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 MRC coating.
It 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. It has a
filter factor of 1.
Important Note Regarding Wide-Angle Lenses
Please
note however that, in contrast to mass-colored (integrally colored)
filter glass, the UV/IR Cut MRC (486M) 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 greater than 60°.
The pictures
gain brilliance and disturbing blue casts are avoided. Because the glass
is colorless, color rendition is not altered, aside from the
elimination of the unwanted blue cast, and no increase in exposure is
required.
That makes a UV filter very suitable as protection of the
front element of the taking lens against dust, flying sand, sea water
spray, and the like, and it can be kept on the lens at all times. It is
recommended for analog color and black-and-white, as well as digital
photography.
MRC - A Special Scratch-Resistant, Water and Dirt Repelling Coating
The left half of this filter has a
traditional coating. The right half
has MRC coating.
The
lens elements of high-quality lenses and the plano surfaces of filters
require a perfect shape and smoothness to
achieve the best optical quality. Dirt, greasy fingerprints, water
marks and scratches reduce the image contrast and the sharpness, which
can result in blooming at light sources and have an effect similar to a
soft-focus lens. A clean front lens element and clean filter surfaces
are therefore an absolute pre-requisite for demanding photographers.
The
MRC coating is first and foremost a broadband anti-reflection coating.
This means that its reflection-reducing effect, which is thus also a
transmission-increasing effect, i.e. one which suppresses scattered
light and ghost images and transmits more light, has a broadband action
over the full spectrum.
In contrast, the (almost always blue)
single-layer coating only has a high effect in the medium wavelength
range around yellow and yellow-green where the eye is most sensitive to
light, while its effect is greatly reduced toward the blue-violet and
purple-red end regions of the visible spectrum.
With the MRC coating,
this blue, violet and red to deep-red light cannot produce any contrast
reducing scattered light, spotty reflections or ghost images. A
broadband effect can only be achieved with a multilayer coating which
requires a much higher effort and precision because unevenness and
irregularities of the individual layers build up on one another and
amplify one another. Schneider therefore uses a plasma-assisted
evaporation coating process in which inert gas ions accelerated in an
electrical field compact the material deposited on the lens surface in
the vacuum chamber.
For
photographers, the main advantage of MRC coating, is it's ability to
combat flare and ghosting. An added benefit is that their filters remain
free of dirt longer, so that they do not have to be cleaned so often.
When cleaning the filter does become necessary, it is a lot easier to
wipe off the dirt with a blower brush, because of MRC's ability to repel
dirt and moisture. This also reduces the risk of micro-scratches which
can occur during cleaning.
