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Baader Planetarium Contrast Booster Filter

Baader Trademark (19,559 bytes) Baader Contrast Booster filters (95,263 bytes) The Contrast Booster is among a series of filters marketed as violet blocking. It is a multi-bandpass filter transmitting light in the visual spectrum but biased in a way so that it eliminates transmission of light in the violet portion of the specutrum. For users of Achromatic telescopes this filter enhances contrast, making the objects appear sharper and more clear particularly so when observing the brightest objects including as the moon and planets. It does this by reducing the violet secondary spectrum that is referred to as "Blue Blur" and "haloing" that is often perceptible when observing with achromatic telescopes. This filter is a good choice for those who use moderately priced achromatic refracting telescopes that are usually not corrected to perform well into the violet portion of the spectrum.

Right: Baader Planetarium Contrast Booster 2 inch filter shown with provided plastic case and box.(95,263 bytes).
Click on image for enlarged view (176,791 bytes).

What Does This Filter Do For Me?
This filter is especially designed to improve the ubiquitous beginners telescopes. Colors of the spectrum have differing wavelengths. In normal optical glass the red, green, and blue rays of light are bent at slightly differing angles as they pass through. This dispersion shows up as color fringing (chromatic aberration) and it tends to reduces sharpness of the image since all three primary colors are not brought to focus at the exact same plane. Achromatic telescopic lenses refract (bend) the light as it passes through the glass, and this magnifies the variation in focus between colors in the extremes of the visual spectrum - the red and blue rays. Therefore, an Achromat can only bring two of the three primary colors to focus. Since most moderate performance telescopes sold are designed for visual use and since the human eye is less sensitive to deep violet than crimson red, these telescopes are corrected accordingly. So when one looks through an Achromat at a bright star such as Sirius or Vega, or when one looks at the Moon, one will see a violet colored halo appearing to surrounding such objects.

Strongly emphasizes surface detail on Jupiter and Mars, and does this without marked changes of the planets natural colors. "You haven't really seen Jupiter's Great Red Spot through your achromatic refractor until you've used this filter."

Provides a more professional replacement for the simple "dark green" Moon made of "raw polished" glass. The Moon appear more natural in color and even with a slight yellowish tint there is a noteworthy improvement in details seen.

Can enhance contrast to reveal finer details when used for solar observation but only in combination with the optional Baader AstroSolar Safety Film!

While this filter may at first glance appear similar to the Moon & SkyGlow, it is primarily designed to serve an entirely different purpose although it too blocks atmospheric sky glow near the city - the night sky background turns pitch black!

For CCD imaging we recommend combines the Contrast Booster with the planoptically polished Baader Infrared Cut Filter. In this combination all blue scatter as well as unfocused near infrared light is completely removed - an absolute must for digital imaging!

Planoptically polished, suitable for being used in front of a binocular viewer, or for afocal image projection during digital imaging anywhere in front of the focal plane!. There is no perceptible deterioration of resolution with magnifications of 200x and more!

The Contrast Booster available in diameters of 1.25 (31.7 mm) and 2 inch (50.8 mm).

How Are These Constructed?
The filter is made with a disc of selected substrate of Neodymium doped glass that has been ground to be plane parallel and then polished until very smooth. The glass undergoes a vacuum deposition multicoating process where twenty three microns-thin layers of various elements are applied one upon another in a precise order and thicknesses to produce the desired bandpass.

The filter element then undergoes a seven layer hard multicoating process to reduce undesired reflections to 0.25%. This improves light transmission and reduce possibility of ghosting or reflected images.

These ion beam deposited coatings on both surfaces are durable and scratch resistant. They will tolerate most common sense cleaning methods.

The filter element is housed in a machined aluminum cell, retained by a thread in retaining ring. The filter name, size and part number are in silver, and this mirror like print when combined with the fine print make this information difficult to read under dim red lighting. Company Seven recommends our customers keep these filters in well organized accessory cases, so that you know which filter is which. It helps to become familiar with how the elements appear too.

Contrast Booster Filter Graph (105,886 bytes) Right: Baader Contrast Booster filter transmission curves in nanometers, with the transmission (permeability) given in per cent. The area under the curve is the spectral region which the filter transmits (105,886 bytes).

Features Of The Baader Filters:

  • The glass elements used to make the Baader Filters are free of striae, optically finely polished plane parallel to within 30 seconds of arc. This eliminates any double images or ghosting due to wedge errors in the glass. These filters tend to far supersede the quality of common color filter elements which are flame polished. The combination of their fine optical craftsmanship and a comparatively thin 2 mm profile allows these filters to be inserted anywhere into the optical path without introducing astigmatism or other noticeable defects into the image. For instance they can be installed in the front of a Binocular Viewer without degrading the image in any way.

  • Transmission in peak areas is better than 95 percent.

  • All filters will thread into conventional slip fit eyepieces or accessories with the common 1.25 inch diameter x 42 tpi (28.5 x 0.6 mm) or 2 inch (50.8 mm) threading. These thread patterns have been tested and optimized to fit allmost all eyepieces on the market.

  • Stackable filters: each filter cell incorporates both a male and a female thread to allow stacking the filters to obtain even narrower passbands or special effects. When stacking filters on an eyepiece, be careful that the eyepiece barrel with the filters attached does not strike the mirror or prism of your diagonal.

  • The filter cells features the largest clear aperture of any 1-¼ and 2 inch filters on the market - for complete freedom from vignetting at any focal length. The front crown of the cell incorporates milled notches which makes handling and threading the filter an easy operation in the dark.

  • Multi-layer coatings on the front surface are a twenty three (23) layer dielectric long pass blocker Ion beam hardened coatings on both faces. This coating is scratch resistant, and may be cleaned with common approved techniques (see below).

  • Multi-layer coatings on the rear surface are a seven (7) layer hard-multicoating, featuring 0.2 percent reflection. This coating are hard and durable ion-beam hardened coatings, and may be cleaned as needed.

  • For protection, each filter is provided with its own transparent plastic case. We are astonished however, that as outstanding as the filters are, plastic case latch tend to fail sometimes even when new. Company Seven therefore offer optional third party cases. And for the most discriminating clients, we even offer a custom made wood accessory case described below.

    Optional Wood Case
    optional wood case for Questar Color Filter Set. (52,803 bytes).

    Company Seven makes available to our customers an optional wood case that is foam lined with cutaway spaces for filters, eyepieces and other small accessories for your telescope. Please refer to our price list for current prices for the filter set and the optional case or contact Company Seven for more information.

    Right: optional wood box for Color Filter Set (52,803 bytes)
    Click on the image to see enlarged view (190,049 bytes).


    • PDF IconBaader Planetarium Professional Astronomical Filters one page color illustrated overview of several Baader specialized astronomical filters including the Moon & SkyGlow, Oxygen III Narrow Band, Contrast Booster, Color Filter Set, UV-IR Rejection, Fringe Killer, Solar Continuum, UHC-S High Transmission Nebula, and U-Filter. Includes filter transmission curve graphs. Publication content by Baader Planetarium, all rights reserved. From Company Seven's Archives (127,011 bytes in Adobe .pdf).

    • PDF IconBaader Contrast Booster Filter one page color illustrated overview of this filter. Includes filter transmission curve graph. Publication content by Baader Planetarium, all rights reserved. From Company Seven's Archives (265,190 bytes in Adobe .pdf).


    1. It is best to protect the filter from sharp edges or any item that could cause a scratch or abrade the glass.

    2. When not in use, store the filter in a its provided rigid container, and it may help you to keep them organized in a fitted carrying case.

    3. Dew may form on the filters, if this happens do not store a wet filter into its airtight container for long periods of time; whenever possible let the filter "dry out" in order to reduce the potential for problems developing associated with Fungus, etc.

    4. Draw any large, loose bits of foreign matter from the surface of the glass with an air bulb or small vacuum. Stubborn particles can be removed with a soft camel's hair brush. Throughout the year, but especially in cold climates when static become more of a problem we particularly recommend the use of a Staticmaster brush.

    5. Place a few drops of an approved lens cleaning solution (by Carl Zeiss or Kodak) or mild soap solution of clear dish washing liquid diluted with distilled water onto a cotton swab. Then gently wipe in a circular motion with little or no pressure. The filter can be damaged if there are tiny abrasive particles on the surface which are pressed in by rubbing hard.

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