Omegon Colour filter set, 1.25 in, six pieces

What a set buys

Six filters for less than three bought singly, in one case, with a thread that fits the eyepiece size almost everyone owns. For a planetary observer starting out, that is the efficient way in — provided the telescope has the aperture to use them.

The two that are named

#21 orange: blocks blue and green, raising contrast in the cloud belts of Jupiter and Saturn and sharpening the boundaries between light and dark regions on Mars. #25 red: blocks blue and green almost completely, giving very high contrast on cloud detail. Both descriptions come from the maker, and both are consistent with what those Wratten numbers designate.

The four that are not

Without Wratten numbers, four of the six cannot be compared with any other maker’s filters. That is the difficulty the designation exists to solve, and a set that names only two of its six leaves most of itself unidentified.

Aperture, again

A deep red filter passes a small fraction of the light. In a 200 mm telescope on Jupiter that is a trade worth making; in an 80 mm it leaves a dim disc. Start with the lightest filter in the set and work down.

Availability

German, French, Italian and Spanish Amazon stores ran from 63 € to 67 € on the day of the survey.

British Amazon store lists it in local currency, which the euro range above sets aside.

American Amazon catalogue holds a record for it that nobody is selling.

Figures as Keepa reported them on the day this page was last updated. Stock and pricing shift without warning.