Explore Scientific 9mm 100° — image 1
Explore Scientific

Explore Scientific 9mm 100°

A 9mm Explore Scientific 100° Series: a medium-high-power eyepiece for planets, globular cores and small planetary nebulae, 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

Medium-high power. At 9mm this is a medium-high-power eyepiece for planets, globular cores and small planetary nebulae; it is not meant for framing large deep-sky objects.

Apparent Field
100°
Barrel Size
2"
Eye Relief
12.5mm
Focal Length
9mm
From$299.99

Lowest in 90 days

Price tracked by PolarisObserved 54 timesTracking since Aug 2026

Try in simulator →
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.

A 100-degree apparent field: the closest thing to a spacewalk short of an Ethos.
Best at
✓A 100-degree apparent field: the closest thing to a spacewalk short of an Ethos.
✓A 100-degree apparent field: the closest thing to a spacewalk short of an Ethos.
✓At 9mm it lands squarely in medium-high power territory, exactly where planetary and lunar detail lives.
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.

53× in a small refractor, 226× in a long SCT

An eyepiece has no magnification of its own — the telescope decides. The same eyepiece becomes 53× and 1.9° of sky in a little refractor, or 226× 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
53×
True field
1.9°
Exit pupil
1.6 mm
53× across a 1.9° field at a 1.6mm exit pupil, crisp medium power for galaxies, clusters and planetary nebulae.
8-inch Dobsonian
1200 mm · f/6
Magnification
133×
True field
45′
Exit pupil
1.5 mm
133× across a 45′ field at a 1.5mm exit pupil, crisp medium power for galaxies, clusters and planetary nebulae.
12-inch Dobsonian
1500 mm · f/5
Magnification
167×
True field
36′
Exit pupil
1.8 mm
167× across a 36′ field at a 1.8mm exit pupil, crisp medium power for galaxies, clusters and planetary nebulae.
8-inch SCT
2032 mm · f/10
Magnification
226×
True field
27′
Exit pupil
0.9 mm
226× across a 27′ field at a 0.9mm exit pupil, high power for planets, the Moon and tight doubles.
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.

9mm FL · 100° AFOV · 2"
Focal lengthHigh power
9mm
About 133x in an 8 inch f/5.9 Dobsonian and 226x in an 8 inch SCT. High enough for planetary detail and resolving globular clusters, and usable on ordinary rather than exceptional nights.
Apparent fieldSpacewalk
100°
The field extends beyond your immediate vision, which removes the sense of looking through a tube entirely. At this power it also gives a true field comparable to a much longer conventional eyepiece, with a darker sky background.
Eye reliefModerate
12.5mm
Twelve and a half millimetres is workable without glasses but restrictive with them. Taking in the whole 100 degree field requires deliberate eye movement rather than a single glance.
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 coatings across many elements hold contrast in a design that would otherwise scatter light badly. Sealed and argon purged, so the internal surfaces stay clear through dewy nights.
04What comes alive

The targets this eyepiece was born for.

Jupiter and its moons, Saturn, The Moon, M13 globular cluster, The Ring and Cat’s Eye…
Jupiter and its moonsComes alive
Jupiter and its moons
Belt detail with room to watch the Galilean moons shift.
SaturnComes alive
Saturn
Rings, the Cassini gap, and Titan in the same field.
The MoonExcellent
The Moon
A high-power tour of rilles, domes and crater chains.
M13 globular clusterExcellent
M13 globular cluster
The core starts to resolve into a spray of suns.
The Ring and Cat’s Eye nebulaeComes alive
The Ring and Cat’s Eye nebulae
Small planetary nebulae take real magnification well.
Excellent
Double stars
Clean, contrasty splits of colorful pairs.
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.

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
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
9 mmThis one
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.
Longer focal length scopes reward it
The higher the scope’s focal length, the more planetary scale you get from this eyepiece.
Pair it
What extends its range
A low-power finder eyepiece (~14mm)
Use the long eyepiece to locate and frame, then drop in this one for detail.
Filter it
What transforms the view
A neutral-density Moon filter
Tames the glare of a bright gibbous Moon at high power so detail returns.
07The Polaris Score

How it scores, and why.

86/100
86/ 100
Explore Scientific 9mm 100°

Judged as a medium-high-power eyepiece for planets, globular cores and small planetary nebulae, 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. It is honest about being a specialist, not an all-rounder.

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 medium-high-power eyepiece for planets, globular cores and small…
Buy it if you
✓Observers who want a medium-high-power eyepiece for planets, globular cores and small planetary nebulae.
✓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.
!Anyone hoping to frame large nebulae; that is a job for a low-power eyepiece.
09The numbers

Full specifications.

4 measured and stated values
Optical
Focal Length9mm
Apparent Field100°
Comfort & handling
Eye Relief12.5mm
Fit & build
Barrel Size2"
Editor’s Take

Point it at a planet on a steady night and the case makes itself. This is where the 100° Series earns its keep.

— The Skynocular verdict
10Alternatives

For a different goal, start here.

3 alternatives, each mapped to the goal it wins at
Wider, lower power

Explore Scientific 100° Series 14mm

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

→
More magnification

Explore Scientific 100° Series 5.5mm

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.

→