The previous double-star results with the Sky-Watcher Skymax 102 MCT were sufficiently pleasing that I decided to try some more-challenging targets with a larger telescope, the Celestron C6 SCT (Schmidt-Cassegrain Telescope). The nominal focal length (1500 mm) of this scope was increased to 3750 mm with a Tele Vue 2.5x Powermate. Combined with the 0.0033-mm pixel size of the E-M5iii camera this yields an image scale of 0.18 arcsec/pixel.
Here is a list of the double stars and their nominal separations in arcseconds:
- Izar (Epsilon Boötis) : 2.9"
- Mizar (Zeta Ursae Majoris) : 14.4"
- Pi Boötis : 5.5"
- Xi Boötis : 4.8"
- Rigel (Beta Orionis) : 9.5"
- Porrima (Gamma Virginis) : 3.4"
Izar is the closest pair in this set and was initially difficult visually, until I realized that the collimation of the scope needed to be tweaked. After a fairly small adjustment it became easy to separate with the bluish secondary appearing as a tiny pinprick next to the yellowish primary. It is hard to capture that view with the camera because atmospheric turbulence blurs the image. Most of these images were taken with a shutter speed of 1/4–1/2 s at ISO 1600 and are stacks of 2–4 of the sharpest separate exposures.
Here is a finder chart showing the location of the three double stars in the constellation Boötes:
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| credit: SkySafariAstronomy.com |
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| Celestron C6 |
As usual, click on an image to get to the larger version.
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