B+W 39mm F-Pro 486M UV/IR Cut Filter MRC
PLEASE NOTE THIS FILTER IS SPECIFICALLY DESIGNED TO BE USED ONLY ON THE LEICA M8 DIGITAL CAMERA.
This B+W Interference Filter has a completely colorless glass carrier coated with a number of extremely thin, partially reflecting layers with precisely computed thicknesses, similar to MC coating. The B+W Filter 486 does not block by means of absorption, but by interference of the unwanted UV and IR radiation that is repeatedly reflected between these layers, affecting the wavelengths on both sides of the visible spectrum with a steep cut-off. It is used mainly on digital and video cameras with CCD sensors without an integrated IR protection filter, because the IR sensitivity of the CCD sensor would otherwise cause color changes and unsharpness. That unsharpness results from the chromatic aberration of the lenses that are only corrected for visible light. In the visible range, the transmission curve is very high and straight. This filter is completely clear and it requires no increase in exposure. Its filter factor is 1.
IMPORTANT NOTE REGARDING WIDE-ANGLE LENSES.
Please note however that, in contrast to mass-colored (integrally colored) filter glass, the (486M) UV-IR cut filter is based on thin-film technology. More than 30 interference coatings are vapor-deposited on one side, while the opposite side is MRC-coated. In wide-angle lenses, the laws of physics lead to shallower incidence angles for peripheral rays. For geometric reasons these rays have to travel further through the interference coatings than rays traveling vertically through the coatings in the center of the lens. With increasing angle of incidence, this leads to a change in light color towards blue. This effect can clearly be seen by looking at an UV-IR barrier filter from an angle. The color of the reflected light changes, with a similar effect on the light traveling through the filter. The filter is therefore not suitable for lens systems with an angle of view of more than 60°
MRC by B+W is not only an extraordinarily effective multiple layer coating, it is also harder than glass, so that it protects filters from scratches (for instance when cleaning the filters), and it is also water and dirt repellent, thus facilitating filter maintenance.