B+W 007 Neutral Clear Lens Protective Filter
This lens protective filter protects the sensitive lens against dirt, water and sanddrift. For the use on expensive lenses, its is a really worthwhile purchase, because replacing a filter is much more cheaper than replacing a lens.
The glass is absolutely plane-parallel and clear. In addition it has a high-quality Multi-Resistant-Coating. This coating makes the filter glass harder than normal glass and very resistant. Nevertheless there is almost no transmission loss. Furthermore the glass is water- and dirt-repellent.
The filter has a CNC machined F-Pro frame made of brass. The high quality standards of the manufacturer ensure that the frame is very robust and precise. B+W filters are very easy to screw on and off. The frame is very thin (approx. 4.5mm) so that it can be used on wide-angle lenses without causing vignetting.