The UHC Ultra High Contrast Filter - 31mm Round Mounted by Astronomik is mounted in a Low Profile Non-Threaded Round Cell.

The Astronomik UHC filter is for visual deep-sky observation. It lets almost 100-percent of the radiation from both O-III lines and the H-beta line pass through. A second bandpass for the H-alpha line ensures that this radiation also reaches the eye, and scattered light from other wavelength ranges is also filtered out. Due to the strong reduction of the sky background, gas and planetary nebulas are visible with an unexpected abundance of detail. Because of the high transmission, the UHC filter provides enough light to successfully observe deep-sky objects with smaller telescopes.

The filters are optimized for use with focal ratios of f/4 to f/15. Unlike other filters on the market, loss of transmission and color displacement with the Astronomik filter occurs only on telescopes with extremely fast focal ratios of f/3 on up. Compared to the UHC filters sold by other manufacturers, the Astronomik UHC filter shows you more stars and more details in nebulas, and because of the high quality of the glass, you will see stars as small pinpoints.

 Now Mounted in Low Profile Non-Threaded Cell: Sometimes unmounted filters can be hard to handle. The smaller diameters, such as this 31mm UHC filter, can be especially difficult to pick up and insert or remove from the filter wheel, and that can lead to possible damage as well as unwanted reflections from incorrectly installed filters. Astronomik has solved this problem by mounting their 31mm and 36mm filters in a low profile (3mm) non-threaded cell. O-rings, washers, or spacers are no longer required to hold the filter in place, and because the cell is only 3mm thick, it works well in all appropriately sized filter wheels. Mounted 31mm and 36mm Astronomik filters will also play nice with unmounted versions in the same carousel.

Astronomik filters are in a class by themselves when compared to other filters made by Japanese and US manufacturers. The coatings are completely sealed and insensitive to moisture. They do not change with the years, but keep their transmission characteristics indefinitely. The coatings are so hard that is it not possible to scratch them by mistake. You would have to rub them with sandpaper to get even the finest of scratches! Due to these outstanding characteristics, Astronomik gives them a 5 year guarantee. Each filter will be sent in a useful protective case.

• Transmission of nearly 100-percent of O-III and H-beta
• Transmission of 96-percent of H-alpha
• Entire blocking of annoying wavelengths
• Ideal all-round Deep Sky filter even for small telescopes
• Not sensitive to humidity or aging
• Scratch-resistant!
• Excellent carrier material. The optical performance of your telescope is not reduced by the filter in any way.
• Parfocal with other Astronomik filters
• Glass thickness: 1mm
• Cell thickness: 3mm
• Diffraction limited, the filter will not reduce the optical performance of your telescope!
• Astronomik filters are delivered in a high-quality, long lasting, filter box

OPT Product Number: AK-UHC-31