The bokeh / depth of field between the Leica and Zeiss is quite different. The Zeiss is like a square wave form, the transition from out of focus to in focus is very quick and the depth of field is more discrete. Whereas the Leica is more like a sine wave form - the transition from out of focus to in focus is more gradual. Broadly speaking, the Zeiss does a better job of isolating the subjects (which is a trait of the Planar design) and the Leica is better at capturing a large depth of field - such as a landscape.

The color from the Leica and Zeiss is also different. The Zeiss produces a more saturated, livelier looking rendition. Whereas the Leica is more subdued, perhaps more neutral. With post-processing in Photoshop, the colors and contrast can be bent either way - so the Leica can have very contrasty colors (such as the windmill above) and the Zeiss 50mm F2 ZM can have great tonality (see the Zeiss 50mm F2 Planar ZM Review). If post-processing in Photoshop is okay, then either lens will work. If shooting JPEGs and you have little or no interest in post-processing, then pick the Leica if you prefer moodier colors. Or pick the Zeiss if you prefer more contrasty, saturated colors.

Both lenses have shown minor amounts of flare. This has happened when shooting sunsets and such, and the lens was pointed into the sun. Under those conditions I expect some flare. Neither lens produced objectionable flare, but there were small amounts. The big question is - how much of that flare was from the lens versus how much was caused by the IR/UV filter. When shooting city lights at night, the IR/UV filter causes ghosting and various other reflections and anomalies. I always have the IR/UV filters on the lenses when shooting the Leica M8, so I cannot say with confidence whether the filters induced the flare, or the flare was is inherent to the lens (design) itself. Though, I am 100% sure that the filters did NOT help.

Thus far I have not encountered any noticeable chromatic aberration (CA) from either lens. Likewise, I have not run into issues with veiling either. In terms of technical performance, both the Leica 50mm F2 Summicron-M and Zeiss 50mm F2 Planar ZM are well managed. The differences really come down to rendering, including - contrast, bokeh, color response and saturation. Some people refer to these traits (and other similar measures) as a lens’ fingerprint, and in that regard, I do prefer the Zeiss 50mm F2 Planar ZM’s fingerprint.

CONCLUSION

The Leica 50mm Summicron is a nice lens, but it is $1995 if purchased new (available at B&H). In comparison the Zeiss 50mm F2 ZM costs ~$800 new at B&H Photo. After using both lenses, I think the Zeiss lens offers a better price performance ratio. Leica no longer makes the 50mm Summicron-M in chrome, so if wanting a chrome finish, Zeiss is a good option because the 50mm F2 Planar ZM is available in both black and chrome.

I have owned two Leica 50mm Summicron-M’s and borrowed a friend’s as well.  The chrome copy seemed fine, but its rendering (bokeh, contrast, etc) did not “wow” me. The second copy (black) was not in the best of cosmetic condition.  Optically and mechanically it could have benefited from CLA (clean, lubricate and align). The last 50mm Summicron was borrowed. The owner had purchased it new, and it definitely it was the best 50mm Summicron-M I had tried. That said, its sharpness and resolution lagged well behind my Leica 50mm F1.4 Summilux-M ASPH. The Summilux had a 1 to 2 stop advantage (in terms sharpness & resolution) at every stop.

Given the Leica 50mm Summicron’s optical performance, it is difficult (for me) to justify spending $2000 on a F2 50mm lens. Used prices are lower, but still on the pricey side. There are many 50mm lens choices on the market today.  Optically the Leica 50mm Summilux-M ASPH is the best 50mm lens I have used on a rangefinder AND dSLR. It is the easy winner, but it has a very high price tag. The “value” choice would the Zeiss 50mm F2 Planar-ZM. The Zeiss has a more distinctive rendering (than the Summicron) and its resolution is very good when stopped to down F4-5.6. The only downside to the Zeiss 50mm F2 Planar ZM is its external hood.

The Leica 50mm Summicron-M does win when comparing build quality. The quality of the materials, the attention to details, smoothness in operation and final finish are all best in class.