CONTAX G BIOGON T* 21mm(Ms-optics)

Review and Photo example of Kyocera CONTAX G mount 21mm f/2.8.

Gallery

CONTAX G1 +KODAK E100G
Film scanning was done with a Minolta DiMAGE Scan Multi PRO.

LEICA M typ240

LEICA M8/R-D1

Review

The BIOGON 21mm for Kyocera/Contax G series is a wide angle lens released at the same time as the CONTAX G2.
The viewfinder is not so good, and the latest COSINA/Zeiss or LEICA 21mm viewfinder provides a clearer view.
As shown in the specifications below, the lens configuration is a symmetrical Biogon type, with the rear element close to the sensor (film) surface, so color casts may occur in the periphery of some digital camera models (color casts can be seen in this example with the LEICA M typ240).
There are five possible ways to deal with color cast, and I personally recommend shooting with film.

Enjoy the results of shooting in monochrome
Boldly drop the peripheral areas in the case of color
Choose a color subject where the cast will not stand out (give up blue sky)
Shoot on film
Choose a camera with a low color cast

As for color cast, the retrofocus Elmarit 21mm does not cause this phenomenon even with the same focal length of 21mm. As with the Super Angulon, there is an impression that the lens is a little difficult to use as long as it is used with Leica M9/M/M10 and other cameras.
When used with the EPSON R-D1 and LEICA M8, which have smaller sensor sizes, the problematic peripheral areas are cut off, making the lens easy to handle even though it is not a 21mm wide-angle lens.
This lens has excellent backlight resistance, probably due to its good coating, and even in situations where sunlight enters the subject, flare and ghosting are rarely encountered.

I used this lens with the Contax G1/G2, but after selling the G1/G2, I had the lens converted by MS-Optics (Miyazaki Kogaku) to work with the Leica M mount distance meter. The converted lens uses a common helicoid for 21mm called MS-21.
If this lens is to be used with the CONTAX G1, the camera must be updated. Used G1s are sometimes sold with an un-updated camera, which does not allow the use of the BIOGON 21mm and PLANAR 35mm. Those with a green label on the film chamber are considered updated.
The original CONTAX G BIOGON 21mm has inner focus and the tip of the lens does not rotate, but the modified lens barrel itself rotates when focusing, so the lens tip also rotates.
The modified BIOGON 21mm lens does not have an aperture click stop, which is a specification of MS-Optics lenses.
The aperture ring is positioned at the narrow end of the lens barrel, so the aperture value does not change unintentionally when the lens is put in the bag.
The Planar 45mm lens modified by Ms-optics has an aperture ring at the front of the lens, which can cause problems when the aperture value is unintentionally changed.
Some mirrorless cameras have mount adapters for the G mount, but if you have converted it to Leica M mount, you can use it on more mirrorless cameras.
This may be due to a lack of research, but while some manufacturers offer modified lenses for 28mm, 35mm, and 45mm, the 21mm M-mount modification should only be available from Ms-optics.

Third party lens hood

A non-original rectangular lens hood purchased when I was using the original Biogon 21mm for G.
It has a screw-in stopper and can be attached to any 57mm diameter lens. The original Biogon for G had a 57mm lens tip, so it is thought that this hood was designed to fit this lens.
Since the front part of the lens barrel of the original Biogon for G does not rotate when the lens is focused (inner focus), a rectangular hood like this hood can be used.
Also, the outer diameter of the genuine CONTAX 55mm lens filter is 57mm to match the Biogon 21mm, and if the lens has a 55mm filter thread, this hood can be attached via this 55mm filter.
However, when the focus ring of the modified BIOGON 21mm is turned, the front part of the lens rotates, and this rectangular hood also rotates with it. Since it is not practical to change the position of the lens hood after fixing the focus, this hood is not used. It is a pity, because I like the appearance of the hood very much and would like to use it.

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	←	←	←	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