Monday, July 14, 2008

Telescope Mounts: What NOT to Buy

There are some telescope mounts that are consistently inferior enough to others that it's safe to say they should always be avoided for an astronomical telescope:

The Ball Joint, or Ball-Head Mount
Ball joint mount

These do a poor job of holding the scope, and even if they have a locking screw, it's not possible to point the telescope accurately or to move it to compensate for the motion of the Earth. In some cases a ball joint may be usable for a camera piggybacked on a telescope (on a good equatorial mount) but it's not adequate for any sort of telescope used for astronomy, even small ones. Personally, I would avoid even low-power spotting scopes that come with this type of mount.

Camera-Style Tripod Mount
Camera Tripod Mount

Again, these aren't adequate for an astronomical telescope. Pointing them at what you want to see is way too difficult. Trying to compensate for the Earth's motion is nothing but frustration. These mounts are OK for cameras, binoculars, and small spotting scopes that give about 20-25 powers of magnification used for terrestrial purposes. They're not well designed for viewing at high angles, so they're not all that useful for astronomy with any instrument. With binoculars they're tough to use because you have to lean forward over the tripod to get your eyes up to the eyepieces. It's not a comfortable way to look through binoculars, and if you can't relax and enjoy the view you're not going to enjoy astronomy.

Cheesy Fork Mount

There are good fork mounts. They are solid, provide smooth motion, and hold the telescope on what it is pointed at. The fork mounts used on most Schmidt-Cassegrain and Maksutov telescopes are quite good.

And there there are monstrosities like the one pictured above. These are still common on many small inexpensive telescopes. They don't move smoothly, they have slack areas where the scope flies through and tight areas where the scope only moves with dificulty, they don't hold the scope in place even if they have impressive-looking slow motion or other support bars. They're junk. If you've already got a scope on one of these, look at retro-fitting it with a nice homebuilt Dobsonian-style mount or some other good mount suited for the telescope.

Mind Killers

If you want to kill a kid's interest in astronomy and science, buy them a telescope on one of these mounts. If you want to convince them (or yourself) that you're incompetant, and that astronomy is difficult, march right into your local camera shop or "Mart" store and pick up a telescope mounted on one of these.

Some newer mounts have lots of fancy molded plastic around them to hide the fact that they are still one of these cruddy mounts underneath. Lots of little refractor telescopes come on a mount that has a bulgy plastic clamp that goes around the telescope and big plastic handles on the motion controls. It's still just a camera mount.

Don't be fooled into buying one of these. No telescope at any price is a bargain when it's sold on one of these. It's not worth buying and thinking that maybe you'll get some light use out if it and upgrade later "when you get serious." You'll never get started with one of these.

Remember, the mount is more important than the optics of the telescope itself. So-so optics on a solid mount will give you far more use and enjoyment than excellent optics on a lousy mount. When you go shopping, don't ask about magnification, don't ask about aperture or light-gathering power, don't worry about accessories. There are three things you want to know about: The Mount, The Mount, The Mount. If you've got room for 4, I'd recommend staying away from telescopes that use .965 size eyepieces. It's often a sign of a cheap, useless scope. Go for something that takes a 1-1/4" eyepiece. After you find one on a good mount.

Wednesday, July 9, 2008

Don't Buy a Telescope That Doesn't Fit

In my post What Can I See With My Telescope I talked about how much detail and what sort of objects you can see with different sizes of scope (the size being measured as how big the light collecting area of the telescope is, like how big the main mirror or lens at the front is.)

The big scopes give the best views. So why not just recommend everyone go out and buy as big a scope as they can afford?

-You have to be able to lift it.
-You have to be able to store it.
-It will probably have to fit in your car.
-You may not want to have to use a ladder to get to the eyepiece.

My recommendation for a first scope is usually a 6" telescope, though anything from about 4.5" to 8" can work. But before you buy any scope, find out its dimensions and weight. Then:

Figure out whether you can lift a bulky, unbalanced weight that weighs as much as the scope without injury or other safety problems. You may be able to lift it, but are you going to have to take it up and down stairs, for example?

Figure out where you're going to store it. Is the space big enough? Are you going to need anything extra to protect the telescope while it's stored? E.g. a cover or carrying case may be required to keep off dust, sunlight, or protect it from damage. What effect will that have on space requirements?

Will it fit in your car alongside whatever else you will be taking on observing sessions away from home? Plan on an ice chest, chairs, accessories box, a few books and magazines, the other people who'll be coming with you, sunscreen, possibly camping equipment and so on.

How high is the eyepiece from the ground? How wide is the range through which it moves? Will you be able to observe without a stepping stool or ladder? Will you have to bend over at an uncomfortable or painful angle? If you plan on observing while seated, will you be able to do so for objects in very different parts of the sky? Find out the measurements for the scope you're interested in (if they're not posted, check in to a forum for that manufacturer's telescopes and ask.) Then break out the tape measure and mock it up somehow to see how the scope measures up against you (and any other potential users of your scope.)

If you're going to need a step stool or ladder for the scope you want, make sure you plan space for it, too!

Sunday, July 6, 2008

What Can I See With My Telescope?

Here are some representative objects, and what they look like, with different instruments (telescopes, binoculars.)

7x35 Binoculars
Planet Jupiter as a bright orange or yellow spot, and 4 of its moons which look lie stars in a row.
Planet Saturn as a bright yellow dot, and its moon Titan, which looks like a star.
The Hercules Cluster (M13) as a fuzzy patch.
Andromeda galaxy (M31) as a large fuzzy area, more condensed at the center.
Alcor and Mizar as a double star.
Herschel's Garnet Star as a dark red star.
Trifid and Lagoon nebulas (M20 and M8) as dim fuzzy patches (more detail under dark skies.)
Orion Nebula (M42) as a light, foggy patch.
Some detail can be seen on the Moon.

60mm Refractor Telescope
Saturn and its rings are clearly visible, along with 3 moons that look like stars.
Jupiter shows a disk with bands, 4 moons appear as stars nearby.
Bright globular clusters like M13 and M22 can be resolved into stars at the edges.
Some detail appears in the bright nebulas like the Orion nebula, Lagoon and Trifid nebulas. They look like wispy cloudy areas. The "Trapezium" appears in Orion, whether it resolves as 4 stars depends on the conditions and the quality of the telescope.
Uranus and Neptune can be seen as colored dots.

20 x 60 Binoculars
At 20x these binoculars require a stand of some sort, you can't hand-hold binoculars over about 10x still enough to see much. I recommend a parallelogram mount.
The planets Jupiter and Saturn don't show a disk, but they and several moons are visible, as are Neptune and Uranus.
Detail of craters and mountains can be seen on the Moon.
Andromeda galaxy shows a difference between the nucleus and halo areas.
Bright nebulas show some detail and some pale green color.
The Moon shows some detail in craters and mountains.

90mm to 4.5" Telescope
Planets are similar to what is seen with a 60mm scope, slightly more detail in Jupiter's bands and a better chance of seeing bands on Saturn. You can go to higher magnifications with these scopes than 60mm (up to about 200x max.)
Nebulas show a lot more detail, trapezium is easy to split into four stars. You can see almost all of the Messier list, all of it under excellent conditions with good optics. The galaxies typically appear as dim fuzzy patches. This size of scope really opens up the heavens for a casual observer, and makes a great starter scope for a dedicated observer, as well as a travel scope for those who've upgraded to larger scopes.

6" (150mm) Telescope
You can see the shapes of galaxies that appeared only as dim patches in a 90mm/4.5" telescope, but no arms or dark lanes yet. The bright nebulas all appear as beautiful showpiece objects. Globulars and open star clusters are very nice, and a 6" does a reat job on lots of multicolored binaries. The 6" makes a good portable all-around scope. All of the Messier list is visible in a 6" with good optics. Details within Jupiter's bands becomes visible. Herschel's Garnet Star is visible as a deep orange-red. A 6" scope can keep a dedicated observer busy with new objects for a few years, and a casual observer busy for life. A 6" scope is also many amateur's favorite second scope, once they get a bigger one.

8" (200mm) Telescope
Galaxies that were visible as shapes in the 6" begin to take on detail. Arms appear, and some faint detail of objects inside the galaxies. Fainter nebulae can be explored, and nebulae visible with smaller instruments take on significantly more detail and greater extent, since the dimmer parts are now visible. Much detail can be seen in Jupiter's bands. Details of star clusters can be seen even under marginal sky conditions. Herschel's Garnet Star is a deep orange. A dedicated observer can stay busy seeing new objects for many years with an 8" scope.

10" (250mm) Telescope
Galaxies that started to show detail in an 8" telescope now show that detail clearly. It's easier to pick out nebulas that were faint in the 8". The planets start to get "too bright", requiring an aperture mask to cut down the light to bring back some detail. Herschel's garnet star starts looking amber. Details like globular clusters and bright nebulas in the Andromeda galaxy become visible. Other galaxies, like the Whirlpool and Triangulum show their arms nicely under good skies. A 10" scope can provide a lifetime of new objects to view to even the dedicated observer.

12" (300mm) Telescope
You can spend all night looking at things in the Andromeda galaxy with a 12" or larger telescope. Many galaxies show details like arms and dark lanes. You can see more detail in tight star clusters. More is visible under marginal sky conditions. Scopes that are 12" and larger provide a lifetime of use, but are best in situations that don't require a lot of moving of the scope. Some are quite portable, but they still tend to be heavy and take up enough room that many astronomers with larger scopes have a smaller scope on hand for when the big one is more than they feel like handling.

There are some great books that cover thousands of objects in the sky, and how they look with different types and sizes of instruments. It's really nice to have these as a reference, so that you don't get all excited about seeing an object that's not suited for your scope, or pass up an object that you think wouldn't look good in your scope. Here are the books I recommend:


Saturday, July 5, 2008

Want to Test Drive a Telescope? Go to a Star Party!

A star party is an event where astronomers get together with their telescopes. Sometimes they are public events, where the astronomers are showing the sky off to anyone who comes by. At other times they are private events, either held for an organization to show off the sky to that organization's members, or it may be an "astronomers only" event.

Chances are that somewhere in your area there are star parties going on. The hard part is finding them. If there's a local astronomer's group you can start by contacting them. If not, find a local science center or museum. Local nature groups are a good place to ask as well. Most public star parties get some form of publicity. You can also ask at a shop that stocks telescopes, they probably have astronomers among their clientele.

Sometimes local events will have someone there. We will be out at our town's 4th of July celebration today (our town has a tradition of doing its 4th of July celebration a day or two away from the actual day. We're near other towns that have celebrations on the actual 4th, so we "extend" the celebration by having a fair and fireworks either just before or just after.)

You might also find that there are individuals who take their telescopes out for impromptu star parties. We enjoy just taking our telescopes along when we go places, then set up on a sidewalk somewhere and start accosting passers-by asking them if they'd like a look at whatever is in our telescope.

And then you can look on the internet, as well.

As to the private star parties, usually you can get an invite. Either an astronomer can bring you along as a guest, or if it's held for some group they may invite you as a prospective member or otherwise allow you to attend as a guest (sometimes there's a fee, particularly if food and drinks are being served as part of the event.)

Once you get to a star party, you've got access to a number of telescopes, and their users. It's not hard to get most astronomers to talk about their equipment. In some cases, they'll be busy with something, but usually the hard part will be getting them to stop talking!

Friday, July 4, 2008

Finding Things to See

I was at a star party one night, and the guy parked next to me had his wife with him, and a brand new telescope. He commented that he'd put out a lot to get the scope, and his wife was skeptical of the value of the money he'd spent. His telescope was a beautiful thing, a very nice size and well designed.

When it got dark, I could hear him struggling. It sounded like something was wrong with his guidance computer, or he had run into some snag with getting it started. It was obvious his wife was getting a bit impatient. My wife was busy looking at Saturn through my telescope, so I walked over and offered to give him a hand.

It turned out he hadn't charged the power pack for his telescope's computer and drive system. He hadn't realized he needed to charge it before using it, or had forgotten. He was about to pack it in, but I offered to point his scope at a few things for him. The fact is, I wanted to get a look through it. As I mentioned, it was a beautiful scope and except for the computer I was a bit envious.

He gave me the go-ahead, so I used the manual controls to put it on Saturn. Then I stood back and let him and his wife have a look. Saturn was crisp and clear, the rings were so sharp you could cut yourself on them. Saturn's moon Titan, and two others, probably Rhea and Iapetus, were on each side of the planet.

After everyone had gotten a good look, I moved on to a series of other showpiece objects in the sky--the Double Cluster, the Ring nebula, and so on. About 1am they were getting tired and decided to pack it in. His wife was in a really good mood, though. As they were packing up, I heard her tell him "That really is a nice telescope. I hope you can get the computer working so we can see that stuff all the time!"

The biggest hurdle to beginning telescope users is getting something interesting to see in the telescope. To do this, you need to know where to point a scope, you need to get it to point there, and it has to stay where you put it.

Where to Point the Telescope

Finding the Moon is easy. Finding bright stars isn't tough (and some of those bright stars may be planets!) Finding other things takes an extra step, but doesn't have to be tough.

Get a book that gently and easily teaches you to find your way around the sky. I highly recommend 365 Starry Nights by Chet Raymo. There are other good books, too, I'll post some reviews later.

Even if you've got a computer on your scope, you'll need to know a few of the bright stars by name. There are different ones up in different seasons. You'll also want to learn at least a few of the easy constellations.

You already have a head start on this. You can probably already find Orion and at least one other constellation (like the Big Dipper if you're in the northern hemisphere--close enough for Ursa Major.) Picking up one or two more will be easy.

Pointing the Telescope

You need a finder that works. Those silly things that look like little telescopes on the side of your telescope don't work. You need a "reflex sight." This is a finder that doesn't magnify the sky, it shows a red dot or red rings on the sky. You look through it and move the scope until the red dot or center ring is on what you want to look at (or use to line up your computer.)

I recommend the Telrad. In my experience it's the best. There are some other good reflex sights out there, too. But get rid of that little telescope finder. Give it to a kid for a toy or something. Some telescopes come with a reflex sight now instead of the little finder scope. This is a plus, if nothing else it shows that the maker of the scope cares about people being able to actually use it.

The Telescope Stays Where You Put It

A mount has two jobs. Hold the scope up where you can look through it, and keep the telescope pointed at what you put it on. No matter how good your telescope is, if the mount doesn't do its jobs the telescope is useless. A so-so telescope on a good mount is worth far, far more than an excellent telescope on a bad or so-so mount.

I like Dobsonian telescopes for beginners. They are stable, easy to use, easy to set up, and they handle a lot of abuse and still work great. The telescopes I throw in my car week after week are Dobsonians.

But, Dobsonians don't have a computer to put them on things in the sky. They don't have a clock drive to keep them pointed at something as the Earth turns.

In spite of that my preference still comes down on the side of the Dobsonian. But a well-made telescope with a computer can work well, too. So long as it has a good mount.

A good mount doesn't let the telescope slowly slide down after you put it on something. It doesn't move the telescope when you lock it into position. It doesn't wobble. You can give the telescope a sharp rap and it will still show the object.

If you're trying a telescope out in a showroom, try to point it at something small and as far away as you can see (don't look toward the Sun, if it's visible!) Even if it's too close for the telescope to focus on it (like a book on the far wall of the store) you should be able to point the scope at it and lock the mount (if it's one that locks--most Dobsonians don't lock, and don't need to) and be able to see your object. It should stay there when you're not touching the scope. It should still be in if you tap the scope, either on top or the side.

High Magnification: Forget it!

One of the things that lots of people worry about when buying a telescope is how high of magnification it will provide. Don't do this!

The magnifications you want are from 50x to 150x (50 power to 150 powers.) That's all. A beginner will do 90% of their observing at around 50x, and the other 10% at 150x or less. And they'll see a lot. As an experienced observer, I still spend nearly all my observing time in this magnification range.

High Magnification is Bad

High magnification is bad for a lot of reasons. I only use it when it's necessary, then switch back to low magnification as soon as I can. Here are some reasons why magnifications over 200x are bad:
  1. It's harder to get what you want to see in the telescope.
  2. Things in the telescope leave its field of view easier.
  3. It's a lot harder to get a good focus.
  4. Any stray light problems get worse (glare, nearby lights, etc.)
  5. Any instability in the telescope gets magnified, too!
For most beginner scopes, you're going to want two eyepieces. One should give you a magnification of about 40-60x, the other should give a magnification of about 100-150x. My two favorite eyepieces give magnifications of about 50x and 120x with my two main telescopes. (Magnification is determined by both the telescope and the eyepiece--more later.)

For most scopes, this means you'll want eyepieces of about 25mm focal length, and about 15mm focal length. A 25mm eyepiece with a 2x Barlow lens can work well, too (a 2x Barlow lens doubles the magnification of the eyepiece.)

Budget to Buy a Telescope

It's a circular discussion I've heard many times:

"I want to buy a telescope. How much should I spend?"

"How much do you want to spend?"

"I don't know. How much should I expect to spend?"

"What do you want for a telescope?"

"I don't know!"

"How much do you want to spend?"

"I don't know, how much should I expect to spend?"

'Round and 'round it goes...

If you're buying the telescope as a gift, you've probably already got an idea of how much you'd like to spend. In this case, you're probably concerned about how much quality you can get for your money, and how valuable a gift a telescope will be versus other gifts you can get for the same amount of money.

Whether you're buying for yourself or as a gift, here are some points to keep in mind:
  1. The telescope will almost certainly require accessories to be easily usable.
  2. Don't expect the first telescope to be the be-all and end-all of telescopes.
  3. A telescope that is easy to use is more important than optical performance for beginners.
  4. The telescope needs to be stored.
  5. The telescope needs to be transportable, either carried to the back yard or fit in the car.
  6. Even if the telescope has a computer built in, the user will need to learn their way around the sky.
This means you're going to want to buy more than a telescope. It's not unusual for the telescope itself to only be about half to two thirds of the total cost. Here are some accessories that you may need:

An extra eyepiece. Many telescopes only come with one eyepiece, you'll probably want one more.

A finder. Most telescopes come with a useless "baby telescope" finder. I highly recommend getting a Telrad finder, or a comparable "reflex sight" finder (more on this later.) I feel the Telrad is by far the best, however.

A carrying case, or some other way to protect the telescope during storage and transport. If the telescope is only going to go from a quiet corner in the house to the backyard, you probably won't need one. Also, some types of telescope are robust enough to transport with some simple breakdown (like a Dobsonian telescope) so these won't need a carrying case.

Star finder charts.

A red flashlight or penlight for reading the star charts in the dark.

A basic book on finding your way around the sky. I recommend Chet Raymo's book, 365 Starry Nights:
365 Starry Nights: An Introduction to Astronomy for Every Night of the Year (Phalarope Books)

You will also want an accessory box of some sort to carry extra eyepieces and such.

Don't be overwhelmed. You have lots of choices to make, and I'll be discussing all of them. But it's important to not spend the entire budget on the telescope itself, then end up with it gathering dust because a couple of simple add-ons are missing.

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First Telescope Buy Guide

Welcome to my guide for people making their first telescope buy! Buying a first telescope can be confusing and difficult. I have over 40 years of experience with telescopes, both as a buying customer and as a maker and designer of telescopes.

I will be discussing both the purchase and the use of scopes. I'll try to keep all my discussions in plain english, as well as giving an introduction into some of the lingo you'll want to know when you buy a telescope.

I'll cover buying a telescope for yourself, or as a gift for someone else.
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