CONTAX G BIOGON T* 28mm(AVENON)

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

Table of contents

Gallery

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

Biogon 28mm is an autofocus lens for Kyocera/Contax G series, and the one introduced here is the M-mount version modified by Ms-optics.

The lens configuration is unique to rangefinder cameras, where the rear lens goes into the film chamber, and is almost symmetrical with three elements in the front group and four in the rear group. Because it has a wide focal length of 28mm, it is a lens that rarely goes out of focus with film, even when shooting with AF on the CONTAX G1, as long as you stop down a little.

In the case of 35mm full-frame digital, there are often no problems, but depending on how the light is inserted, color casts may occur in the peripheral areas, and purple fringes may appear around trees, although it is unclear whether this is due to the old design or lens coating.

In the case of cameras with APS-C size sensors, the focal length is 42mm, which is the focal length of a semi-standard lens, making it a lens that is easy to use. There is no negative effect that occurs with the 35mm full-frame sensor mentioned above. I had planned to convert this lens to M mount when I got rid of my CONTAX G1/G1, but I got a second-hand CONTAX G 28mm converted to Leica M mount by AVENON, so I still have it unmodified.

AVENON Optical Co., Ltd. (hereafter AVENON), which converted this lens, is no longer in existence, but in the past they released original lenses for the Leica L39 screw mount, AVENON-SUPER-WIDE 21mm, AVENON 28mm, pinhole lenses, etc.
AVENON offered a service to convert CONTAX G mount 28mm lenses to M mount and modify them to work with Leica M-type camera rangefinders. This lens is one of those modified lenses.

Before I got the black Biogon 28mm in the photo, I had a champagne gold version, but I sold it when I got the black one. The sad thing about the black body conversion is that the aperture range ring is silver. I think the design would be more complete if this was a black plate with white lettering.
The helicoid modified for manual focus is very smooth and has a moderate weight, so there is no problem with focusing.

The aperture ring is the same as the original, and it stops with a satisfying click every click stop.

The aperture blades are the same as the original six-blade design.

The minimum shooting distance of the modified lens has been changed from 0.5m to 0.8m. This lens was modified during the heyday of film cameras and the time when mirrorless cameras did not exist, so it is thought that there was no point in extending the lens to a point where it was not linked to the Leica M-type rangefinder. The reason why it cannot get as close as the Leica M-type rangefinder linkage limit of 0.7m is thought to be due to concerns about the deviation in the shooting results due to parallax at 0.7m, or concerns about insufficient focus accuracy when shooting close up.

Avenon’s modification is different from the Ms-optics (Miyazaki Optical) total lens barrel replacement method, in that it maintains the original lens barrel and only replaces the mount with the Leica L39 rangefinder linkage mount.

In 2005, the BIOGON ZM 28mm was released as a combination of COSINA and Zeiss. This lens has a lens length of 37mm from the mount surface, while this lens has a lens length of 31mm from the mount surface, which is more compact, but the flange back of the G mount is 29mm, which is 1.2mm longer than the Leica M mount’s 27.8mm, so if you convert it to an M mount like this lens, the lens length will be 32.2mm.

Even so, this lens is more compact than the BIOGON ZM 28mm, but this is also thought to be due to the era. When the Contax G Biogon 28mm was released, it was only necessary to consider compatibility with film, so the angle of incident light on the film was not an issue and it was possible to move the rear lens closer to the film surface. ZM lenses were released in an era when digital compatibility had to be considered, and the lens length was thought to be a little longer because the angle of incident light was taken into consideration to some extent when designing them.

Specification

Name	HOLOGON	BIOGON	BIOGON	PLANAR	PLANAR	SONNAR	VARIO SONNAR
Focal length(mm)	16.5	21	28	35	45	90	35-70
Max aperture	8(fixed)	2.8	←	2	←	2.8	3.5-5.6
Min aperture	16(Attached filter)	22	←	16	←	22	←
Lens Construction	5elements in 3groups	9elements in 7groups	7elements in 5groups	←	6eleme0nts in 4group	5elements in 4groups	13elements in 8groups
Min distance(m)	0.3	0.5	0.5 0.8(*2)←	0.5	←	1.0	←
Lens length(mm)	11	35.5	30.5	31.5	38.5	63.0	54.0
Max diameter(mm)	57	59	56	56	56	56	60
Filter size(mm)	– Dedicated ND filters are available. Changes to f/8 > 16 to alleviate peripheral light attenuation.	55	46	46	46	46	46
Weight(g)	120	200	150	160	190	240	290
Weight(g) M-mount	124	151	194 (222)*1	115	161	219 (259)*1	–
Release date	1994	1996	1994	1996	1994	1994	1999