Baader Planetarium

Baader Classic Ortho 18mm

A 18mm Baader Classic Ortho: a low-power eyepiece for framing large nebulae, galaxies and open clusters, from a four-element orthoscopic built for maximum contrast on planets and the Moon.

79/ 100

Polaris Score

Optical quality · Immersion · Comfort · Value

See the breakdown ↓

What it's for

Low power · wide fieldHigh power · narrow field

Low power. At 18mm this is a low-power eyepiece for framing large nebulae, galaxies and open clusters; it is not the eyepiece for high-power planetary detail.

Apparent Field

50°

Barrel Size

1.25"

Eye Relief

15mm

Focal Length

18mm

From$108

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The spacewalk

You don’t look at a field.
You look into the sky.

Every number on the spec sheet matters less than one feeling: how much sky wraps around your eye. Widen the apparent field and watch the black edge of the eyepiece slip away.

50° apparent field

At 50°, you are aware of the field edge, like looking down a short, comfortable tube.

See this field in your own scope in the Simulator →

01What it's good at

What it's best at — and the trade-offs.

Best at

✓The purist’s choice for planetary and lunar detail and tight double stars.

✓Beautifully made and, for the optical quality, inexpensive.

✓At 18mm it lands squarely in low power territory, exactly where wide star fields and large objects belong.

Trade-offs

!A narrow 50-degree field; the object drifts through quickly on an undriven mount.

!Tight eye relief at short focal lengths, which is uncomfortable for eyeglass wearers.

!Not the eyepiece for large deep-sky objects that want a wide field.

02In your telescope

One eyepiece. A different job in every scope.

An eyepiece has no magnification of its own — the telescope decides. The same eyepiece becomes 27× and 1.9° of sky in a little refractor, or 113× and a tight frame in a long SCT. Here’s what it does across common scopes.

Small apo refractor

480 mm · f/5.5

Magnification

27×

True field

1.9°

Exit pupil

3.3 mm

27× across a 1.9° field at a 3.3mm exit pupil, right in the deep-sky sweet spot, bright and easy on the eye.

8-inch Dobsonian

1200 mm · f/6

Magnification

67×

True field

45′

Exit pupil

3.0 mm

67× across a 45′ field at a 3mm exit pupil, right in the deep-sky sweet spot, bright and easy on the eye.

12-inch Dobsonian

1500 mm · f/5

Magnification

83×

True field

36′

Exit pupil

3.6 mm

83× across a 36′ field at a 3.6mm exit pupil, right in the deep-sky sweet spot, bright and easy on the eye.

8-inch SCT

2032 mm · f/10

Magnification

113×

True field

27′

Exit pupil

1.8 mm

113× across a 27′ field at a 1.8mm exit pupil, crisp medium power for galaxies, clusters and planetary nebulae.

Exit pupil is how wide the beam of light leaving the eyepiece is. Around 5–6 mm is bright and immersive under dark skies; push much past 6 mm and you waste light, and under light pollution a smaller exit pupil shows more contrast.

02In plain English

The numbers, in plain English.

Focal lengthMid power

18mm

About 67x in an 8 inch f/5.9 Dobsonian and 113x in an 8 inch SCT. Longer than most orthoscopics are used at, which makes this a good double-star and small-cluster eyepiece as well as a planetary one.

Apparent fieldClassic

50°

The narrow field keeps the design simple and the contrast high. At this focal length the true field is still usable for finding, though a 68 degree eyepiece of the same power would show noticeably more sky.

Eye reliefComfortable

15mm

Fifteen millimetres is genuinely comfortable, and a marked improvement over the shorter orthoscopics in this family. Longer focal length orthoscopics are where the design stops punishing your eye position.

BarrelStandard

1.25"

Fits every focuser and diagonal, and the eyepiece is light enough that swapping it in never disturbs the balance of a Dobsonian.

OpticsPlanetary specialist

Fully multi-coated

Four coated elements mean minimal scatter and very high contrast for the money. The design shows its age only in field width, not in image quality on axis.

03What comes alive

The targets this eyepiece was born for.

Comes alive

The Orion Nebula (M42)

Wings of nebulosity fill the field with the Trapezium embedded.

Excellent

The Andromeda Galaxy (M31)

The bright core with its two companion galaxies framed.

Excellent

The Pleiades (M45)

The whole cluster with dark sky to spare around it.

Comes alive

The Double Cluster

Two open clusters glittering side by side in one view.

Excellent

The Beehive (M44)

A loose scatter of bright stars, best at low power.

Excellent

Large open clusters

Bright, wide targets that want field, not magnification.

04Role in a collection

Where it sits in your eyepiece case.

A good eyepiece collection isn’t a pile of glass — it’s two or three focal lengths that hand off from wide to tight. This is the anchor at the bottom of the ladder: the one you find and frame with. You buy it once, and it stays your low-power eyepiece for life.

32 mm

Low power · wide field

Find, frame and sweep. Your widest true field and the lowest useful magnification, the eyepiece you reach for first.

Veil Nebula · Pleiades · Milky Way star clouds

18 mmThis one

Medium power · the workhorse

Where most deep-sky objects look their best, galaxies, globulars and planetary nebulae at a comfortable scale.

M13 · Ring Nebula · most galaxies

7 mm

High power · detail

Planets, the Moon at the terminator, tight double stars and the smallest planetary nebulae. Steady-air nights only.

Jupiter · Saturn · lunar craters

04Build around it

What it pairs with.

The telescope

What it goes into

Any 1.25-inch focuser

Fits essentially every telescope made.

Fast, short scopes love this field

A fast Newtonian or refractor turns this focal length into a rich, wide sweep.

Pair it

What extends its range

A high-power eyepiece (~11mm)

Locate and frame with this one, then swap to high power for planets and small objects.

Filter it

What transforms the view

A UHC or OIII nebula filter

At low power this eyepiece frames big emission nebulae; a narrowband filter makes the Veil and North America jump out.

02The Polaris Score

How it scores, and why.

79/ 100

Baader Classic Ortho 18mm

Judged as a low-power eyepiece for framing large nebulae, galaxies and open clusters, it earns its score on superb on-axis contrast and light throughput; four elements scatter almost nothing. The comfortable eye relief lifts it further. A wide field is what this focal length is for, and it delivers.

Optical quality

Immersion

Comfort

Value

Polaris weighs how well the eyepiece does the job it was designed for — optics, immersion, comfort and value — never list price or brand.

03Who it's for

An honest fit check.

Buy it if you

✓Observers who want a low-power eyepiece for framing large nebulae, galaxies and open clusters.

✓Anyone who observes in eyeglasses; the eye relief here is long enough to see the whole field.

✓Observers who value on-axis contrast over a sprawling field.

Look elsewhere if you

!Anyone who has looked through a wide-field eyepiece and cannot go back to a 52-degree tunnel.

!Grab-and-go observers watching every gram, since this is not the lightest option.

!Planetary specialists who want the last ounce of high-power contrast from an orthoscopic.

05The numbers

Full specifications.

Optical

Focal Length18mm

Apparent Field50°

Comfort & handling

Eye Relief15mm

Fit & build

Barrel Size1.25"

Editor’s Take

Sweep it across a rich star field and the reason to own this focal length is obvious in a second. That is what the Classic Ortho is for.

— The Skynocular verdict

06Alternatives

For a different goal, start here.

Wider, lower power

Baader Classic Ortho 29mm

The same optics with more true field, for framing larger objects and finding your way around.

More magnification

Baader Classic Ortho 11mm

The same line at higher power, for planets and the smallest deep-sky detail.

Cross-shop

Celestron X-Cel LX

A natural alternative at a similar price point, if you want to compare field and feel before committing.

→

Baader Classic Ortho 18mm

You don’t look at a field.You look into the sky.

What it's best at — and the trade-offs.

One eyepiece. A different job in every scope.

The numbers, in plain English.

The targets this eyepiece was born for.

Where it sits in your eyepiece case.

What it pairs with.

How it scores, and why.

An honest fit check.

Full specifications.

For a different goal, start here.

You don’t look at a field.
You look into the sky.