Binoculars are frustratingly difficult to keep steady.
There are goto Dobsonians now.
It’s your second guess. In fact, it’s even worse with a Newtonian than it is with camera lenses generally. There are lots of degrees of freedom (lots of variables to tweak) in a camera lens, because every element (separate piece of glass) in the lens has two radii, one thickness, one location along the optical axis, and (simplifying) one index of refraction plus one index of dispersion. Unfortunately for camera lenses the index of refraction is different for each wavelength, whereas in a Newtonian nothing is wavelength dependent. But other than that camera lenses have way more options for the designer to work on distortion.
But the Newtonian has zero degrees of freedom! The main mirror is a paraboloid of revolution, whose shape is dictated by the choice of focal length. If you could get your head in to the main mirror’s focus, you wouldn’t need the secondary mirror at all; as it is, the secondary is nothing but a flat mirror to get the image out of the main optical path so you can look at it without blocking the light entering the scope.
A paraboloid of revolution perfectly focuses the light from a practically infinitely distant on-axis point source, to a point at its focus. Well, to a tiny pattern whose size and light distribution is dictated by the laws of diffraction – but as close to a point as any optical system could possibly get.
For a point source that is not exactly on-axis, the Newtonian does not focus to a point, but rather a distinctive pattern. IIRC this is the distortion called “coma”.
In practice, you make this OK by choosing a slow enough focal ratio, and also by paying more attention to the center of the field. Note that wide angle eyepieces that give low magnification let you see the edge of the field, but if you use really high magnification, you’re not looking at the edge of the field anyway, so this turns out not to be so bad, if you’re doing visual observing.
Now, if you are taking photographs at the prime focus and therefore using all the field you can, and you hope to examine the entire photograph in minute detail, then this coma will be a much bigger problem – leading to bigger compromises in designing scopes intended for photography (or other whole-field pursuits). Using more mirrors and/or adding refracting glass lens elements becomes necessary.
You might say that a Dobsonian is devoted to visual observing, so we let go of edge-of-field sharpness and also the practical ability to compensate Earth’s rotation. And it’s also intended to be cheap and transportable, which means that for whatever aperture you buy, you grind the mirror steep and get a short tube and more edge distortion.
Thanks! That was incredibly informative.
But they all seem to be huge and super expensive. Mrs. Charming and Rested has decided she doesn’t want a GoTo mount in any event.
They’re certainly more expensive - it’s like another $800 for the 8" - but they’re not really any bigger than Dobsonians usually are. It’s likely my next move. Still, that’s a lotta bread, and if you want to run it in a field somewhere you need a power source, which will easily run $100-$200 more.
If Mrs. Charming and Rested has decided she doesn’t want a GoTo mount, then she absolutely should not mess with one! It used to be that much of the fun of amateur astronomy was learning where things are.
As a young astronomy student, when I got an internship at a small observatory that hosted public nights, I had to learn how to entertain with a telescope. A couple of the other interns were a huge help. They knew a few great targets that were easy to acquire even with impatient people in line. They’d point out a major constellation feature and then start navigating, “so you go right to that little pair, then you go jump jump jump aaaaaaand long jump up to that faint one, and it’s just left of it”. This is called “star hopping” and you even do it looking through the eyepiece to more difficult targets.
One thing that is really helpful now (which didn’t exist then) is a laser pointer. They are so much more accurate for pointing out locations in the sky. A red one tends to preserve your vision for observing. If you want to be able to see the pointer itself more clearly, a green one is much brighter in the sky. Finding somebody in a local astronomy club who is willing to show you around with a pointer is a very pleasant start.
I’ve never actually used a go-to mount. I don’t feel like I remember much in the sky, but, even so, I don’t especially think I’d get one if I started observing again. It’s more fun to learn the sky than to learn yet another user interface. The sky doesn’t get changed all around every couple of years, and, if it suddenly goes blank, it means you have to stop observing anyway because it’s full of clouds.
Almost. Aperture is the second-most-valuable. Most valuable is quality. This doesn’t seem to be an issue for the OP, since the scopes he’s looking at (Celestron and Orion) are both as high quality as the laws of physics will allow, as is Meade, the other big brand name. But I mention it for the sake of completeness, for anyone else reading this thread looking for advice.
My other recommendation, especially if you want the fun of finding objects for yourself in the sky, is to get a good naked-eye reticle, such as a Telrad: This is a device that will let you look at the unmagnified sky, with a red bullseye projected over it. This will often let you get close enough to your target that you can skip right past the finder scope.
I’ll check these out. Thanks!
From my experience ant that of many others I’ve known — The moons of Jupiter and rings of Saturn are easy to see in your first hour with a $50 scope. Then, it takes a huge leap in dedication to move on to the next level of interest. So be sure that enthusiasm for hard work is there, before making a big commitment.
The OP may be past that stage, this is for other readers.
Thanks everyone!
For what it’s worth, based largely on the recommendations here, I went with a 6" Dobsonian. The slightly smaller size being a bit easier for Mrs. Charming and Rested to manage while hopefully still being big enough to see interesting things. We went with Orion Skyquest XT6 Plus recommended by @gnarator, with a moon filter, a planisphere, red flashlight (although we already have red headlights), and an astronomy book. Thanks for all the help and here’s to wishing you clear skies and nice weather!
Congratulations! Report back when you two have given it a good spin!
That was SunWife’s first scope after graduating from binoculars. Judging by how it suited her, I’m guessing you’re in for plenty of happy nights stargazing!
Good luck and let us know how it goes.
I’ve been meaning to update this thread for a while but, as seems to be the way with telescopes, we’ve gotten less use of it than we’d planned. So far, in four months, we’ve coincidentally had four nights for free time and clear weather. But at least they’ve been great!
We love the telescope (Orion Skyquest XT6 Plus, linked to above). Our first night, we got our bearings using the Planisphere and a free app. We didn’t see much that we couldn’t see with binoculars from our backyard but we had a great time. On other nights, we watched Jupiter and its moons and Saturn. It’s pretty awe inspiring to see the red storm and the bands through the planet with your own eyes in real time. Weird to think the storm is fading and our grandchildren may not really get to see it. We also had our own moon watching party, which was spectacular. It’s been a lot of fun. Thanks for everyone’s advice!