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

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

Table of contents


  • Film scanning was done with a Minolta DiMAGE Scan Multi PRO.
  • LEICA M typ240
  • LEICA M8/R-D1


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.


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)
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.
Release date1994199619941996199419941999
*1:Hoo +Filter
Biogon 21mm lens configuration for CONTAX G (scanned and traced from the lens manual)

Reference links


  • 2024.01.21:Modify the article
  • 2022.03.07:first article

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