Explore Scientific 52° Series 4.5mm Waterproof Eyepiece

Product Overview

The Explore Scientific 52° Series 4.5mm is a short focal length, argon-purged waterproof eyepiece with a 1.25-inch double-taper barrel. Six elements in three groups sit behind EMD (Enhanced Multi-Layer Deposition) coatings on every lens-to-air surface, and the edges of the elements are blackened to hold contrast. At 4.5mm it sits at the high-magnification end of the 52° range — in a 988mm refractor it yields 220x, in a 1200mm SCT 267x.

The 52° apparent field is a flat, well-corrected view rather than a wide one. Against a comparably priced Plössl, the gain is in edge correction and in the sealed, gas-purged housing.

Who It's For

• Planetary and lunar observers: 4.5mm is where surface detail on Mars, the Jovian belts and the Cassini division live, seeing permitting.
• Double-star observers: the 15mm eye relief and 4.1mm field stop make splitting close pairs comfortable rather than a squint.
• Compact deep-sky observers: planetary nebulae and globular cores scale up to fill the field, and the background sky darkens as magnification rises.
• Anyone observing in dew or damp air: the O-ring sealed, argon-filled body is built for it.

Key Features & Design

• 6 elements in 3 groups: edge-blackened to suppress internal reflections and scatter.
• EMD coatings on all lens-to-air surfaces: raises transmission and holds contrast on low-surface-brightness targets.
• Argon-purged, O-ring sealed: tested under 1 metre of water for 30 minutes. Argon does not support internal fogging the way trapped air does.
• 15mm eye relief: workable for most observers at this focal length, where eye relief is usually the first thing sacrificed.
• 4.1mm field stop: defines the true field — divide by your telescope's focal length to get it in degrees.
• 1.25″ double-taper barrel: the taper resists the eyepiece being pulled out of a diagonal by a slipping thumbscrew.
• Standard 1.25-inch filter thread (1.125″ x 42 TPI) for lunar, planetary and narrowband filters.
• Removable flip-down silicone eyecup and slide-on caps top and bottom.
• Laser-engraved markings: focal length, series, serial number and brand.

Recommended Uses

• High-power visual observing of the Moon, planets and double stars.
• Bright, compact deep-sky objects — planetary nebulae, globular cluster cores, small galaxies.
• Filling out a focal-length set alongside longer 52° Series eyepieces for a consistent view across the range.
• Damp-climate and dew-heavy observing sites where a sealed eyepiece earns its keep.

Compatibility and Accessory Notes

• Fits any 1.25-inch focuser or diagonal. No adapter needed. In a 2-inch focuser it needs a 2-inch to 1.25-inch adapter.
• Filter thread: accepts standard 1.25-inch threaded filters — lunar, neutral density, colour and narrowband.
• Magnification: telescope focal length ÷ 4.5. An 80mm f/6 (480mm) gives 107x; a 152mm f/6.5 (988mm) gives 220x.
• Focal extenders: pairing a 2x, 3x or 5x extender with a 4.5mm pushes past the useful magnification of most apertures. Longer focal lengths in the series are the better partner for an extender.
• Eyeglass wearers: 15mm of eye relief is usable but not generous. If you observe with glasses on, the 72° ED Series carries more.

Good to Know Before You Order

• Aperture sets the ceiling on 4.5mm. Around 220x in a 6-inch and 267x in an 8-inch, this is a night-dependent eyepiece — steady seeing rewards it, turbulent seeing will not. It is the eyepiece you reach for on the good nights.
• The 52° field is a corrected field, not a wide one. If immersion is what you are after, the 68°, 82° and 100° Series cover that; the 52° Series is built around edge sharpness and value.
• Short focal length means a small exit pupil. In an f/6.5 scope the exit pupil is 0.69mm, so floaters in your own eye can become visible — a normal effect of high magnification, not a fault in the optics.
• Waterproof covers immersion, not submersion in use. The 1 metre / 30 minute rating is there so dew, rain and a dropped eyepiece in wet grass are non-events.

Frequently Asked Questions

Is it difficult to set up?

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

What magnification will I get?

Divide your telescope's focal length in millimetres by 4.5. A 1000mm telescope gives 222x.

Can I use filters with it?

Yes. It takes any standard 1.25-inch threaded filter, which screws into the bottom of the barrel.

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

Six elements against a Plössl's four, a wider 52° field against roughly 50°, EMD coatings on every air-to-glass surface, and a sealed argon-purged body. The practical difference shows at the edge of the field and in damp conditions.

Will it work with my Dobsonian or SCT?

Yes — any telescope with a 1.25-inch focuser, or a 2-inch focuser with a 1.25-inch adapter. On longer focal length instruments 4.5mm produces very high magnification, so it will be a good-seeing eyepiece.

Does it work for astrophotography?

This is a visual eyepiece. Eyepiece-projection imaging is possible with the right adapter, but it is not what the eyepiece is built for.

Bottom Line

In short: a sealed, argon-purged 4.5mm eyepiece with a flat 52° field, 15mm of eye relief and a standard 1.25-inch filter thread — the high-power end of a series built around edge correction and durability. If you are not sure which focal lengths would round out your set for the telescope you own, send us your scope's aperture and focal length and we will work it out with you.