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I have a B+W Circular Polarizer (67 mm) that fits onto my amazingly brilliant Canon 70-200mm f/4 USM Lens. This is a polarizing filter whose function is to limit the reflections within a scene as well as to increase the colour saturations to make the photo more intense and dramatic. I particularly wanted this filter to enhance my wildlife and landscape photography.
It fits onto the front of my lens by screwing on to it. It fits onto the lens easily without having to line it up manipulate it in any intricate way. However, the filter can be a difficult to remove as it gets stuck onto the front of the lens and, on more than one occasion, I have had to take some forceps to the filter's edge in order to give me enough purchase to unscrew it. It could be that I leave the filter onto the lens for long periods.
This polarizing filter is single coated and so it is preferable to uncoated as it improves the amount of light that it transmitted through the lens to 98% - which is pretty fantastic. In order to use, I simply rotate the outer rim on the filter to get the desired effect. The varied effects are often subtle but if you take the time to look at it on the viewfinder, it really can make a big difference to the overall quality of the shot.
I have noted that since I have been using the filter, my photos have improved. In particular I love the fact that the colours and contrasts are so accentuated, although it does so in an authentic way. When I have shot scenes with sunsets, the colours are just so bright and vivid - and it looks amazing. I have a particular shot at Foz do Iguassu which is brilliant - partly due to this filter. I have also noted that my urban scene photos have been improved as reflections are removed from all of the metal and glass surfaces that are in the scene (and surprisingly there are a lot within urban scenes).
This polarizer cost me £51.50 from Jessops (new) and it came with a ten year warranty. I've had it about 3 years and, so far, it remains in great condition without any serious wear and tear or scratches on the glass itself. There are some scratches around the outer rim but these are superficial and do not affect the function in any way.
I would recommend this filter to anyone who has a 67mm lens that they use a lot, especially if you take a lot of landscape photos.
When i upgraded my Nikon 18-105 lens to the Nikon 16-85mm lens I decided it was time I also invested in a better circular polariser. Up to that point I was using a Hoya HMC Circular Polariser which after a few years started to have a few tiny specks on the glass after some light cleanings.
The B&W I have is the MRC version which has a tough multi coating which is tougher than glass and will resist scratching. B&W claim the coating repels water so you do not get dried water marks. This was put to a test when I dropped the camera with filter attached into a stream! Off course I killed the camera but did not even have to dry the filter. It is a bit slimmer than the Hoya filter I was using previously yet it still has the option to add a further filter or clip style lens cap to the front. I believe that this is not the case with the very slim profile filters on the market.
Optical quality is very good and I can see that there is a more even, pleasing look to blue skies using this filter, when compared to the Hoya filter I was using. As with all polariser filters you can control the amount you want to polarise by rotating the outer ring.
A circular polariser is recommended for auto focus digital cameras and will help clouds stand out in the sky or darken the blue in the sky. It is also useful to cut down on reflection from leaves, water and glass. When using it in some instances you get the best effect when the sun is at 90 degrees to you.
After using this filter for 7 months I can highly recommend it as you do get what you pay for in terms of quality.