Explore Scientific

Explore Scientific 5.5mm 100°

A 5.5mm Explore Scientific 100° Series: a dedicated high-power eyepiece for planets, the Moon and tight double stars, 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

High power. At 5.5mm this is a dedicated high-power eyepiece for planets, the Moon and tight double stars; it is not meant for framing large deep-sky objects.

Apparent Field

100°

Barrel Size

Eye Relief

10.5mm

Focal Length

5.5mm

From$299.99

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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.

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

✓A 100-degree apparent field: the closest thing to a spacewalk short of an Ethos.

✓At 5.5mm it lands squarely in 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.

An eyepiece has no magnification of its own — the telescope decides. The same eyepiece becomes 87× and 1.1° of sky in a little refractor, or 369× 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

87×

True field

1.1°

Exit pupil

1.0 mm

87× across a 1.1° field at a 1mm exit pupil, high power for planets, the Moon and tight doubles.

8-inch Dobsonian

1200 mm · f/6

Magnification

218×

True field

28′

Exit pupil

0.9 mm

218× across a 28′ field at a 0.9mm exit pupil, high power for planets, the Moon and tight doubles.

12-inch Dobsonian

1500 mm · f/5

Magnification

273×

True field

22′

Exit pupil

1.1 mm

273× across a 22′ field at a 1.1mm exit pupil, crisp medium power for galaxies, clusters and planetary nebulae.

8-inch SCT

2032 mm · f/10

Magnification

369×

True field

16′

Exit pupil

0.6 mm

369× across a 16′ field at a 0.6mm exit pupil, very high power, worth it only on the steadiest nights.

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 lengthVery high power

5.5mm

About 218x in an 8 inch f/5.9 Dobsonian and 369x in an 8 inch SCT. That needs genuinely steady air, so this is an eyepiece for the best nights of the year on planets, tight doubles and small planetary nebulae.

Apparent fieldSpacewalk

100°

A hundred degrees is wider than the eye takes in at once, so you look around inside the view rather than at it. At very high power in a manual telescope it is also intensely practical, since the target takes far longer to drift out.

Eye reliefTight

10.5mm

Ten and a half millimetres is the tightest in this range, which is the usual cost of a very short focal length. Glasses are impractical, and reaching the outer edge of a 100 degree field means real eye movement, so try before buying if you have astigmatism.

BarrelRequires 2 inch focuser

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 on a complex many-element design keep transmission and contrast high where lesser coatings would scatter. The waterproof, argon-purged body also resists internal fogging on damp nights.

03What comes alive

The targets this eyepiece was born for.

Comes alive

Jupiter’s cloud belts

The two main belts and festoons resolve on steady nights.

Comes alive

Saturn’s rings

The Cassini Division opens up at this magnification.

Excellent

Lunar craters at the terminator

Crater walls and central peaks throw hard shadows.

Excellent

Izar and tight double stars

Splits pairs under an arcsecond apart when the air is calm.

Excellent

Mars at opposition

Polar cap and dark albedo markings when Mars is close.

Excellent

The Ring Nebula (M57)

Tightens the smoke ring and darkens the sky around it.

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

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

5.5 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

04Build around it

What it pairs with.

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 (~9mm)

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.

02The Polaris Score

How it scores, and why.

86/ 100

Explore Scientific 5.5mm 100°

Judged as a dedicated high-power eyepiece for planets, the Moon and tight double stars, 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

Immersion

100

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 dedicated high-power eyepiece for planets, the Moon and tight double stars.

✓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.

05The numbers

Full specifications.

Optical

Focal Length5.5mm

Apparent Field100°

Comfort & handling

Eye Relief10.5mm

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

06Alternatives

For a different goal, start here.

Wider, lower power

Explore Scientific 100° Series 9mm

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

More magnification

Explore Scientific 100° Series 3mm

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.

→

Explore Scientific 5.5mm 100°

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.