Two famous double stars with the Sightron inifini D50 refractor

 The inifini D50 refractor is a 50-mm aperture, 540-mm focal length (f/10.8) achromatic refractor manufactured by Sightron Japan.  It was designed primarily as a visual instrument, but it is of course fun to see how it performs photographically as well.

Polaris (Alpha Ursae Minoris) is well known as the "North Star", but it has other qualities which are of interest to astronomy enthusiasts.   It is the closest Cepheid Variable, which makes it an important part of the cosmic distance ladder.  It is also a triple-star system.  Two of the components are visible with modest amateur telescopes.  The third component is a close companion of the massive primary star and has only been resolved with the Hubble Space Telescope.

 

Polaris.  Sony A7iii + Rokinon 75mm f/1.8 + Hoya Softon filter.

Polaris B is a magnitude-8.7 companion separated from Polaris A (mag 2) by 18 arcsec.  To photograph this star with the D50, an Astro-Tech 2x telecentric focal extender was used with an Olympus E-M5iii camera.   The camera and extender was inserted directly into a Baader 90-deg Amici prism diagonal.  The telescope was mounted on a manual alt-az mount.  Polaris is close enough (0.62°) to the north celestial pole that a tracking mount is not required for short exposures.

Sightron infini D50 + Baader prism and camera.

 

Polaris A and B with the infini D50 refractor. 2-sec exposure.

 Mizar and Alcor is a well known naked-eye double star in the handle of the Big Dipper. What is less well known is that this is actually a six-star system.  Mizar, the brightest component of the pair, is easily resolvable in small telescopes into two components, each of which is also a spectroscopic double star.  Alcor, the fainter companion to Mizar, is a spectroscopic double as well.

Mizar and Alcor (center). Rokinon 75mm f/1.8 + softon filter.

 The Mizar and Alcor system was photographed with the D50 refractor mounted on a ZWO AM3 tracking mount.

Mizar (top) and Alcor (bottom). 2-sec exposure.