Baader Hyperion 68° 21mm Eyepiece - 1.25"/2"

8-Element Optical Design with a 68° Field of View

The Hyperion 21mm eyepiece uses an 8-element, 5-group optical formula to deliver its immersive 68° apparent field of view. The field stop diameter is 24.9mm. The series is designed as a way to get more from a telescope than the simple eyepieces often supplied with it.

Baader's technical data lists the 21mm in the parfocal group of the series, together with the other focal lengths except the 24mm, so little refocusing is needed when exchanging them.

Phantom Group Coatings for Maximum 520nm Transmission

Every air-to-glass surface in the Hyperion 21mm eyepiece is treated with Baader's proprietary 7-layer Phantom Coating® Group anti-reflection coatings. They are optimised to be most effective at about 520nm, in the green region where the night-adapted eye is most sensitive. A strong green reflex shows light between 500 and 550 nm being reflected and lost, while Phantom Group coatings appear almost colourless.

Baader's aim is that the least amount of light is lost for a night-adapted eye, without stray light, with extremely low residual reflection.

1.25" and 2" Barrels

The Hyperion 21mm comes with both barrels. The 1.25" barrel (27mm long) holds the first group of lenses, and its slip protection is a classic undercut. Unscrewing it exposes the 2" barrel (49.3mm), for 2" focusers and diagonals.

This modularity extends to filter usage. The 1.25" barrel is threaded for standard M28.5 filters. The connection point between the 1.25" and 2" barrels features an M48 thread, allowing a 2" filter to be placed between the barrels, which also changes the focal length.

Modular Focal Lengths: From 21mm Down to 14.0mm

The Hyperion 21mm is not limited to a single focal length. By unscrewing the front lens group (housed in the 1.25" barrel), you can insert optional Baader Fine Tuning Rings (FTRs) to decrease the eyepiece's effective focal length, increasing magnification without adding the extra glass of a Barlow lens. This works without loss of sharpness.

• 21mm: The native focal length with all components assembled.
• 18.5mm: Achieved with a Baader 2" eyepiece filter of 6mm height in the M48 thread.
• 17.6mm: Achieved by adding a 14mm Fine Tuning Ring.
• 15.5mm: Achieved by adding a 28mm Fine Tuning Ring.
• 14.0mm: Achieved by combining both the 14mm and 28mm Fine Tuning Rings.
• 32.2mm: By removing the front lens group entirely, the eyepiece becomes a 2" eyepiece of 32.2mm focal length. Use it this way only for afocal projection imaging; in visual use a loss of edge sharpness will be experienced.

Photographic Integration: M43 and SP54 System Threads

All Hyperion eyepieces are suitable for afocal and classical eyepiece projection. Removing the folding rubber eyecup and the large silicone thread-protecting ring exposes two male system threads.

• M43 Thread: This is the primary thread for classical eyepiece projection. With the Hyperion M43/T-2 ring (#2958080), the Baader Astro T-2 System adapters for Moon and planetary photography can be used, and any T-2 camera ring with an SLR or DSLR camera may be attached.
• SP54 Thread: This larger diameter thread is designed for afocal projection, where a camera with a non-removable lens (such as a point-and-shoot camera or camcorder) is used. Baader DT-rings such as SP54/M28 (#2958028) and SP54/M37 (#2958037), used with the Hyperion 11mm extension ring (#2958090), adapt the SP54 thread to the camera's filter thread.

20mm Eye Relief in a 0.42 kg Body

Eye relief is 20mm. The folding eyecup sits on the M43 thread; it can be stored folded down, especially for persons who wear glasses, or folded up. The winged rubber eyeshield of the Hyperion 68° eyepieces is ideal for binocular use.

The eyepiece has an outer diameter of 58mm and a net weight of 0.42 kg (the design data gives 393g for the eyepiece); the body stands 56mm above the reference plane. The package includes a 1.25" dust cap, 2" dust caps and a soft-leather bag. Baader asks that the eyepiece only be opened at the M48 thread at the top of the 1.25" barrel; other joints are secured with Loctite, and disassembly elsewhere voids the warranty.