The Contax G 28mm Biogon was considered one of the best 28mm available on film, but suffers serious issues on digital due to sensor cover glass. Can a simple filter make the lens a competitive performer on Sony cameras? Find out below.
I have shot this lens for years on the Sony A7 and more recently with a PCX filter and then on a Kolari UT modded A7. Unless otherwise noted, all of the tests in this review were performed on a Sony A7RII with a reversed 1.5m PCX filter on the lens (Thanks again to Nehemiah for lending me the A7RII). Check captions on sample pictures to see what camera was used. Bonus: The Contax G 28mm Biogon is both Phillip and my favorite lens on aps-c cameras, so I will also add a second installment later reviewing the lens for aps-c provocatively titled How the A6000 + Contax G 28/2.8 is better than an RX1.
|Length||31mm (+ 3-6mm for PCX filter)|
|Close Focusing Distance from the sensor||50cm|
|Number of aperture blades||6|
More information in Zeiss’ official data sheet.
There is only one version of this lens. It comes in two colors: Titanium and black but black is much rarer (and more expensive).
The Carl Zeiss Contax G lens line was originally developed in the mid 90’s for the Contax G1 and it’s successor the Contax G2. Both are AF rangefinder cameras.
Adapting Contax G lenses to modern digital cameras comes with two challenges. Since the Contax G cameras have a rather short flange focal distance of just 29mm you cannot adapt them to DSLRs. The advantage of this short flange focal distance is that adapters for mirrorless systems are only about 11mm thick. The other problem is that the lenses do not have a focusing ring, just AF coupling so the adapter must provide some means to focus the lens.
There are two kinds of adapters, purely mechanical and electronic adapters.
Mechanical adapters are available for EOS M, Fuji X, M43 and Sony E-mount. They come with their own focusing ring. They range in price (affiliate link) from $25 to $140. I own the Kipon one (or possibly a cheap knockoff since I got it second hand for ~$30) and it works fine on all the lenses but the 90mm (which I had trouble focusing accurately at near distances with). Focus is a little rough and in the wrong (Nikon/Pentax) direction, but perfectly serviceable. I have heard good things about the Metabones and Fotodiox Pro adapters but I haven’t used them personally.
The Techart TA-GA3 adapter is very interesting because you can use AF with newer Sony E-mount cameras! AF with the Sony a7, a7r and a7s is unusable (very slow and unreliable) but with the newer cameras it works quite okay most of the time and gives you all the quickness and accuracy of a screw-drive AF lens on a dslr from 2005 (if you have used one of these you will know what I mean).
The AF experience is certainly not as smooth as with native lenses. The screw driven AF is rather loud and while it tracks small changes in focusing distances well it is quite slow to realize larger changes in focusing distance. Reliability was mediocre and not near the same level as the native lenses. It also fails when it is a bit darker in situations where native lenses still work reasonably well. I it found unusable, but then that performance level of AF is what drove me to manual focus in the first place, and some people seem to use it without major complaints. I changed to manual focusing which is realized with a small wheel at the 2 o’clock position. Manual focusing with this method works better than I would have expected but can be a bit fiddly at long distances.
The Techart TA-GA3 adapter sells for about $250 at ebay.com or amazon.com (affiliate links).
The Contax G 28/2.8 feels very nice and solid.
The barrel is made of aluminum.
All markings are engraved.
The Biogon is made in Japan.
I have disassembled the lens and while it is well engineered and made mostly of metal it does not seem as robustly constructed as typical Leica, Zeiss, and Cosina/Voigtländer manual focus rangefinder lenses. I would expect it to be more likely to develop problems due to a sudden impact than the previously mentioned manual focus rangefinder lenses.
Size, Weight and Handling
The Contax G 28mm is very well balanced on any Sony e-mount camera. At just 150g with a small diameter and the short adapter it is significantly smaller than the FE 28/2.0 (even with the added filter) or most adapted 28mm lenses (even many rangefinder 28mm lenses).
The Contax G lens line does not have a focusing rings. How you focus depends on the kind of adapter you use. I convert my lenses to m-mount with a real focus helicoid, but have found the Kipon adapter to be perfectly serviceable as well for non-moving subjects. Info on how I did my conversions can be found on this Fred Miranda thread. For info on AF with the Techart adapter, see the compatibility section above.
The aperture ring has full stops from f/2.8 to f/22 which register nicely but it isn’t too easy to select half-stops because the aperture ring doesn’t travels very far.
If you use the Techart adapter it won’t record the actual aperture you used. You can change the aperture in the camera but all this does is that it overexposes your image by as many stops as you have stopped down (e.g. f/5.6 will result in a 3 stops overexposed image).
The Contax Metal Hood GG-1 screws into the filter ring, has a little larger diameter than the lens, has 55mm filter threads, and it is about 10mm deep. It is made of aluminum and provides decent protection for the front of the lens.
The 46mm filter thread is made from metal.
The front of the lens does not rotate so polarizers are easy to use.
At f/2.8 vignetting is very strong and it remains quite strong as you stop down. According to Zeiss, small improvement in vignetting on stopping down is one consequence of Biogon lens designs. In addition to strong vignetting, there is also significant color shift towards the edge of the frame when used on cameras without backlit sensors (A7, A7R, A7S, A7II, A7SII). This color shift can be eliminated with a few clicks using the Lightroom Flat Field Plug-in once you have made a profile photo by shooting a uniformly illuminated white subject (like I did to generate the vignetting examples below). Correcting this level of vignetting will definitely increase noise towards the corners of the frame.
On my A7 the wide open vignetting is around 2.5 stops and never drops below 1.5 stops. The backlit sensors reduce the vignetting as well as the color shift. On the A7RII vignetting is only 2 stops wide open and falls to 1 stop by f/8.
In some cases I actually prefer the color shift effect:
The flare resistance of the Contax G 28/2.8 is good but not great. Under extreme conditions with the sun in the frame you can see some slight veiling flare which causes slight contrast loss, but contrast remains better than any other 28mm lens I have used in such situations (including the FE 28/2). In most situation contrast is great. Unfortunately, ghosting can also occur with the sun in the frame as well as long streaks of light.
Sony A7 Kolari UT | Carl Zeiss Contax G 28mm f/2.8 + 5m PCX | f/5.6
The Contax G 28/2.8 will also very occasionally show a smear of light in the image when the sun is just outside the frame.
At f/2.8 the Contax G 28mm has somewhat busy bokeh with more defined out of focus highlight discs towards the corners of the frame and significant business in the transition zone.
Stopped down to f/4.5 the bokeh is much smoother but you will clearly see the hexagonal shape of the aperture blades at f/5.6 and smaller.
Hint: larger images can be viewed by clicking on the image.
So all in all bokeh is not a strength of this lens, but it is better than many of other 28mm lenses. I tend to like it better at a distance than closeup.
The Carl Zeiss Contax G 28mm f/2.8 Biogon has negligible pincushion distortion on it’s own that can be corrected with -1 correction in Lightroom. Adding the reversed 1.5m PCX filter induces a little bit more pincushion distortion. This can be easily corrected using -3 correction in Lightroom.
There is some lateral CA, but it is small enough to be easily corrected with minimal loss in image quality.
Coma correction is not great wide open, but improves a great deal stopping down to f/4.
Even at f/2.8 coma is not so bat that it will ruin astro or night cityscapes.
Note, these coma tests were done on a Sony A7 with the Kolari UT mod and 5m PCX filter, not the A7RII with 1.5m PCX filter. I don’t believe there would be any significant difference, but I haven’t been able to test yet due to uncooperative weather.
A much bigger concern than coma for shooting cityscapes is sensor reflections when using the original A7. In my experience, sensor reflections seem to be worse when using wide angles designed for rangefinders such as this Biogon.
The Contax G 28mm has only 6 aperture blades so sun stars have only 6 rays and are not well defined. In fact, they remain more diffuse balls (which I personally prefer) than stars till f/8 or smaller.
When used on Sony cameras without a correction filter the Contax G 28mm shows extremely strong field curvature and astigmatism. The reversed 1.5m PCX filter does wonders to correct this though. See here for a comparison of the naked lens to different correction lens configurations on an A7. See here for a comparison of the lens on a stock A7RII with a reversed 1.5m PCX filter to the lens on a Kolari UT modded A7 with and without a 5m PCX filter. Finally see here for a direct comparison of the Contax G 28/2.8 to the Sony FE 28/2. Note: the linked comparisons use my (rather aggressive) print sharpening rather than the Adobe defaults used above.
f/2.8: Excellent contrast and sharpness in the center, the midframe region is good, but the edges and corners are considerably weaker.
f/4: The edges are excellent as well now, corners remain a little weaker.
f/5.6: The corners are very good as well now.
f/8: Excellent across the frame.
f/11: A little less sharp due to diffraction.
For landscape photography if you have a lot of detail into the corners you should stop down at least to f/5.6. For other applications with a three dimensional subject at any aperture you can put your focus anywhere in the frame without worrying about sharpness.
I have always really liked the colors I get with Zeiss Contax lenses (as well as Minolta and Leica lenses) and have generally been unable to replicate them in post using lenses from other brands. Here is how the colors of the Contax G 28/2.8 Biogon (left) compare to those of the FE 28/2.8 (right) at f/5.6 (shot on the Kolari UT A7):
It seems clear from this comparison that the differences in color between the Zeiss and Sony lens are actually quite small, which goes against my impressions from real world shooting with both lenses. Looking closer at the images does show that there is a little more fine differences in brightness within each color square with the Zeiss lens. Perhaps it is actually better high frequency contrast with the Zeiss lens that is contributing to my impression of better color by making subtle tonal gradations more visible (or maybe it’s just the placebo effect).
The differences is more noticeable at f/2.8 (all these shots were taken at the mfd of the FE 28 where neither lens should really be at it’s best):
Sony FE 28/2: The Sony is a stop faster at f/2 with fast autofocus, smoother bokeh, and less ghosting in extreme conditions. Downsides are worse build quality, lower contrast, and strong distortion which needs to be corrected as well as the higher price.
Voigtlander 28/2 VM: A modern manual lens which is more expensive, bigger, and heavier, but faster with very good sharpness from wide open, good flare resistance and nicer sunstars. It has some issues with the Sony a7’s thick sensor stack that can’t be easily corrected with filters, so it is not as good for landscape.
Pentax K 28/3.5: I have not shot this lens, but it is Phillip’s favorite legacy 28mm for landscapes. It appears to have better flare resistance and substantially less vignetting. It is much larger though and probably slightly lower in contrast.
Zeiss Distagon 28/2.8: The Contax/Yashica Zeiss is SLR contemporary of the Contax G. It is much bigger and has similar contrast and flare resistance. The Contax G Biogon (+ PCX filter) has slightly better corners and lower distortion, while the Contax/Yashica Distagon has slightly better midzone performance at large aperture and much better vignetting performance.
Nikkor 28/2.8 AIS: Unlike the rest of the legacy lenses listed above, the Nikkor has a floating element for better closeup performance. It’s bigger and not as sharp in the corners near infinity (though not far behind), but has better bokeh and very good closeup performance.
Minolta MD 28/2: This is the only other 28mm I have kept. It lacks the small size, contrast, flare resistance, and corner sharpness of the Contax G. It does have a lower contrast look wide open that I enjoy for people and bokeh though and is a solid performer for landscape.
The Zeiss Contax G 28/2.8 Biogon is one of the smallest FF 28mm lenses that can be mounted on e-mount cameras. It also has very good performance across the frame from wide open (with the PCX filter). No matter the aperture or location in the frame the lens has incredible bite at the focus point. It outperforms the native FE 28mm and all of the legacy SLR 28mm lenses I’ve tested in terms of sharpness and contrast at large apertures. Unfortunately, The ergonomics are substantially behind even that of your average legacy manual focus lens. In addition, vignetting and and flare resistance are well below the level of modern native lenses.
If you are looking for a landscape or street shooting 28mm and don’t mind pre-focusing or slow manual focusing the Biogon is a tough lens to beat, particularly for the price. For those who demand fast focusing, good sunstars, or imperviousness to flare the Biogon’s performance represents a serious compromise.
All in all the Contax G 28/2.8 Biogon is an excellent performer from wide open with a good price to performance ratio and fantastically compact size. Adapter focusing is a serious compromise though that will turn off many users, while using PCX filters adds additional complexity and cost.
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More Sample Images
Additional samples are available here: Contax G 28/2.8 set on flickr.
All images are processed in Lightroom from Raw.
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