Explore Scientific 52° Series 30mm Waterproof Eyepiece

Product Overview

The Explore Scientific 52° Series 30mm is the long focal length end of the 52° range: a four-element, argon-purged waterproof eyepiece in a 1.25-inch double-taper barrel, with a 27.2mm field stop and 19.9mm of eye relief. At 75.5mm long, 47.8mm wide and 204.1 grams (7.2 oz.) it is a light eyepiece for what it delivers.

A 27.2mm field stop is close to the physical limit of what a 1.25-inch barrel can pass, and that is what makes this focal length interesting. In a 1200mm telescope the true field works out to about 1.3°; in an 826mm refractor, about 1.9°. Magnification is the telescope's focal length divided by 30, so 27.5x in that 826mm refractor and 40x in the 1200mm one — low power, wide field, and a bright image.

Four elements in two groups keep the light path simple, every lens-to-air surface carries EMD (Enhanced Multi-Layer Deposition) coatings, and the element edges are blackened to hold contrast against internal reflections. The housing is O-ring sealed and argon-purged, tested under 1 metre of water for 30 minutes.

Who It's For

• Deep-sky observers working at low power: 30mm produces a large exit pupil, which is what makes faint extended objects such as galaxies and large nebulae stand out from the background.
• Observers who locate by star-hopping: a 1.3° field at 1200mm is a wide window to find things in before switching to higher magnification.
• Open cluster and Milky Way observers, where the whole object fitting inside the field is the point.
• Eyeglass wearers: 19.9mm of eye relief is generous, and enough that the full 52° field stays visible with spectacles on.
• Anyone observing in dew, damp air or coastal humidity, where a sealed argon-filled body earns its place.

Key Features & Design

• 4 elements in 2 groups, edge-blackened: a simple, high-transmission path with the element edges treated to suppress scatter.
• EMD coatings on all lens-to-air surfaces: Enhanced Multi-Layer Deposition, applied to raise throughput and hold contrast on low-surface-brightness targets.
• 27.2mm field stop: near the maximum a 1.25-inch barrel can carry, which is what gives this eyepiece its true field. Divide 57.3 × 27.2 by your telescope's focal length for the field in degrees.
• 19.9mm eye relief: comfortable for extended sessions and workable with glasses.
• 1.25″ O.D. double-taper barrel: the taper resists the eyepiece being drawn out of a diagonal by a thumbscrew that is not quite tight.
• Argon-purged and O-ring sealed: tested under 1 metre of water for 30 minutes. Argon does not carry the moisture that trapped air does, so internal fogging has nothing to condense from.
• Standard 1.25-inch filter thread (1.125-inches x 42 TPI) at the base of the barrel.
• Removable flip-down soft silicone eyecup, with slide-on lens caps top and bottom.
• Optical glass, aluminium, steel and silicone rubber construction, at 204.1 grams (7.2 oz.).
• Laser-engraved markings: focal length, series, serial number and brand.

Recommended Uses

• Low-power sweeping of the Milky Way, large open clusters and nebulae.
• Finding and framing before moving to a higher-power eyepiece.
• Faint galaxy and extended nebula observing, where a large exit pupil carries the surface brightness.
• Whole-disc lunar viewing at low magnification.
• Damp-climate and dew-heavy sites where a sealed eyepiece is worth the difference.

Compatibility and Accessory Notes

• Fits any 1.25-inch focuser or diagonal directly. In a 2-inch focuser it goes in through a 2-inch to 1.25-inch adapter, which we stock.
• Magnification: telescope focal length ÷ 30. A 1200mm Dobsonian gives 40x; an 826mm refractor gives 27.5x; a 2000mm SCT gives 67x.
• Exit pupil: 30 divided by the telescope's focal ratio. At f/4.7 that is 6.4mm and at f/10 it is 3mm — worth working out, because an exit pupil larger than your own dark-adapted pupil wastes some of the light the telescope collected.
• Filters: takes any standard 1.25-inch threaded filter on the 1.125-inches x 42 TPI thread. UHC and O-III filters are the usual pairing at this focal length.
• Within the series: the 52° Series shares an apparent field across focal lengths, so a set holds a consistent view as you change power.
• Focal extenders: a 2x extender turns this into an effective 15mm while keeping the eye relief of the 30mm, which is a useful trick at this end of the range.

Good to Know Before You Order

• The 52° field is a corrected field rather than a wide one. This series is built around edge sharpness and value. If immersion is the priority, the 68°, 82° and 100° Series cover that ground and we carry them.
• The 27.2mm field stop is a 1.25-inch ceiling. A 2-inch eyepiece of the same focal length can pass a wider true field simply because the barrel is bigger. Within a 1.25-inch focuser, this is close to as wide as it gets.
• Very fast telescopes give a large exit pupil at 30mm. At f/4.7 the exit pupil is 6.4mm, which some observers cannot fully use as their eyes age. A shorter focal length in the same series is the straightforward alternative, and we can suggest one for your telescope.
• Waterproof here means sealed against immersion, not built for use underwater. The 1 metre, 30 minute rating exists so that dew, rain and a drop into wet grass are non-events.
• It is a visual eyepiece. Eyepiece-projection imaging is possible with the right adapter, though the design target is the eye.

Frequently Asked Questions

Is it difficult to set up?

No — it slides into any 1.25-inch focuser or diagonal and is ready to use immediately. There is nothing to assemble, collimate or adjust.

What magnification will I get?

Divide your telescope's focal length in millimetres by 30. A 1000mm telescope gives 33x, a 1200mm gives 40x and a 2000mm gives 67x.

How wide is the true field?

57.3 multiplied by the 27.2mm field stop, divided by your telescope's focal length. In a 1200mm telescope that is about 1.3°, which is around two and a half full Moons across.

Can I use it with glasses on?

Yes. 19.9mm of eye relief is generous for a 30mm eyepiece, and the flip-down silicone eyecup folds back to let spectacles sit close enough to take in the whole field.

Does it take filters?

Yes, any standard 1.25-inch threaded filter on the 1.125-inches x 42 TPI thread at the bottom of the barrel. Nebula filters are a natural match at this focal length.

How is it different from a Plössl at a similar price?

Four elements in two groups with EMD coatings on every lens-to-air surface and blackened element edges, a 52° field against a Plössl's roughly 50°, nearly 20mm of eye relief where a 30mm Plössl has considerably less at the eye lens, and a sealed argon-purged body. The eye relief and the sealing are where the practical difference lives.

Will it work in my 2-inch focuser?

Yes, through a 2-inch to 1.25-inch adapter. Many 2-inch diagonals include one, and we stock them if yours does not.

Bottom Line

In short: a 204.1 gram, argon-purged 30mm eyepiece with a 52° field, a 27.2mm field stop that runs close to the 1.25-inch limit and 19.9mm of eye relief — the low-power, wide-field, comfortable end of a series built around edge correction and durability. If you would like help working out which focal lengths would round out your set for the telescope you own, send us its aperture and focal length and we will map it out with you.