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Arbo
06-08-2004, 12:39 PM
Evan,

I am somewhat interested in stargazing. I have no idea where to start when looking for a scope. I have talked to some ams, and they all tell me to try a reflector type. Thats fine...Now, where to check these out, I have nothing, and no knowledge, and a limited budget. Can you give me some pointers on what to look for, where to look, and what to avoid? Thanks in advance.

Evan
06-08-2004, 12:43 PM
A few questions first. What is your budget? Where do you intend to use the telescope? Do you have a pair of good quality 10 X 50 binoculars? Is there a local club?

Arbo
06-08-2004, 01:12 PM
Evan,

Under $400.00

I live in the country...very little light pollution. (Central PA)

No clubs...that I am aware of.

Yes, I have binocs, but not really good...(Tasco)


[This message has been edited by Arbo (edited 06-08-2004).]

Evan
06-08-2004, 02:15 PM
That is just enough money to buy a decent starter scope. Do you anticipate doing astrophotography? I asked about the binocs because that is a relatively cheap way to get into astronomy. It doesn't take much magnification to see a lot more of the night sky that you can with your eyes. This is the single most common misconception and is pushed by the clueless marketing droids for the big stores. What matters above all else (assuming reasonable optics) is size. This is a case where not only does size matter it is by far the most important consideration.

High magnification is only useful for a few select specialized activities. They are planetary viewing, double star observing and observing a variety of small non-extended objects. The best telescopes for that application are the refracting telescopes, the type with an objective lens like binoculars. I advise you to forget about buying a refractor because a good one worth spending any money on will cost more than $1000.

So, that leaves an assortment of reflecting types. You can look at standard Newtonian, modified Newtonian, Schmidt Cassegrain and Dobsonian. We drop out Schmidt Cassegrain since it also doesn't fit your budget. This leaves Newtonian and Dobsonian. The main difference between a Dob and a Newt is the mount. The Newt (not counting cheap crap) will be on an equatorial mount whereas the Dob will be on an altitude-azimuth mount.

The equatorial mount allows for the telescope to track the apparent motion of the night sky, either by hand controls or with a motor drive. They are also available with computerized finding and tracking devices. I have one and don't recommend them. More on that later. The ability to track is especially important if you plan to do any sort of photography. 35mm photography really won't be possible in the size range you can afford but web cam certainly is.

The Dobsonian is a Newtonian telescope without the ability to track. It is possible to fit tracking motors to a Dob and the use of computer controls makes it easier. Generally though the Dob is for eyeball observing only using low powers and wide fields. Once again, the bigger the light collector the better taking portability and quality considerations into account.

I did mention modified Newtonian. This is a Newt with a corrector plate on the front allowing for a much shorter and compact tube. It does introduce two more surfaces in the light path which reduces light collecting efficiency.

In the case of standard Newtonian scopes they are available in a range of focal lengths. The cheaper ones will usually be fairly long, that means anything over f6. This is because the mirror is cheaper to make. f6 is considered a "standard" focal length and is a compromise between size, cost and field of view as well as magnification. Today with the advances in mirror cutting and grinding good mirrors are available at short focal lengths at low prices. Don't buy anything with a focal length higher than f6, meaning no f7 or f8 or higher. The field of view will be too narrow for someone starting in the hobby and will simply be frustrating.

It is essential that the telescope be equipped with a parabolic mirror. Many cheap one have only a spherical mirror and that just doesn't cut it unless a corrector plate is used.

On the subject of computer controls; they work, sort of. Initial alignment can be difficult and if it is off a bit then you are completely lost. I recommend learning how to find your way around the sky the good old fashioned way, with star charts and starhopping to find those dim objects. Don't waste the money on a computer control scope. Spend it on the mirror and eyepieces.

Bottom lines.

For eyeball observing buy the biggest Dobsonian you can afford that comes with at least a couple of eyepieces. Plan on spending more money later (much more) for better eyepieces.

If you envision doing work at higher powers or want to do some sort of image capture then buy a Newt on an equatorial mount.

In either case a focal length of f5 to f6 or even as short as f4.5 will be suitable. You will be able to afford perhaps a 6" Newt and maybe even an 8" Dob.

Do not pay any attention to any telescope where the most prominent claim is it's magnifying power. That simply is not a consideration. The magnifying power of a telescope is determined by the size of the objective lens or mirror and it's focal length, it's a law of optics determined by the resolving ability of an optic. That is directly related to size.

Here are a couple of available scopes that fit the bill as excellent quality Made in USA. This first one is a bit over your budget but it will blow you away with what you can see. This is an 8" Dobsonian with excellent optics. Keep in mind that a Dob can be mounted on an equatorial mount at a later date if need be.

http://www.astronomics.com/main/product.asp?cata log_name=Astronomics&category_name=4SRW6A37XHQP9KPDRMSRJ6JVQ1&product_id=DHQ86 (http://www.astronomics.com/main/product.asp?catalog_name=Astronomics&category_name=4SRW6A37XHQP9KPDRMSRJ6JVQ1&product_id=DHQ86)

For a decent quality 6" Newtonian I would recommend this one. It only comes with one eyepiece but does have available an optional one or two axis motor drive. This isn't quite as good a scope as the Dob above but will be a worthwhile investment. I bought one similar to this for my daughter and grandkids and they have a blast with it.

http://www.astronomics.com/main/product.asp?catalo g_name=Astronomics&category_name=CHGX2TH1U6M49HTV5XM3GKHQ74&product_id=C6N (http://www.astronomics.com/main/product.asp?catalog_name=Astronomics&category_name=CHGX2TH1U6M49HTV5XM3GKHQ74&product_id=C6N)




[This message has been edited by Evan (edited 06-08-2004).]

Tomzhere
06-09-2004, 06:51 AM
Evan, I enjoyed reading your post. My wife and I would love to have a nice scope and this will help me learn what/how to look at them in the future.

Right now we live on outskirts of city, lot of lights nearby. This make seeing difficult.

Soon we hope to find a small plot of land in the country. Then we can consider a nice scope. I'd lean toward only making one purchase though rather than a starter scope and upgrading later.

Thanks for the insight.
Tom

Arbo
06-09-2004, 07:48 AM
Evan,

Thank you very much for taking the time to write such an informative post. I have one more question about the Dobsonian type mount. Should that be mounted on a tripd of some sort, or is it designed to sit on a table top? That looks like a really nice scope for the money. I'll let you know if I decide to take the plunge.

bernie
06-09-2004, 10:27 AM
I love this bbs.

Evan would you possibly be kind enough to elaborate on the eyepiece issues. I have a small 3" reflector and really enjoy some of the views. It came with 2 eyepieces, 1 @ 4mm and the other is 20mm. I am considering trying some better quality eyepieces but they sure get expensive quick. My current scope has 1 1/4" eyepieces. Thank-you

Evan
06-09-2004, 11:27 AM
Tom,

I hope you find a nice dark sky location. Astronomy is a lot of fun. Your idea to buy a really good scope to start with is an excellent idea. Plan to spend between $1000 to $2000. Look for a deal on eyepieces. My sister live about 90 miles north of Austin and last year bought her husband an 8" Schmidt Cassegrain from Meade. They had a special deal (!!!!!) on eyepices where you could buy a set of nine for $100. What a bargain!

Arbo,

The dob is intended to sit on the ground. It isn't obvious from the picture but if you read the specs closely the tube is 50" long so the entire scope on the mount is nearly as tall as you are. Sitting as it is in the pic on the ground the eyepiece is almost at eye level when you are standing.

Bernie,

Assuming you have a scope with good optics (primary mirror and secondary diagonal) then the eyepieces are the next most important thing. Good quality eyepieces make a HUGE difference. There are half a dozen different types and each has advantages and disadvantages. The cheapest ones aren't worth accepting as a gift. 1 1/4" are the most common but 2" is also available. The dinky .965" eyepieces are uniformly crap and the sign of a junk telescope.

For most uses the Super Plossl design is the best compromise between quality and cost. However, the cost can vary greatly depending on features like full multicoating. Buy the best you can afford and you won't be disappointed. The 4mm eyepiece is nearly useless as it is pushing the maximum magnification beyond the theroretical ability of such a small mirror (even though I don't know the focal length). Magnification is determined by the ratio of the focal length of the telescope and the eyepiece. Simple, if the focal length of the primary is 1000mm and the focal length of the eyepiece is 10mm then the magnification is 100X. Magnification = primary focal length divided by eyepiece focal length.
If you are going to have only two eyepieces then you should have one around 10mm to 20mm and one around 30mm to 35mm.

Here is a good reference for various formulas relating to telescopes:

http://www.astro-tom.com/technical_data/useful_formulas.htm

The difference a good eyepice makes is astounding. I have a 35mm Super Plossl that weighs over half a pound and the exit lens is nearly 3/4" in diameter. It is amazing. Unfortunately it is also very expensive. You can easily spend more money on eyepieces than the telescope.

For the Canadians on this BBS I recommend this dealer. Brian is a good guy and excellent to deal with. I am not affiliated with him, just a satisfied customer.

http://www.islandeyepiece.com/

bernie
06-09-2004, 11:50 AM
Thanks for that Evan. The scope that I have is a Bushnell "goto" (can't remember the focal length). It was only a couple hundred dollars and given to me by my wife for a b'day gift in December. It really isn't much but has got me hooked. I can see Saturn really well, 4 moons around Jupiter and even some bands on Jupiter. Haven't done much other observing other than our moon, which is also very interesting to me. I can't wait till I get to look through a "good" scope. There is a local club that meets monthly and I am hoping to join this fall. Just not enough time in a day.

Sorry but I think I screwed up on the eyepieces that I do have, I think the one is a 9mm not 4mm. Also have a 3x Barlow that is useluss with the 9mm eyepiece. I suppose that is because of the small dia. of the main mirror. Otherwise I'm really enjoying sitting out in the cold and dark. (Cats sure can startle you when you can't see them coming.)

Many thanks for your words of wisdom.

Added: after re-reading, I don't mean musical "bands" on jupiter. I can see the comments already.

[This message has been edited by bernie (edited 06-09-2004).]

Evan
06-09-2004, 11:54 AM
I forgot to mention that as a general rule of thumb the most magnification a telescope can provide is approx 50X per inch of primary diameter. BTW, Bushnell makes usable stuff.

vinito
06-09-2004, 02:06 PM
Arbo,
You have a good plan for getting a scope and I agree with Evan. Getting the best optics you can afford is THE thing. My first scope was a little Tasco refractor when I was a kid. It was enough to give me the bug, but the optics quickly became a source of frustration. The colorful (prismatic) images were annoying and I was constantly wishing I had a higher quality scope. Over the years I settled into wanting a good 8" Schmidt-Cassegrain for my purposes.

A few years ago I ran across a Celestron C-8 with a clock drive and tripod for $150 at a pawn shop. I thought "great. I found what I always wanted for a great deal". But once I got the scope out I found that the optics are mis-aligned or otherwise need some attention that I don't know how to give them. It stays in the case at least 10 times more than it would if it worked properly. Someday I'll find a competent telescoper to check it out and/or show me how to tweak it properly. In the meantime, I am stuck realizing that a new scope with this problem could have been taken care of under warranty - and that a Newtonian is more user-servicable.

I'm missing some looking, but I guess I'm learning.

p.s. Anybody know how likely it is that the primary mirror needs re-aluminized? It looks OK to the naked eye, but since I got it used I don't know for certain how old it is or how many times it has been taken apart and wiped with a shop rag. I know it might not be very likely, but this question has been nagging me in a paranoid corner somewhere in the back of my brain.

[This message has been edited by vinito (edited 06-09-2004).]

debequem
06-09-2004, 02:10 PM
Great job Evan!

I might add one thing. Evan implies this, but buying a cheap scope is a great way to get OUT of the hobby. Cheap scopes do more to frustrate prospective new members than they do to encourage exploration.

The Dobsonian is an excellent scope that will be something you can always keep, even if you advance to other more expensive scopes. A manual Dobsonian is easy to set up (great for impromptu outings) compared to motorized scopes. Also, you can get great optics for these scopes, which yield stunning views that will ignite your appetite. Highly recommended for a starter.

Good luck!

Marv

Involute
06-09-2004, 02:50 PM
I have to jump in here myself. This is something I've been wanting to do, but haven't done it yet. (Already have binoculars, though).

With a higher budget, like the $1000-$2000 you mentioned, would you still go for a Dob/Newtonian, only larger or would you go to a Schmidt-Cassegrain or maybe something else?

Is there a line where quality wins out over size? Maybe not a good exmple but, say, a 4" apo refractor vs an 8" Dob?

Just "go big" with quality eyepieces?

I don't have any experience with telescopes myself. I'm somewhat familiar with the types, but don't know how the design theory applies to the real world.

Thanks,
Joe

Evan
06-09-2004, 03:36 PM
Vinito,

Don't mess with the mirror unless it is filthy. The basic rule is to leave it alone. There can be quite a lot of dust on it and it won't hurt a thing. It also depends on what the mirror coating is. Mirrors are available with two types of coatings. Standard is aluminized with a silicone dioxide overcoat. These have reflectivity at around 88%. The biggest advantage of these is durability. It's really difficult to damage the SiO2 overcoat. The other type of coating is usually called "enhanced" coating and is a multilayer coating with reflectivity up to around 96% or even slightly higher. These are very fragile and easily damaged by moisture plus cost quite a lot more. They are best used in sealed units like the Schmidt Cassegrain or modified Newt.

The biggest problem with the Celestron and Meade Schmidt Cassegrains is a thing called "mirror flop". As the position of the telescope changes the mirror will move slightly on it's mount disturbing alignment. This still seems to be a problem and is considerably worse on the older models. There are some fixes that can be applied.

The best I have seen is by Chris Heapy and is perfect for the home machinist as a project.

See here:

http://easyweb.easynet.co.uk/~chrish/lx_flop.htm

BTW, if you havent already been to his web site then poke around. He has a lot of cool stuff and projects.

Joe,

Unless you are really interested in small bright objects like the planets I wouldn't spend the money on a 4" refractor. (unless I win the lotto) I bought the Newt for my Daughter and grandsons for portability reasons. They live right in town and it is easier and smaller to pack up than the Dob. For Arbo I think the Dob is the best choice since it sounds like he will be doing his observing mostly in his back yard. The eight inch Dob is approaching the largest size that is reasonable to transport unless you have a large capacity vehicle or some sort of trailer.

The biggest advantage of the Schmidt Cassegrain is compactness. Second is the sealed optical system. I don't really care for them though because of the mirror flop problem. I overhauled a C-8 for the Prince George chapter of the Royal Astronomical Society. I didn't go to the trouble of fixing the mirror flop as it is used strictly for public viewing sessions. For me the mirror flop would be intolerable as I do electronic photo work with many exposures. The pic of the moon on my astrophotos page is a composite of 240 individual exposures over 1 1/2 hours.

My advice as always is to go with the biggest scope you can make use of easily. In my case I am considering building an observatory in my back field in which case I would build something around 12" or 14".

Do keep in mind that a smaller easy to set up scope will actually get used whereas if it is a pain/cumbersome to set up then you will likely not bother very often.



[This message has been edited by Evan (edited 06-09-2004).]

vinito
06-09-2004, 04:09 PM
Joe,
That comes down to what you want to do with the scope vs. budget.

With all scopes, optics quality is key.

(I'll apologize here for any wrong information that follows. I'm a telescope rookie)

As for aperture, you don't want to get a scope so large that you would otherwise use it if it wasn't such a pain to drag it around. A really small one could even fit around luggage for vacation fun. A larger one that fits in a trunk or back seat is still easy to haul and set up for viewing near your home, and you'll see dimmer objects. If you have a truck, a 10" Newtonian is a beautiful thing if you don't mind the extra effort. Just don't be overly optimistic about how much effort will be deemed "too much" in the future. If you are looking at an hour of loading/unloading each time you get the urge, the urge won't come as often.

If you are mainly using the scope just to observe objects, a dobsonian mount with a cross-hair spotting scope to help aim it in the right direction will give you less cost overall since the mount is simple. They are usually Newtonian reflectors (larger) so they take up more space, but they're simple to set up, operate, and maintain.

The same scope can be mounted on an equatorial mount with setting circles to aid in aiming and data recording. These mounts cost more money because of the added complexity (also worth paying more money for higher quality. Inferior mounts are also a source of frustration). This makes setting up more time consuming and reduces portability, but once set up it makes viewing more convenient and more fun (IMO) as long as it doesn't affect the aforementioned urge factor.

You can add a clock drive to an equatorial mount for more money and add the ability to track the night sky. A good mount with a good drive adds the ability to take long-exposure photographs. If long-exposure astrophotography is your thing, this is the minimum requirement point for a telescope set up.

All of the above can use the same telescope - Newtonian reflector (optics and tube).

At more expense (everything else being equal), you can get into reflector scopes with names like Schmidt, Cassegrain, Maksutov (mix, match, and add hyphens). These scopes are more portable, a bit more solid (less collimating, etc.), and have different characteristics you can look up.

Good refractors are really pricey. I understand they are really nice to view through by eye. Bad refractors are not worth the tube they are mounted in.

In hindsight, I see that I should have just got a good Newtonian on a Dobson mount and used it until I could afford the astrophotography setup. I got into photography first, so it probably clouded my judgement a little. My history with scopes may have contributed to why astronomy is only a passing interest with me instead of a heavy hobby.

Then again, it could be that adult attention deficit thing.

p.s. Thanks for the reply Evan. I'll check that page out. I've never heard about the mirror flop issue. I figured that my primary was probably OK, but I lean pretty hard on paranoid sometimes. I must just have alignment issues (focusing is a process of deciding whether I like the smeared light on the left or the right). Thanks again.

[This message has been edited by vinito (edited 06-09-2004).]

Evan
06-09-2004, 05:17 PM
One note about astrophotography. Many scopes cannot be used for 35mm astrophotography due to focuser height limitations. It is 2.1 inches from the front ring to the film plane on a 35mm camera. Add to this the height of the focuser and adapter to mount the camera on the focuser and in many cases it is not possible to achieve focus for prime focus photography. Also, for 35mm use a 2" focuser is really needed to avoid vingetting. That Dob I recommended has a 2" focuser and mounted on an equatorial might make a decent photography scope. In some cases a new low profile focuser can be fitted to solve the problem.

On a six inch scope like the one I built 35mm photography just isn't practical as it involves too much compromise. In order to avoid serious vingetting at the edge of field on a fast scope (f4.5) the secondary has to be so large that it obstructs a totally unacceptable amount of the aperture producing serious contrast loss and diffraction.

Deciding what telescope to buy or build is all about compromises, always. No one scope can do it all.

Involute
06-10-2004, 07:15 AM
Evan, vinito -
Thanks for the information. I still haven't won the lottery yet, so I don't see myself buying a refractor anytime soon. I wasn't aware of the mirror flop problem of the Schmidt-Cass either.

Great topic Arbo!
Here I go again... off into another hobby. http://bbs.homeshopmachinist.net//biggrin.gif

Gary Helmick
06-10-2004, 06:45 PM
Arbo,
I have been thinking about selling my home built Dobsonian. It is a 13" mirror (factory bought) and it has two Orion eyepieces, 40mm and a 18mm, it has two Meade eyepieces 25mm and 12.5mm it also has a 3x Barlow type lens.
If you think you might be interested, please email me with your phone number and we will talk.
Thanks,
Gary Helmick

Evan
06-10-2004, 07:11 PM
Gary,

That ought to shell shock him pretty good. That should be good enough to see some color in the Orion nebula. I'm curious, how tall does it stand? I hope you're willing to give some lessons. I see you aren't all that far away.

jeastwood
06-10-2004, 07:27 PM
I note that no one mentioned "Sky and Telescope" magazine; this is a great source for finding suppliers of astro gear, as well as articles of interest. See also www.skyandtelescope.com. (http://www.skyandtelescope.com.)

As to mounts: sturdy and massive is good. These are often difficult to find in commerical scopes; they will put the money into the optics, and skimp on mechanical stability of the mounting. Apply the "tuning fork" test to any scope you are looking at: tweak the scope at the eyepiece end while looking through it and note how long it takes for the vibrations to damp down to near 0. A second or less is ideal.

As an HSM, you might make the tradeoff to buy good optics on a so-so mount with the intent to beef it up later.

Did anyone mention local star parties as a great way to look through lots of scopes and find out which types you like? Most areas have amateur astronomy groups, and summer is high season for start parties. See Sky&Telescope again for listing of groups near you.

Astro
06-11-2004, 06:55 AM
Arbo, if you get a Newtonian on any type of mount, you will also need some way to collimate the optics. If you have a lathe you can make your own tools. Tectron in Florida has a nice set of tools with an excellent book titled "Perspectives on collimation". The best quality optics are only as good as their alignment. Another good magazine is Amateur Astronomy. It is a quarterly. They can be found at www.AmateurAstronomy.com (http://www.AmateurAstronomy.com)
Also check out:
www.scopereviews.com (http://www.scopereviews.com)
www.cloudynights.com (http://www.cloudynights.com)
www.astromart.com (http://www.astromart.com)
Clear skies,
Robert

Gary Helmick
06-11-2004, 10:47 AM
Evan,

The colors in the Orion nebula are great, along with some of the messiers that are in Andromeda (I really like Andromeda).

Yes this is a serious telescope. It stand about 6 ft and is about a f4.5 focal length.
It is not hard to collimate and is pretty easy to use. That is what would make it a pretty good scope for Arbo to use.

It does take some studying to get up to speed on it, but it is no different than anything else, just a matter of learning about it.

Yes I would be able to give some basic leasons on it.
Gary Helmick

bernie
06-11-2004, 10:59 AM
13", wow! Can't even imagine the views. If I were a little closer I certainly would look it to that scope. Why are you considering selling that scope Gary? Did you get somthing BIGGER?

Evan
06-11-2004, 11:04 AM
A laser collimator is an easy shop project to make and makes it a piece of cake to collimate a scope. Here is mine.

http://vts.bc.ca/img/coll1.jpg

It uses a cheap dollar store laser pointer. The pointer is mounted with two trios of set screws. The nylon knob screws in to push the on button. The collimator itself is aligned by chucking it in the lathe so the laser shines out the spindle on the wall. Rotate and adjust the setscrews until the spot of light doesn't move.

I won't go into more detail here but there is a lot of info on the web.

This is a good place to start:

http://www.starastronomy.org/TelescopeMaking/Links/

Gary Helmick
06-11-2004, 11:34 AM
Bernie,
Just thought I would try somthing different in the scope line, not sure what it will be yet.

But also trying to get someone else interested in skywatching like the person that sold it to me.

This scope sure brings in the light though.

Evan,
Sure do like your laser collimator. I just might make one of them. Nice idea, thanks.
I have a few of the laser around and had also thought about making a laser sight for sighting in a gun.
Gary Helmick

[This message has been edited by Gary Helmick (edited 06-11-2004).]