Explore Scientific 25mm 100° — image 1
Explore Scientific

Explore Scientific 25mm 100°

A 25mm Explore Scientific 100° Series: a low-power eyepiece for framing large nebulae, galaxies and open clusters, from a 100-degree hyper-wide that puts the field edge out past the corner of your eye.

86/ 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 25mm 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
100°
Barrel Size
2"
Eye Relief
14.5mm
Focal Length
25mm
From$899

Lowest in 90 daysLowest ever tracked

Price tracked by PolarisObserved 99 timesTracking since Jul 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.

100° apparent field

At 100°, the edge slips into your peripheral vision, you stop looking at a field and start looking into the sky.
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, so it will not fog in cold, damp air.
Best at
✓Argon-purged and waterproof, so it will not fog in cold, damp air.
✓Excellent correction across a field this wide.
✓At 25mm it lands squarely in low power territory, exactly where wide star fields and large objects belong.
Trade-offs
!Big and heavy; the long focal lengths need a sturdy focuser and can shift balance.
!Eye relief is tight for the field, and eyeglass wearers will miss the last few degrees.
!Expensive, and you pay for the field more than for on-axis sharpness.
02In your telescope

One eyepiece. A different job in every scope.

19× in a small refractor, 81× in a long SCT

An eyepiece has no magnification of its own — the telescope decides. The same eyepiece becomes 19× and 5.3° of sky in a little refractor, or 81× 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
19×
True field
5.3°
Exit pupil
4.5 mm
19× across a 5.3° field at a 4.5mm exit pupil, a bright, low-power sweep for framing the largest objects.
8-inch Dobsonian
1200 mm · f/6
Magnification
48×
True field
2.1°
Exit pupil
4.2 mm
48× across a 2.1° field at a 4.2mm exit pupil, a bright, low-power sweep for framing the largest objects.
12-inch Dobsonian
1500 mm · f/5
Magnification
60×
True field
1.7°
Exit pupil
5.0 mm
60× across a 1.7° field at a 5mm exit pupil, a bright, low-power sweep for framing the largest objects.
8-inch SCT
2032 mm · f/10
Magnification
81×
True field
1.2°
Exit pupil
2.5 mm
81× across a 1.2° field at a 2.5mm 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.

25mm FL · 100° AFOV · 2"
Focal lengthLow power
25mm
About 48x in an 8 inch f/5.9 Dobsonian and 81x in an 8 inch SCT, with an exit pupil around 4.2 mm in the Dobsonian. That is a bright, well matched low power for sweeping large objects.
Apparent fieldSpacewalk
100° claimed, ~94° by field stop
Explore Scientific markets the whole range at 100 degrees, but this model's own 41 mm field stop works out to about 94 degrees at 25 mm, and the rest of the line reconciles to exactly 100. Observers do report it as slightly narrower than its siblings, so treat the 100 figure as the series name rather than a measured value. It is still an enormous field.
Eye reliefComfortable
14.5mm
Comfortable for the long scanning sessions low power involves, and workable with thin glasses. Of the three specifications that decide whether a wide-field eyepiece is pleasant to use, this one is not the compromise here.
BarrelRequires 2 inch focuser
2"
Every eyepiece in the 100 degree range uses a 2 inch fitting, so a 2 inch focuser or diagonal is required; only the 30 mm model steps up to 3 inch. These are also heavy pieces of glass, so expect to rebalance a Dobsonian and to check that a light focuser holds one securely.
OpticsFlagship wide-field
EMD fully multi-coated
Enhanced multi-layer coatings and a sealed argon-purged body. In a fast Newtonian a coma corrector is worth adding, since at this field width any residual coma is visible against the star field.
04What comes alive

The targets this eyepiece was born for.

The Orion Nebula (M42), The Andromeda Galaxy (M31), The Pleiades (M45), The Double Cluster…
The Orion Nebula (M42)Comes alive
The Orion Nebula (M42)
Wings of nebulosity fill the field with the Trapezium embedded.
The Andromeda Galaxy (M31)Excellent
The Andromeda Galaxy (M31)
The bright core with its two companion galaxies framed.
The Pleiades (M45)Excellent
The Pleiades (M45)
The whole cluster with dark sky to spare around it.
The Double ClusterComes alive
The Double Cluster
Two open clusters glittering side by side in one view.
The Beehive (M44)Excellent
The Beehive (M44)
A loose scatter of bright stars, best at low power.
Large open clustersExcellent
Large open clusters
Bright, wide targets that want field, not magnification.
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.

25 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 (~15mm)
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.

86/100
86/ 100
Explore Scientific 25mm 100°

Judged as a low-power eyepiece for framing large nebulae, galaxies and open clusters, it earns its score on a 100-degree apparent field: the closest thing to a spacewalk short of an ethos. Tighter eye relief at this focal length is the main thing holding it back. A wide field is what this focal length is for, and it delivers.

Optical quality
88
Immersion
100
Comfort
76
Value
76

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 low-power eyepiece for framing large nebulae, galaxies and open…
Buy it if you
✓Observers who want a low-power eyepiece for framing large nebulae, galaxies and open clusters.
✓Observers happy to take their glasses off at the eyepiece.
✓Deep-sky observers chasing the most immersive, wrap-around field they can get at this price.
Look elsewhere if you
!Anyone chasing the absolute widest field, who should look at a 100-degree eyepiece.
!Eyeglass wearers, who will not comfortably reach the full field at this focal length.
!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 Length25mm
Apparent Field100°
Comfort & handling
Eye Relief14.5mm
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 100° 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 100° Series 14mm

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

→
Cross-shop

Tele Vue Nagler

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

→