Buying a scope, $500 or less
Ok, so here's aanother Quora post I'm cross-posting. I get questions like this a lot. In this case the person was asking about a telescope for $500 or less and was looking for one which could automatically find and point to things for him. Here's my answer:
First off, let me recommend you NOT buy a telescope right away. The best thing you can do before buying a telescope is to find and join a local astronomy club or society. Most such clubs conduct regular star parties. Right now, due to the pandemic, there's not a lot of that happening... but as soon as the pandemic is over, I suspect a lot of clubs will be eager to start holding them again soon.
A star party is an event at which those who have them bring out their telescopes and everyone spends the night observing. During a star party, you are likely to get a chance to look through a wide variety of telescopes of all types... giving you a chance to try before you buy.
Most clubs are also happy to help people new to the hobby learn the basics as far as using and maintaining a telescope. This is something that's likely to be very helpful down the line.
In the US, you can find a club in nearly every medium to large city, and in a lot of smaller communities as well. I've never seen membership dues exceed $50 per year, and there's often some great benefits that come along with it.
So, that's my first recommendation.
Now, as for telescopes... Choosing the right scope can be tricky, because telescopes aren't really a one-size-fits-all item. Different telescopes are better for different needs.
One thing that's generally true for most amateurs is that the larger the aperture (the diameter of the objective lens or primary mirror), the better. The aperture is what controls how much light the telescope can collect and focus into your eye, and a larger aperture means more light is collected. Aperture also determines the level of detail that the scope can show you, and, again, larger is better.
Generally speaking, other than weight and transportation/storage concerns, you really can't have too large an aperture. This isn't the only thing to look for, but it's one of the most important.
Magnification is not as critical. When a telescope advertises magnification, that's a good sign it's not a good telescope. I've seen plenty of scopes with claims like "Over 575X magnification" right on the box... and while that's not a lie, it's very misleading.
Magnification is determined by the focal length of the telescope and that of the eyepiece being used. If you have at telescope with a focal length of 1,000 mm (focal length is usually described in millimeters) and use a 25 mm eyepiece, you get 40X magnification (1,000 / 25 = 40). If you switch to a 10 mm eyepiece, you get 100X. Eyepieces down to about 5 mm aren't hard to find, and you can sometimes find even shorter focal length eyepieces (though the quality tends to get lower and lower if you're not looking at premium brands, which are expensive). But you can also use an optical device known as a Barlow Lens to increase magnification. A Barlow Lens is an optical element that typically is placed in the path of light before the eyepiece to increase focal length. Most Barlow lenses are 2X Barlows, meaning that they increase the telescope's effective focal length by 2 times. So, in the previous example, the 25 mm eyepiece with the 1,000 mm focal length and a 2x Barlow would give you 80X ((1,000 x 2) / 25) and the 10 mm eyepiece would give you 200X. And, theoretically, you can stack Barlows in series. If you were to use two 2x Barlows with the previously mentioned scope, the 25 mm eyepiece would now give you 160X and the 10 mm eyepiece would give you 400X
But there's a couple problems here. First, even with high quality Barlows, the more optical elements you add, the more you will degrade the view. So while you CAN stack Barlows, it doesn't do you much good. More importantly, however, is that while you can technically magnify to infinity, every telescope has a limit to how much detail they can show, meaning that they have a maximum useful magnification. Above this limit, the view is going to be too blurry to be worthwhile.
The commonly used method of calculating maximum useful magnification is to multiply the telescope's aperture in inches by 50X. So an 8 inch telescope would be good for up to 400X, while a 4 inch would be good up to 200X. But this is the MAXIMUM useful magnification and assumes ideal atmospheric conditions. For most people, the limit is likely to be closer to 25 to 30X per inch. And due to atmospheric limitations, anything above about 350X is usually not worthwhile as the view is just too distorted by the atmosphere.
So, magnification is not the thing to look for. It's not unimportant, but most decent amateur scopes can provide plenty of magnification given the right eyepiece options.
Now, one of the things you said you want is for it to be able to automatically find and move to the coordinates of an object. The common term for this is GoTo. In a GoTo system, the telescope has a computer which models the night sky internally. When you start it up you have to make sure hit has the correct local time and date and the correct latitude, longitude, and altitude (these can all be obtained through GPS if the scope has a built-in GPS system, otherwise you need to manually enter them through the control hand box). Once that is done, most such scopes will ask you to select from a list of named stars. It will slew (move) to where it thinks the stars should be and you look through the scope to confirm that it's on-target and, if not, use the hand control to move it to where it should be and confirm its position on the control. In most cases you'll need to do this 2 or 3 times, sometimes more. When this is complete, the scope has synchronized its positioning and aim with the sky, and now should be able to calculate the relative position of any celestial object in its database and move to that object - assuming the object is currently above the horizon).
GoTo can be extremely helpful, but its usefulness is also very much circumscribed.
The GoTo system is not part of the telescope itself, but what we call the mount. The mount is the device that holds and aims the telescope. People who have little or no experience with telescope are likely to refer to this as the tripod, but it's more than just a tripod, and not all mounts use a tripod.
Not all mounts are made equal. Mounts typically are rated for a certain total payload weight (meaning the weight of the telescope, finder scope, eyepiece, etc...), and exceeding that weight can damage the mount and render it inoperable. Mounts also vary in precision and accuracy. A lower-cost GoTo mount is likely to be less accurate than a mount made by a higher-end manufacturer.
There are several manufacturers out there, though the bulk of the lower-cost brands are all manufactured by only a couple Chinese companies. Celestron is one of the most popular. They were bought out by the Synta Technology Corporation of Taiwan in 2005. Prior to that, much of their equipment was already being made by Synta. Synta is also one of the main suppliers of telescopes and equipment sold by Orion, though Orion is a US-owned and operated company. SkyWatcher is also made by Synta, they created the SkyWatcher brand in 1999 to have their own company to sell products under. Meade is owned by Ningbo-Sunny out of China, and in recent court cases it's been shown that Ningbo-Sunny and Synta have colluded to fix prices and, it appears, possibly share manufacturing. This can actually be seen in a particular telescope they sell. Meade sells an 80 mm f/5 refractor that is also sold by Orion, SkyWatcher, and Celestron under different product names, but the optical tube, focuser, and objective lens are exactly the same, just with different paint jobs and brand decals.
Simply put, at the lower and mid-range of the price spectrum, there's very little difference, or, in most cases, none between products by any of those named companies and several others.
Now, I say this in preface to discussing the mounts available with or for scopes in your price range. They are mostly made by Synta at the Suzhou Synta Manufacturing plant in Mainland China. Overall the quality of these mounts, regardless of brand, is roughly equal. And most in this price range are junk.
Some of them use plastic or nylon gears and mechanical components, which are easily damaged or broken. I've seen plenty of cases of gears with teeth broken off or just plain broken in two. Often this happens when the telescope is over-stressed, usually by trying to move it into position or if it hits something when moving and keeps trying. While you may take good care of it, accidents like this can happen all to easily. And when these mounts break, the cost to repair is usually high enough to make repair impractical. Further, these mounts typically have NO manual backup. If the mount's mechanical or electrical components fail or you don't have power to run them, they are essentially expensive doorstops. In most cases, you can unlock the clutch on the motor and manually move the instrument, but this is not practical for actually using it. The instrument won't stay on-target when you stop touching it, and when you are touching it, you're imparting vibration that makes the view intolerable. No, if the mound has no power or is broken, it's useless.
When you look at the price of GoTo scopes, you have to consider that a significant portion of the price paid goes to the computerized mount, meaning less goes into the optics. These lower-priced GoTo scopes usually offer the worst of both worlds; a weak and easily damaged mount and poor optical performance. These are what I call interest killers. They leave users frustrated and feeling it's not worth it.
Even when they function, their function isn't always all that helpful. If the alignment isn't right, the telescope isn't properly balanced on the mount (balance is often critical for accurate GoTo performance), or the mount isn't functioning properly, you may not know if its on-target or not. When you look into the eyepiece to see a nebula or galaxy, you may not see it because the scope isn't pointing at it properly, or because it's too fain for this telescope to show.... and unless you know your way around the sky to begin with, you won't know which it is.
I should mention here that a lot of these mounts advertise things like "Able to find Over 40,000 objects." This, like with magnification, is misleading. The database contains those objects, yes. Usually the databases include the Messier catalog along with the NGC/IC catalog and one or two star catalogs. Those 40,000 objects are likely to include things far too faint for the scope as well as stars that you're very unlikely to ever go looking for. In reality, most of them have a couple thousand objects that you can see, and thousands you can't. The scope itself won't know if you can see them or not, so It'll happily slew to the target, but you won't see a thing... at least not with these optics.
My strong opinion here, and I know plenty of people who agree, is that the best bet for a beginner is NOT a computerized GoTo scope with mediocre electronics and/or optics, but a manual scope of a higher quality.
This is where my recommendation comes in: get an 8 inch Dobsonian.
A Dobsonian, or Dob, is not a brand, it's a combination of a Newtonain reflecting telescope OTA (optical tube assembly, the telescope portion itself) and a very simple rocker-box mount. John Dobson was one of the leaders of the San Francisco Sidewalk Astronomers club in the 60s and 70s and was looking for an option to get telescopes into more people's hands. He came up with the concept of the Dobsonian telescope as a very low-cost solution.
Newtonian telescopes are some of the most cost-effective scopes available. The average price per inch of aperture is typically significantly less than that of other designs. An 8 inch Newtonain OTA can be found for around $300 +/- brand-new. An 8 inch Schmidt-Cassegrain Telescope (SCT) will typically cost closer to $1,000 new. If you can even FIND an 8 inch refractor, it's likely to cost several thousand (in excess of $10,000), and need a humungous mount. For people interested in making their own telescope from scratch, the Newtonian is one of the easiest to make (though it's cheaper to buy), and manufacturers can churn them out rapidly for low prices.
The rocker-box mount of a Dobsonian was inspired by a ship's canon. Essentially, the telescope simply rotates up and down on a box-like structure which is in turn mounted on a turntable base. They are very easy to build and manufacturers can churn them out rapidly and inexpensively. As such, an 8 inch Dobsonian with a couple eyepieces and other accessories can be found for under $500. They require no power and there's little that can go wrong with them. And with the 8 inch mirror and usually fairly long focal length (usually around 1,200 mm), they offer very good optical performance for the price.
The downside here, if you want to call it that, is that you have to learn to find things manually.
Everyone wants the shortcut, wants to cut corners and not have to put in the time to learn. But let me tell you this: learning to find things manually through star-hopping is not difficult and FAR more rewarding. You get a lot more out of the scope and end up enjoying it a lot more, especially more than a lower-end GoTo scope.
Star hopping isn't difficult. You look on a star chart for the object you want to see, then look to find a bright star nearby that you can identify in the sky above you. You look at the chart, then, and find a path from star-to-star to get to the object. Then you move the scope to your starting point and "hop" from star to star until you're on-target.
For example, here's my method of finding M31, the Andromeda Galaxy, which Happens to be in a good place right now. Start by identifying the constellation Cassiopeia. It's fairly easy to find and looks a bit like a lopsided M or W. If you look at it as two triangles that share one point (the middle of the M or W), and then look at the larger of the two as an arrow, that arrow points a little way across the sky toward a relatively bright star about 20°away. 20° is about twice the width of your fist from thumb-knuckle to pinky knuckle if you hold your fist out at arm’s length (that's a common estimate). So look for the brightest star that's about two fist-widths away from the point of the larger part of Cassiopeia. That star is Mirach, and that's our first hop.
Mirach itself is worth a glance. If you look carefully through a decent telescope, there's a faint fuzzy spot next to Mirach. This is known as Mirach's Ghost and is a galaxy (NGC 404) far beyond our own.
From Mirach, if you move a little bit north and east you will find a smaller star. Under relatively dark skies it should be visible naked eye, from a more light-polluted area it's hard to see without binoculars or a finder scope. That star is about 3-4°from Mirach. 5 degrees is about the width of your index, middle, and ring finger together held at arm's length, and 1 degree is about the width of your pinky finger. So estimate that distance north-east of Mirach and you'll find this next star. It doesn't have a name, just a few different numeric designations (Hipparcos 4436 or SAO 54281... neither of which really roll off the tongue, do they?). This is your next hop. Move from there almost the same distance, a little less (around 3 degrees) north north east. This star is a little fainter than the last, but not by much. I won't bother with the number, just know it's there. Now, once you're on this star, move again a little north and east, maybe 2 degrees, maybe less, and you'll find M31. In fact, odds are you won't be able to miss it if you get close - its' pretty big and bright and looks like a fuzzy cloud in the eyepiece. If you're under fairly dark skies, you can even see it naked eye if you follow my hopping instructions. Incidentally, M33, the Pinwheel Galaxy (or Triangulum Galaxy) is almost the same distance on the opposite side of Mirach from M31. If you can find M31 this way, with a little more effort you can find M33.
You can find pretty much any deep sky object this way. You just have to find the right landmarks. The best part is, you find it yourself, you get the satisfaction of the hunt and finally finding your target.
But by doing it this way, you also tend to see and experience a LOT more. You're forced to look more carefully at the sky. When you finally find the target, you're more likely to notice things around it. for example, with M31, there are two satellite galaxies, M32 and M110, that you can usually make out without difficulty. If you didn't star-hop to M31, you'd likely never see Mirach's Ghost. Through star hopping, you're likely to run across interesting things that you'd never have even thought of looking for. And by looking through the eyepiece this way, by pending the time to really look at what's there, you star to train your eye to see more and more. If you're just using GoTo to move from object to object, you'll find that gets old pretty fast. You're likely to tend to look at the same few things every time, and when you look, you're less likely to really spend the time observing. Through most amateur telescopes, most of these objects just look like faint clouds or cotton balls deep in space. But when you take the time to linger, to let your eye soak up the faint light from the object, your brain will start processing things differently and you'll start to see more and more in the target object.
Again, GoTo can be helpful. I use it for astrophotography because it's really tricky to have to find an object, then re-attach the camera and re-focus and THEN start an image. I can focus on a bright star nearby, then slew to my target to start imaging. But when I'm just observing for fun, I much prefer my 10" or 6" Dob.
Another great thing about a Dob: you can set them up in about 2 minutes. A GoTo scope will take time to set up and align. A Dob can be set up in about 2 minutes, just put the base down and put the tube on the base. Usually there's a spring or other attachment, and you're done: pop in an eyepiece and start observing.
Again, don't take my word for it: join a local club and see for yourself. You'll be really glad you did.
Note: there was another answer posted to this question from someone who suggested the NexStar 4SE from Celestron and said its popularity speaks for itself. I mean no disrespect to the other person, but I personally feel this scope is a bad choice for many reasons, but the statement that its popularity speaks for itself is a poor argument.
Lastly... Not to be rude to the other answer from [Name Omitted], but don't buy that scope, at least not without trying out others. The quality of Celestron equipment has gone downhill over the past several years, and those NexStar scopes are not all that great. My club has had several of the NexStar 4, 5, and 6 SE series, and they’ve all had problems. In one, we went through a few hand controllers (at $100 each) before we found out there was a fault in the mount. On another one, the on-board electronics were fried due to a lose power connector. Another one suffered mechanical problems.
For the same price or less you can get an Apertura AD8 or Zhumell Z8 (they're actually the exact same scope from the same manufacturer - GSO of Taiwan - sold under different brand names) or an Orion XT8. The 8 inch aperture has roughly 4 times as much light gathering capability and twice the detail resolution capability and is far more reliable. The Celestron optical tube of the NexStar 4SE is fine... but the mount is just bad news.
Comments
Post a Comment