Discovery 12.5 Dobsonian: Initial Thoughts
| Discovery 12.5" at its new home - many new deep sky explorations await! |
The scope and everything around it was with coated with a thick layer of frost. 19 degrees this morning but, thankfully, no wind. There were birds though, lots of chirpy birds. And a very pretty sunrise. And Jupiter which you don't see in this picture because the gas giant was out of the range of the photo, just a pinpoint of light high in the western sky. To the untrained eye the largest planet in our solar system would have looked like a star about to fade from view in the brightening sky.
I'm glad I got up when I did because had I waited another 15 minutes I might not have found it. As it was I had just enough time to tilt the scope over and place the Tetrad's red center point on the fading pinpoint. I was treated to the best view of Jupiter I've ever had. Even with the coming daylight I saw three bands of reddish clouds stretching across the white sphere of the planet. The two main bands even hinted at a bit of detail along the edges which exhibited irregularities. Even more, the white base color of the planet turned into a gradient of a fainter red over the north and south poles. Four moons were easily visible as pinpoints of light.
For a little treat after Jupiter I swung over to the moon (top right corner of the photo) and in its current crescent stage it's possible to see many more craters along the edge and it was a fantastic view.
This marks the 5th viewing session with the new scope. Well, new to me. It's actually about 14 years old. Handmade by the folks at Discovery Telescopes, it was a chance find on Craig's List. With a mirror of 12.5" it's only slightly larger than the Zummel's 12" mirror. I am not at all unhappy with the Zummel and have enjoyed it a great deal over the past three years but this was a chance at a better scope and thus a better visual experience at a good price so I went for it. Not only are the optics better but it came with an equatorial platform for tracking objects in the eyepiece. So, what are some of the differences and how does it perform?
Most importantly, the Discovery scopes are built with hand-made mirrors that are a step up from mass produced mirrors used in scopes by Zummel, Orion and others. Or so it is said. In terms of the visual experience I have to also mention that the Discovery is built using cardboard Sonotubes. Yes, cardboard. Very well painted and the Sonotube is very, very sturdy so this is not something that will bend or break easily as long as it is taken care of. But most importantly, the interior of the tube is pitch black. Unlike an unflocked metal scope that's been painted black but appears gray this is completely black. Set this next to the Zummel on a dark night and you'd be amazed at the grayish blue glow that you see when looking down the tube of the Zummel. Look down the tube of the Discovery and it is pitch black. The only light to be seen is that being reflected back up by the primary mirror at the base of the tube.
The result of the improved mirror and the blackened tube in the eyepiece is not just noticeable but dramatic. I can't say for certain how much of the improvement is the mirror and how much is the darker tube but I can say that in the five sessions I've had I am thrilled. As mentioned above, the view of Jupiter this morning was the best I've ever had. Did I think my views before were lacking? At the time, no. I was always very happy with them. But it is greatly improved with this scope. I'm looking forward to more viewings with darker skies and greater contrast. I suspect that for the most part the views will only be better.
Another object I've viewed during four of the sessions that needs special attention is the Orion Nebula. WOW. The view with this scope is nothing short of spectacular. When viewing astronomical objects, especially nebulosity, the key is contrast which translates into increased detail. With such low light the observer is always looking for the subtle details to be found in gradients of gray and usually blueish light. So, in an object such as the Orion Nebula which is easy to see even in binoculars the details emerge as you improve your practice viewing and as you observe with better equipment. I’ve had a good bit of practice and am seeing more all the time just because I’ve been looking at it now for 3+ years with several different scopes. In some ways it's like other visual activities that one learns in practice.
For example, as a bird watcher I'm still learning new things about birds and learning how not just identify them but to really see the details. With birds it's everything from the shape of the beak to the colorful feather markings, the shape of it's body, to the way the bird flies and more.
In visual astronomy practice helps one to see more details in any instrument but it also helps one notice the refined details in better instruments. If I were to look at the Orion Nebula with my 8" scope now I would see more than I did 3 years ago when I first looked using that scope because I know how too look. I know about averted vision and about spending enough time on an object. I know more of the details and about looking at dark areas as much as the light areas. So, regardless of instrument the view is always getting better with practice and familiarity. But with the Discovery I can safely say that I am seeing an amazing amount of new detail. The increased contrast means the subtle details that would have been lacking before now stand out. Differences in color and brightness mean differences in gradient which, in the case of this particular object, means a new sense of visual depth, of dimension. Honestly, this wasn't something I was expecting. Yes, I was hoping for a better view, better detail, but I didn't quite understand what that would be. Now I know.
Viewing the nebula now means seeing new detail everywhere which leads to this added sense of dimension. It's no longer a flat view. Now, I expect not all objects will benefit in the same way. In fact, I know they will not. My view of the Crab nebula is improved but not by much. It is a much dimmer object to begin with and as I understand it details only emerge with scopes larger than 16". I can't say that's true but I can say that my view is largely the same with all three of the scopes I have at my disposal: 8", 12" and the 12.5". In all three it is an irregular, somewhat spherical gray nebulosity that offers little to no detail. But M82, one of the two Bode's galaxies? I've not had nearly as much time with M82 with the new scope but in the brief time I've had I'd say it is improved a good bit. It might not prove to be as dramatic as the view of the Orion Nebula but it's definitely better. The same for the Andromeda Galaxy and the Triangulum Galaxy. My expectation is that objects such as galaxies that can offer a view of spiral arm structure will benefit a good bit which is great because they are some of my favorite objects to view. Some nebulae will be improved, others won't. I doubt larger open clusters of stars will be improved but I suspect the resolution of some of the fainter stars in some open clusters will be as will some globular clusters.