Carl Zeiss Distagon T* 18mm f/4
Carl Zeiss Distagon T* 18mm f/4

 

Introduction

Carl Zeiss Distagon T* 18mm f/4 is one of the widest prime lenses that Carl Zeiss manufactured in the now defunct C/Y mount. As mentioned in my other reviews, Zeiss discontinued all C/Y mount lenses after Kyocera, which was its business partner and joint holder of Contax brand name development rights, exited business in 2005. Zeiss recentrly reintroduced a number of its popular SLR lenses in ZF (for Nikon Ai-S mount) and ZA (for Sony alpha) format, but Distagon T* 18mm was left out and as of mid 2007 does not seem to be on the company's development roadmap.

Distagon T* 18mm f/4 is a classical Zeiss manual lens. The optical construction of the lens consists of 10 elements in 9 groups, including a single floating low dispersion glass element for correcting chromatic aberration at close range. The build quality of the lens is superb, a common trait of Zeis lenses in C/Y mount - barrel is metal and both focus and aperture rings are rubberized. The lens looks as if it has an inner focusing mechanism, but the lens barrel actually extends (very) slightly when focusing towards closup. The lens is relatively compact and lightweight (for such an ultra-wide lens), measuring 7.0 x 5.15cm (2.75 x 2in) and weighing 350g (12.3oz). The minimum focusing distance is 30cm (1ft) and the minimum aperture is f/22. The lens accepts 86mm screw-in type filters, but requires a 70mm/86mm adapter ring. On an APS-C cameras with 1.6x crop ratio, the lens has field of view similar to that of a 28mm lens on a full-frame body.

Image

The lens used in these tests was an AE type, manufactured by Carl Zeiss in Germany. The serial number is 6000053. Good quality used copies of the lens could be found on eBay for about US$750. As with other Carl Zeiss manual lenses in C/Y mount I used a generic Fotodiox Contax/Yashica to EOS adapter without AF confirmation. I used camera in aperture priority mode, which along with the fully manual are the only two modes available to anyone using this type of an adapter. Some users report that MM variants of Distagon T* 18mm f/4 hit the mirror of Canon 5D. Other full frame cameras like 1Ds series don't seem to have this problem.

 

Summary
Lens Composition 10 elements in 9 groups
Angular Field 100 degrees
Minimum Focus 30cm/1ft
Focusing Action MF
f-stop Scale f/4-f/22, manual
Filter Size 86mm with 70/86 ring
Lens Hood N/A
Weight 350g/12.3oz
Dimensions 70x51.5mm/2.75x2"
Lens Case No.2 (included)

 

Field Tests

Carl Zeiss Distagon T* 18mm f/4 showed somewhat uneven overall performance. Image quality was quite good in the center both on APS-C and FF cameras, but images were noticably soft around borders, especially at wider aperture settings. Border quality improved somewhat once I stopped down the aperture to f/11 but even then borders remained a tad soft.

 

Vignetting @ f/4 - full frame vs 1.6x crop
Vignetting @ f/4 - full frame vs 1.6x crop

The lens showed pronounced vignetting on a full-frame Canon 5D at f/4, which is reduced substantially at f/5.6 and by f/8 becomes practically non-existent. Vignetting was practically non-existent on an APS-C camera streight from f/4. Color rendition was pretty accurate albeit a bit saturated. The lens held up well against flare, which is a positive news for such a wide lens and showed very minimal color fringing around borders, even with wide open aperture. The lens also showed quite minimal (for an UWA lens that is) distortion.

 

ISO 100, 1/2000, f/4, 18mm (100% crop)
ISO 100, 1/2000, f/4, 18mm (100% crop)

 

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.

 

Canon APS-C: Distagon T* 18mm f/4 showed rather unusual characteristics in the lab. THe lens performance was outstanding in the center starting at f/4, but quality somewhat degraded with stopped down aperture. By f/11, performance is still decent, but not impressive. Border quality on the other hand was completely unsatisfactory at f/4, slowly improving with stopped down aperture and reaching more or less acceptable level by f/11. Hard to generalize here: if you care about center performance, then shoot at f/4, otherwise stop down to trade image quality in the center for quality around borders. At f/11, which is the most balanced aperture setting for the lens, the lens produces outstanding 11in and decent 16in prints. Conclusion? The overall results are not impressive for a fixed focal lens, and especially for a Zeiss lens. However, keep in mind that we're dealing with an ultra-wide prime here and most lenses in this category would show weakness around borders.

 

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

 

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

On an APS-C camera, Distagon T* 18mm f/4 suffers from somewhat higher then expected (for a Zeiss lens) chromatic aberration. CA in the center is more or less under control, averaging ~0.6px throughout the aperture range. CA creeps up to ~1.1px around borders at f/4 and unfortunately doesn't really go away with stopped down aperture.

 

Image borders @ 18mm (100% crop): f/4 vs f/8
Image borders @ 18mm (100% crop): f/4 vs f/8

 

Canon FF: The lens did not fare any better on a full-frame Canon 5D. Performance was outstanding in the center streight from f/4, slowly degrading with stopped down aperture. At f/11 center performance is still solid, so nothing to worry about here. Like with APS-C camera, border quality suffers. Borders are very soft at f/4, but improve once you stop down the aperture. By f/11 border performance becomes acceptable, but still lacks the punch expected from Zeiss glasss. Conclusion? At least the lens performance is consistent on both APS-C and FF cameras, but other then that, there are no miracles here - for best performance stop down the lens to improve border quality.

 

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

 

CA on a full-frame camera was moderate in the center, averaging ~0.5px across the tested aperture range and somewhat higher around borders, averaging ~1px. Considering that CA can be easily corrected during post-processing, I wouldn't stress to much about these somewhat higher levels around borders,

 

Image borders @ 18mm (100% crop): f/4 vs f/8
Image borders @ 18mm (100% crop): f/4 vs f/8

Alternatives

As mentioned earlier in this review, Distagon T* 18mm is one of the widest prime lenses in Carl Zeiss arsenal for the C/Y mount. The two other lenses that are even wider then this lens are Carl Zeiss Distagon T* 15mm f/3.5 and Carl Zeiss F-Distagon T* 16mm f/2.8. If you're willing to go with a slightly narrower angle, you might want to consider Carl Zeiss Distagon T* 21mm f/2.8, which by now has achieved a legendary status among photographers. Outside of the 'Zeiss camp', take a look at Leica Super-Elmarit-R 15mm f/2.8 ASPH and Leica Elmarit-R 19mm f/2.8. You also might want to take a look at Olympus OM Zuiko 18mm f/3.5 and Olympus OM Zuiko 21mm f/3.5. There are obviously other high quality ultra-wide lenses available on the market, so this list is just a starting point.

 

Recommendation

It is rather hard to render a recommendation on Distagon T* 18mm f/4. The lackluster performance around borders is the biggest concern here. But as I have been saying in other reviews, most wide angle lenses show weakness around borders. So if you're willing to use the lens at narrower aperture levels, it can still produce very decent results. At the same time, the lens is one of the more affordable UWA primes in the now defunct Contax lineup - compare it for example to 21mm or 16mm Distagons. But affordable is a relative term here - what is affordable in the world of Carl Zeiss (Contax) does not mean a bargain in a general sense, since there are quite a lot of UWA primes that are priced even more competitively. As such, unless you have to have a Zeiss glass and you cannot afford (even more expensive) Distagon alternatives, you might as well expand your search and consider non-Zeiss lenses.