A more technical view on the Zeiss Contax G 90/2.8 and Techart AF adapter

Recent followers of my blog might have already noticed that in the last few weeks, I have developed a certain addiction to the Contax G 90/2.8 lens on my Sony A7 II. Now I own the lens for around two years already, but only recently got the A7 II – and in contrast to my previous A7R I only now can make full use of the Techart AF adapter that I got together with the lens.

Zeiss Contax G 90/2.8 on A7 II
Zeiss Contax G 90/2.8 on A7 II

The Zeiss Contax G 90/2.8 is a super high-quality lens that was introduced – together with the whole Contax G system – in 1994 and produced until 2005 when the system was dropped. The build and finish are close to impeccable. It does not have internal focusing – the front lens barrel will extend when focussing (but of course not rotate, good if you want to use a polarizing filter). But every part does feel extremely solid. The only piece of plastic on the outside is the black part at the rear that covers the focusing screw. (The AF motor is in the camera body or AF adapter, not the lens itself. Similar to old Nikon AF lenses.) The lens itself is only 190 grams. The Techart AF adapter feels very well made and solid as well. The weight of the adapter might be another 100 grams.

There is not a lot of talk about the lenses and that Techart AF adapter in the net – mainly it was covered by some review websites and photo bloggers at the time it was presented to the market and seen as a “novelty” but I have the impression that not many folks are really using them on a daily base now.

Note about the pictures in this blog entry

I provide some pictorial results here. Click on most of the pictures below and they will download in 100% (6000×4000 pixels out of the Sony A7 II) if you want. But I ask you do so only for your personal reference as they are copyrighted as is every of my photos.

All these are converted in Lightroom. I did adjust white balance and color fidelity to my likings. But I did not adjust vignetting. Color corrections (CA) were only applied to some of these shots where mentioned. Sharpness parameters are always the default “landscape” setting of Lightroom.

Autumn colors. (Contax G90 at f/2.8)
Autumn colors. Contax G90 at f/2.8. (Click image to see full resolution.)

1. Do you want AF? It’s definitely a matter of taste – but I want it!

Before talking about the adapter and lens itself, I’ll start with a short explanation why I wanted them in the first place. For me, having AF is crucial in really enjoying my gear because I find manual focussing just a bit destracting when I shoot any EVF camera, even though it definitely is super precise and perfect with all the digital helps (loupe view, focus peaking etc.). But all those helps just take me away from the basic, uncluttered view on my subject. This, of course, might only be me. On a tripod, things are very different: Here I don’t find it distracting at all to first compose the shot, then zoom in to achieve critical focus. On a rangefinder or SLR camera, I also enjoy manual focusing much more, but I don’t use any of these any more for other reasons.

As always, “your mileage may vary”. But I mention this to make my point clear why I so much support the idea of having AF in all frequently used lenses.

2. Do you like classic lenses? Again, a matter of taste … as the Sony FE system offers many modern choices by now:

As of late 2016, we have a choice of nice AF lenses even for the Sony FE system. Only considering primes, let’s have a look:

  • 14/1.8 Samyang
  • 18/2.8 Zeiss Batis
  • 25/2.0 Zeiss Batis
  • 28/2 Sony
  • 35/2.8 Sony Zeiss
  • 35/1.4 Sony Zeiss
  • 50/2.8 Sony Macro
  • 50/1.8 Sony
  • 50/1.4 Sony Zeiss
  • 50/1.4 Samyang
  • 55/1.8 Sony Zeiss
  • 85/1.8 Zeiss Batis
  • 85/1.4 Sony G
  • 90/2.8 Sony Macro

Quite a few! Yet still, there might be reasons why you want to switch to other lenses, and then you’re normally in for manual focusing. For example if you consider a lens to big, or frankly just too expensive. This might apply to the famed focal lenght of 35mm – there definitely is a gap between the very good, tiny, but slooow AF Sony 35/2.8 and the fast but huge 1.000+ EUR AF Sony Zeiss 35/1.4. Similar with 85/90 mm: You have the beautiful yet big and 1.000+ Zeiss Batis AF 85/1.8 or the even bigger, even more expensive AF 85/1.4 Sony G …

Sony A7 II with 35/2.8 + 50/1.8 + 90/2.8.
Sony A7 II with 35/2.8 + 50/1.8 + 90/2.8. This shows the compactness of the Contax lens.

Classic lenses provide such an ample choice of vintage / age / quality / price range / speed etc. that I am sure everyone would find a classic that will suit every personal taste perfectly. But what if you insist of using AF? First there are the Canon EF lenses with e.g. a Metabones adapter – but these combos tend to be somewhat bulky though on the A7 bodies, so I am personally not interested.

If you want to stick to classic rangefinder lenses (meaning much, much slimmer adapters and often also smaller lenses itself) and want AF, then say hi to the Techart AF adapter!  And yes, I think a lens like the Contax G 90/2.8 is a very sensible classic choice: It’s much smaller than the Batis 85/1.8, much cheaper (even including the “expensive” adapter), and both optics and build quality are very, very good.

But one thing you should be aware of is that even with 90mm on a full frame 24x36mm digital camera, this f/2.8 lens does not give you the super extreme shallow depth of focus that you probably might expect! So if you want “more” shallowness or a more soft bokeh, you should go for a f/1.8 or even f/1.4 lens:

Autumn leaves. (Contax G90 at f/2.8)
Autumn leaves. Contax G90 at f/2.8. (Click image to see full resolution.)

3 = 1+2 … welcome the Techart AF adapter

As of late 2016, Techart provides a selection of AF adapters. I think they started their idea of providing AF through the adapter with the Contax G adapter though. See this early video from late 2012 on youtube. The adapter itself and also the firmware have gone through numerous updates since then, and so I can only really comment on what I am using by now, late 2016. Actually, I got my adapter used from Roberto who did a review on the same sample that I use right now, when he first bought it in 2014. Read it here.

But again, between 2014 and 2016 there have been more firmware updates. Also Sony changed from the original A7 / A7R series to the newer A7 II / A7R II series, adding built-in stabilisation. That’s a treat, especially as there is electronic communication between the Contax G lenses through the adapter to the body, so you don’t need to fiddle in any menu settings if you use these lenses!

Techart developed another new adapter in 2016 that supports even Leica M lenses – and if you then stack adapters on top of that one, you can basically fit any lens, even Leica screw mounts or SLR lenses, and get AF. But I like my Contax G adapter. It’s somewhat a “cleaner” solution. Also these Contax lenses are little and somewhat inexpensive gems. And they are native AF lenses, after all – in contrast to shifting a lens mount forth and back which means a lot of weight moved. Last not least, you have the electronic communication of focal length, as stated above.

4. How well does it work in practice?

That’s where the controversy starts. Some reports are enthusiastic. Others sceptical. It seems some folks got severely annoyed by unconstistent focus results or even software crashes when using their camera with the Techart adapters.

For me, it’s basically just point and shoot as with every lens to get results like this. Very easy, very unobtrusive over all:

Autumn colors. (Contax G90 at f/4 or f/5.6; I forgot.)
Autumn colors. (Contax G90 at f/4 or f/5.6; I forgot.)

Here’s an excellent and recent (March 2016) review of the Contax G 90/2.8 on an A7 series camera, also mentioning the Techart adapter, by Phillip Reeve. As to the adapter, he concludes … “AF with the Techart adapter works okay sometimes but I wouldn’t want to rely on it and it is noisy.”

I understand that conclusion. Yes the AF adapter is definitely not perfect like a native lens. However, after using it now for a while, I did in fact add the G  90/2.8 lens and this adapter to my “daily” used gear. I use them without any hesitation and enjoy it so much I am now considering to add the other Contax G lenses that work well on the Sony digital sensor (the G 45/2 and G 35/2) as well.

5. The shortcomings, in a nutshell:

  • AF is only accurate when you manually open the lens’ aperture (but that also applies to native Sony lenses! Read below, section 8 …)
  • AF uses the phase detection system only, and that means you’re back to all the possible errors (especially: front / back focussing issus) that are inherent to that system
  • Due to that, AF is less accurate in some situations then a sensor based AF
  • In certain situations, it might not lock focus where a native lens probably still would
  • AF might be slower than a native lens (but I can’t really comment, I am completely not a sports or action photographer in any way!)
  • The “user interface” is really weird if you want to change any settings or update firmware etc.

Sounds bad? Well I used a Canon 7D, 1Ds2 and 5D2 body with 50/1.4 and 50/1.8 lenses some years ago, before switching to mirrorless systems. Let’s just say that I found all those older Canon bodies with that 50mm lenses overall to be much less enjoyable and much more faulty when it came to AF. You see, I do come from a background where we all just were used to work around certain imperfections of the camera gear …

Here’s an example of a subject that is rather close to me. With distances like this, AF is just 100% accurate all of the time. AF on my sample also works about 100% reliably with mid distances (like the autumn tree shown above):

Car eyes. (Contax G90 at f/2.8)
Car eyes. Contax G90 at f/2.8. (Click image to see full resolution.)

6. My way of taking photos:

I only photograph static subjects. I do take shots and portraits of people, but as those are either shots for paid customers, or private shots of family or friends, I never show them here. However, a portrait shot also is “static”. I am not a street photographer or something like that. So, this is how I set up my A7 II’s AF. I explain all this for reference – if you have a different style of shooting / operating your camera, this might explain if mine and your experience differs!

  • Always use AF-S and select the smallest single AF point (moveable)
  • Compose the shot
  • Open aperture fully (even when using a native Sony FE lens, this is crucial!)
  • Move the AF point to the desired subject in the photo
  • Half press shutter button / custom button to achieve focus
  • Close aperture in case I want to
  • Snap the picture

7. Speed and AF operation

Actually I consider AF speed to be very good. Again, I am not a sports photographer. I don’t even shoot moving kids or driving cars. But what I do notice, in contrast e.g. to Sony’s own FE 50/1.8 lens, is that with the G 90/2.8, the lens immediately moves towards the right direction to achieve focus. It never “pumps”. This is an advantage of using the phase detection AF system. It does feel very snappy due to this.

Now the FE 50/1.8 is Sony’s slowest-ever lens. But still that 50 represents a part of what they consider to be state-of-the-art in 2016. And if you can live with the AF speed of that lens (well … I can), you will never have trouble with the Techart AF adapter.

Then there is noise. The Techart adapter includes an electric motor to move a screw in the lens to move the lens assembly. Yes it makes noise. The loudest noise is if you turn on the camera and the AF motor racks forth and back once, to adjust to infinity or some other ideal “idle” position (I assume). During actual shooting, I don’t find the noise of the AF motor to be very intrusive. If you ever used AF cameras in the 1990s, you might be less picky to these kinds of things.

For the shot below, I used AF at f/2.8 and then stopped to f/8. On large distances like this, the AF is sometimes inconsistent at f/2.8. Stopping down to f/8 will basically always yield a consistent, very sharp outcome. But sometimes I just fine adjust with the manual focus wheel and EVF loupe. Note on the shot below I did not correct lateral CA so you can see false color around the frame edges. This can easily be corrected with one click in Lightroom or other RAW converters:

Autumn colors. (Contax G90 at f/8)
Autumn colors. Contax G90 at f/8. (Click image to see full resolution.)

Below, that one was focused and shot at f/2.8. At those kinds of distances (or even closer), I find AF to be accurate all the time. If there is a focusing error, it’s cause the sensor locks onto a detail you didn’t want it to (for example, the reflection in the car’s window or paint instead of the car’s door handle). So, no problems that would be inherent to the Techart AF adapter, I guess:

Toyota GT86. (Contax G90 at f/2.8, slightly cropped.)
Toyota GT86. Contax G90 at f/2.8, slightly cropped. (Click image to see full resolution.)

Your mileage may vary. Again! I am just writing this as I want to say don’t throw the idea of using a Contax G lens over the border just because you read somewhere it is emitting a noise. Try for yourself.

After all, the Contax G system was not a noiseless system at all, and it also never had a super-fast auto focus system … and you should just be aware that if you are using a lens of this system, you’ll also get a bit of its inherent operating characteristics.

Probably AF is even better with the Sony A7 right now, then it used to be on an original G1 or G2 body.

8. Why I even prefer shooting the Contax G lens over a native Sony FE lens

One of the weirdest decisions by Sony of all times might be that they changed their cameras’ firmwares to support closed-aperture AF only. Yes: If you stop down the lens to f/8, the camera is forced to focus at f/8 as well. This leads to a terrible inaccuracy in AF that really makes you wonder what on earth Sony was thinking of. Here I already wrote something about this issue. I have to say this seriously upsets me as it is such a stupid choice by Sony to opt for stop-down focusing, being just utterly unreliable.

However, within the scope of the Contax G lenses, they were designed with fully manual aperture only – just like a rangefinder lens. So in this case, you’ll of course just have to live with that.

Now, it’s so much easier to change aperture on a Contax G lens after auto focussing is finished, then if you use a native lens. This is because the Techart AF adapter’s firmware allows you to let off the shutter button (after you half pressed it to AF), and take all the time needed to close aperture if you want (just operate the manual aperture ring of your Contax G lens), and then you just press the button again and the shot is taken.

But if you want to change aperture after AF is done on a native lens, it’s only possible if you assign AF to a custom button, seperate from the shutter button. It is not the biggest of deals … but still weird.

This issue might be (hopefully) solved by a future Sony firmware update that would enable open-aperture focussing again.

Looking down. (Contax G90 at f/5.6 or f/8)
Looking down. (Contax G90 at f/5.6 or f/8)

9. Again, so AF is sometimes inaccurate? How does that affect your results?

So I (and others) said AF with a Contax G lens through Techart AF adapter might be inaccurate at times. But “might be” or “sometimes” … what does that mean? Well I found that AF is very accurate most of the time. In fact, all shots in this blog post were taken with AF. Just press the button to focus and snap and you’re done.

The only exeption from this is the power pole shot shown below, as it does sometimes fail if you focus on very far away distances. I had it never fail in any way on shorter distances (portraits, or distances like 5-10 metres) so far. Only at much bigger distances than that, you can get the same kind of slight focusing errors as with a lot of typical (older) DSLRs.

After achieving AF, you might use the small focusing wheel on the adapter and fine adjust. Or you take the shot two or three times – at or near infinity, you might get some variations in focus and one of them should always be spot-on. Last not least, if you stick to focussing at f/2.8, and then close aperture to f/8, the slight focusing errors that might happen should be covered in the ample depth of focus.

This sounds bad but in practice I found that focus is much, much more often accurate then it is not, and I mostly don’t even bother to check or fine-adjust or whatever. I just snap away.

In bad light, you might have more issues. But again, every lens reacts differently. My FE 35/2.8 and FE 28/2 give better results then the somewhat sluggish FE 50/1.8 already. I don’t own (or used extensively) a Batis 85/1.8 or a Sony G 85/1.4 – so I can’t comment on how good their AF is in bad light, compared to the Contax G 90/2.8.

9. Finally, what about the Contax G 90/2.8 lens itself?

Go back to the link to Phillip Reeve’s review that I already mentioned above. All technical aspects are covered there in great detail. Here’s his conclusion: “The Zeiss Sonnar has all the qualities you would want in a landscape lens: It is small and light , it is very sharp, it is flare resistant and it has quite high contrast.”

Ken Rockwell also extensively covers the Contax G 90/2.8 here (and the other Contax G lenses and cameras). There you’ll also find all the technical specifications.

I second what the reviews above already state. They went to much more technical detail than me, and show and highlight all the qualities of the lens, as well as its (very few) shortcomings. This lens completely outresolves my A7 II sensor when stopped down a bit. Even at f/2.8 it is super sharp. There are color issues at f/2.8 though. Personally, I sometimes even like them!

This is a classic lens design: 5 lens elements in 4 groups. No aspherical elements or low dispersion glas in it. You basically get all character traits of such a classic design – and that includes color fringes at open aperture – but in a kind of textbook quality. No centering issues whatsoever. Stop down to f/4 and f/5.6 and it gets perfect. The only optical flaw there remains when stopping down is lateral CA (color fringes towards the edges of the frame) which you can one-click correct in your RAW converter.

Here’s an example of the false color at open aperture (click on the picture to see it at 100% size). Also this is an example of a far-away subject where you might get AF issues. I snapped three frames to be sure to have one that was 100% on focus. Alternatively, I could have used the manual focus wheel and EVF loupe to fine adjust:

Power pole. (Contax G90 at f/2.8)
Power pole. Contax G90 at f/2.8. (Click image to see full resolution.)

Also, the build quality is just awesome. This definitely is more Loxia than Batis or Sony. The champagne finish seems to be realy hard wearing, scratch and dent resistant.

Finally here’s a subject that I took at f/2.8 through f/5.6. Notice how depth of field changes, see the slight vignette at open aperture, and also see how the color fringes at open aperture diminish as the lens was closed down:

Contax G90 at f/2.8.
Contax G90 at f/2.8. (Click image to see full resolution.)
Contax G90 at f/4.
Contax G90 at f/4. (Click image to see full resolution.)
Contax G90 at f/5.6.
Contax G90 at f/5.6. (Click image to see full resolution.)

Again, I hope these sample shows well what I mean with “classic textbook performance”. This 1990s Zeiss lens is not about utter perfection in a way some more recent lens designs are. It is a lens with no fancy glass elements in it, but within these boundaries, it is perfectly executed.

And I do like it this way, cause this is why it has some classic character – yet it combines it with really high quality. A joy to use, including the Techart AF adapter (again I am not are not a sports or action photographer).

One last word: The Contax G 90/2.8 was designed as a classic “portrait lens” for the Contax G1 and G2 cameras. Those were supposed to be a more modern alternative to the Leica M system. As such, the 90/2.8 only focuses down to 1 metre. It might be distracting nowadays. The shot below was taken at maximum close focus (and also, not corrected for false color in Lightroom):

Autumn spider. (Contax G90 at f/2.8)
Autumn spider. Contax G90 at f/2.8. (Click image to see full resolution.)

10. What about software or firmware crashes?

You read about those sometimes. But all I can say, I did never ever experience a single glitch or firmware crash or whatever so far.

My copy of the Techart AF adapter together with my A7 II and my Contax G lens just all work 100% reliably.

Let’s hope it stays that way :)

11. My personal conclusion

I am very happy with the lens due to its inherent quality, small physical size, beautiful finish and the images it delivers. Plus I am very happy to be able to use it with AF and image stabilisation on the A7 II body. This speeds up shooting and takes out the “distraction” of using the EVF loupe or focus peaking all the time. It allows you to concentrate more on framing and capturing the moment!

AF is generally very accurate but it does might miss over very long distances. So I am prepared to sometimes adjust manually, but overall the results are consistent. It happens to suit my personal style of photography very well and I find myself even choosing this lens and the Techart AF adapter over the more modern FE alternatives.

Also, AF might be a little bit less responsive in low light conditions. But I have to say that the 90/2.8 is not a first choice for low light photography anyway – being “only” a f/2.8 …

So, my conclusion is very positive. There are shortcomings but they don’t affect me very much – overall all I can say is don’t just trust negative voices out there, rather give it a try for yourself.

The blue way. (Contax G90 at f/5.6)
The blue way. (Contax G90 at f/5.6)

12. Where to get a Techart AF adapter for Contax G?

Techart Pro’s website is here. However at first glance, I don’t find the Contax G adapter right now – only the Leica M AF adapter they now released in 2016. So, I am not sure if they are still producing the Contax G adapters at all. But, as of late 2016, I did find it on sale as a new item on ebay for $250 (plus shipping and taxes, where applicable). I got my own one used through a private sale two years ago.

Contax G lenses can also be adapted to Micro Four Thirds, Leica or Fuji X series camera bodies (but not to any DSLR due to the flange distance), but to my knowledge Sony is the only system that such an AF adapter was ever made for. Don’t forget that Sony and Leica M / SL are of course the only systems with 36x24mm sensors (as of late 2016), which is the image size that the Contax G lenses were designed for.



5 thoughts on “A more technical view on the Zeiss Contax G 90/2.8 and Techart AF adapter

Add yours

  1. “But if you want to change aperture after AF is done on a native lens, it’s only possible if you assign AF to a custom button, seperate from the shutter button. It is not the biggest of deals … but still weird.”

    Wait, you mean you *don’t* use back-button autofocus?

  2. Hi Tomas,
    interesting article indeed.
    I’m getting crazy to find the right adapter for the Zeiss Contax G 90 2.8 to be mounted on Leica M body; could you help?
    Thanks an lot in advance.

  3. Hi Gian, aaauw sorry … I somehow missed your message. Zeiss G to Leica M sadly is impossible as the Leica M’s flange distance is too big. So there is no space for such an adapter … Thomas

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