This auction is for a 1991 Celestron (Carton or Nihon Seiko of Japan) 1.25-inch orange #21 color filter. This is complete to code and will come with its original foam interior plexiglass case and the original box. The dealers price tag is original, so don't remove it.

In the scheme of the Celestron filters; this is a 3rd generation model and would have existed from about 1986 until 1995. Prior to 1986 would have been the milled, anodized dark black aluminum filters with a brass retainer and no characters to notate the filter number or brand affiliation. And prior to that generation (before 1981), the filters would be drop-in only and feature no threads. These filters only worked by resting on the inner flange of the male threads of the visual back attachment and would be held in place by the actual attachment of the 1.25-inch visual back adapter.

From November/December of 1995 into 2005, these filters would remain virtually unchanged from the 3rd gen models, but would now be sourced from Synta Technology Corp of Taiwan. After 2005, they would be sourced from Suzhou Synta of China and then Kunming Optical of China, which were/are still very good filters, but do not exhibit absolute equal color tint across the plane as the Japanese units.

It is interesting to discover that from the time the mpn code was created for this filter by 1986 and at least until 2017, whether it was sourced from Japan, Taiwan, or China, the mpn never changed. And unlike eyepieces, diagonals, and finders, which did or did not have the suffix "-A" to indicate country of origin, it is not reflected on  these filters.

The Number 21 filter is important in its own right. Use it in your eyepiece for making Jupiter's equatorial belts stand out far better than if observing filter-free. It will also bring out festoon visibility, particularly in high quality 4-inch and larger refractors and medium-size maksutovs; such as the Meade 125-ETX, Orion Argonaut 150, and the Meade 7-inch LX200.

It will definitely help enhance dust storm clouds on Mars (if present) and also brings out the maria better; definitely witnessed this in my Celestron C11 Edge and Meade 10-inch LX200.

Like Jupiter, on Saturn it will bring out the brighter cloud bands near the equatorial regions. This was fun to see these last (2) summers in the Takahashi FS-152sv, Celestron C80, and Celestron C8-DX. And, of course, since this filter only allows for 46% incoming light transmission, it does very fine work on lunar detail at any phase in telescopes under 12-inches.

Made of solid milled aluminum construction and real-tinted glass, this filter will thread to nearly ANY 1.25-inch eyepiece made over the last 45 years. It will not thread to Bausch And Lomb, Criterion, Questar, or Vernonscope-branded eyepieces as they have specific brand-loyal threads on their barrels. The very first years of the NJ Japan Tele Vue Plossls and Wide Fields do have issues with certain years of Japanese-made filter threads. They can work, but may not thread all the way on.