Baader Hyperion 31mm, aspheric eyepieces

Manufacturer's product description:

Normally, light rays which pass through a lens nearer its edge are refracted more than rays closer to the lens axis. This means the image of an uncorrected system can be blurred out towards its edge. Aspherical correction of an optical system takes care of multiple types of aberration at a stroke. Sharpness is achieved over the entire field of view, distortions are reduced to a minimum and the eyepiece can be made much smaller and lighter.

The eyepiece comes with 1 1/4" and 2" barrels.

The advantages in a nutshell:

• high quality workmanship

• relaxed viewing

• large field of view

• perfect sharpness

• excellent colour fidelity

• dual use with 1.25" and 2" barrels

• low distortion

• low astigmatism

• no 'kidney bean' effect

Baader Phantom Group coating™ - this is a 7-layer broadband anti-reflection coating with extremely low residual reflection. The designation 'Group' indicates that the most effective anti-reflection layer system is worked out for each type of glass used in the respective eyepiece.

All these various antireflection coatings, on each type of glass surface, have then been optimized so that they are most effective where the human eye is at its most sensitive at night - i.e. at about 520nm, which is in the green region of the spectrum.

The best anti-reflection coatings appear almost colourless - this proves that the coating is functioning equally well over the entire visible spectrum. Phantom Group antireflection coatings are - depending on the type of glass - almost entirely colourless. In this way it is ensured that the least light is lost to the night-adapted eye and that no scattered light will interfere.

If you look directly at a coated lens (eyepiece or objective) and can see a strong green reflection, then it is not a Baader Phantom Group coating! An intense green reflection is indicative of a relatively low-tech coating technology and means that light is being wastefully reflected - i.e. lost - right in the useful spectral range between 500-550nm.

Our expert comment:

We have tested the eyepieces with an f5 Newtonian telescope and can confirm their excellent edge correction. Compared to cheaper 70 degree eyepieces, the aspheric Hyperion eyepieces give a significant improvement in field correction! Despite the 1.25-inch eyepiece adapter supplied, the eyepieces can only be effectively used with a 2 inch focuser.

(Bernd Gährken)