The Leica Summarit-M 90mm f/2.5 is a fine piece of optics, with a reasonable price tag. It was one of the four lenses of the ‘new’ Summarit-M family unveiled in 2007.
This lens (Part No: 11646, black anodized) has come to my attention because it is one of the long telephoto lenses in the lineup (The longest is the Leica APO-TELYT-M 135 mm f/3.4) of the Leica M lenses. The specifications provided by Leica on their product page (technical data sheet downloadable) are as follows:
Number of lens elements/groups: 5/4
Number of aperture blades: 11
Minimum distance: 1 m
Filter size: E46
Weight: 360 g
Length: 66.5 mm
Diameter: 55 mm
6-bit coding: Yes
Minimum aperture: f/16
Some reviewers such as Ken Rockwell does not think Summarit-M series are made to the usual Leica standard. I may not have too much experience on using Leica M lenses but my initial hand-on feeling is that it is on par with my Summicron-M 50 mm f/2.0. The things that are ‘sub-standard’ are no built-in lens hood and no leather case ( instead the lens is protected by a soft pouch).
Some criticise the focus ring on the lens body is made of rubber. However, I find it comfortable holding in my hands and the focusing is quite smooth.
The external dedicated lens hood (Part No: 12460, designed also for the Summarit-M 75 mm, purchased separately) for Leica Summarit-M 90mm f/2.5 is made of light metal and in no way I find it cheap and sub-standard. It is far better than some of the plastic lens hoods from Canon. The hood fits with a metal cap so it serves as a very solid protection used in real world. To attach the hood on the lens, you have to detach the external thread ring at the front of the lens by turning anti-clockwise.
There is no need to attach a filter to the front of the lens after the hood is attached because it is big enough to withstand some unexpected force or little splash of water onto the front. This is a lens of course not made water proof or shock proof.
At first glance, I have to agree what Leica claims in its product brochure that a Summarit lens is a lens with amazing quality plus outstanding value.