Filters explained: VIS, Astro, UV/IR-cut, dual-band, CLS and solar

Five makers, five vocabularies. DwarfLab's "Astro" is ZWO's "UV/IR-cut" is Vaonis's nothing-fitted; ZWO's "LP filter" is DwarfLab's "Dual-band" is Celestron's "Nebula Filter". This page says what each position does, what it is called on each scope, and which ones the calculator models.

What the calculator means

The model has two positions. No filter is the scope's normal deep-sky state: whatever sits in the light path when no light-pollution filter is engaged. Dual-band is the narrow Hα plus OIII filter, built in or added. Everything else on this page either does the same job under another name, or changes the numbers too little and too unpredictably to model.

The filters, one by one

UV/IR-cut (ZWO), Astro (DwarfLab)

Silicon sensors see from the near ultraviolet to about 1,000 nm, far beyond the eye. Lenses do not bring that infrared to the same focus as visible light, so without a cut you get bloated stars and soft detail; skyglow and airglow are strong in the infrared; and the colour dyes on the sensor leak infrared into all three channels, which turns everything a muddy pink. A UV/IR-cut filter passes roughly 400 to 700 nm and blocks the rest. It is not a light-pollution filter; it is what makes the camera a colour camera. DwarfLab's Astro position is this filter (430 to 690 nm on the DWARF 3 and mini). ZWO's wheel has it as the plain position. Vaonis, Unistellar and Celestron do not name theirs; "no filter" on this site means nothing added.

VIS (DwarfLab)

Full spectrum, no infrared cut. The DWARF doubles as a daytime spotting scope and VIS is for that, and for the Moon and planets where a little infrared sharpens the image through unsteady air. For deep sky it is the wrong position: star bloat, poor colour, brighter sky. The DWARF mini's tele camera has no VIS position at all.

Dual-band: LP filter (ZWO), Dual-band (DwarfLab), Dual Band clip-on (Vaonis), Nebula Filter (Celestron)

Two narrow windows, one around hydrogen-alpha at 656 nm and one around doubly-ionised oxygen at 500 nm (ZWO quotes 20 and 30 nm wide; DwarfLab 656 and 501 nm). Emission nebulae, planetary nebulae and supernova remnants shine almost entirely in those two lines, so they pass nearly intact while most of the skyglow and moonlight do not. Galaxies, clusters and reflection nebulae shine across the spectrum and lose most of their light. ZWO's app calls it the LP (light pollution) filter, which is fair for nebulae and misleading for everything else. When it helps and when it hurts, with numbers.

Light pollution / CLS (Vaonis clip-on, and third-party)

A broadband filter that blocks the yellow sodium and mercury lines of old streetlights and passes the rest. Under modern white LED lighting, which is broadband, it blocks little of the glow, so the gain from a town has shrunk to a modest amount and it adds a blue-green colour cast. On a Vespera it is the only filter that helps a galaxy at all, and only slightly. Not modelled: treat it as "no filter" with a small bonus that depends on what your council installed.

UHC and other nebula filters

Wider nebula filters that pass Hβ, OIII and Hα with bands of 25 to 100 nm. They sit between the two model positions: less sky rejection than a dual-band, less colour loss on stars. The Origin's drawer takes any of them; the DWARF II once had a UHC option that is no longer sold. Not modelled; expect a result between the two columns on a target page.

Solar

Front-mounted, blocks all but a hundred-thousandth of the light, and is the only way to point any of these scopes at the Sun. Vaonis and Unistellar sell theirs as app-detected clip-ons; DwarfLab and ZWO sell theirs as caps. Never for anything else, and never the Sun without one: the sensor is not the only thing that burns.

Dark

An opaque position on the ZWO and DwarfLab wheels. The app uses it to shoot dark frames, which measure the sensor's own thermal signal so it can be subtracted from your stack. You do not choose it; it is why the scope sometimes sits still with the lens covered before a session.

Why only two are modelled

The dual-band filter changes the photon budget by a large, repeatable amount: it passes a known fraction of an emission line and blocks a known fraction of the sky. A CLS filter's effect depends on the spectrum of your local streetlights, which the model cannot know, and a UHC sits somewhere between. Rather than print a false precision, the target pages show both modelled positions and this page tells you where the others fall.

More guides

• Which smart telescope should you buy?
• How long should my subs be?
• Integration time explained
• The Bortle scale for smart telescope owners
• EQ mode and field rotation on smart telescopes
• Dual-band filters on smart telescopes: when they help and when they hurt

Updated 2026-08-28. Corrections: about page.