Zeiss C Sonnar T* 1,5/50 ZM

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Last updated September 26, 2012

The Zeiss description for this lens

The Fast and Compact Photojournalist

This standard focal length offers special qualities which make it well suited for portraiture. The ‘C’ designation in the C Sonnar T* 1,5/50 ZM name means both ‘compact’ and ‘classic’. The lens design and aperture geometry reflect its predecessor from the 1930s, the Sonnar 1,5/50, which was the fastest standard lens of its time. The excellent flare control inherent of the Sonnar lens design is further optimized with the ZEISS T* anti-reflection coating. This new lens stays true to its heritage, physically resembling the objectives of by gone days. With its fast aperture, taking photographs with a beautiful ‘bokeh’ that reflect the ambiance of the golden age of rangefinder photography is as simple as pressing a button.

Important specifications

Focal length 50 mm
M8 equivalent 67 mm
Aperture range 1.5 - 16 (1/3 steps)
Aperture blades 10
Focusing range 0.9 m – infinity
No. of elements/groups 6/4
Angular field, diag./horiz./vert. 45.7/38.4/27 °
Filter M 46 x 0.75
Dimensions (with caps) ø 56 mm, length 63 mm
Weight 250 g

Performance Data

The following graphs were gleaned from the Zeiss-provided datasheet (PDF) for this lens:

Introduction

A full review of the Zeiss C Sonnar T* 1,5/50 ZM lens, including specifications, performance charts, overview, sharpness and vignetting tests as well as sample images and links for further research.

The C Sonnar T* 1,5/50 ZM is a bit of a controversial lens. There are basically two camps; those that like it and those that don't - as it's that kind of lens. The issue at the heart of the matter is the focus shift, which we'll get into below. If you can deal with this issue (and it's not really difficult, but it is something to think about when shooting) the reward is a very unique character; the so-called "Sonnar look." Wide open, this lens has a fantastic old quality to the bokeh with a rapid transition from in- to out-of-focus regions.

Consider reading about all the things they have in common in our Zeiss ZM Lenses overview.

The Lens

Like the other ZM lenses, the Sonnar is well-built and solid-feeling. The materials and craftsmanship are both of a high-order. The aperture ring has positive, somewhat firm detents from f/1.5 to f/16 in third-stops. This differs from the Leica standard of half-stops, so it's something to keep in mind if you have a mixed bag. It's useful especially if you shoot slide film but also with the M9 if you're used to dialing in exposure compensation - which is also in third-stops. The focus ring is smooth and well-damped, but not as much as Leica lenses.

When it comes to performance, the Sonnar is almost like having two distinct lenses. Wide open at f/1.5, the lens is well-known for the "Sonnar look." Very hard to define, but one you'll know when you see it. The bokeh is unique and the rapid transition from in- to out-of-focus regions makes the depth of field appear thinner than you might expect. Some unfairly call the lens "soft" wide open, but that's not entirely true. The central region is sharp and well defined, but due to curvature of field - the corners and edges soften up from the center. This makes for dramatic separation of your subject from the background. As you stop down, especially from f/2.8-4 and down - the lens sharpens up across the field quite rapidly and approaches the level of modern lenses. This is the behavior that fans of this lens really enjoy.

Compared to other ZM lenses, the Sonnar is a bit shorter and a bit wider. The 46mm filter size is common among ZM and Leica lenses, making it easy to share filters - especially the pricey UV/IR filters for use with the M8. It does have a unique hood among the ZMs, unlike some that can share a hood. It's an additional expense, hovering around $100 - but worthwhile to have. Made of metal and attached quickly via a bayonet mount, it's angled and vented to allow for a better view through the finder. While Zeiss was smart to offer lens caps with both side and center "pinch" tabs, they really dropped the ball on the grooves - which run perpendicular to the ideal. This makes for a bit of a slippery, fidgety affair. But they work well otherwise, especially with a hood attached.

Focus Shift?

As supplied from Zeiss, it is optimized for shooting at f/2.8. That means that at f/2.8 - what you focus on is accurate. The focus shift issue rears its head when you start to open up the lens, especially wide open. The focus shifts towards the front of your focal point and the amount of which depends on subject distance. It's not a huge shift, some 1-2" depending. There are a few options to deal with this. The first, is stopping down. At f/2.8-4 or smaller, the depth of field will cover any shifting. The second option is to learn to "zen" the focus. That is, you focus normally, but "lean into" your shot a little bit, thus moving the focal point further back. A similar approach would be to just focus a little further back that you normally would (e.g. focus on a person's ears instead of eyes). The last option is a bit more drastic, but if you plan to shoot this lens wide open most of the time (and I know I do) you can send the lens to Zeiss under the warranty period and they'll optimize the lens for shooting at f/1.5. The focus shift will still be there, but it's more hidden as you stop down - until the depth of field masks it.

Zeiss has provided the following additional information regarding the Sonnar:

C Sonnar T* 1,5/50 ZM Information about special features for dealers and users The C Sonnar T* 1.5/50 ZM is a very special lens; based on a classical lens design concept from the 1930´s. The additional letter “C” in the name of the lens expresses this designation. This lens design helps to achieve pictures with a special artistic touch. This lens ‘draws’ your subject in a fine, flattering manner and is therefore ideally suited for portraiture. It renders a sharpness that is slightly rounded, being less aggressive than in contemporary lens designs, but at the same time not soft in its rendition. Many famous portraits of glamorous and prominent people during the 1930´s used this technique to great effect. These images are characterized by portraying the person in a shining, nearly celestial way. This effect is very well balanced and not exaggerated; therefore many viewers see it in a subconscious way. The trained observer, however, understands the underlining technique and enjoys the results. This lens design exhibits some additional effects, which should be understood to achieve the maximum benefit from the C Sonnar T* 1.5/50 ZM: Because of the above mentioned classical characteristic of the lens the best focus position in the object space can not be kept exactly constant for all f-stop settings. The passionate photographer might notice a slightly closer best focus in his pictures than expected. When stopping down the lens to f/2.8 or smaller this effect is minimized, so the focus position will be as expected. In order to balance the performance at full speed and other f-stop settings the lens is adjusted with above described characteristic. The special features of the C Sonnar T* 1.5/50 ZM are best used in emotional, artistic, narrative images, portraits or atmospheric landscapes. For documentation or technical subjects Carl Zeiss recommends to stop down the lens at least to f/5.6 or to use the Planar T* 2/50 ZM lens.

The focus shift can be seen illustrated below, in the "Sharpness" section. This represents the worst-case scenario; at minimum focus distance and wide open.

Coding for Digital Ms

This lens is typically given the 6-bit code of the Leica Summilux 50mm f/1,4 ASPH (11891) - which works well on both the M8 and M9 bodies. The code for this is 100000 and can be either marked with a template and a Sharpie marker or machined into the flange and properly painted for a more permanent solution via a third-party. The 50mm focal length doesn't typically need to be coded for in-camera corrections, at least - but is still useful for the EXIF info and to differentiate between lenses.

Other Thoughts

Many want to compare this lens to other 50mm lenses, especially the Planar T* 2/50 ZM and wonder which they should get. The Planar is almost, but not quite a stop slower than the Sonnar. It is a more modern design and does not have the focus shift (or the unique character) of the Sonnar. It can be described as "more clinical." You could say the Sonnar is an "artistic lens" whereas the Planar is more of an "everyday lens." With the Planar, there's nothing to think about when shooting it (focus shift) and it's very sharp from wide open, even into the corners. If you do a lot of shooting with the 50mm focal length, you might consider owning both depending on what you like to shoot. The Sonnar is definitely worth checking out in any event.

Vignetting

Vignetting was tested using the M9 at ISO 160, firmware version 1.162:

Lens detection set to OFF

f/1.5

f/2.0

f/2.8

f/4.0

f/5.6
 
 
Lens coded as a Summilux 50mm f/1,4 ASPH (11891) and lens detection set to AUTO

f/1.5

f/2.0

f/2.8

f/4.0

f/5.6
 

Sharpness

This test is preliminary, and only tests the center performance - but it should give you an idea of what to expect. It was conducted by shooting a test target at MFD (.9m) which represents a worst case scenario as non-macro lenses are generally optimized for infinity. Images were shot at the various apertures with an M9, mounted on a tripod. No alterations were done to the image except for auto level and they are 100% crops:

f/1.5 f/2 f/2.8 f/4 f/5.6

Since this lens is optimized at f/2.8, that's where you'll see the most accurate focus. However, as the lens is opened up to f/1.5, the focus shifts forwards, or closer to the camera. That's why the f/1.5 and f/2 images above seem so soft. In order to compensate, the camera was moved forward in increments until relatively accurate focus was achieved. This test is more for illustrating the focus shift effect and not ultimate sharpness at f/1.5 - though it does come close. Further movements of the camera in 1mm increments may have revealed a sharper image therefore. Testing at the minimum focus distance (.9m) is also the worst case scenario of focus shift and improves at greater distances and as the lens is stopped down towards f/2.8. Beyond that the depth of field also helps to hide any remaining shift.

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Sample Images

Flickr Pool Images

Further Research

Sample images thread in forum  
   
C Sonnar T* 1,5/50 ZM zeiss.com
ZM C Sonnar 50mm flickr.com
Zeiss 50mm f/1.5 Review kenrockwell.com
Zeiss 50mm f/1.5 C Sonnar ZM luminous-landscape.com
Carl Zeiss 1.5/50 C Sonnar T* ZM Review photoog.com
Zeiss 1,5/50 C Sonnar in ZM mount rogerandfrances.com
Zeiss 50 Sonnar 1.5 For Leica M Lens Review stevehuffphotos.com