Carl Zeiss Distagon T* 25mm f/2.8 Carl Zeiss Distagon T* 25mm f/2.8

Introduction

Carl Zeiss Distagon T* 25mm f/2.8 is a classical manual focus lens for the Contax series of SLR cameras. Along with its slightly longer cousins Distagon T* 28mm f/2.8 and Distagon T* 35mm f/2.8, the lens was often regarded as one of the more affordable wide angles in the Contax lens lineup. Regretfully, all Contax branded cameras and lenses were discontinued in 2005 after Kyocera, a joint holder of the development rights for the brand name, discontinued its camera business. As of 2008, Carl Zeiss has not yet announced any definitive plans for resurrecting this great brand name, but the good news is that the company recently re-introduced a number of SLR lenses, including Distagon T* 25mm f/2 for Nikon F, Pentax K and M42 universal screw mounts.

The origins of the lens actually go way back to early 70s when Carl Zeiss used to offer its lenses for Rollei SL35 series of cameras. The Contax version of Distagon T* 25mm f/2.8 was originally manufactured as an AE version, and later was replaced by an MM variant. According to Carl Zeiss, the optical performance of both versions are identical, but there are plenty of rumors floating aroun on the web with claims that the later MM version is optically superior to the older AE one. Both variants were manufactured by Carl Zeiss itself in West Germany, as well as by Kyocera in Japan, hence you can encounter a total of four different variants of this lens - AE manufactured in Germany, MM manufactured in Germany, AE manufactured in Japan and MM manufactured in Japan. Both AE and MM variants are more or less common on used markets, with good quality used MM copies fetching ~US$500 (as of May 2007).

The optical construction of the lens consists of 8 elements in 7 groups - nothing particularly fancy. The build quality is simply outstanding - the barrel is all metal and both focusing and aperture rings are fully rubberized for comfortable grip. The focusing ring is well-damped and the aperture ring snaps into positions with a satisfying click. The lens is pretty light and compact, weighing 360g (12.7oz) and measuring 6.25 x 5.6cm (2.4 x 2.2in). The inner cam of the lens actually extends slightly during focusing towards closeup, and thus makes the lens slightly longer when fully extended. Fortunately, the front element does not rotate, thus allowing attaching circular polarizers to the front thread. The lens accepts 55mm screw-in type filters and has the minimum focusing distance of 25cm (10in). The minimum supported aperture is f/22 (the aperture ring moves in one full f-stop increments).

Image

Like all Contax branded Carl Zeiss lenses, Distagon T* 25mm f/2.8 is a full frame lens, so when used on an APS-C body with 1.6x crop factor, the field of view of the lens will resemble that of a 40mm prime on a full frame body. The lens is easily adaptable to a number of modern digital SLR cameras, including Canon's APS-C and FF bodies. When testing the lens on Canon cameras, I relied on generic, non AF-chipped Contax to EOS adapter.


Summary
Lens Composition 8 elements in 7 groups
Angular Field 80 degrees
Minimum Focus 25cm/10in
Focusing Action MF
f-stop Scale f/2.8-f/22, manual
Filter Size 55mm
Lens Hood G-12 soft hood or No.1 metal hood
Weight 360g/12.7oz
Dimensions 62.5x56mm/2.4x2.2"
Lens Case No.1 (included)

 

Field Tests

Like any other adapted lens, operating Carl Zeiss Distagon T* 25mm f/2.8 on a modern dSLR feels a little bit archaic. Gone is auto focusing as is auto aperture control. Manual focusing on modern cameras is not as trivial as it used to be with older manual focus bodies, primarily because most cameras now have smaller and darker viewfinder with basically no focusing aids. You can obviously replace your focusing screen with one that is more suitable for manual focusing - if you are a Canon user you have a choice between EE-S and EE-D OEM screens as well as a few custom ones from companies like Katz Eye and Brightscreen. However, regardless of which screen you use, as you stop down the lens and close its iris (remember, no auto aperture control with adapted lenses, so the stopped down aperture really means smaller iris hole) less and less light gets through into the viewfinder. By f/5.6 viewfinders in most cameras will be so dark that precision manual focusing will be practically impossible. Hence you will need to revert to using a trick from the good old days called stop down metering - you focus the lens with wide open aperture, then stop down the aperture, meter and take the shot.

As mentioned earlier, you can encounter a total of four different versions of Contax Carl Zeiss Distagon T* 25mm f/2.8, with most users chasing the newer MM versions of the lens, with MM copies made in Germany being particularly thought after. The general feeling is that samples made in West Germany have lower variance in quality and hence have a tighter match to the original spec. With the increase in use of older Contax lenses on modern digital cameras, another possible contributing factor to this general preference for MM versions of the lens is the general belief that old AE copies often don't clear the mirror box of the immensly popular among alternative gear-heads Canon 5D and Canon 5DMkII full frame cameras. While the first theory requires testing a large sample set of lenses to obtain a valid proof, which falls outside of the scope of the reviews done here, the second theory seems to be more of a myth then the truth, since both AE made in Germany and MM made in Japan versions of the lens tested in this review showed no operational issues on Canon 5D. It seems that the Canon 5D's variance in the mirror box size and assembly can be a contributing factor to this myth.

Operation-wise, there is nothing particularly special about Contax Carl Zeiss Distagon T* 25mm f/2.8 - after all, a manual lens is a manual lens and it really puts full control into the user's hands. Its light weight and compact size are obviously a major benefit, and one might think of using it as a walk-around prime on a APS-C type body (the lens gives you a 40mm equivalent field of view with 1.6x crop sensors). That is definitely possible, although keep in mind that there are even more compact lenses out there (for example a recently released Voigtlander Ultron 40mm f/2 SLII) that would probably allow you to be more discreet. The lens has a traditional for manual focus lenses DOF scale engaved on the side of the body, which can be helpful when you choose to preset the lens using hyperfocal focusing method for example. Although keep in mind that like with most wide angle primes, Distagon T* 25mm f/2.8 sports a rather short focusing thrust - the focusing ring rotates for ~90 degrees when going from the closeup to the infinity. So if you set the aperture to f/11, using hyperfocal focusing distance, you will get everything from about 80cm all the way to the infinity in focus.

 

ISO 400, 1/50, f/2.8, 25mm (Canon 5D)
ISO 400, 1/50, f/2.8, 25mm (Canon 5D)

Wide angle primes are not your typical bokeh kings. There are obviously a number of variables that affect the look and feel of the bokeh, but generally speaking, in most cases you would try to achieve a shallow DOF to isolate the subject in focus from the fore/background. The shallower, the better. However, even if you manage to achieve a shallow DOF with blurred background, the general feel of bokeh will be affected by a number of additional factors such as shape of out of focus highlights, presence of double-edging around blurred objects and the levels of contrast in the background. Take an example above, which was shot with the wide open aperture and close to the minimum focusing distance (~40cm to the porcelain cat's right eye, serving as a focusing point). It is doubtful that anyone looking at the shot will get overwhelmed by the quality of its bokeh - DOF is not shallow enough, background remains pretty contrasty, even OOF highlights create a 'busy feeling', with somewhat harshly lit edges.

Carl Zeiss Distagon T* 25mm f/2.8 showed somewhat mixed performance in the field. The lens demonstrated pretty good overall performance on a cropped camera, and rather average performance on a full frame body. But one thing at a time. The center performance was quite good throughout the aperture range. However, border image quality seemed to be a little bit softer at f/2.8, but not terribly bad. On the other hand, performance on a FF body was truly mixed. Center image quality remained excellent throughout the aperture range, but border quality suffered significantly more then on an APS-C camera. As a matter of fact, borders remained soft not just at f/2.8 but also at f/4, which is quite disappointing.

Like most wide angle lenses, Contax Carl Zeiss Distagon T* 25mm f/2.8 fell prone to some flare. Well, saying some actually understates the issue as can be seen from the images below. With a strong direct light source positioned near the picture frame (in these cases sun was hitting the front element of the lens under ~70 degrees), the lens produced pretty severe flare with signs of ghosting and rainbow looking glare at wide open aperture. As you stop down the lens, the amount of flare is reduced somewhat, although never completely disappears - at f/8 you see aperture ghosting as well as minor rainbowish looking glare. Bottom line is that you do need to use a lens hood with this lens if you are planning to shoot in challenging lightning conditions.

 

ISO 100, 1/1000, f/2.8, 25mm (Canon 5D)
ISO 100, 1/1000, f/2.8, 25mm (Canon 5D)
ISO 100, 1/60, f/8, 25mm (Canon 5D)
ISO 100, 1/60, f/8, 25mm (Canon 5D)

 

The lens showed moderate level of vignetting on a FF Canon 5D with wide open aperture. Vignetting continued to persist, albeit at a lower level at f/4 and pretty much disappeared around f/5.6. On an APS-C body the lens takes full advantage of a smaller sensor - with extreme borders clipped, the lens shows pretty minimal vignetting at f/2.8 and practically no vignetting once stopped down to f/4 and beyond.

 

Vignetting @ f/2.8 - full frame vs APS-C
Vignetting @ f/2.8 - full frame vs APS-C

Color reproduction was pretty decent overall, although images at f/2.8 lacked contrast somewhat (obviously this is a direct derivative of a lower resolution at f/2.8). The lens showed minor color fringing, which was mostly noticeable around borders. Distortion was surprisingly well contained for such a wide angle - you could see minor signs of barrel distortion around frame edges with straight lines, but the artifact was not extreme to cause an alarm.

 

ISO 100, 1/1600, f/2.8, 25mm
ISO 100, 1/1600, f/2.8, 25mm

 

Lab Tests

Please note that MTF50 results for APS-C and Full-Frame cameras are not cross-comparable despite the same normalized [0:1] range used to report results for both types of cameras.

Two lens samples were tested (both in the field as well as in the lab) - an MM version manufactured in Japan and an AE version manufactured in West Germany. Both lenses produced similar performance in the lab, with average performance variance of 1.2% in the center and 4% around borders. The review includes results from the MM version of the lens that showed slightly better results.

 

Canon APS-C: The lens produced top notch results in the center throughout the tested aperture range. The center performance peaks around f/4-f/5.6 and in this range it is clearly one of the best among all fixed and zoom lenses I have tested to date. Borders remain sharp throughout as well, albeit not at the same level as the center (also peaking at f/4-f/5.6). The border performance at f/2.8 leaves some room for improvement but is certainly not disastrous. Most importantly, the overall results are well balanced, without any major falloffs - this is quite a welcoming characteristic in any lens. At its peak, the lens would give you outstanding 16in and very good 19in prints, which is a common range for most of Carl Zeiss prime lenses. Conclusion? Carl Zeiss Distagon T* 25mm f/2.8 might not be the fastest ultra wide lens available on the market, but the overall performance is good enough to warrant a second look and serious consideration.

 

MTF50 (Line Width/Inch on the Print) @ 25mm
MTF50 (Line Width/Inch on the Print) @ 25mm

 

Normalized raw MTF50 @ 25mm
Normalized raw MTF50 @ 25mm

 

The lens showed minimal to moderate levels of chromatic aberration on an APS-C camera. Center CA was minimal throughout the tested aperture range, basically never exceeding ~0.25px. Border CA, while slightly higher, was also quite manageable (for a wide angle lens that is), reaching ~0.9px at f/2.8 but then gradually dropping to ~0.7px by f/11.

 

Chromatic Aberration (APS-C) @ 25mm
Chromatic Aberration (APS-C) @ 25mm

Here are 100% crops, taken with an APS-C type Canon Digital Rebel XTi, comparing image borders at f/2.8 and f/8.

 

Image borders @ 25mm (100% crop): f/2.8 vs f/8
Image borders @ 25mm (100% crop): f/2.8 vs f/8

 

Canon FF: Performance on a full-frame Canon 5D was disappointing. Borders were quite soft with wide open aperture and while quality improves with stopped down aperture, it does not get to an acceptable level until f/5.6. On a positive side, center performance was excellent pretty much throughout the tested aperture range. Overall performance peaks at f/8, where borders reach very respectable level and the center quality is simply exceptional. Conclusion? This is clearly not a hidden gem in the Carl Zeiss lineup that I was expecting it to be. Not that the performance is disastrous - not at all. The lens performs quite well from f/8, but the border performance at f/2.8 is what bothers me.

 

Normalized raw MTF50 @ 25mm
Normalized raw MTF50 @ 25mm

 

Contax Carl Zeiss Distagon T* 25mm f/2.8 showed moderate level of barrel distortion on a full frame Canon 5D - at ~1.2%, distortion should not pose any major problems for photographers in real life situtations but it will be visible in certain cases, particularly around borders.

 

Distortion (FF) @ 25mm
Distortion (FF) @ 25mm

Like with an APS-C camera, Distagon T* 25mm f/2.8 produced minimal to moderate amount of CA on a full frame body. CA was averaging ~0.15px in the center (across all tested aperture settings), with border CA reaching ~0.8px at f/2.8 and then gradually falling to ~0.5px. Nothing major to worry about.

 

Chromatic Aberration (FF) @ 25mm
Chromatic Aberration (FF) @ 25mm

Here are 100% crops, taken with a full frame Canon 5D, comparing image borders at f/2.8 and f/8.

 

Image borders @ 25mm (100% crop): f/2.8 vs f/8
Image borders @ 25mm (100% crop): f/2.8 vs f/8

 

Alternatives

As mentioned earlier, Carl Zeiss stopped manufacturing Contax branded lenses for quite some time now. So if you are looking  for a 25mm Carl Zeiss prime, then you need to look at one of the recently released Carl Zeiss Distagon T* 25mm f/2 primes in Nikon F (ZF). Pentax K (ZK) or M42 (ZS) mounts. However, if you're willing to go for a slightly longer focal length, then Contax version of Carl Zeiss Distagon T* 28mm f/2.8 is going to offer you one of the best price/performance ratios among wide angle lenses. Alternatively, look at the re-released Carl Zeiss Distagon T* 28mm f/2 ZF (or ZK). For an even wider angle, go for Carl Zeiss Distagon T* 21mm f/2.8, assuming your wallet can take a ~US$3,000 hit that is. Also don't forget Leica lenses. Here the best option is to go for Leica Elmarit-R 28mm f/2.8 (latest E55 revision with built-in hood), and if you are willing to tinker with a lens, then Leica Elmarit-R 19mm f/2.8 (also latest edition, however keep in mind that this version requires pretty significant alteration when used on Canon full frame cameras). Finally, take a look at older, Ai-S versions of Nikon Nikkor 28mm f/2.8 AiS and Nikon Nikkor 24mm f/2.8 AiS.

 

Recommendation

Carl Zeiss Distagon T* 25mm f/2.8 shows somewhat mixed overall performance. Hence the recommendation is also going to be a little bit mixed. You will be happier with this lens if your primary system is an APS-C type with a 1.5x/1.6x/2x crop sensor. The main difference you will notice when using this lens on a FF body is the lackluster border image quality at wider apertures. The lens would still produce decent results even on a FF camera, if you stop it down to f/5.6 or better yet f/8. One other somewhat negative aspect that needs to be considered here is the lower level of contrast that you'd typically see at wider apertures (f/2.8-f/4). So with such mixed results, would it really make sense purchasing this lens? You should certainly seriously consider whether you really need that extra 3mm of focal length this lens provides when compared to Carl Zeiss Distagon T* 28mm. After all, the 28mm version of Distagon showcases outstanding overall performance and costs about US$100 less on the used market. So which one to choose? This depends on your needs, but unless you're into collecting lenses, then there's very little reason to own both 25mm and 28mm variants (here I'm referring to the f/2.8 variant of Distagon 28mm, not the 'Hollywood' Distagon T* 28mm f/2, which costs about twice as much compared to its slower cousin). Of course you still need to keep in mind that this is a fully manual lens and as such you should consider all the downsides it brings.