Deep Sky filters

Deep-sky filters: get the universe through light pollution

For the serious deep-sky observer, a quality filter is not a luxury, but a necessity. Especially in a country with a lot of ambient light, a deep-sky filter the only instrument that makes the difference between a gray haze and a high-contrast nebula. These filters work by specifically blocking wavelengths from artificial light (such as sodium and mercury lamps), while light from emission nebulae (H-alpha, OIII and H-beta) passes through unimpeded.

At Telescoop.nl, we carry only top brands such as Bresser, Explore Scientific and Omegon. Whether you observe visually or do astrophotography, our selection is based on maximum transmission and a flawless finish on the optical glass.

The technology behind contrast enhancement

Deep-sky filters are designed ‘narrowband’ or ‘broadband’ depending on your purpose:

• UHC Filters (Ultra High Contrast): The perfect all-rounder from brands such as Omegon and Explore Scientific. They block light pollution and allow the emission lines of nebulae to pass through. Ideal for the Orion Nebula or the Lagoon Nebula.

• OIII Filters (Oxygen-III): For the advanced observer specifically hunting planetary nebulae and supernova remnants. An OIII filter of Bresser allows only a very specific part of the spectrum to pass through, giving a jet-black background and unprecedented detail in objects such as the Veil Nebula.

• CLS Filters (City Light Suppression): The broadband solution for locations with moderate light pollution, preserving the natural color image of star clusters and galaxies as much as possible.

From eyepiece to filter

A deep-sky filter performs optimally only if the rest of your set-up is correct. Within our telescope accessories Therefore, you will find filters that seamlessly match the eyepieces and barlows that you are already using.

It is crucial that the mechanical mount of the filter (often made of anodized aluminum) fits exactly to the filter thread of your eyepiece. At Telescoop.nl, we guarantee that the 1.25″ and 2″ standards of our brands (Bresser, Omegon, Explore Scientific) are universally interchangeable, provided the diameter of your accessories matches.

What to look out for in Deep-sky filters?

The choice of a filter is closely related to your telescope aperture and the degree of light pollution:

1. The Size (1.25 inches & 2 inches): Many deep-sky observers use wide-field eyepieces. Therefore, we offer our filters from Explore Scientific and Omegon to in both the standard 1.25 inches as the larger 2 inches implementation.

2. Filter cell quality: The filters of Bresser and our other top brands are encased in precision-milled aluminum mounts. This prevents ‘stress’ on the glass, which could cause optical distortion.

3. Transmission curve: A good filter allows more than 90% of the desired light to pass through. We do not sell ‘colored glass,’ but interference filters constructed with dozens of wafer-thin coatings to isolate exactly the right nanometers.

Advice from the specialist

Do you have a telescope with a smaller aperture (under 150mm)? Then an aggressive OIII filter often too dark. We then recommend a high-quality UHC filter from Explore Scientific or Omegon for best results. Want to know which filter will transform your particular wide-field scope into a deep-sky monster? Ask us. We've tested them all under the stars.