Telescope Selection Help, Please!

[ob1dob]

Hi There!,

I am looking to invest in a telescope. I am very picky about quality of the view. Here is what I want:

- I want clear, detailed and crisp views
- I want them to be sizable - I do not want to look through a scope and use my imagination :)
- I want something easy to use
- I would like something automated GOTO, I do not know my way around the sky
- Portability is NOT an issue
- I do not have an interest in AstroPhotography
- Budget is open, let's say a big max of $3000

Thanks for any advice you could provide.

Dave
Quebec, Canada

[Fr. Wayne]

I don't sell telescopes but may I ask what would you like to see in particular if you had a very clear dark night and the atmosphere was relatively calm?

[ob1dob]

Primarily planets, especially Saturn & jupiter + their moons.

I would also like to view deep space objects such as galaxies, etc.

Thanks for your help!

Dave

[Tog_]

You may run into a few different problems there. The four basic designs for telescopes all do some things better than others.

Refractors are the traditional long, thin tubes with a lens in the front and the eyepiece in the back. These usually have a small aperture (lens diameter) and have three different grades. Think of these as the sports cars of the telescope world. Small, high performance, and no cargo room.
Pros:
Simple to use (no collimation needed).
No central obstruction, giving the light a full and complete path to your eye.
Very good views of bright objects, like planets.
Cons:
The red end of the spectrum reaches focus in a slightly different place than the blue end. This means that when a bright object is in sharp focus, it may have a purple halo around it. Saturn is notorious for this. Achromatic refractors reduce this a bit, but the effect is still visible. Apochromatic refractors basically eliminate it.
Cost. $3000 will get you a pretty good 5 or 6 inch achromatic or a really good 3 to 4 inch apochromat. Neither will give great views of galaxies.

Newtonian Reflectors tend to be long, fat tubes, with an opening on one end and the eyepiece located near the front. The light enters the open front and hits a mirror at the bottom. The light is reflected back to the front where it hits a smaller flat mirror, set on an angle that will reflect the light to the eyepiece. These tend to have much larger apertures, and have two main mounting styles. These are the SUV’s. Big, lots of room for everything, but not something you’d want to race through a canyon in.
Pros:
Light buckets. The size of the mirror means a lot of light is gathered. The (normally) short focal length means the field of view is kept large. This makes them good for deep sky objects, like galaxies and nebulae. You can get them in a Dobsonian mount, or and equatorial mount. The Dob mount is as basic as it gets. It’s got two sides that keep the scope off the ground and allow for elevation adjustments, mounted to a rotating base that allows for azimuth changes. The EQ mounts will be required for a goto system in most cases. Dobsonian mounts cannot track an object on their own. You will be constantly pulling the scope across the sky to keep an object in view. There are accessories that can help with this.
Cost. I have a Meade 16” in the more simple dobsonian mount that I got for about $1500, new… from the mall. The whole scope is about the size of a water heater.
Cons:
Portability. I know that wasn’t a factor for you, but that water heater sized bit is the smallest part of it. Smaller ‘Newts’ can be as short as 4 feet, and some are built in sections that you can assemble in the field using a set of poles. These are called truss tubes and can really up the cost.
Collimation: You have two reflecting surfaces. One is heavy and large, the other is smaller and hangs in the center of the tube on a set of metal rods. In order to get the best views, you have to get all of these lines up properly. This can take a lot of work. The good news is that once you have the smaller mirror (secondary) in position, you should be able to leave it alone. The primary may need to be adjusted every session. If you won’t be moving it, this is not as much of a concern. I think it is still the most difficult part of using a telescope though.
Central Obstruction: That secondary mirror hangs directly in the path of the light. This casts a shadow on the primary mirror, which makes an out of focus star or planet look like a doughnut. If the secondary is too large, it will severely affect the amount of detail you can see. If it is too small, the light coming from the primary may have a diameter too large to fit on the secondary, causing the image to be dimmer than it could be. The metal vanes that hold the secondary in place will also cast a shadow. These are responsible for the 4 spikes that come off of bight stars in many photos. This obstruction will also affect planet detail to some degree. To minimize the effects when looking at planets, you can make an ‘aperture mask’. This is a sheet of cardboard with a hole cut in it to allow a smaller column of light to enter the scope between the vanes. It basically reduces your mirror to whatever the size of the hole is. Mine turns my 16” into a 6”, but it does help to clean up the view of planets and the moon.
Spherical distortion. For similar reasons to the color shift in a refractor, the further you get from the center of the eyepiece, the more the stars will take on a tear drop shape. This can be corrected in part with a field flattener accessory, but unless you are looking at a large cluster at low power, it may not become an issue.

SCT or Schmidt-Cass scopes are the most common for most people. They are short, fat tubes with a flat glass sheet over one end, and the eyepiece on the other. The incoming light will hit that flat glass plate and refract a bit at the edges, it will then hit the mirror at the base of the scope, bounce up to a centrally mounted secondary mirror, then bounce back, through a hole in the primary mirror to the eyepiece. This makes for a long focal length in a small package. My 8’SCT has a focal length of 2000mm. That’s over 6 feet of light bending in a tube about 18 inches long. That 16” water heater has a focal length of 1830mm. Longer focal lengths mean higher magnification, but reduced field of view. These are more the classic Jeep. Small enough to be maneuverable, but cargo room enough to haul stuff.
Pros:
Cost: fairly cheap for the size. An 8” goto scope can be had for around $2000.
Variety: This seems to be the market most companies want to corner. These scopes are available in sizes from 4” to 16”, EQ mounts, fork mounts, with or without GPS set up assistance.
Simplicity. There may be a time when the secondary mirror needs to be adjusted, but once it’s set, you will probably never need to touch it again.
Accessories: Like a Jeep, if you can think of something to put on it, someone probably makes it.
Cons: Minor distortion at the edges, but much less than with a Newt. Fork mounts can be hard to use in some bits of the sky. Looking straight up with a alt-az set up will require you to get very low and place your head nearly inside the mount.
Central Obstruction: The secondary mirror will have a much larger diameter for the primary than in a Newtonian. This means a bit more detail and contrast loss.

Maksutov, or Mak, is a variation on the SCT. In this case, the front glass is very deeply curved, and the secondary is a much smaller spot that needs no adjustments. These are the limited edition Jeeps of the (basic) scoping world.
Pros:
No distortion of shape or color. Stars will be round edge to edge and there will be no halo effects.
Everything else under SCT’s applies, except Variety. There are not many choices for large Maks. Meade makes 3 sizes, and Celestron makes a couple. There are other companies out there as well, but the selection of SCT’s is much greater.
Cons:
Cost. These little buggers tend to be pricey. Not as much as an Apochromatic, but still way up there.
Focal length. Because the light starts bending at the front, and bending a lot, Maks tend to have very long focal lengths for their diameters. Several years ago, Meade put out one called the ETX. This is a 3.5” (90mm) diameter scope with a focal length of 1250mm. With a focal reducer in my 8” SCT, I can get that same length and still have twice the aperture (4X the light gathering). This makes them well suited for planets and other bright objects, but less than ideal for deep sky objects.

Summary of types:
Refractors: Good on planets. Simple. Expensive. Too small for detail in most deep sky objects. Goto scopes possible
Newtonians: Excellent deep sky. Cheap. Collimation can be tricky. Goto available in EQ mounts. Central obstruction reduces contrast and detail in planets.
SCT: Good all around performance. Less contrast than the others. Moderate price. Goto options nearly impossible to avoid. Pretty Simple.
Mak: Similar to SCT in most respects. Better performance on planets. Less on deep sky. Expensive. Simple.

Additional costs. Most scopes come with one eyepiece. Some may have a few different ones. You’ll probably want at least three. You’ll also want some filters. A minus violet will be a help if you go with a refractor. A broadband light pollution filter will help with any of the others, and a neutral density filter will be a good idea if you go with anything over 6 inches and look at the Moon. In that 16”, the Moon hurts without a filter. Oh, and you’ll probably want a Telrad too. Handy little 1 power finder that projects red rings on a glass plate you can see the sky though. Many computer star charts, and paper star charts have options or Telrad based finding built in. All of this will add up, so plan on at least $300 for add ons. Now, the nice thing about astronomy as a hobby is that initial investment is likely the ONLY investment. If you take care of your equipment, that $3000 purchase can last for decades with minimal upkeep costs.

On Goto Scopes:
My personal feelings on goto scopes is that it’s a nice option. Option being the key word. My first real scope was a 16” Dob. That, a telrad and a sky chart and I was off. It took a while to learn the sky, but it was worth it to me. My SCT (LX90) has the goto ability, and I like it most of the time. One thing I’ve noticed though is that in the time it takes to get the goto scope et up, aligned, and told where and when it is, I can have the Dob set up, collimated, and the finder scopes aligned. Since I know where many of the showpiece objects are I can swing over and star hop to them faster than the SCT can autofind them most of the time. I have spent a good deal of time looking for things that I’ve never found, but it has been worth it to me.

Keeping with the car analogy above, a goto scope is like a chauffer. If you never drive yourself in a new city, could you even find the store on your own? With a goto scope, you will end up learning the named or numbers of many of the objects you look at often, but without it, you will learn this s well as being able to tell if there is a chance to see it when you look at the sky. Like I said, I like the goto function, but I think every ‘First Scope’ should be manual. (Just an opinion, it’s neither right or wrong, and if others feel the opposite, our opinions merely differ.)

So, after all this, my recommendation, as a lurker and amateur observer would be either a Meade or Celestron SCT. Based on your price range, and wants. One thing to look at though might be a Tele-vue Ranger to piggyback to the main scope. This is a small refractor that gives amazing views of open clusters and (when mounted to a driven scope) can get good detail and magnification of planets. Don’t bother at all with the polar alignment mount. Those scopes will track the sky without it. It is only used for long term photos (to cancel out field rotation).

Please see below for any corrections others may add.

[andyschlei]

Great survey of scope types!

I'll add one thing on goto -- it is very usefule for light polluted areas. Without dark skys, it is much harder to find objects, even objects that are quite visible with the scope. Goto gets you the object and increases what you can see.

I'd also recommend going to a good store in your area (in LA that would be OPT, Scope City, and several others) and talking to the people there. They are very good at helping in this area and it helps to actually see the scopes.

Clear Skies!

--Andy

[Dave Mitsky]

For 3 grand, you could get a 12.5" truss-tube Dob from manufacturers like Discovery or Night Sky Scopes (or even a finished AstroSystems TeleKit), but they will require you to learn the sky. GoTo systems like the ServoCAT are available but will double the price.

http://www.discovery-telescopes.com/discovery/td.html

http://www.nightskyscopes.com/site/pricing_index.shtml

http://www.astrosystems.biz/telekitfinished.htm

Starmaster, Obsession, and Portaball scopes will run more than your budget with shipping but are the cream of the crop.

There are also the brand new Meade truss-tube Dobs, which are relatively inexpensive. Nobody knows much about them at this point.

http://www.meade.com/lightbridge/index.html

A solid tube Dob of the same or larger size will be far less money and since you don't seem to have to travel to observe (no star parties in your future?), you could put it on an equatorial platform and have tracking, if not GoTo.

If you really, really have to have GoTo (learning to star-hop isn't all that hard), an 8 or 10 inch Schmidt-Cassegrain is probably your best choice if you want to still have a reasonably large aperture. One possible alternative is the 10 inch Orion Atlas GoTo Newtonian.

http://www.telescope.com/shopping/product/detailmain.jsp?itemID=137953&itemType=PRODUCT&iMainCat=4&iSubCat=8&iProductID=137953

For that matter, the 8 inch Meade Schmidt-Newtonian has GoTo as well but I wouldn't particularly recommend it for planetary observing.

http://www.meade.com/catalog/lxd75/index.html

I suggest you pick up a copy of Phil Harrington's _Star Ware_ at a bookstore or library and research all your options.

If you're interested in the used telescope market, try Astromart.

(BTW, the Maksutov-Cassegrain is a variant of the Cassegrain design, just as the Schmidt-Cassegrain design is.)

Dave Mitsky