So you decided to gift yourself a Leica M 240. If anybody else bought you this - let me know :) Now it may be little intimidating to choose a lens. For Leica there are many options for lenses in same focal length. First someone has to choose a right focal length. For me it was 50mm. It may vary person to person but for rangefinder it is logical to have either a 50mm or a 35mm. You can get both if you have money but I prefer single lens at any given time for Leica to keep things simple in Leica style. Carrying multiple lenses with Leica may defeat the purpose of having a light weight high end camera. Plus I assume when a person buys a Leica s/he already passed through the initial days of lens craze when every one wants every single lens and want to capture every kind of picture. I believe a single mounted lens on Leica and take only selected shots just like a matured hunter does. Anyway that’s very philosophical - lets get into the lens selction. I bought 50mm for myself along with the camera. Summilux 50/1.4 ASPH 2012 version. Now is that the best lens for Leica? Nope - it absolutely depends. Lets see the options available for us. Remember we are going to discuss the first lens that one may want to have and considerations to choose one. Since we are talking about first lens - I assume thats pretty much going to either 50mm or 35mm in rare case we can remotely consider 28mm too but all others would be too wide or too tele to be used as a first general purpose rangefinder lens.
50 mm is my favorite rangefinder lens. I never had a 50mm on my Canon 5D MK2 that I own since 2008. But when I bought my Leica M 240 the lens I bought with it is 50mm Summilux. It is personal preference between 50mm and 35mm; I personally prefer 50 for several reasons - it allows comfortable distance between subject and the photographer at the same time close enough to have interaction if required. Another characteristics it has due to its semi-tele focal length is tighter image with close to real shape of the subject. You got it 50mm is my thing for general purpose and street photography and that’s my first lens. Now we have many choices in this focal length. Let me tell you one thing is most of these lenses are superb and none of them are absolutely better than other. In fact most of them have very high quality. The choice boils down to the characteristics of the lens we prefer and/or can utilize. With right skill all these different characteristics can be used in different situations. Lets see the options in this category:
Leica Summicron-M 50mm f/2:
I do not own this particular one but let me tell you absolutely love this lens and love it more than my own summilux 50 for most scenarios. It has nice "bokeh" or background blur ability; compare to Summilux this has different bokeh style and personally I don't care much about different kinds of bokeh in most sitations. I care about nice creamy bokeh only for portraiture and sometimes for macro for anything else micro quality in bokeh doesn't bother me. Right framing, focusing, color rendering these are more important to me in most style of photography. Another thing loveable about this lens is its incredibly small size - very much Leica type. Summilux is larger and heavier and only thing it has better than summicron is bigger aperture so faster in low light. Other than that no practical difference that will make ot ruin any shot. Even though I don't own this lens; I would suggest any Leica street photographer to buy this one. Unfortunately Leica is not making this lens any more - so you got to buy a used one :(
Leica Summilux-M 50mm ASPH f/1.4:
Two distinct things it has compare to the summicron - it is faster since it is f/1.4 and it is ASPH. One minor thing, admittedly minor for me, is - it has creamier bokeh. The farthest our of focus area appears to be painted with translucent paints, which is great but as I said does not matter much in street photography as long as there is good bokeh. I have this lens and always mounted on my Leica M 240 because of my newfound love for 50mm focal length. Now lest talk about the primary two characteristics this lens has - it is fast, at 1.4 it is crazy fast, not as fast as noctilux (f/0.95) though :) This is good while doing indoor photography; I found this today rescuer many times. The second thing is it is ASPH. ASPH means Aspherical; and it is a different lens design compare to spherical design. What’s the big deal anyway?
Above is the picture of Aspheric lens, as you see the curvature is not constant, it is different towards the edge than it is in the middle. Instead of going into too much of theory what I can tell you in short is - aspherical design reduces spherical aberration in lens. Look at the self-explanatory picture below.You got it. That’s the reason aspheric design is used to correct the aberration or focus smear. Correcting it in spherical design requires more lenses to be used leading the lens to be larger in size. Aspheric design reduces number of lenses required to correct this aberration and that works really favorably for Leica users - the correct and compact lens. So you know it now - ASPH is much better in getting microscopic focus. Does it matter in street photography? A little bit may be :) Hell I am biased towards my own lens - don't listen to me. BTW every lens has its sweet spot - this lens' sweet spot is at f=5.6.
Leica APO-Summicron-M ASPH:
Well a new term APO, and this is the new Leica 50mm Summicron in production, the one that it preceded is not aspherical and not APO. We already know what aspherical means and what benefit it brings. If you don’t know yet browse up - there is a picture of aspherical design. Now what is APO? Does it make sense to pay almost double the price for this APO thingy? APO stands for "apochromatically corrected" lens. Traditionally lenses are designed to focus blue and green on a single plane. As we know (hopefully) different colored lights have different frequencies and hence their diffraction varies too - so its quite a bit of work to make sure blue and green falls onto same plane while in focus. Traditionally, all the lenses do this but one other light gets left out - that is red. Using traditional lens - red falls slightly on different plane than green and blue due to its much lower frequency and much higher wavelength. Due to this optical behavior, red and blue-green are never in focus together – either blue-green are in focus or red - not these combination together. May not matter in most cases, but in enlarged print or digital display it can be seen. APO corrects that error almost entirely. That also makes the feel of the picture much different, sharper edge, smoother finish, creamer bokeh - as the out of focus colors does not appear discrete, they rather gets a smooth translucent cover on top. If money is not issue buy APO version, especially for portraiture work.
Leica Noctilux-M 50mm f/0.95:
Hehe this one is a sex machine. I did not get a chance to touch it yet but with Leica you cant go too wrong. What I hear and am sure of is about its low light capability when wide open at f=0.95. It will surely give you a possibility to see the night with an additional pair of eyes that your own eyes can't see. The super thin DoF provides whole lot of options for creativity - if you want to experiment. If you have money buy this :) I am planning to rent it soon and then I will write detailed review about it. For this post though, we are choosing first Leica lens - this is definitely not the first not because of it is expensive, but it is heavier than its brothers lux and cron. Another thing is it is not optically superior to APO Summicron-M 50mm as it lacks apochromatic corrective engineering. So if you have money to buy more than a summilux and you don’t care about ultra low-light performance then gift yourself a APO-Summicron - optically that’s the best piece of glass you can own in Leica M world. Canon, Nikon and likes they just have no clue about this high quality.