Wandering around in photoforums, one will sometimes read about the particular characteristics of some lenses. Some brands are qualified with almost magical properties.
The most famous is indeed the "Leica glow". Since it is relatively trivial to check hundreds of pictures taken with a given lens on flickr, I tried to find out if there was some truth in the legend.
The answer is interesting. Pictures taken with Leica M lenses have indeed a special "look" to them, most of the time. The reason is not some magic, but simply that Leica rangefinder users predominantly use wide angles and fast lenses wide open. What we see is the result of good lens design which gives high detail level but also residual spherical aberration. Spherical aberration, sometimes described as "veiling" gives this "glow" effect, when the light is right. It is quite easy to check the effect with a lens designed to manipulate spherical aberration (like the "soft focus" lenses)… instant glow!
Leica M lenses are great, but indeed they are not the only one with "glow". The Minolta 28mm f/2.0 is another one. Used at f/2.0 or 2.8, it gives this effect too. This should not come as a surprise, considering the previous tests: the lens has the combination of:-wide angle
-wide aperture
-high detail level, especially at the center
-corner shading ("vignette"), which emphasizes the subject
-high color contrast and slightly warm colors (the famous "Minolta colors").
So optically, on a test bench, a very imperfect lens. But in practical use a wonderful low-light lens. I would not part with it…
The lens has however a real drawback: coma. Look at these picture, this is the full frame:
Do you see the headlights on the bottom left? They look strange at this reduced size already. Here is what you see cropped at pixel level: almost like birds.
This is a real problem and it may ruin your picture. And it is not only headlights or lamps. Look for example at this tree. OK, there was not much to ruin but do you see the leaves in the corners? Quite ugly in my opinion.
But coma is somewhat linked to spherical aberration and you can rarely have one without the other. If you want the glow effect, you will have some coma.
