CONTAX G BIOGON T* 28mm(AVENON)

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

Table of contents

Gallery

写真作例の撮影は、Leica M-P typ 240を使用

写真作例の撮影は、SONY α7SIIを使用

Review

The Biogon 28mm F2.8 is an autofocus lens released by Kyocera along with the Contax G1 in 1994. Here, we introduce a lens that was modified by AVENON Optical Co., Ltd. to Leica M mount (rangefinder camera rangefinder linkage).

AVENON Optical Co., Ltd. (hereinafter AVENON), which modified this lens, was founded around 1982 and is no longer in existence as of 2024. However, in the past, they released two original lenses for the Leica L39 screw mount, AVENON-SUPER-WIDE 21mm and AVENON 28mm, as well as a Leica M mount pinhole lens, which are still traded on the second-hand market.

AVENON offered a service to convert CONTAX G mount 28mm lenses to M mount and modify them to link with Leica M type camera rangefinders. This lens is one of those modified lenses.

The characteristic of AVENON modified lenses is that they add a Leica rangefinder linkage mechanism to the G lens while using the original lens barrel almost as it is. Therefore, the aperture ring is the same as the original and stops with a satisfying click every click stop. The aperture blades are also the same as the original 6 blades.

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 one of the reasons for this is that there was little point in extending the lens to a point where it was not linked to the Leica M-type rangefinder. Also, the reason why it cannot get as close as 0.7m, the limit of rangefinder linkage for the Leica M-type, is thought to be due to concerns about the deviation in the shooting results due to parallax at 0.7m, or the lack of focus accuracy when close up.

Ms-optics, which I requested to add other Contax G mount lenses, also modified the G Biogon 28mm, but since I got this lens first, I did not request a modification for this lens.

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 version. The sad thing about the black Biogon 28mm is that the aperture range ring is silver and doesn’t match the black body. If this part was a black plate with white text, I feel that the design would be more complete. The helicoid modified for manual focus is very smooth and has a moderate weight, so there is no problem with focusing.

The lens itself has a lens configuration 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. This reduces distortion of the subject when shooting, and allows you to comfortably shoot lattice-shaped objects. However, the lens configuration and coating do not take into account the digital age, and depending on the camera sensor used, color casts may occur in the peripheral areas of the captured image and purple fringes may appear on the edges of the subject.

The BIOGON ZM 28mm was released in 2005 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 light incident on the film was not an issue and it was possible to move the rear lens closer to the film surface. ZM lenses were produced in an era when digital compatibility had to be considered, and the design took the angle of light incident into account to some extent, which is why the lens length is thought to be a little longer.

Specification and Competitor

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