Sat, 15. September 2012
Astrophotography Without a Telescope - 5
I bought this really useful device back on the 3rd July but I have not been able to try it out in the field in the long 11 weeks that have elapsed since then, due to personal health reasons.
The Polarie is a motorised "equatorial" camera mount, with single-directional tracking to follow the stars. (It can also track the Moon or Sun). It can be used in both hemispheres and it is the white box in the images. I bought it complete with the manufacturer's tripod. The camera is my Canon EOS 60D, with Tamron 10-24mm wide angle lens.
I conducted a couple of tests which confirmed the ability of the Polarie to take pinpoint star images of up to three minutes duration but the light pollution from my back garden is so bad that none of the images are interesting enough to post. However, I have not been well enough to take on a field trip with Macarthur Astronomical Society.
The home tests did not last very long because of the onset of dew.
The manufacturer claims that the Polarie, when used with a 15mm focal length lens, can track for up to almost seven minutes at the celestial equator and over thirty-nine minutes near the celestial poles. With the higher magnification of a 100mm lens, it can track for over one minute at the celestial equator and almost six minutes near the celestial pole. These times were calculated on the assumption of a two degree polar alignment error, so the quoted times may even be improved on.
The Polarie has a viewfinder (8.9 degrees diameter) for locating the Celestial Pole, a small magnetic compass and an inclinometer. I am fairly certain that I will find the viewfinder of little value in finding the dim stars around the South Celestial Pole. The compass will be useful and the inclinometer will be used - but it can only give an approximate latitudinal setting.
In my second test, I aligned it to true South by first using the compass to align to Magnetic South and offsetting 12.5 degrees to compensate for the differential here in Sydney. I then use the inclinometer to aim the Polarie 34 degrees from the horizon and refined it using my old draughtsman's adjustable set square and a spirit level (see image below). It seemed to work during the tests at home and hopefully the method will be adequate enough in the field, although it would be more accurate if the Polarie enclosure was flat instead of being slightly rounded. Maybe in the darkness I will be able to get a look at Octans through the viewfinder but I am not confident about that.
I think this camera mount is going to do wonders for my astro-imaging efforts and I also expect it (and other similar devices) to become extremely popular amongst astronomers in the years ahead. The only down side is the maximum loading weight of 2.0 kg. My heaviest lens, 70-200mm f/2.8 weighs almost exactly that (with camera), so I will have to use it sparingly. (EDIT: Vixen have now posted on their website that the Polarie will take equipment up to 7 lbs - or just over four kilograms).
All I have to pay attention to now, before going out in the field in three weeks time, is getting the dew management sorted out. In the meantime, my friend Chris Malikoff took one look at my Polarie, ordered his own and has already started to produce some astonishing images. My turn soon!
I purchased my Polarie from http://www.vixenoptics.com/mounts/polarie.html for $US649.00, including tripod and shipping. (It can be purchased without the tripod for$US429.00). It arrrived here in Australia only six days later, too late for me to start using it before surgery.