Carl Zeiss Distagon T* 18mm f/3.5 ZF

Introduction

Carl Zeiss Distagon T* 18mm f/3.5, first announced in the Summer of 2008, is currently the widest lens offered by the company in its modern SLR lens lineup. The lens, which is currently offered in Nikon and Pentax mounts, is a replacement of the older, now discontinued Contax version. Carl Zeiss discontinued its immensely popular Contax branded SLR cameras and lenses in 2005 after Kyocera, which jointly owned the development rights for the brand, pulled out of the camera market. Carl Zeiss has been indicating that it is going to bring back the Contax brand name eventually, but in the meantime the company introduced the ZF, ZS and ZK series of SLR lenses (for Nikon F, M42 universal screw and Pentax K mounts). The new 18mm Distagon is currently offered in ZF and ZK formats for Nikon and Pentax mounts and retails for ~US$1,450 (as of August 2008) at retailers like B&H.

Carl Zeiss has given its 18mm Distagon lens a complete face-lift. The lens sports a new optical formula, consisting of 13 elements in 11 groups, organized in a floating design, compared to the older version of the lens, which had 10 elements in 9 groups. The new optical formula is also slightly faster - f/4.5 versus f/4, although the slight improvement in speed might be considered marginal by some users. The new version of the lens is also slightly heavier, 470g (1.03lb) vs 350g (0.77lb), and larger, 87 x 84mm (3.4 x 3.3in) vs 70 x 51mm (2.75 x 2in) when compared to the older Contax version of the lens. But like its older incarnation, Distagon T* 18mm f/3.5 sports excellent build quality with all metal barrel, aperture and focus rings. There is absolutely no wobbling inside or out and the lens looks and feels pretty sturdy.

Like all ZF/ZS/ZK series lenses, Carl Zeiss Distagon T* 18mm f/3.5 offers fully manual focusing and aperture control. The ZF version of the lens is essentially an Ai-S  lens, which technically speaking makes it compatible with the widest range of Nikon's modern and not no modern cameras. As an Ai-S lens, Distagon T* 18mm f/3.5 ZF will also allow for the in-camera aperture control for aperture priority and even shutter priority modes (with cameras like F5). On the other hand, the ZK version of the lens incorporates an electronic contact pin, which makes the lens fully compatible with aperture priority, shutter priority, and automatic exposure modes on pretty much all modern Pentax cameras.

The lens has the minimum focusing distance of 30cm (0.98ft) and the minimum aperture of f/22 (the aperture ring stops in half f-stop increments). Some users have complained about the aperture ring operation - the ring is located pretty close to the base of the mount, making it a little bit hard to reach and rotate. From my experience, the aperture ring on this lens is not any different then the aperture rings found on any of Nikon's Ai-S or AF-D lens, so if you don't like how it operates on this 18mm Distagon lens, my guess is that you would not like the aperture operation on any Ai-S/AF-D lens either.

One interesting, and useful improvement over the previous version of the lens is that the new Distagon T* 18mm no longer requires a step up ring for attaching filters or lens hoods - Carl Zeiss made the front of the lens significantly wider, essentially welding the step up ring into the barrel. Users can now screw in 82mm filters directly to the barrel as with any other lens. This of course makes the barrel look significantly bulkier/wider then it really is.

Image

The factory box includes Carl Zeiss Distagon T* 18mm f/3.5 ZF lens, front and rear lens caps, metal lens hood, manual and registration card. The lens tested in the review was manufactured for Nikon F mount. It is obviously a full frame lens, so when used on APS-C type cameras its field of view will resemble that of a 27mm prime on a full frame body. Still a wide angle, but not ultra wide.

 

Summary
Lens Composition 13 elements in 11 groups
Angular Field 99 degrees
Minimum Focus 30cm/0.98ft
Focusing Action MF
f-stop Scale f/3.5-f/22, manual
Filter Size 82mm
Lens Hood Metal (included)
Weight 470g/1.03lb
Dimensions 87x84mm/3.4x3.3"
Lens Case N/A

 

Field Tests

Carl Zeiss Distagon T* 18mm f/3.5 ZF is a classical manual focus Ai-S lens. As such, there are really no particularly distinguishing features that differentiate this lens from any other manual focus Ai-S lens out there. And like any Ai-S lens, Distagon T* 18mm f/3.5 ZF can be easily adapted to a number of alternative SLR mounts, including Canon EF/EF-S and Olympus Four Thirds. Once adapted to an alternative mount, the lens will have to be used exclusively in manual mode - the in-camera aperture control will be gone and you would need to rely on stop down metering when shooting with the lens. Also be prepared for some differences in the effectiveness of your camera's TTL metering - if you are shooting in aperture priority mode, many cases cameras will overexpose images that were taken with alternative lenses (and the amount of the overexposure depends not only on the particular lens being used, but also the aperture level used).

Setting aside the somewhat mundane question of handling, Carl Zeiss Distagon T* 18mm f/3.5 ZF showed somewhat mixed results in the field. The lens excelled in the center throughout the aperture settings on both full frame as well as APS-C cameras. However, border image quality was a little bit mixed, with f/3.5 and f/4 delivering somewhat softer results, and visually, there was a noticeable change in quality when going from the wide open aperture to f/8 or f/11. Moreover, quality around borders at closer distances (up to ~1m focusing distance) seemed to suffer regardless of the aperture setting - this can be observed in the flowers shot in the sample image gallery below.

 

ISO 200, 1/800, f/3.5, 18mm (Nikon D3)
ISO 200, 1/800, f/3.5, 18mm (Nikon D3)

Carl Zeiss DIstagon T* 18mm f/3.5 ZF fell prone to flare and some ghosting when used in harsh lightning conditions such as with a direct strong light source positioned near or within the picture frame. The image above showcases such scenario, with the sun hitting the lens at about 50 degrees from the top right corner. You can notice that the flare resulted in slightly lower contrast (which is expected) and blown out highlights near the top corner where the light source was positioned. There are the usual 'rainbow' patches that can be noticed in the lower left and upper right corners. At the same time there are some traces of ghosting, which can be noticed between the white and black cars in the middle of the frame. Despite all that, the flare is not the worst one would expect from such a wide angle lens.

 

Vignetting @ f/3.5 - full frame vs 1.6x crop
Vignetting @ f/3.5 - full frame vs 1.6x crop

The lens produced noticeable amount of vignetting on a full frame camera at f/3.5, which continued to persist all the way through f/5.6, eventually dropping to minimal around f/6.7. Vignetting on an APS-C camera was somewhat lower, but still visible at f/3.5 as well as f/4, but then dropping to more manageable levels by f/5.6. Not a big surprise for an 18mm prime. If you are using a camera with a build-in vignetting control, configure it for moderate or even heavy setting. Vignetting was not the only artifact with the lens - most ultra wide angles showcase some level of distortion and Carl Zeiss Distagon T* 18mm f/3.5 ZF is no exception. Barrel distortion is visible in all shots on both APS-C as well as FF cameras - the farther from the center, the heavier was the distortion.

Color reproduction was pretty accurate, with the color palette remaining mostly neutral, although at f/3.5 and f/4 images seemed to be a little bit less contrasty (typically caused by a somewhat lower resolving power at wider apertures). Regretfully, Distagon T* 18mm f/3.5 ZF showed noticeable color fringing. You can observe some sagittal CA in the parking lot shot above, around the chimney pipe on the right hand side of the picture. And minor degree of halation can be noticed in the shot of flowers in the image gallery below - notice the purple glow around bright red flower petals positioned over the much darker background.

 

ISO 100, 1/800, f/3.5, 18mm (100% crop)
ISO 100, 1/800, f/3.5, 18mm (100% crop)

 

Lab Tests

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

 

Nikon APS-C: Coming soon...

 

Nikon FF: Carl Zeiss Distagon T* 18mm f/3.5 ZF showed excellent performance in the center with resolution remaining top notch throughout the tested aperture range. Border performance on the other hand was somewhat mixed, with image quality at wider apertures, specifically f/3.5 and f/4 being kind of average. As the aperture is stopped down further, the lens finally starts to deliver better and better results - with f/5.6 being somewhat of a transitional point, and f/8 and f/11 finally delivering excellent border performance. Conclusion? The overall results are quite good, although one usually expects miracles from a Carl Zeiss lens. A miracle did not really happen here though - border image quality with wide open aperture is not very impressive. Not bad, but not impressive either.

 

Normalized raw MTF50 @ 18mm
Normalized raw MTF50 @ 18mm

 

Chromatic aberration on a full frame Nikon D3 was more or less under control. Center CA was quite negligible, never exceeding ~0.5px across the frame. Border CA, while somewhat higher, was still manageable, reaching ~0.8px at f/3.5 and gradually dropping to ~0.65px by f/11.

 

Chromatic Aberration (FF) @ 18mm
Chromatic Aberration (FF) @ 18mm

 

Here are 100% crops, taken with a full frame Nikon D3, comparing image borders at f/3.5 and f/8.

 

Image borders @ 18mm (100% crop): f/3.5 vs f/8
Image borders @ 18mm (100% crop): f/3.5 vs f/8

 

Canon APS-C: The lens showcased decent overall performance. Center image quality was absolutely flawless, with performance staying at very high level throughout the aperture range. Unfortunately, border performance suffered, especially at wide open apertures. In the f/3.5-f/4 range borders are OK, but not really that impressive. f/5.6 is better, but still not quite there. And f/8-f/11 range is where the lens is finally starts to deliver very good performance around borders. Overall, the leans performance peaks in the f/8-f/11 range, where it is capable of delivering very good 16in prints and can deliver decent 19in prints in the f/5.6-f/11 range. Conclusion? Impressive center performance. Excellent border quality at moderate to small apertures. Not bad, not bad at all. But would have been better if the border performance at wider apertures was slightly better as well.

 

MTF50 (Line Width/Inch on the Print) @ 18mm
MTF50 (Line Width/Inch on the Print) @ 18mm

 

Normalized raw MTF50 @ 18mm
Normalized raw MTF50 @ 18mm

 

The lens showed OK handling of chromatic aberration on an APS-C type camera. CA in the center was quite low throughout the tested aperture range and never exceeded ~0.3px. Border CA was noticeably higher, averaging ~1px throughout the tested apertures. Higher then hoped for, but not quite as bad as with some other ultra wide angle lenses.

 

Chromatic Aberration (APS-C) @ 18mm
Chromatic Aberration (APS-C) @ 18mm

 

Here are 100% crops, taken with an APS-C type, comparing image borders at f/3.5 and f/8.

 

Image borders @ 18mm (100% crop): f/3.5 vs f/8
Image borders @ 18mm (100% crop): f/3.5 vs f/8

 

Canon FF: The lens continued to showcase decent overall performance, with the overall pattern resembling performance seen on the Canon APS-C as well as the Nikon FF cameras. Center image quality remained excellent throughout the aperture range, but border quality still suffered at wider apertures. Nothing new in this regard - f/3.5 and f/4 border performance remains the weakest, and f/8-f/11 showcasing solid performance. Conclusion? Well, at least the results are consistent on both FF and APS-C cameras. Border quality at f/3.5 and f/4 disappoints somewhat (mostly because the expectations are so much higher for a Carl Zeiss lens), however, most lenses, and especially wide angles, suffer to some degree at wide open apertures. Hence this does not come as a major surprise, but I think I repeated this sentence at least three times now...

 

Normalized raw MTF50 @ 18mm
Normalized raw MTF50 @ 18mm

 

Carl Zeiss Distagon T* 18mm f/3.5 ZF showed pretty heavy barrel distortion, which does not really come as a major surprise for such a wide lens. At ~1.78%, barrel distortion will be visible in pretty much all shots.

 

Distortion (FF) @ 18mm
Distortion (FF) @ 18mm

 

Chromatic aberration on a full frame Canon 5D was mostly under control, with center CA averaging ~0.2px and border CA averaging ~0.9px throughout the aperture range. Center CA is quite negligible and border CA is still manageable so all in all, it is not a disastrous performance.

 

Chromatic Aberration (FF) @ 18mm
Chromatic Aberration (FF) @ 18mm

 

Here are 100% crops, taken with a full frame Canon 5D, comparing image borders at f/3.5 and f/8.

 

Image borders @ 18mm (100% crop): f/3.5 vs f/8
Image borders @ 18mm (100% crop): f/3.5 vs f/8

 

Alternatives

Assuming you are looking for an ultra wide angle lens for a Nikon mount camera, then you might want to take a look at two Nikon AF-D lenses - Nikon AF Nikkor 14mm f/2.8D and Nikon AF Nikkor 20mm f/2.8D (or its older, manual focus version Nikon Nikkor 20mm f/2.8 Ai-S). Speaking of the older lenses - you might also want to take a look at a couple of now discontinued Nikon lenses such as Nikon AF Nikkor 18mm f/2.8D and Nikon Nikkor 15mm f/3.5 Ai-S, assuming of course you can find one in good condition and at a reasonable price. Alternatively, take a look at Sigma's discontinued Sigma 14mm f/2.8 EX ASPH HSM, which was manufactured in a number of mounts, including Nikon F and Canon EF.

On the other hand, if you are looking for an alternative ultra wide angle prime, then you can expand your search to include a couple of older, Contax branded Carl Zeiss lenses, including Carl Zeiss Distagon T* 21mm f/2.8 and Carl Zeiss Distagon T* 15mm f/3.5. Don't forget to try out a trio of Olympus super wide angles - Olympus OM 18mm f/3.5, Olympus OM 21mm f/2 and its slightly slower variant Olympus OM 21mm f/3.5.

One might wonder why the older Contax version of Carl Zeiss Distagon T* 18mm f/4 is not mentioned here as an alternative. Unfortunately, the tested copy of the lens delivered rather mediocre overall results. It is not quite clear whether the tested lens sample was poorly calibrated or the lens design did not really deliver, so I feel that another lens sample needs to be run through the tests before a final performance comparison between the old and new designs can be made.

 

Recommendation

Carl Zeiss Distagon T* 18mm f/3.5 ZF is a lens with a couple of caveats and gotchas. The lens delivers exceptionally good center image resolution but suffers somewhat around borders at wider apertures, where performance is rather average. The good news is that the image quality does improve quite nicely with stopped down apertures and by f/8-f/11 border quality becomes excellent. 'So does it mean the border performance at wider apertures is going to significantly affect real-life photographers?' - one of the readers asked. Unlikely, since the falloff in quality is not too drastic and can be relatively easily corrected with a little bit of sharpening. Additional points going for the lens are the excellent build quality, more or less decent handling of flare (for a super wide angle that is) and good overall color reproduction. Color fringing, vignetting and distortion are the weaknesses to be aware of, however, these issues are quite common among wide angle primes, so you should not probably overreact here. The main question however is - given the combination of performance and handling, is this lens really worth ~US$1,500? At this price, the lens is clearly not going to be appealing to mainstream users. Also, we need to keep in mind that this is still a fully manual lens. Whether the price is going to cause a sticker shock or not, you should probably still look into a few alternatives before plunging that much money for the newly released Distagon T* 18mm f/3.5...