Sony RX1 Sonnar 35mm vs. Leica M9 and Biogon 35mm ZM lenses review

Sony DSC-RX1 Carl Zeiss 35mm f/2 Sonnar vs. Carl Zeiss 35mm f/2 Biogon ZM comparison review

The Sony DSC-RX1 ultra-premium compact full frame camera with Carl Zeiss 35mm f/2 Sonnar lens has received a lot of praise for its technical achievements. Not only is it the smallest camera in its class (it’s perhaps in a class of its own at the moment), but it also attains very high levels of image quality, comparable to what one can produce from full frame interchangeable lens systems.

The Sonnar lens is the purpose of this review. More specifically, an examination of how well it and the RX1 hold up against currently available Carl Zeiss 35mm ZM-series lenses on the Leica M9 full frame 18MP camera.

Why the ZM lenses and not the ZE/ZF lenses? For a couple reasons:

1) It has been stated by some that for the price of the RX1 and a few accessories, one comes into used M9 territory. This is more so the case now that Leica has released the ‘M’ and used M9 prices have dropped below $4,000. For ‘only’ another $1,000 or so, one can add a quality ZM lens to the M9 and benefit from an interchangeable lens system not much larger in size with more flexibility than the RX1. Both options are much smaller than currently available full frame DSLRs with Zeiss ZE/ZF lenses.

2) I happen to use the M9 and am curious about how well the RX1 compares, and have access to both ZM 35mm lenses. If time and opportunities permit, I may revisit this comparison with some additional Leica M-series lenses.

Somehow, Sony has become the first camera manufacturer to release a full frame digital “Point & Shoot” camera comparable in size, if not smaller, to the previously mundane class of lower-end fixed prime lens film pocket cameras that no one really seemed to care about in the 1990s. But rather than landing at $200, the RX1 will, at the time of writing, set you back about $2,800.

Well, it’s not entirely true no one cared about fixed-lens non-zoom film camera backs in the 90s because there were some notably high-end cameras, such as the Nikon 35Ti and 28Ti, Contax T series, Konica Hexar AF, Leica Minilux, Ricoh GR series… and at the lower end, costing only a few hundred dollars, cameras such as the Olympus XA, Stylus and Pentax Espio Mini. Other than the Hexar AF though, the Sony RX1 outclasses all of these on the spec sheet by offering a faster f/2 lens than the more commonly found f/2.8.

Due to the current uniqueness of the RX1, it has already garnered significant attention and been the subject of many thorough reviews. I don’t intend to delve into point by point comparisons or evaluate all of the camera’s features. This review will primarily be about the lenses.

RX1 vs. Leica M9 and 35mm Sonnar vs 35mm Biogons:

The test photos can be considered a couple ways:

1) As a comparison of 35mm lenses and their optical characteristics, such as sharpness/resolution and how they render subject and foreground/background details through a range of distances and aperture settings. This is the primary interest of this review.

2) How the renowned Sony CMOS 24MP sensor stacks up against the often maligned, dated, 18MP CCD sensor in the M9. I would love to run this comparison with the new Leica M and its 24MP CMOS sensor, but regrettably don’t have one on hand. Due to the fixed lens on the RX1, it’s of course impossible to remove and test with the other lenses on the same sensor, eliminating differences in sensor performance and RAW converter interpretation that will inevitably color these results.

The lenses:

Carl Zeiss Sonnar T* 35mm f/2 permanently attached to the Sony RX1
Carl Zeiss Biogon T* 35mm f/2. For use on the M9, this lens was coded as the 35mm f/2 Summicron ASPH.
Carl Zeiss C Biogon T* 35mm f/2.8. For use on the M9, this lens was coded as the 35mm f/2.5 Summarit.
Voigtlander Nokton 35mm f/1.2 Aspherical VM II. For use on the M9, this lens was coded as the 35mm f/1.4

Note that the selection of Leica ‘equivalent’ lens codes may have influenced some imaging characteristics for each lens, such as overall color balance as well as vignetting characteristics. I’ve also found that the 35mm f/2.5 Summarit code is not an ideal match for the C Biogon due to residual magenta edge color shift along the left edge. But because I don’t use the lens much any more, I haven’t run the needed tests to determine if there is a better code match.

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Sony DSC-RX1 camera
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Leica M body (black) (the M9’s replacement) or (silver)
Zeiss Biogon T* 35mm f/2 ZM (black) or silver
Zeiss C Biogon T* 35mm f/2.8 ZM (black) or silver
Voigtlander Nokton 35mm f/1.2 Aspherical VM II

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Rob has also recently posted a ‘brick wall’ comparison of the RX1 against the ZM Biogon 35mm f/2.

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The test images:

On offer are a range of landscape scenes at different distances. Sorry, at this time a sample portrait was not possible. For all RX1 images, the camera was set to manual focus and focus magnification in the external EVF was used. For all lenses focus was set once, with the Sonnar’s focus determined visually via the EVF at f/2, and left at that focus distance for all apertures. There was no attempt made to compensate for any focus shift. Scenes were all shot on a tripod, first with the M9 composed in such a way that the rangefinder patch covered the desired point of focus in order to avoid the need for recomposing the scene for each lens, thus maintaining consistent framing. My apology that some of the images are a bit tilted – it’s one of the drawbacks of rangefinder composing.

The infinity scene of downtown Hamilton photographed from the escarpment edge was made by setting all M-mount lenses at infinity. The RX1 was focused via EVF as stated in the previous paragraph due to the lack of an infinity hard stop on the focusing ring.

For the remaining M9 sets, lenses were focused using the camera’s rangefinder. After the test, it became evident that the ZM 35/2 front focuses somewhat with my camera and that the Voigtlander back focuses. Unfortunately issues of time and weather have prevented reshooting the scenes most affected by this and is most noticeable in the ‘far’ focus set of Dundurn Castle (an old mansion in Hamilton), but are also noticeable in the various ‘near’ sets. These factors will need to be kept in mind by the viewer.

Except for the ‘Near 4’ set, each of the f/1.2, 1.4 and 2.0 images from the Voigtlander were too far overexposed due to direct sunlight for suitable recovery in software, therefore images made with a 3-stop neutral density filter have been substituted. Due to the ND filter, there will be slight white balance and tint differences. The process of physically attaching the ND filter may have also caused slight shifting of the camera, resulting in slight differences in composition.

RAW conversions were made with Adobe Lightroom 4.3 at the default settings. The only changes were to white balance, tint and exposure in order to get all images in a similar ballpark. This is partly because at equivalent ISO, shutter speed and aperture settings, the RX1 appears to be up to about a half-stop brighter than the M9. All were processed with the Adobe profile, except for the ‘Near 4’ scene of the trees, where the RX1’s profile was set to Camera Standard. Lens corrections, such as chromatic aberration, vignetting and distortion were disabled.

The differences in sensors and camera profiles adds variables to the images, which to my eyes results in the RX1 images sometimes looking a bit flatter, possibly due to somewhat wider dynamic range. Only in the infinity scene were the RX1 images tweaked with minor curves adjustments to bump up the contrast a touch. The RX1’s files are also quite robust for overexposure recovery. While the sunny f/2 and f/2.8 scenes were also photographed with the same ND filter used for the Voigtlander lens, the non-filtered images were recoverable without apparent loss in image quality.

It should be noted that any of these images can be considerably enhanced ‘to taste’ as the image at the very top of the page was, and while the samples provided may be a bit on the flat/dull side, the viewer should focus more on aspects of sharpness and background/foreground rendering characteristics than degree of contrast and saturation.

The images are available as full resolution sets in zipped folders hosted on Google Drive. The zipped folders range in size between 125-235MB. Click on an image below to access the file.

Infinity:

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Far (~15-20m):

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Near 1:

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Near 2:

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Near 3:

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Near 4:

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Close (closer than 1m):

My thoughts:

An immediate observation about the RX1’s Sonnar lens: it’s considerably wider than the other 35s tested, with the C Biogon being the narrowest angle of view. While most will likely never use these lenses at f/22, there was one interesting observation about the Sonnar at this setting seen in each set. The lens’s field of view suddenly ‘jumps’ slightly wider between f/16 and f/22. None of the other lenses did this, nor can I say I’ve ever seen this with any other lenses. I’m at a loss to explain why this happened.

Infinity: I read discussions about the RX1’s Sonnar lens not performing well at infinity and was curious about how it would compare against the Biogon 35 f/2, which is reputed to be very good for infinity/landscapes stopped down a couple stops. The Sonnar is quite impressive, if perhaps not optimized for infinity. Central sharpness is already good at f/2 and peaks between f/4-5.6. Edge sharpness seems to equalize between f/5.6-8. Softening due to diffraction begins to set in around f/11. Something I’ve not seen discussed is what appears to be a persistent dip in mid zone sharpness/resolution similar, though less severe, to the mid zone dip I pointed out for the Leica 21mm f/1.4 Summilux-M ASPH in the 21mm lens shootout. In the Sonnar’s images, this is particularly visible when viewing the green and white train in the train station.

The central area of the Sonnar at f/4:

The right end of the train:

Upper left mid zone area of the image:

Upper left edge of the image (is sharper than the mid zone area):

At moderate apertures such as f/4 or f/5.6, the left end of the train is sharply defined while the right end, as well as the buildings around that area, have a softer, slightly smeared look. This can also be seen in the high-rise buildings of the skyline at the top left, halfway between the left edge and the Sheraton hotel building. Unlike the 21 Summilux though, the Sonnar’s mid zone resolution dip is not nearly as annoying or noticeable. For most ‘normal’ uses, it likely will not be a factor and is perhaps a tradeoff for the lens’s close range performance. There is also what appears to be some purple fringing along high contrast edge transitions towards the edges of the frame at apertures between f/2 and f/4. While chromatic aberration exists, it is minor and not much of a factor.

In comparison, the 35 f/2 Biogon exhibits a fair amount of contrast and detail robbing glow across the frame wide open but progressively improves from the center as it’s stopped down. Sharpness is really impressive by f/4 across most of the frame and edges seem to improve somewhat until about f/11, when diffraction effects become evident. We’re probably also seeing some sensor characteristics affecting perception of these images relative to the 24MP Sony sensor. Lacking an anti-aliasing filter, the M9’s sensor will result in images that appear sharper, but the consequence is a greater degree of moire effects as well as false detail/sharpness and color. For example, the twin glass towers to the right of the Sheraton hotel. The window frames are a sky blue color, which is faithfully seen in the RX1 images but is lost between f/2.8 and f/11 on the M9. Inducing diffraction degradation at f/16 and f/22 seems to be comparable to ‘dialing in’ an anti-aliasing filter for the M9. CA is practically a non-issue with the Biogon, though there might be a slight red edge seen in certain situations with extremely critical examination. I am a bit suspicious that this copy of the Biogon front focuses slighlty at infinity.

The C Biogon is a pretty close copy of the Biogon when stopped down. Centrally it’s a hair sharper but the edges take longer to catch up. At f/2.8, it’s better across the frame than the Biogon. At equivalent apertures it appears to have a slight amount higher contrast than the Biogon. CA is non-existent throughout the aperture range. Something I noticed between the two Biogons, and might be related to the equivalent Leica lens codes I selected for use on the M9, is that the C Biogon appears to underexpose slightly, and vignettes a bit more. My copy might be a touch soft along the upper left edge.

The Voigtlander (which I will refer to as ‘CV’ for Cosina-Voigtlander) is included because it’s the only other M-mount 35mm lens I have available for comparison. I suspect most would buy this lens for wide open use – a necessity at times with the M9. The tradeoff is its considerably larger size and greater weight than the other lenses. But as the CV 21mm f/1.8 proved in my 21mm shootout, these recent high speed lenses from Cosina are surprisingly well rounded. Central performance wide open is remarkably good with some glow, though can be plagued with a fair amount of purple fringing. Contrast improves at f/1.4 and sharpness is already moire-inducing at f/2. Across frame performance is impressively good at f/2.8 and arguably better than all the other lenses. The Biogons seem to pull ahead slightly in the f/5.6 range with a touch better micro contrast. The CV exhibit the most CA of the bunch. It’s possible my copy is slightly off in the upper right corner.

It’s difficult to draw a clear conclusion because each of us will have our own priorities, and for some it won’t be infinity performance. The Sonnar holds up well, though is not the best. The Biogons, coupled with the M9’s sensor, seem to give the best snap/micro contrast, but at least the 35 f/2 needs to be stopped down a couple stops to remove contrast robbing residual glow. As with the CV 21mm f/1.8, the 35 f/1.2 might be the best ‘all-round’ performer here, considering it’s good wide open central sharpness and very good across frame performance by f/2.8. It’s only surpassed at a very fine level of detail rendering by the Biogons past about f/5.6 and suffers the greatest amount of CA. As far as micro contrast and image ‘snap’ is concerned, I’m not sure how much this is a factor of the different sensors, particularly the lack of anti-aliasing filter on the M9’s. The RX1’s images do have a slightly mushy character viewed at 100%. Some of this difference could possibly be reduced by resizing the 24MP files to the same dimensions as the M9, along with additional sharpening.

Far distance scene (Dundurn Castle): Here the RX1’s EVF and ability to zoom into the live view image for precise wide open focus was of value compared to the near-infinity calibration of my M9’s rangefinder and these three lenses. Unfortunately the Biogon is considerably front focused and the CV might be a touch back focused. In a more ‘normal’ scene, the Sonnar holds up well. Again, the Biogons seem to have a bit more snap stopped down, but it’s difficult to say how much this is the lack of anti-aliasing filter. All of the lenses purple fringe to some degree in the tree branches. The Sonnar clears at around f/4 while the CV takes until about f/5.6 and is the worst of the bunch. The Biogons also fringe a bit wide open, but it’s more difficult to see than the others, in part due to sensor related false color artifacts.

Near distances: This is where the RX1 will probably be most used – for people photography, daily life events, and so on. It’s also where the unique rendering characteristics of each lens becomes more evident. Here the Sonnar stands apart from the others with the calmest, smoothest background rendering. Out of focus objects such as tree branches retain their shape and volume with good contrast but soft edges. The Biogon is comparatively the harshest rendering with lots of double edges and hard edged out of focus specular highlights. The C Biogon is very similar, though a touch smoother in some instances. Both Biogons appear to have field curvature that bends away from the camera towards the edges, resulting at times in distant objects coming nearly into focus in the frame corners. I personally dislike this characteristic and it’s unfortunately quite common with many rangefinder lenses. The Sonnar seems to maintain a fairly flat plane of focus and the CV falls somewhere between the Biogons and Sonnar. Of the rangefinder lenses, the CV comes closest to the Sonnar with similar smoothness in lower contrast out of focus areas. But with out of focus tree branches, especially towards the image edges, and specular highlights, the harder edged rendering feels closer to the Biogons. It also has the strongest out of focus green/purple fringing in such areas. Wide open, the Biogon has a fair amount of spherical aberration (SA) that kills overall contrast and even stopped down has slightly flatter rendering than the C Biogon.

Conclusion:

Each of us will have different opinions about the RX1 on the whole and compared to other system options such as DSLRs or digital rangefinders. As a result, there are a number of arguments for and against the Sony RX1. In my opinion, one aspect that cannot be denied is the impressively high quality of the permanently attached Zeiss 35mm f/2 Sonnar lens. It’s fabulous with a wonderful balance of sharpness, contrast, color and smooth background rendering. I would love to have a lens like this for my M9. Is it worth buying the RX1 package (in my opinion the $500 EVF is mandatory – just watch that it doesn’t slip off the hot shoe unnoticed)? Again, a subjective and individual consideration. For me, the timing is not right at this price point, especially with my strong attachment to the Leica M system. I would rather put the money towards a lens or the new M. But as stated, this Sonnar, if it could be redesigned for M, would be an amazing lens. Speculation is Zeiss will release a 35mm f/1.4 in ZM mount… I can only wish it will be similar to the Sonnar.

Here are some random near-distance hand held shots between the RX1 and M9 with the Biogon. Keep in mind that because the images are hand held the framing will only be approximate. RX1 first, then M9:


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Download these and a couple more in high resolution here.

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Live in Canada and are looking for Zeiss lenses? Buy from Rob Skeoch at the Rangefinder Store or his sister site Big Camera Workshops, mention this site and receive a free B+W UV filter with your lens purchase, as well as free shipping (in Canada only).


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