Quote Originally Posted by freelanceshots


Can't find or understand what the explanation for the term Extra Wide means. From what I've understood in the past the slim mount is the one for really wide angle glass


B+W mounts are as follows:
  • Standard (aka F-Pro) - 5 mm thick, has front threads (standard CPL is 8 mm thick)
  • XS-Pro - 3.4 mm thick, has front threads
  • Slim - avoids vignetting by being thin, 3 mm thick, no front threads (Slim CPL is 5 mm thick)
  • Extra Wide - (referred to as oversize in the B+W handbook, but EW on the B+W web catalog), avoids vignetting by having larger diameter glass, 5 mm thick (I think), has front threads, filter glass is wider than lens thread (e.g. a 77mm oversized filter will have 77mm threads on the lens end, but the filter glass, and the front threads, will be 82mm).



So, the slim mount will generally do a good job at preventing vignetting, but the extra wide filter will do an even better job and is useful in cases where even a Slim filter would cause vignetting. I don't think you'd need an extra wide for any Canon lens, more likely for a wide angle medium format lens or a view camera.


Regarding the various types (and prices) of polarizing filters, the linear polarizers are always cheaper than the circular polarizers within a given mount size and optical quality. Mount sizes increase in price from standard to slim to extra wide. Optical quality increases in price from non-MRC to MRC toKäsemann. There are some gaps (e.g. none of the linear polarizers have the MRC coating). There's often a big jump from standard/slim to extra-wide, because the EW filters have larger diameter glass which adds a lot to the cost.


There's a description of their mounts, except the XS-Pro which is somewhat new, and more information including tables of which filters are available in which sizes and mounts, in the B+W Filter Handbook.