Freshly starting an M-mount kit is daunting to the wallet. On the Leica side of it, the average price for a moderately-fast M prime is around $3000. Zeiss will sell you similar & compatible lenses for about $1000 apiece, and Voigtlander will do the same closer to $500. When there is overlap between the three offerings, the more affordable (sic) options make a strong impression for would-be adopters.
The ZM 4/18 Distagon T*, ZM 2.8/21 Biogon T*, ZM 2/35 Biogon T* and ZM 2/50 Planar T* are all highly regarded by seasoned Leica photographers even. I would pick them up without hesitation. The premium of the ZMs over the Voigtlanders appears justified, by available analyses, and the premium of the Leicas not always. That has got to have Leica worried.
The adopter’s dilemma then, to Leica’s benefit, is when there are no alternatives or they are just as expensive. For example the Zeiss alternative for the 75~90mm length, the ZM 2/85 Sonnar, is overpriced to the point where there’s no reason to choose it over the legendary 75mm / 90mm APO Summicron-M lenses.
[Op-ed] If you’re going to spend $2900 on the “alternative”, why not spend $3500 and get the real APO original? – Zeiss missed the boat on this one; note the Sonnar is still not available anywhere for purchase after being announced almost 2 years ago.
Luckily, the Leica Summarit-M lenses sit right at (well, just slightly above) the price point I would have expected Zeiss to strike for the ZM Sonnar. The 75mm and 90mm Summarit-M lenses are available today for $1500, a clever pricing move on Leica’s part that will surely attract new photographers to their fold if they manage to solve the camera’s value-for-dollar issues (previous stories: part 1, part 2). Then which is the one to choose between these two lenses?
Leica 75mm Summarit-M
The 75mm Summarit-M is a very sharp, well-balanced lens. Performance is relatively even across the frame, particularly stopped down where detail treatment is essentially flawless. Wide open the corners dip pretty abruptly at f/2.5 and f/4, in a way that is probably more appropriate for its price class – it handily bests the cheaper Japanese competition but is bested by its more expensive German siblings. On a 1.3x crop frame where the far corners are not recorded, this lens a solid performer from corner to corner.
Leica 90mm Summarit-M
The 90mm Summarit-M performs only slightly worse than its 75mm sibling across most of the frame, except in the far corners where it picks up and shines. Stopped down, the gap closes in to an even 4~6% contrast difference across the entire frame, to the 90mm’s loss overall. Beyond 18mm along the frame the 90mm lens is best at all apertures, but the margin is slim from f/5.6 on. On a 1.3x crop frame the 90mm lens puts up a weaker performance, with its corner advantage negated.
The choice is imposed
In my opinion the choice between these two lenses comes down to the sensor formats and personal preferences. I am not fond of the 75mm focal length on 24x36 format (I revile 50mm on 16x24), but on 18x27 its performance turns unimpeachable and the picture angle equivalence changes into a pleasing 100mm even. The 90mm lens is close enough to this picture angle naturally, but on an 18x27 format however its performance lags behind. The stretch to a longer 120mm will make it harder to focus via rangefinder as well.
For now the winner seems to be 75mm Summarit-M. I doubt an affordable digital M-type would adopt the 24x36 sensor format early-on, rather it’s likely we’ll see a more common 18x27 or 16x24 sensor format. On film - or a hypothetical future high-end M-type with a 24x36 format sensor - I might prefer the 90mm Summarit-M.
Comparison to the 75mm APO Summicron-M
For a little over twice the price of the 75mm Summarit-M you can get the bar-setting 75mm APO Summicron-M ASPH, the class champ for the category. This extra expense gets you 2/3 of a stop more aperture, true apochromatic performance (of only a dozen APOs on the market), a faint improvement in detail sharpness and a marked improvement in close-focus ability. The true value of the APO Summicron is the "APO" aspect, of course, and for its intended audience that seals the deal.
Comparison to the Carl Zeiss ZF 2/100 Makro-Planar T*
As the price of even an “affordable” M-type kit will compete with mid-range 24x36 offerings from both Canon and Nikon, it’s worth comparing to their performance. The highest available performance at this focal length on DSLRs today is the Zeiss 2/100, often featured on this blog: part 1, part 2, part 3, part 4, part 5, part 6. The Zeiss is a smidge more expensive which means, factoring-in brand values, it ought to be quite a bit better.
On paper the Zeiss offers many of the same benefits as the APO Summicron-M, except of course apochromatic performance. The Zeiss is 2/3 of a stop faster, performs much better wide-open and focuses in much closer (advantage of SLRs over rangefinders). It performs only slightly better stopped-down however, is much larger and weighs several times more (a disadvantage of rangefinders over SLRs).
The Summarit-M offering from Leica is well balanced, both in terms of optical properties and in terms of value and pricing. In particular, the 75mm Summarit-M comes out as a good choice for a future M-type adopter, rounding out what is likely to be a kit mostly based on Zeiss ZM lenses.