Baader Planetarium

Baader AstroSolar Telescope Filter (ASTF) — 80 mm

The gold-standard white-light film, ready-mounted in a rigid cell. A neutral, razor-sharp view of sunspots and granulation for the price of an eyepiece, the solar filter to buy first.

93/ 100

Polaris Score

#1 of the white-light solar filters we recommend

From$101

Where to buy

High Point ScientificBest price$101→

Affiliate link — we earn a commission, you pay the same. We rank on fit, not payout.

What changes

You can’t look at all.
Now you can see the surface.

Drag to compare. Without the filter the Sun is a blinding, featureless glare no eye can face. Cut it to a hundred-thousandth and the photosphere appears, limb darkening, and a group of sunspots.

No filter

solar filter

◄►

01What you see

What the Sun actually shows.

A white-light filter shows the photosphere, the Sun’s visible surface. No exotic gear, no darkness required: these are daytime sights any small scope can reach, safely.

The main event

Sunspots

Cooler magnetic storms, often larger than Earth. They drift across the disk over days and cluster near solar maximum, the reason most people buy a solar filter.

Fine detail

Granulation

The Sun’s surface is a boiling mosaic of convection cells. On a steady day, a good filter and small scope resolve the mottled “orange-peel” texture between the spots.

Near the limb

Faculae

Bright magnetic patches, easiest to spot near the darkened edge of the disk. They often mark where new sunspot groups are about to appear.

Rare events

Planetary transits

Mercury and (very rarely) Venus cross the disk as a crisp black dot. A safe solar filter is the only way to watch one, the next Mercury transit is worth planning for.

When they come

Partial eclipses

The Moon takes a bite from the Sun. A full-aperture filter lets you follow every phase of a partial, or the partial stages either side of totality, without ever risking your eyes.

02Read this first

Safety is the whole product.

A solar filter is the one accessory where a mistake blinds you, instantly, painlessly and permanently. Four rules matter more than anything else on this page.

✕Full aperture, over the front

A safe solar filter mounts over the front of the telescope, stopping the light before it is ever focused. Never use a small filter that screws into the eyepiece, focused heat shatters them.

✕Never look without it fitted

Not even for a second, not to “line it up.” Unfocused sunlight through a scope causes an instant retinal burn with no pain to warn you. Fit the filter before the scope ever points near the Sun.

✕Inspect before every use

Hold the film or glass up to a bright lamp. Any pinhole, scratch, tear or crease means it is done, into the bin, not onto the scope. Store it flat and capped.

✕Cap the finderscope

A finder is a small unfiltered telescope. Cap it or remove it, or it will scorch the mount, your hand, or your eye the moment you look through it out of habit.

03Where it fits

It goes over the front, not the eyepiece.

This is the one filter that lives at the very front of the light path. It cuts the sunlight to a safe fraction before the telescope ever focuses it, which is exactly what makes it safe.

01

The Sun

Far too bright

Never look directly

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02

This filter

Over the front aperture

Blocks ~99.999%

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03

Telescope

Now safe to point

~1/100,000 gets through

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04

Eyepiece

Frames the disk

Low–medium power

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05

Your eye

Sees the photosphere

Sunspots, granulation

04Which kind

How solar filters compare.

All four let you observe the Sun safely, but they show different things, and cost wildly different amounts. Most people should start with white-light.

This one

White-light film

Baader / Thousand Oaks

Bandpass

Full visible

Best for

Sunspots, transits

The affordable standard. A sharp, neutral-to-pale-orange view of the photosphere. What almost everyone should buy first.

Full-aperture glass

Coated optical glass

Bandpass

Full visible

Best for

Sunspots, eclipses

Sturdier and usually warmer-orange than film, in a rigid cell. Pricier, can be a touch softer, but hard to damage.

Herschel wedge

Refractors only

Bandpass

Full visible

Best for

High-contrast white light

Diverts the heat out the side instead of blocking it at the front. Superb contrast, but only ever on refractors, never reflectors or SCTs.

H-alpha

Dedicated instrument

Bandpass

≈ 0.5–0.7 Å

Best for

Prominences, flares

A different view entirely, the chromosphere, with flares and prominences arcing off the limb. Costs many times more than white-light.

05The numbers

What These Numbers Mean

DensityVisual safe

ND 5.0 solar film

It transmits about one hundred-thousandth of the sunlight reaching it, which is what makes solar observing safe. This density is rated for visual use; photographic ND 3.8 film is not, and must never be used at the eyepiece.

What you seeWhite light

Neutral white Sun

AstroSolar film renders the Sun close to neutral white rather than the orange of most glass filters, and it shows sunspot umbra, penumbral structure and surface granulation with unusually high contrast for the price.

MountingCritical

Full aperture, front of tube

It fits over the front of the telescope so sunlight is rejected before it enters and heats anything. Filters that thread into an eyepiece sit at the focus of concentrated sunlight and can crack without warning, which is why they are no longer sold.

FitMeasure first

Sized for 80 mm outer diameter

The number is the tube outer diameter it clamps onto, not the aperture of your telescope. Measure the front of your tube or dew shield before ordering, and confirm the cell grips firmly enough that wind cannot dislodge it.

Before every sessionSafety

Inspect for pinholes

Hold the filter up to a bright lamp and check for pinholes or scratches in the film before each use. A damaged filter is unsafe, and film is consumable in a way glass is not.

Optical

TypeWhite-light, full aperture

MaterialBaader AstroSolar Safety Film ND 5.0

DensityND 5.0 (visual)

Transmission≈ 0.001%

View colourNeutral / faint blue-white

BlocksUV, IR, 99.999% visible

Fit & build

Cell size80 mm OD (front cell)

Also available50–280 mm ASTF sizes

MountRigid aluminium cell, foam-gripped

UseVisual & imaging

ReusableYes, if undamaged

NeverOn the eyepiece end

06Pairs with

Compatible gear.

Match by aperture

Fit is by outer diameter (OD)

Measure the OD

Across the front of the tube or dew shield

Pick the range

Each filter lists an OD window it fits

Snug, not loose

Set screws or a foam grip hold it firmly

Best telescopes

For daytime solar

Small refractor

Sharp, high-contrast disk, the classic solar scope

80–150 mm aperture

More than enough resolution for the Sun

Any cappable scope

If it has a lens cap, it can take a front filter

Handy extras

Make it easier

Solar finder

Point at the Sun without looking up the tube

Continuum filter

Sharpens sunspot detail on white-light views

Steady alt-az mount

Daytime tracking is easy and quick to set up

07Learn more

Guides for solar observing.

Guide · 5 min

How to observe the Sun safely (and what you’ll see)

The rules that keep your eyes safe, how to fit a front filter, and a tour of what a small scope reveals on the daytime Sun.

Read the guide →

Guide · 6 min

White-light vs H-alpha: two very different Suns

One shows sunspots on the surface, the other shows flares leaping off the limb. Which view each filter gives, and what each one costs.

Read the guide →

Baader AstroSolar Telescope Filter (ASTF) — 80 mm

You can’t look at all.Now you can see the surface.

What the Sun actually shows.

Safety is the whole product.

It goes over the front, not the eyepiece.

How solar filters compare.

What These Numbers Mean

Compatible gear.

Guides for solar observing.

You can’t look at all.
Now you can see the surface.