Zeiss Planar T* 50mm f/2 ZM on Sony NEX - Review / Test Report

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Review by Klaus Schroiff, published September 2010 Welcome to the start of our quite extensive "Vintage Lens" test series based on the Sony NEX-5. Every once in a while we're having a look at one of the more unusual camera-lens combinations and this time it's about the Zeiss Planar T* 50mm f/2 ZM - a Leica M-mount lens adapted via a Metabones Leica M to Sony NEX adapter[img]http://rover.ebay.com/roverimp/1/711-53200-19255-0/1?ff3=11&pub=5574877069&toolid=10001&campid=5336703554&customid=&store=modpointer_metabones&mpt=[CACHEBUSTER][/img]. Such adapted lenses can only be used with manual focusing and "working aperture" - there's no data coupling whatsoever here. However, due to the lack of fast prime lenses it's surely one of the more interesting fall-back solutions for the NEX-system. The field-of-view is equivalent to about 75mm in and in terms of depth-of-field it behaves like a f/2.8 lens in this scope - a rather obvious solution for portrait photography for instance. At around 650EUR the Zeiss lens isn't exactly a budget lens but compared to native Leica M lenses it is actually very affordable.

I reckon you'll agree that the Zeiss is a beauty of a lens. It's a full-metal construction build to the highest standards - except for the lens cap which is rather crappy. The focus ring operates as smooth as silk (dampened). The aperture is set in 1/3EV steps at the front of the lens. Any change of the aperture is applied immediately so you can check the effect on the depth-of-field on your screen (without the darkening like when stopping down a DSLR with a conventional optical viewfinder). The lens extends a bit when focusing towards closer focus distances. The front element does not rotate.


Manual focusing may sound like a major annoyance but it is not that bad actually. On Sony NEX cameras you can easily switch to a magnified focus view so accurate manual focusing is really simple ... unless you try to track a moving object of course. We recommend this camera-lens combination for static scenes only.

Specifications
equiv. focal length (full format)	75mm
equiv. aperture (depth-of-field)	f/2.8
Optical construction	6 elements in 4 groups
Number of aperture blades	8
min. focus distance	0.7m (max. magnification ratio 1:12)
Dimensions	52x68mm
Weight	230g
Filter size	43mm (non-rotating)
Hood	optional
Other features	-

DistortionsThe Zeiss lens produces a negligible amount of barrel distortion (~0.1%) which is irrelevant in field conditions.


VignettingTypical for full format lenses it has a walk-over on APS-C cameras with respect to light fall-off. Even at f/2 it's barely something worry about in real world situations and it's absolutely negligible from f/2.8 onwards.



MTF (resolution)The Zeiss lens delivers a fairly impressive resolution across the tested aperture range. The center quality is already very good at f/2 and f/2.8 and the borders follow on a good level here. There's a boost in quality at f/4 - the center is lifted to excellent quality and the borders are also very sharp. Diffraction effects reduce the quality from f/11 onwards.
Below is a simplified summary of the formal findings. The chart shows in line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations.


Chromatic Aberrations (CAs)Lateral CAs are very well controlled with an average pixel width of less than 0.8px at the image borders. This isn't really objectionable in field conditions.


BokehThe quality of the bokeh (out-of-focus blur) is, of course, a primary aspect of a fast prime lens. The Zeiss ZM produces a decent bokeh albeit not a perfect one. Out-of-focus highlights show an outlining effect at f/2. The highlight discs are perfectly even at f/2.8 but the circular aperture shape is already deteriorating at this settings and beyond. The quality of the blur in the critical focus transition zones is pretty smooth in the foreground, somewhat less so in the image background.


Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)LoCAs (non-coinciding focal planes of the various colors) are a common issue with relatively fast glass. As you can notice below the halos have different colors - magenta (red + blue) in front the focus point and green beyond. This is primarily a problem at f/2 and f/2.8. The issue dissolves from f/4 onwards.
Upon closer observation you may also be able to spot a slight focus shift towards the background (when stopping down) - this is rather typical for fast lenses but we've seen worse lenses here.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs f/2 f/2.8 f/4

Sample ImagesHere're some RAW-converted images taken with the NEX-5. Please note that there's no valid EXIF data due to the lack of electronic coupling. Most images were either taken at f/2 or f/8 so you may roughly conclude the aperture settings from the depth-of-field. Click on a thumbnail to view the original file (opens in a separate window). Please note that the originals are FULL SIZE samples (=several megabytes) thus requiring a significant amount of bandwidth so please take care of the limited resources here.

Make SONY Model NEX-5 ISO Speed 400 Focal Length 50mm Aperture: f/1.0 Exposure 1/320s	Make SONY Model NEX-5 ISO Speed 200 Focal Length 50mm Aperture: f/1.0 Exposure 1/1250s
Make SONY Model NEX-5 ISO Speed 800 Focal Length 50mm Aperture: f/1.0 Exposure 1/2000s	Make SONY Model NEX-5 ISO Speed 800 Focal Length 50mm Aperture: f/1.0 Exposure 1/500s
Make SONY Model NEX-5 ISO Speed 200 Focal Length 50mm Aperture: f/1.0 Exposure 1/400s	Make SONY Model NEX-5 ISO Speed 200 Focal Length 50mm Aperture: f/1.0 Exposure 1/2500s
Make SONY Model NEX-5 ISO Speed 200 Focal Length 50mm Aperture: f/1.0 Exposure 1/320s	Make SONY Model NEX-5 ISO Speed 200 Focal Length 50mm Aperture: f/1.0 Exposure 1/800s
Make SONY Model NEX-5 ISO Speed 200 Focal Length 50mm Aperture: f/1.0 Exposure 1/1000s	Make SONY Model NEX-5 ISO Speed 200 Focal Length 50mm Aperture: f/1.0 Exposure 1/1600s

Verdict
The Zeiss Planar T* 50mm f/2 ZM may be an exotic choice for Sony NEX users but it's certainly a highly interesting one. The lens shows no major weaknesses but there's still room for improvement. The center resolution is on a very high level at large aperture settings and the borders are pretty good here. The sweet spot is reached somewhere around f/5.6 with a very sharp results across the image frame. Lateral CAs are well controlled and not overly relevant. Distortions are basically absent. There's a tiny bit of light fall-off at f/2 but it's really nothing to worry about on the Sony NEX. The quality of the bokeh is generally fine although we've seen lenses producing a more buttery background at max. aperture actually. The build quality is just stellar thanks to an all-metal body and super-smooth controls. In a world of plastic lenses this rocks! As mentioned the Zeiss lens is actually designed for the Leica M mount (and Zeiss Ikon) so you've to live with an adapter solution and as such without AF. However, thanks to the EVIL design of Sony NEX cameras (magnified focus view, LiveView) this is less of an issue compared to adapter solutions on DSLRs. However, make sure that you can live with this manual workflow prior to rushing out and go for it.


ref: http://www.photozone.de/sony-alpha-aps-c-lens-tests/545-zeisszm50f2nex

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