Apertura

Apertura Plössl 40mm

A 40mm Apertura Plössl: a wide-field, low-power eyepiece for the biggest objects and rich star fields, from an honest, sharp 52-degree Plössl at the lowest sensible price.

74/ 100

Polaris Score

Optical quality · Immersion · Comfort · Value

See the breakdown ↓

What it's for

Low power · wide fieldHigh power · narrow field

Low power · wide field. At 40mm this is a wide-field, low-power eyepiece for the biggest objects and rich star fields; it is not the eyepiece for high-power planetary detail.

Apparent Field

45°

Barrel Size

1.25"

Eye Relief

28mm

Focal Length

40mm

Try in simulator →

Where to buy

High Point ScientificCheck price→

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.

45° apparent field

At 45°, 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

✓Cheap enough to own several and cover a whole range of magnifications.

✓Light and unfussy in any focuser.

✓At 40mm it lands squarely in low power · wide field territory, exactly where wide star fields and large objects belong.

Trade-offs

!Very short eye relief below about 10mm, which is genuinely uncomfortable.

!A 52-degree field is narrow by modern standards.

!Simple coatings and build; this is a value tool, not a showpiece.

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 12× and 3.8° of sky in a little refractor, or 51× 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

12×

True field

3.8°

Exit pupil

7.3 mm

12× across a 3.8° field at a 7.3mm exit pupil, a bright, low-power sweep for framing the largest objects.

8-inch Dobsonian

1200 mm · f/6

Magnification

30×

True field

1.5°

Exit pupil

6.7 mm

30× across a 1.5° field at a 6.7mm exit pupil, a bright, low-power sweep for framing the largest objects.

12-inch Dobsonian

1500 mm · f/5

Magnification

38×

True field

1.2°

Exit pupil

8.0 mm

38× across a 1.2° field at a 8mm exit pupil, a bright, low-power sweep for framing the largest objects.

8-inch SCT

2032 mm · f/10

Magnification

51×

True field

53′

Exit pupil

4.0 mm

51× across a 53′ field at a 4mm exit pupil, right in the deep-sky sweet spot, bright and easy on the eye.

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 lengthLow power · wide field

40mm

Sets the magnification: shorter is higher power. At 40mm this is a wide-field, low-power eyepiece for the biggest objects and rich star fields.

Apparent fieldStandard

45°

A traditional field; the object drifts through faster on an undriven mount.

Eye reliefGlasses-friendly

28mm

Long enough to take in the whole field wearing eyeglasses.

Barrel1.25-inch

1.25"

Fits the 1.25-inch focuser on virtually every telescope.

OpticsCoatings

multi-coated optics

Multi-coatings hold contrast and cut internal reflections on bright objects.

03What comes alive

The targets this eyepiece was born for.

Comes alive

The Veil Nebula

With an OIII filter the lacework wraps across the field.

Excellent

The North America Nebula

A wide, faint target that only fits at long focal length.

Comes alive

The Pleiades (M45)

The full cluster framed with room around every star.

Excellent

Milky Way star clouds

Sweeping the summer Milky Way at its richest.

Excellent

The Andromeda Galaxy (M31)

The full span of the galaxy and its dust lanes.

Comes alive

The Double Cluster

Both clusters with a generous star field between them.

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.

40 mmThis one

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

13 mm

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 (~24mm)

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.

74/ 100

Apertura Plössl 40mm

Judged as a wide-field, low-power eyepiece for the biggest objects and rich star fields, it earns its score on classic four-element plössl optics: crisp and high-contrast on-axis. 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 wide-field, low-power eyepiece for the biggest objects and rich star fields.

✓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 Length40mm

Apparent Field45°

Comfort & handling

Eye Relief28mm

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 Plössl is for.

— The Skynocular verdict

06Alternatives

For a different goal, start here.

Wider, lower power

Apertura Plössl 64mm

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

More magnification

Apertura Plössl 24mm

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 nearby price point, if you want to compare field and feel before committing.

→

Apertura Plössl 40mm

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.