Something new and different: photography with a 6-inch reflector

 The waxing moon is lighting up the sky when the rain clouds aren't obscuring it.  This is not the time for wide-field astrophotography.

Last night (Friday 12 July) the late-night sky was clear, so I decided to try out a telescope that has been unfairly neglected: a 6-inch (150 mm) f/5 Newtonian reflector.  This is a superb telescope for visually scanning the star clusters and nebulas ("nebulae" for the overly pedantic) of the Milky Way, but I have never used it photographically.  

During the day I prepared a motorized equatorial mount that would be suitable for carrying this telescope.  But that mount is heavy and requires some effort to set up and balance, so I decided instead to first try some test images with a much lighter non-tracking alt-az mount.  It turns out that the simpler mount was all that was needed for doing short (< 0.1 sec) exposures.

Here is a picture of the telescope and mount:

The 6.7-d moon was a good first test subject:

E-M5iii. ISO 400, 1/640 s.

The primary photographic goal was the double star Albireo (Beta Cygni).  Albireo is a double star in the constellation Cygnus (The Swan).  It is famous for its appearance in small telescopes.  The two components are separated by 35 arcsec and have contrasting colors of golden orange and sapphire blue.  Albireo is located at the bottom of the "Northern Cross", or in traditional constellation art, at the head of the Swan.

Constellation Cygnus. credit: IAU

I have imaged Albireo several times before with smaller-aperture optics and it is easy to separate the two stars.  The trick is to get an exposure that also also displays the colors. My hope was that the natural diffraction pattern of the Newtonian secondary-mirror holder would spread out the light of the two stars enough to prevent the colors from overexposing and washing out.  Here is an image of the bright star Vega that shows the four-spike diffraction pattern:

Vega, ISO 1600, 1/10 s, untracked.

The image of Albireo was successful, even though the diffraction pattern is not seen, and probably had little effect:

Albireo (Beta Cygni), ISO 1600, 1/10 s, untracked.

The trial images with the alt-az mount were so successful that it was not necessary to haul out the heavier equatorial mount.  This is my best image yet of Albireo that shows that contrasting colors of the two stars.

There has been a long-standing debate about whether the two stars are gravitationally bound to each other or just a chance optical alignment.  The current consensus is that the two stars are not connected and just a chance alignment.