mm converted to Leica M mount by AVENON (AVENON), so it is still with me without being converted.
AVENON Koki (henceforth AVENON), the company that converted this lens, is no longer in existence, but in the past it has released original Leica L39 screw mount lenses, the AVENON-SUPER-WIDE 21mm, the AVENON 28mm, and a pinhole lens.
AVENON has been offering a service to convert 28mm lenses with CONTAX G mount to M mount to work with Leica M camera rangefinders. 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 sad part of the black body modification is that the aperture range ring is silver. If it had a black plate with white letters, it would be a more complete design.
The helicoid converted to manual focus is very smooth and has a moderate weight, so there is no problem at all in focusing.
The original aperture ring is used as is, and it clicks to a stop at each click stop.
The aperture blades are the same as the original 6 blades.
The minimum focusing distance of the modified lens was changed from 0.5m to 0.8m. This is thought to be because the time when this lens was modified was the heyday of film cameras and there were no mirrorless cameras, so there was no point in extending the lens to a distance that was not linked to the distance meter of the Leica M model. The reason why the lens could not be moved closer than 0.7m, the limit of the Leica M’s rangefinder linkage, may have been due to concerns about parallax at 0.7m, or lack of focusing accuracy at close-up.
Unlike the total replacement of the lens barrel by Ms-optics (Miyazaki Kogaku), Avenon’s modification is characterized by the fact that only the mount was replaced with the Leica L39’s rangefinder-coupled mount while maintaining the original lens barrel.

Specification

NameHOLOGONBIOGONBIOGONPLANARPLANARSONNARVARIO SONNAR
Focal length(mm)16.5212835459035-70
Max aperture8(fixed)2.822.83.5-5.6
Min aperture16(Attached filter)221622
Lens Construction5elements in 3groups9elements in 7groups7elements in 5groups6eleme0nts in 4group5elements in 4groups13elements in 8groups
Min distance(m)0.30.50.5
0.8(*2)←
0.51.0
Lens length(mm)1135.530.531.538.563.054.0
Max diameter(mm)57595656565660
Filter size(mm)
Dedicated ND filters are available.
Changes to f/8 > 16 to alleviate peripheral light attenuation.
554646464646
Weight(g)120200150160190240290
Weight(g)
M-mount
124151194
(222)*1
115161219
(259)*1
Release date1994199619941996199419941999
*1:Hoo +Filter
*2: Minimum focus distance of AVENON modified lens
CONTAX G用ビオゴン 28mmレンズ構成図(レンズマニュアルの記載図をスキャンしトレース)

Update

  • 2024.01.22:Update
  • 2022.04.10:First post

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