DIY camera platform and the beehive cluster
My experiments with ‘piggy-back’ astrophotography have shown that it’s much easier to point the camera at a stellar target using the telescope’s Telrad finder sight than using the camera’s viewfinder. But when I set out to get wide-field shots of constellations etc I don’t need a telescope because its magnification is too great – I just need a regular camera lens and a good equatorial tracking mount to allow very long exposures without star trails. So I did a bit of DIY to achieve ‘piggy-back’ astrophotography without the ‘pig’. That makes setting up, quite a bit easier because I don’t need the big SkyWatcher Explorer 200P or its tube rings or its big heavy counterweights. I just bought a spare mounting base for the finder sight and fixed that to a simple plywood platform. Then I added a quick-release mount for the camera and bolted on a short dovetail bar designed to fit the SkyWatcher EQ5 mount.
I wanted to try it out of course so I decided to have a go at the Beehive cluster without a telescope.
This famous cluster, Messier 44 (M44, NGC 2632), is also called Praesepe (Latin for “manger”), or the Beehive cluster. It is also one of the objects easily visible to the naked eye, and thus known since prehistoric times. Some ancient lore is associated with it: Greeks and Romans saw this “nebula” as the manger (Greek: Phatne) associated with two asses who eat from it, Asellus Borealis, the Northern Ass (Gamma Cnc; Spectral type A1 V, mag 4.7, distance 155 ly) and Asellus Australis, the Southern Ass (Delta Cnc; Spectrum K0 III, mag 3.9, distance 155 ly).
Messier 44 is an open cluster in the constellation Cancer, and one of the closest clusters to our Solar System. It was also among the first objects that Galileo studied with his telescope!
The nebula called Praesepe contains not one star only but a mass of more than 40 small stars. We have noted 36 besides the Aselli [Gamma and Delta Cancri].
With larger telescopes, more than 200 of the 350 stars in the cluster area have been confirmed as members (by their common motion). Some others are foreground or background stars, and others may not yet have been determined.
According to the new determination by ESA’s astrometric satellite Hipparcos, the cluster is 577 light years distant (previous estimates have been at 522 light years), and its age was estimated at about 730 million years.
The Beehive cluster may have been easily visible to Galileo’s naked eye in 1609 but it’s certainly not visible to my naked eye through Glasgow’s light pollution in 2015. What we need is a bit of magnification and a very long exposure. Cue my new camera platform gadget on the telescope’s equatorial mount. As the target is invisible to my naked eye it’s difficult to frame in the viewfinder – but I can use the mount’s Synscan controller to GOTO Beehive cluster – the mount doesn’t know or care that it’s aiming a camera, not a telescope. And I can use Cartes du Ciel‘s Finder Rectangle mark to give me a rough preview of what might be my field of view, see below. The left image is a Cartes du Ciel screen shot and the right image is a shot I took with the actual Canon EOS 500D + 300mm, as the Finder Rectangle mark is labeled. There is only one bright star in each image, Asellus Australis, the ancients’ Southern Ass (actually although it’s the brightest star in the field of view it’s quite a dim one relative to ‘proper’ bright stars – magnitude 3.8, which is dimmish).
The orientation of my camera in its mount puts the main Beehive cluster below and right of Asellus Australis in my image so I have cropped and rotated it to match the screenshot of a closer view via Cartes du Ciel.
This was a 5 minute exposure with a 300mm lens (the Canon image information does not include the lens because the camera doesn’t recognise it – it’s actually a Tamron lens fora Nikon camera with a simple Nikon-Canon adapter!).
I know my image is not exactly spectacular but I was pleased to be able to identify some stars that Galileo first spotted in 1609.