Well, “perfect” is a strong word. No matter what you’ve got, there’s always something better. This article is about my hunt for some suitable equipment for deep-space astro-imaging, inspired by the recent purchase of a new telescope for imaging. Ideally I’d be out using it right now, but it’s forecast to be cloudy until further notice 😦
Meade TeleStar 60AZ-A2
I’ve always had a vague interest in astronomy since childhood but I picked up more of a serious interest a couple of years ago when my interest was rekindled after finding a basic telescope – a Meade 60AZ – at a car boot sale for a giveaway price. It wasn’t very good optically and the tripod was made mostly of cocktail sticks and coat-hangers, but it showed detail on the moon and even some of the bands on Jupiter. I was hooked.
As I was already well into photography and owned a DSLR, it was inevitable the two would mate. Using a T-mount adapter and no astronomical knowledge, I roughly pointed the telescope at bright objects that could be seen with the naked eye. Using this setup and taking just one frame, I managed this picture of Jupiter.
Not bad for a cheap telescope, but not suitable for long exposures or for any photography of anything dimmer than Jupiter. It was time for an upgrade.
Celestron NexStar 127 SLT
It is an excellent telescope for visual observation, especially of planets due to its long focal length. It also does a reasonable job of the brighter Messier objects. I had a lot of fun with it and I took pictures of planets and some deep space objects, such as these pictures of Jupiter and the Orion nebula (Messier 42).
However, despite my promising results, the I soon ran into the limitations of the NexStar 127. Maksutov telescopes are not ideal for astrophotography due to their slow focal ratio (this one is f/12), and the alt-azimuth mount is also not appropriate for tracking objects for long exposures. Not only does it use the wrong co-ordinate system but the coarse stepper motors also jerk the image every 10 seconds or so.
Celestron AstroMaster 130EQ-MD
After a little bit of research, it became clear that the “correct” mount for astrophotography is a German equatorial mount. I managed to buy a second-hand Celestron AstroMaster 130EQ for a bargain price, and I then added a motor drive to upgrade it to a 130EQ-MD. The Newtonian optical tube has a much faster focal ratio at f/5.
On paper, it is a much more appropriate telescope for astrophotography than the NexStar 127. I haven’t owned it for very long, but I did take this photography of the Andromeda galaxy (Messier 31).
While the optical tube was pretty good for astronomy (although I did have to modify the focuser to allow infinity focus, and the 1.25″ eyepiece holder causes vignetting, as you can see), the mount wasn’t great. In theory with careful alignment and with the motor running it would allow much longer exposures of dim objects. However, the mount was a bit flimsy and the camera was a bit heavy, so it was hard to keep it all stable. In the end I mostly used the Newtonian telescope on the NexStar goto mount, which was the best compromise (this is how I photographed Andromeda, above). Using an equatorial mount and a Newtonian telescope really opened my eyes to the possibilities. I just needed higher quality components.
GSO 6″ f/5 imaging Newtonian
Now I know my way round a telescope a bit better, I felt more confident mixing and matching components. I liked the look of the Celestron Advanced VX mount, which is designed for astrophotography, and combines the benefits of a German equatorial mount with the convenience of a goto system. But I wasn’t keen on the 6″ Newtonian that Celestron recommend to go with it – it had a pretty poor focuser and mediocre reviews for imaging purposes.
I had assumed that a faster focal ratio would be extremely important for astrophotography as the camera can gather more light, but after consulting with some extremely helpful people at AstronomyForum one of the most important things they said to me was
In visual, aperture is king. In astrophotography, the quality of the optics and mount are king.
The take-home lesson is that a 6″ Newtonian is likely to provide better photographs than an 8″, simply because it is lighter and will be more stable on its mount and easier to guide. With this in mind, I put thoughts of a cheaper 8″ or even 10″ telescope out of my head, and concentrated on a high quality 6″. I decided to pair the VX mount with a lesser-known brand called Guan Sheng Optical (GSO) who get excellent reviews, but seem to offer significantly more telescope for the same price as other manufacturers. The tube I chose is a 6″ f/5 Newtonian, designed for imaging, and equipped with a coma corrector and a 2″ Crayford 1:10 focuser.
These toys only arrived yesterday and it has been cloudy since, so I haven’t had a chance to test it out yet. However, first impressions are excellent. The mount and the telescope feel solid and make all my previous telescopes feel like mere toys. The site I bought the GSO telescope from included a sample picture of Andromeda (M31) taken by one of its customers – Ingo Klever – using this telescope. Ingo is obviously an experienced astrophotographer, but this demonstrates to me that my equipment is now capable of making images like this. If I am still not able to achieve this quality after practice, then the fault lies with me and not my equipment!
Keep your eyes peeled for astrophotographs appearing on this blog using my new toys. Don’t expect anything up to the standard of Ingo’s work just yet, but I’ll do my best to practice and improve.
Facts & figures
Here are the facts & figures relating to all the telescopes mentioned here.
|Telescope||Diameter||Focal ratio||Focal length||Design|
|Meade TeleStar 60AZ-A2||60mm (2.3″)||f/12||700mm||Refractor|
|Celestron NexStar 127 SLT||127mm (5″)||f/12||1500mm||Maksutov-Cassegrain|
|Celestron AstroMaster 130EQ||130mm (5″)||f/5||650mm||Newtonian|
|GSO 6″ f/5||150mm (6″)||f/5||750mm||Newtonian|