The Orion V-Block works amazingly well with achromatic refractors of any aperture or focal length that use 1.25” eyepieces. Its sophisticated multiple interference layers selectively block wavelengths in the violet and blue (<450nm) end of the visible spectrum where chromatic aberration is most visible, while allowing up to 95% transmission of the other wavelengths. The filter imparts a slight yellow-green tint to lunar and planetary images, but it’s a small penalty to pay for the elimination of the image-degrading haze of spurious color.

You can push the magnification higher with the filter than without it because of the improved image definition. Objects also snap into focus more readily now that the fuzzy blue-violet fringe is attenuated.

The V-Block is a multi-layer glass interference filter, not a dyed glass color filter. To maintain the highest optical integrity, it is not laminated with a cover glass to protect the multilayer interference coatings. Consequently, the coatings are delicate and easily scratched if cleaned too vigorously. It is mounted in an anodized 1.25” aluminum cell and comes in a protective plastic case. It threads into eyepieces, diagonals, and Barlow lenses that are threaded to accept 1.25” filters. It is effective for visual use as well as CCD or film imaging.

To keep moisture from forming on the coatings, it is advisable to keep the filter attached to the eyepiece, particularly when bringing it indoors from a cold night. Allow all moisture to evaporate from the eyepiece and filter before removing the filter for storage.