Explore Scientific 40mm 68° — image 1
Explore Scientific

Explore Scientific 40mm 68°

A 40mm Explore Scientific 68° Series: a wide-field, low-power eyepiece for the biggest objects and rich star fields, from a waterproof 68-degree wide-field that hits the sweet spot of field, comfort and price.

81/ 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
68°
Barrel Size
2"
Eye Relief
16mm
Focal Length
40mm
From$309.99

$21 above 90-day lowLast $289 in Aug 2026

Price tracked by PolarisObserved 53 timesTracking since Mar 2026

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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.

68° apparent field

At 68°, the black rim sits out at the corner of your attention rather than in front of you.
Try this eyepiece on your own scope in the Simulator →
01What it's good at

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

Argon-purged and waterproof against dew and cold.
Best at
✓Argon-purged and waterproof against dew and cold.
✓Well corrected for a wide-field at this price, even in moderately fast scopes.
✓At 40mm it lands squarely in low power · wide field territory, exactly where wide star fields and large objects belong.
Trade-offs
!The outer field softens in very fast scopes below about f/5.
!The 2-inch long focal lengths are heavy.
!Not as immersive as an 82-degree or 100-degree eyepiece.
02In your telescope

One eyepiece. A different job in every scope.

12× in a small refractor, 51× in a long SCT

An eyepiece has no magnification of its own — the telescope decides. The same eyepiece becomes 12× and 5.7° 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
5.7°
Exit pupil
7.3 mm
12× across a 5.7° 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
2.3°
Exit pupil
6.7 mm
30× across a 2.3° 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
1.8°
Exit pupil
8.0 mm
38× across a 1.8° 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
1.3°
Exit pupil
4.0 mm
51× across a 1.3° 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.
03In plain English

The numbers, in plain English.

40mm FL · 68° AFOV · 2"
Focal lengthLowest power
40mm
About 30x in an 8 inch f/5.9 Dobsonian and 51x in an 8 inch SCT. In the fast Dobsonian the exit pupil reaches roughly 6.8 mm, wider than most adult pupils open, so some of the gathered light never reaches your retina. In an f/10 SCT it is well matched.
Apparent fieldWide
68°
The widest true field this range offers, which is exactly the point at long focal lengths. Its value depends heavily on the telescope: excellent in slow scopes, wasteful in fast ones.
Eye reliefComfortable
16mm
Comfortable with or without thin glasses. At the lowest powers you spend most of your time scanning, so a relaxed eye position matters more than usual.
BarrelRequires 2 inch focuser
2"
Needs a 2 inch focuser or diagonal, and it is a physically large eyepiece. Match it to a slow telescope and it earns its place; in a fast Dobsonian a 28 to 34 mm will serve you better.
OpticsAll-rounder
EMD fully multi-coated
Enhanced multi-layer coatings keep transmission high through a long optical train, in a sealed argon-purged body that resists internal dew.
04What comes alive

The targets this eyepiece was born for.

The Veil Nebula, The North America Nebula, The Pleiades (M45), Milky Way star clouds, The…
The Veil NebulaComes alive
The Veil Nebula
With an OIII filter the lacework wraps across the field.
The North America NebulaExcellent
The North America Nebula
A wide, faint target that only fits at long focal length.
The Pleiades (M45)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.
The Andromeda Galaxy (M31)Excellent
The Andromeda Galaxy (M31)
The full span of the galaxy and its dust lanes.
The Double ClusterComes alive
The Double Cluster
Both clusters with a generous star field between them.
05Role in a collection

Where it sits in your eyepiece case.

Where it sits across 3 focal lengths

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
06Build around it

What it pairs with.

The telescope · Pair it · Filter it
The telescope
What it goes into
Any 2-inch focuser
A 2-inch focuser or a 1.25-inch adapter; most Dobsonians and larger refractors qualify.
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.
07The Polaris Score

How it scores, and why.

81/100
81/ 100
Explore Scientific 40mm 68°

Judged as a wide-field, low-power eyepiece for the biggest objects and rich star fields, it earns its score on a 68-degree field that frames deep-sky objects with room to spare. The comfortable eye relief lifts it further. A wide field is what this focal length is for, and it delivers.

Optical quality
80
Immersion
79
Comfort
84
Value
84

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

08Who it's for

An honest fit check.

Observers who want a wide-field, low-power eyepiece for the biggest objects and rich star…
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 want a comfortably wide field without paying ultra-wide prices.
Look elsewhere if you
!Anyone chasing the absolute widest field, who should look at a 100-degree eyepiece.
!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.
09The numbers

Full specifications.

4 measured and stated values
Optical
Focal Length40mm
Apparent Field68°
Comfort & handling
Eye Relief16mm
Fit & build
Barrel Size2"
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 68° Series is for.

— The Skynocular verdict
10Alternatives

For a different goal, start here.

2 alternatives, each mapped to the goal it wins at
More magnification

Explore Scientific 68° Series 24mm

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

→
Cross-shop

Baader Hyperion

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

→