Explore Scientific 100° 9mm Waterproof Eyepiece - 2"

An Immersive Eyepiece for High-Power Observation

With an apparent field close to the maximum for hyper-wide designs, objects are easier to locate, and in a non-driven telescope an object stays in the field a very long time before any adjustment is needed. The huge field also relaxes the eye, so you can pay attention to subtle details for extended periods.

You may be startled at the wide expanse of inky black sky the first time you look through a 100° Series eyepiece, and may even forget there is an eyepiece between you and the universe.

The 100° Apparent Field and 9mm Focal Length

The 100° Series are hyper-wide class oculars that can transform your visual astronomy experience, with a panoramic view.

The 9mm focal length gives high magnification in most telescopes: 133x at 1200mm focal length. There is no specific target list for it.

12.5mm of Eye Relief and Averted Vision

The Explore Scientific 100° 9mm eyepiece features an eye relief of 12.5mm. This specification defines the distance from the eyepiece's top lens to the point where your eye must be positioned to see the full field of view.

Explore Scientific does not say how much of the field eyeglass wearers see. It does say hyper-wide eyepieces make averted vision easy: looking slightly to the side of a faint object puts the image on a part of your eye that is more sensitive to light, allowing you to see fainter images.

A 9-Element Design

The 9mm uses 9 lens elements. It has an optimized optical design, exotic glass combinations for optimum results and durable coatings, and all 100° Series eyepieces are fully multi-coated and edge-blackened to produce maximum contrast.

Waterproofing: Argon-Purged and Tested to 1 Meter

Each 100° Series eyepiece is internally sealed and purged with inert, dry argon gas, with a waterproof, fog-proof housing.

The purge also maximizes the life of the internal coatings, and every 100° eyepiece is tested by submerging it to 1 meter of water for 30 minutes.

A 602g, 2-Inch Tapered Barrel Design

This eyepiece is built with a standard 2-inch barrel, requiring a telescope equipped with a 2-inch focuser or diagonal. At a weight of 602 g (21.2 oz), it is a substantial ocular that adds considerable mass to the focuser end of a telescope. It measures 145mm long and 60mm wide. Expect to rebalance when switching from small 1.25-inch eyepieces.

The barrel is tapered for extra security.

The 15.7mm Field Stop and True Field of View

The field stop is a physical ring inside the eyepiece that defines the sharp edge of the field of view. The Explore Scientific 100° 9mm has a field stop diameter of 15.7mm. This value, along with your telescope's focal length, determines the actual patch of sky, or True Field of View (TFOV), that you will see.

You can calculate the TFOV in degrees using the formula: TFOV ≈ (Field Stop Diameter / Telescope Focal Length) × 57.3. For example, in a telescope with a 1200mm focal length, the TFOV would be approximately (15.7 / 1200) × 57.3 ≈ 0.75 degrees. At 2000mm it is about 0.45 degrees.

Calculating Magnification with a 9mm Eyepiece

The magnification of any eyepiece is determined by dividing your telescope's focal length by the eyepiece's focal length. With its 9mm focal length, this eyepiece is designed to produce high power in most amateur telescopes.

• Formula: Magnification = Telescope Focal Length (mm) / 9mm
• 1200mm focal length: 1200 / 9 = 133x magnification.
• 2000mm focal length: 2000 / 9 = 222x.
• 700mm focal length: 700 / 9 = 78x.

Expanding Magnification with 2-Inch Focal Extenders

You can increase the versatility of the 9mm eyepiece by pairing it with an Explore Scientific Focal Extender. Because this eyepiece uses a 2-inch barrel, it is compatible with Explore Scientific's 2-inch focal extenders. Optional focal extenders are available for the 100° Series.

• With a 2x Focal Extender (FE02-020): The 9mm eyepiece behaves like a 4.5mm eyepiece, doubling the magnification. In a 1200mm telescope, this would increase the power from 133x to 266x.
• With a 3x Focal Extender (FE03-020): The eyepiece performs like a 3mm eyepiece, tripling the magnification. In the same 1200mm telescope, this provides a very high power of 400x.

Care and Contents: Maintaining Your Waterproof Eyepiece

Because the housing is sealed, only the outer lens surfaces ever need cleaning, and only when needed.

The box holds the eyepiece itself.