Answers to the most frequently asked questions (FAQ ) 
of our customers about B+W filter products:

• How much do B+W filters cost, and where can I buy them?

• What items of information are necessary to order a B+W filter?

• For my camera, do I need a linear or circular polarizing filter?

• What is different about a Käsemann polarizing filter?

• Is the additional expense for a filter with MRC coating worth the money?

• How is my filter coated?

• Can I leave the filter on my camera all the time?

• Should I buy UV or Skylight?

• Are filters necessary at all for taking pictures?

• And in digital photography?

• How do I clean my filter?

• What does the multiplying factor mean?

• Can I attach several filters on top of one another?

• Does a B+W SLIM Filter really have advantages?

• Are digital filters different from "normal" filters?

• Why should I buy a B+W Filter?

How much do B+W filters cost, and where can I buy them?

B+W products are available photographic supply stores only in Germany or through our representatives world-wide. In Germany, that can be your local photography supply dealer, a mail order firm, or a firm selling through the Internet. There you will also find information about prices.

What items of information are necessary to order a B+W filter?

In buying a filter, two items of information are important. For one thing, the filter type or the B+W filter number, and for another, the thread on the front of the lens. You can find the description of the filter with the B+W type number in the B+W brochure or on the corresponding Internet pages, the information about the required size of connection in the directions for use of your camera, or from the manufacturer of your lens. 

IMPORTANT : the diameter and pitch of the thread.

Do I need a linear or circular polarizing filter for my camera?

For cameras with through-the-lens measuring (exposure measurement) -- whether manual or automatic -- and autofocus, polarizing filters in circular configuration are necessary in order to prevent errors in measuring the exposure time. Today this applies to well over 90 % of all cameras. Linear configurations are used, today as formerly, in professional photography, stereo projection, and in industrial applications. 

TIP: In any case in which linear polarizing filters suffice, circular polarizing filters can also be used, but not the other way around. 

A detailed description of the physics of the way linear and polarizing filters work can be found in the B+W brochure or in the relevant technical literature.

What is different about a Käsemann polarizing filter?

Of all the B+W polarizing filters which we offer, the Käsemann configuration has the highest optical quality. The polarizing film is more neutral in color, the efficiency (extinction of distorting reflections) is higher, and the cover glasses are additionally ground and polished. For this reason, the image sharpness (MTF) of a high quality camera lens is not impaired (particularly applicable to aspherical zoom lenses). In addition, the centered edge of the glass of the polarizing filter receives a lacquered edge which protects it against moisture, a feature which prolongs the useful life of the filter and improves the usefulness of the filter in tropical climates. All of these factors are very important criteria in deciding on a good polarizing filter. 

For this reason, professionals (professional photographers) use exclusively B+W Käsemann polarizing filters.

Is the additional expense for a filter with MRC coating worth the money?

Quality begins in front of the lens, and that, as everybody knows, is where the filter is placed. A filter must not diminish the performance of a lens. MRC (Multi Resistant Coating) coated filters have a Multi-Coating layer on both sides, which assures the maximum reduction of reflections and distorting scattered light. Because of their increased hardness, the layers on both sides of the filter protect it from scratches, and thus insure its high optical quality. In addition, this MRC layer repels dirt and moisture (hydrophobic). 

For this reason, cleaning it is child's play.

How is my filter coated?

Certain information is engraved on every filter. These data have to do with diameter, filter type, or type number, and when required, the multiplying factor and details regarding the coating.

For example, if the filter is inscribed with MRC (in the case of older versions, written out in full as "Multi Resistant Coating"), then it is an MRC-coated filter. If this indication is missing, then it is not MRC-coated. If it is a photo filter, then in most cases it has a simple coating on both sides (= B+W Standard). Filter types like trick and contrast filters, as well as infra-red and strong grey filters, are not coated. Additional details may also be found on the B+W complete list .

Can I leave the filter on my camera all the time?

Filters with which an image is visibly corrected (e.g., polarizing or conversion filters) or through which an image is to be deliberately changed (e.g., special effect filters such as diffusion filters) should not be left on the camera, but mounted only when specifically required. In practice, two types of filters which have proved to be reliable can be left on the on the lens permanently, and which also serve as ideal protection for the front lens. These are the UV- or Skylight filter.

Should I buy UV or Skylight?

The UV filter blocks intrusive UV radiation which otherwise could cause a lack of sharpness. The contrasts are heightened, and unpleasant fog is avoided. The UV filter is used with color-reversal (slides) and black and white / color negative films, and in digital photography. In order to avoid blue cast or to achieve a warmer image, the Skylight filter is used for color slides.

The Skylight filter (KR 1.5) absorbs the excess blue which is present in daylight, and thus produces a warmer color tone. At the same time, it blocks UV rays, and reduces the haze around distant objects.

Both filters are exceptionally well suited as protection for the front lens, and can be left permanently on the lens.

Are filters necessary at all for taking pictures?

In order to achieve more brilliant results with your pictures, filters are indispensable. They solve a multiplicity of problems. A UV- or Skylight filter blocks UV components (UV filter) and hinders blue cast (Skylight). On a vacation in the mountains or at the seashore, they are an indispensable companion. Both filters can be permanently left on the lens and are ideal protection for the front lens. Polarizing filters help produce stronger colors and suppress distorting reflections. Color filters prevent color distortion. B/W filters help achieve greater contrast. Light reduction is achieved by neutral grey filters . The invisible is made visible by the infra-red filter. Small subjects look quite large with the close-up or macro lens. Trick and supplementary lenses enhance the creativity of the photographer and allow compositions which would be simply impossible without them. 

Filters increase individuality and creativity. 

  Filter Catalog

And in digital photography?

In digital photography, despite a plethora of comprehensive image-processing programs, filters have to be used. Image data which are lost when taking the picture cannot be reproduced later on the computer, e.g., in connection with reduced reflections with polarizing filters. Precisely in the area of the digital photography, it is important to use filters of excellent quality, such as those which B+W produces.

In particular, the enormous resolving power of the lenses of digital cameras requires the highest optical quality.

How do I clean my filters?

First of all, loose dust must be removed. This is best done with compressed air,
a bellows, or with an appropriate brush. Solid particles can be easily removed with
B+W Photo-Clear. Tough smears can be removed with the liquid cleanig solution
B+W Optic Cleaner which you can obtain from your photography supplies dealer. 

IMPORTANT : When cleaning your optical devices, always follow the manufacturer's
directions.

What does the multiplying factor mean?

Almost every filter holds back a part of the light (absorption) by virtue of its monochromatic character. This loss of light is compensated for when taking the picture by a corresponding increase in the exposure. The required correction value is called the multiplying factor or the filter factor. The factor itself is indicated on every B+W photo filter. The factor can also be found in your brochure.

The multiplying factor is not a constant; rather, it varies according to the lighting conditions and the kind of film. As part of the filter information, the factor most used for daylight is given. Depending on the situation when the picture is being taken and on individual preferences, it is always possible to adjust these values. Of course, instead of increasing the exposure time, the aperture can be increased to obtain the necessary amount of light.

The factor does not mean increasing the diaphragm or the exposure time by the value indicated. When the indication is 2x, this does not mean, as is so often assumed, that the diaphragm or the exposure time is to be changed by two steps. 

IMPORTANT : The exposure time measured without the filter must be multiplied by the filter factor! 

If, for example, the exposure time is set at 1/500 sec, the correct exposure time with a multiplying factor of 2x is now 1/250 sec. 

In practice, the exposure correction is usually converted and the exposure adjusted by means of the diaphragm. The following table shows the conversion of the most important filter factors to stop values.

Almost all cameras today have a built-in light meter. The multiplying factor is then automatically included in the calculation.

T

 Can I several attach several filters on top of one another?

Filters can be combined. This is of importance, e.g. in connection with polarizing filter and  Redhancer, close-up lenses of different strengths, (e.g., NL+1 with NL+3 equals NL+4), or grey filters, in order to allow for intermediate steps. This also applies to experiments in the area of trick and effect filters.

IMPORTANT : When combining filters, the filter factors must be multiplied and not
simply added together! 

More than one filter of the same category should not be used. It makes no sense, e.g., to mount a SW filter and a yellow and a red filter at the same time, since only the strongest filter, in this example the red filter, will have any effect. In order to maintain picture quality, not more than two filters should be mounted on top of one another. With short focal lengths, it should be kept in mind that vignetting can occur.

Does a B+W SLIM Filter really have advantages?

The B+W SLIM Filter is a filter which is placed on a very flat filter mount. The height is only 3 mm, in the case of rotatable polarizing filters 5 mm. This makes it possible to achieve vignette-free photos from extreme wide-angle shots, even at very short focal lengths (up to = 17 mm/KB). 

Are digital filters different from "normal" filters?

With digital cameras, new and, in particular, smaller thread diameters are constantly coming onto the market. In this camera segment, silver-colored filters are in demand. B+W has expanded its product line by include the diameters in question, and the result was the filter series B+W Digital Pro. This filter series is, in design and in connection sizes, specifically conceived for digital cameras and camcorders. The filter glasses correspond to those of "normal" photo filters.

The B+W Type 486 UV-IR CUT filter (Transmission curve) can characterized as specifically a digital filter. This interference filter blocks the UV and IR components which interfere with the electronic photographic medium. 

Why should I buy a B+W Filter?

As far as filters are concerned, B+W's competence is unique. In over 50 years of manufacturing experience, we have developed first-class know-how. A B+W filter stands out, especially because of its excellent optical and mechanical properties. B+W has a very widely differentiated product line with the most varied filter glasses and diameters. After outstanding quality, for B+W customer satisfaction and service have the highest priority. The B+W team would be happy to answer any further questions you might have. Of the entire field, B+W sets the standards in the photo filter sector.