What does the Altair Solar Contrast Booster do?

It passes a 7 nm band of green light centred on 540 nm and blocks ultraviolet and infrared from 200 to 1250 nm. Altair designed it to lift the contrast of sunspots, granulation and fine detail in the photosphere.

Can I look at the Sun through it on its own?

No. It is not a solar filter. Altair's instruction is to use it with a professional solar filter or a Herschel wedge of at most 0.024% transmission placed before it, with the booster just in front of the camera or eyepiece.

Will it show prominences?

No. It works on the white-light photosphere: sunspots and granulation. Prominences and filaments need a hydrogen-alpha filter, such as the DayStar Quark Chromosphere.

Why is the Sun green through it?

It passes only a narrow band of green light around 540 nm and blocks the rest, so the whole disc turns green; my Short shows it behind my Altair solar wedge.

Which size is this page about?

The 1.25 inch filter. Altair sells it now as the V3: 7 nm wide with 97.5% transmission, in a standard 1.25 inch filter thread (F125SCB5407). Earlier 1.25 inch boosters were 8 nm wide, and the 2 inch booster (F200SCB5408) is a different filter, 8 nm wide with 90% transmission.

What have I not tested on the Solar Contrast Booster?

I have not imaged through it with a camera or measured its bandpass: my only recording through it is a phone view at the eyepiece behind my Altair solar wedge.

Altair Solar Contrast Booster review: 1.25 inch, 540 nm

Where does it rank on our leaderboard

Nine of the 13 filters on my board, against price
Rank	Filter	Stars for Your Buck	Recorded UK price
1	Scorpio HSO 3nm	100 out of 100	£448
2	Laida HSO 5nm 1.25″	94 out of 100	£154
4	Altair LRGB	79 out of 100	£240
6	QuarkStar Chromosphere	76 out of 100	£1,149
7	Antlia 2.5nm HSO	75 out of 100	£1,740
9	Altair Solar Contrast Booster Filter	73 out of 100	£80
10	ZWO LRGB	70 out of 100	£332
12	Optolong L-Ultimate Dual-Bandpass 3nm	43 out of 100	£216
13	ZWO HSO 7nm Narrowband	32 out of 100	£734

Contents

01 Where does it rank on our leaderboard
02 Specifications and features
03 In my words
04 Watch it in my videos
05 Should you buy it?
06 Questions and more about this review

In 30 seconds

Stars for Your Buck 73/100

Reviewed 17 Nov 2025 Updated 26 Sep 2026

Rank: #9 of 13 filters
Verdict: Worth a look

Written by Damon Scotting 2 min read

Buy it if

You already view or image the Sun in white light behind a Herschel wedge or a solar filter.
Your eyepiece, diagonal or camera train takes 1.25 inch filters.

Skip it if

You want prominences and filaments: that is hydrogen alpha.
You have no solar filter or Herschel wedge yet.

A 1.25 inch, 7 nm green continuum filter for white-light solar work: it goes behind a proper solar filter or Herschel wedge, never in front of the Sun on its own.

Specifications and features

Altair Solar Contrast Booster Filter reviewed #9 of 13
Recorded UK price	£80
Type	Solar continuum contrast filter for white light
Bandpass	7 nm
Lines passed	540 nm green continuum
Peak transmission	97.5%
Sizes	1.25 inch, standard filter thread, aluminium cell
Thickness	1.85 mm, λ/4, 30 arcsec parallelism
Coating	Hard SiO2 overcoat, anti-reflection, UV/IR block 200 to 1250 nm, OD5 in the visible, blackened edges
In the box	not recorded

In my words

“I'm using an Altair solar wedge to view the Sun in white light as well as an Altair contrast filter to make the sunspots on the surface of the Sun appear clearer.”

From the description of my Short, written

“Why is the Sun green? That's because of the filter I'm using.”

From the description of my Short, written

Watch it in my videos

IT'S BACK!?! · published 17 November 2025 · 0:15 · Watch on YouTube · 65,015 views, 618 likes on 2 Oct 2026

Jump to

0:00 My Altair solar wedge on the telescope
0:05 The zoom eyepiece in the wedge
0:06 The Sun in green light
0:12 The sunspot group up close

Should you buy it?

73/100 Stars for Your Buck

Pros

A 7 nm band centred on 540 nm, the green solar continuum.
97.5% average transmission at 540 nm, with ultraviolet and infrared blocked from 200 to 1250 nm and OD5 blocking across the rest of the visible range.
A standard 1.25 inch filter thread in an aluminium cell, with blackened edges against stray reflections.
Behind my Altair solar wedge it makes the sunspots stand out more clearly.

Cons

It is not a solar filter: it must sit behind a solar filter or Herschel wedge of at most 0.024% transmission.
It shows the photosphere only, never prominences or filaments.
It fits 1.25 inch trains only: a 2 inch train needs Altair's separate 2 inch booster.

Buy it only as the second filter in a white-light solar setup: behind a Herschel wedge or a proper solar filter it narrows the view to green continuum light, and on its own it is not a solar filter at all.

Who the Solar Contrast Booster is for

Herschel wedge user

Buy

Altair made it to sit behind a Herschel wedge or a solar filter, just in front of the camera or eyepiece.

White-light solar imager

Buy

A narrow green band aimed at sharper sunspots and granulation in white light.

Hydrogen-alpha observer

Skip

It shows the photosphere only; prominences and filaments need a hydrogen-alpha filter such as the DayStar Quark.

No solar filter yet

Skip

On its own it is not safe for the Sun: the solar filter or Herschel wedge comes first.

2 inch-only kit

Skip

It threads into a 1.25 inch train; a 2 inch-only kit needs the larger version.

Three alternatives I have reviewed

Questions and more about this review

Reviewed by

Damon Scotting

The Telescope Man Verified

BSc (Hons) Physics with Astrophysics and Cosmology, Loughborough University PGCE / QTS, University of Nottingham

About Damon About Damon Damon Scotting is The Telescope Man. He holds a BSc (Hons) in Physics with Astrophysics and Cosmology from Loughborough University and a PGCE with QTS from the University of Nottingham, and taught physics in secondary schools before becoming an astronomy creator. He is a contributing writer for BBC Sky at Night Magazine and the author of 42 Wonders of Our Night Sky, and his photograph of the galaxy M100 with the dwarf planet Ceres was Highly Commended in the Astronomy Photographer of the Year 2024 competition run by Royal Observatory Greenwich. He has appeared on the BBC's Blue Peter. More than 750,000 people follow his astronomy channels on YouTube, Instagram and TikTok, and he has reviewed more than 140 telescopes, mounts, cameras, filters and accessories hands-on for this site. More about Damon · How I test · Damon's book

I review all kinds of gear: most of it I buy, some is gifted and some is loaned, and all of it is reviewed the same way. How this site is funded

Six questions, answered

Questions about the Altair Solar Contrast Booster Filter

Reviewed 17 November 2025 ·Updated 26 September 2026

I review all kinds of gear. Most of it I buy, some is gifted and some is loaned, and all of it is reviewed the same way: no company sees or approves a review before it is published. How this site is funded

What does the Altair Solar Contrast Booster do? It passes a 7 nm band of green light centred on 540 nm and blocks ultraviolet and infrared from 200 to 1250 nm. Altair designed it to lift the contrast of sunspots, granulation and fine detail in the photosphere. The specifications ↓
Can I look at the Sun through it on its own? No. It is not a solar filter. Altair's instruction is to use it with a professional solar filter or a Herschel wedge of at most 0.024% transmission placed before it, with the booster just in front of the camera or eyepiece. The specifications ↓
Will it show prominences? No. It works on the white-light photosphere: sunspots and granulation. Prominences and filaments need a hydrogen-alpha filter, such as the DayStar Quark Chromosphere. The specifications ↓
Why is the Sun green through it? It passes only a narrow band of green light around 540 nm and blocks the rest, so the whole disc turns green; my Short shows it behind my Altair solar wedge. Watch it in my videos ↓
Which size is this page about? The 1.25 inch filter. Altair sells it now as the V3: 7 nm wide with 97.5% transmission, in a standard 1.25 inch filter thread (F125SCB5407). Earlier 1.25 inch boosters were 8 nm wide, and the 2 inch booster (F200SCB5408) is a different filter, 8 nm wide with 90% transmission. The specifications ↓
What have I not tested on the Solar Contrast Booster? I have not imaged through it with a camera or measured its bandpass: my only recording through it is a phone view at the eyepiece behind my Altair solar wedge.