The Sharpstar hyperbolic astrograph

SHARPSTAR, A NEW BRAND in the astronomy market, is offering an attractive line of premium refractors and two unique reflectors specifically for astrophotography. The larger astrograph is the Sharpstar 20-cm PNT Newtonian, which offers a focal ratio of f/3.2 using a traditional parabolic primary mirror coupled with a coma-correcting lens.

We tested the smaller reflector, a 15-cm f/2.8 Newtonian. The 150 f/2.8 HNT (Hyperbolic Newtonian Telescope) is designed specifically for imaging.

While a supplied adapter enables an eyepiece to be attached, any eyepiece with a focal length longer than about 16 mm or so will produce a view with a dark shadow from the large secondary mirror floating in the middle of the field. This is not an instrument intended for wide-field views of the night sky. However, it does work superbly for its intended purpose: wide-field astrophotography.

Optical performance

Jiaxing Ruixing Optical, the company manufacturing the Sharpstar line, has created an instrument with an optical design similar to the legendary Takahashi Epsilon 130