AF Biogon T* 21 +CONTAX G1,G2

A review and sample photos taken using the CONTAX G BIOGON 21 with the CONTAX G1.

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Gallery
Review
1. About
2. Usage
3. Summary
Specification
Reference links
Update history
Affiliate link

Gallery

The sample photos were taken with a CONTAX G1 camera body and KODAK E100G film.
The film was scanned with a COOLSCAN 5 ED.

1．Overview

The CONTAX G BIOGON 21mm is an autofocus lens for the CONTAX G released in 1996.

Its main specifications are a focal length of 21mm, maximum aperture of F=2.8, and a minimum shooting distance of 0.5m.

This wide-angle lens was released along with the CONTAX G2, and in order to use this lens with the CONTAX G1, you will need to apply a ROM update service to your camera.
If you are buying a second-hand camera, make sure that there is a green label on the film chamber.

Third-party lens hood

The hood in the photo is a square lens hood that I purchased when I was using the original G Biogon 21mm.

It has a screw-in stopper, and can be attached to any lens with a diameter of 57mm. The tip of the original G Biogon is 57mm, so it is thought that this was made to match that.

As mentioned above, when focusing the lens, the front part of the lens barrel of the original G Biogon moves in a straight line only, not rotates, so a square hood like this hood can be used.

In addition, the outer diameter of the genuine Contax 55mm lens filter is 57mm to match the Biogon 21mm, so if the lens has a 55mm filter thread, this hood can be attached via this Contax 55mm filter.

2．Usability

The CONTAX G BIOGON 21mm was used with a CONTAX G1 with an updated ROM.

Focusing is possible with autofocus, just like with other G-mount lenses. However, the CONTAX G1 and G2 viewfinders do not cover the 21mm focal length range, so the composition is decided with an external viewfinder.

The CONTAX G viewfinder does not show the focus position, so the general shooting style is to decide the composition with the external viewfinder and leave the focus to the camera.

Using manual focus is troublesome, as there is no distance display on the lens barrel, so you rely on the rangefinder displayed in the camera viewfinder to adjust the shooting distance with the focus ring on the top of the camera, and then decide the composition with the external viewfinder.

Under clear skies, I shot with the aperture stopped down to about F5.6, so the autofocus rarely focused on a place that was far from the intended focus position. Therefore, I rarely used the troublesome manual focus mentioned above.

The Biogon 21mm is designed so that the rear lens goes inside the camera, so when it is attached to a mirrorless camera via a mount adapter, the metering may be unreliable. However, the TTL (Through the Lens) actual aperture metering (center-weighted average metering) of the original CONTAX G series body determined the exposure with satisfactory accuracy.

When using the G Biogon 21mm with a CONTAX G, vignetting may be noticeable when shooting blue skies.
In close-up shots, there is no distortion of the image at the periphery, and a uniform image can be obtained throughout the film.

Since a dedicated hood is not provided, a square hood made by a third party was used. Since the original Biogon G 21mm is an inner focus, the front frame does not rotate, so a square hood fixed to the front frame like this can be used.

The lens modified with Ms-optics rotates the front frame of the lens barrel when focusing, so this square hood can no longer be used. Examples of lenses modified with Ms-optics are uploaded using digital cameras.

3．Summary

There are four 21mm focal length lenses for 35mm format bearing the BIOGON name. The CONTAX G Biogon 21mm is the only autofocus lens, while the remaining three are manual focus lenses.

The CONTAX G Biogon 21mm’s direct competitor is the Biogon 21mm ZM, designed by Carl Zeiss and manufactured by Cosina, which has the same maximum aperture. The Biogon 21mm ZM is a modern lens with a lens configuration similar to the retrofocus DISTAGON, with the rear lens relatively far from the film plane.

The lens construction diagrams are quoted from each company’s materials, and the sizes have been adjusted by us, so they are not exact.

The Carl Zeiss C Biogon 21mm ZM is a lens specification that pays homage to the oldest Contarex Biogon 21mm. However, the lens configuration is completely different, with a lens design that has less protrusion of the rear lens, making it easier to handle with modern cameras.

Finally, the Contarex Biogon 21mm is an even older Biogon 21mm that was sold for the Contarex mount SLR camera. Because the rear lens protrudes significantly, it could only be used with cameras equipped with a mirror lock-up mechanism.

Therefore, before mirrorless cameras became popular, this lens had few uses, and adapters were sold that convert the Contarex mount to a Leica M mount for use with other cameras; they only change the shape and cannot be linked to the rangefinder of a Leica M rangefinder camera. Using this, you can use this lens with M-type Leica cameras, although focusing must be done by eye.

However, because the lens guard on the rear lens is large, it is safer for the camera if you remove it before using the lens. However, you need to be careful not to touch the rear lens when removing the lens, etc.

Specification

項目	BIOGON G	BIOGON ZM	C BIOGON ZM	CONTAREX BIOGON
焦点距離(mm)	21	21	21	21
最大絞り	2.8	2.8	4.5	4.5
最小絞り	22	22	22	22
絞り羽根	7	10	10	8
レンズ構成	7群9枚	7群9枚	6群8枚	5群8枚
最短撮影距離(m)	0.5	0.5	0.5	0.9
レンズ長(mm)	35.5	51	31	35
レンズ最大径(mm)	59	53	53	55
フィルター径(mm)	55	46	46	49
重量(g)	200	280	190	271 レンズのみ
フード	サードパーティ	Carl Zeiss レンズシェード 21mm/25mm	Carl Zeiss レンズシェード 21mm/25mm	専用バヨネットフード
マウント	CONTAX-G	ライカM	ライカM	ライカM
製造年	1996年	2005.10.29	2010.1.17	1958