# Stargazing Need some advice on telescope

1. May 20, 2003

### kleinma

well im looking to buy a telescope... I want something with power.. I live somewhat near NYC (about 40 min) so I get a lot of city light in the sky...

what do you guys think of this

other than the fact that it weighs a lot.. its not something I would be lugging around.. only on rare occasion...

I am open to all suggestions though... I know this one if a hefty price.. 1300 but that includes the stand and everything...

I dont want to spend too little and get something that all I can see is bigger dots in the sky

2. May 20, 2003

### Labguy

A 10" is a good size for anyone if the optics are quality. On the scope you show, about 50% is for the EQ mount and does nothing to improve the optics. Unless you are quite familiar with the location of "deep-sky" objects, you could spend about 1/2 that amount and get a 10" scope on the so-called Dobson mount. Add a Telrad or a Rigel Quick-Finder, get some good sky charts and you would be set. Also, setting up a Dob scope is 10 times faster than trying to set up and polar-align an equatorial mount. The EQ mount is needed only if you plan on doing long exposure photography. If so, the good equipment for that would cost about as much as your $1300 scope. I would prefer the Dob. Also, junk the eyepieces that come with the scope and get a few good plossl eyepieces. Many good ones can be had for far less$ than the TeleVue eyepieces that all your friends will tell you that you need.

There are a lot of other makers, but most have a long waiting list while Orion usually ships from stock. Don't underestimate what a good 8" scope can do, for a lot less money. Power is not what you want! Most good seeing is done at 20 to 30 power per inch of aperture. You need to be in very dark skies with great "seeing" to get a decent image at 35 to 50 power per inch. This does not happen often.

3. May 26, 2003

### LogicalAtheist

All I can suggest is you do alot of research. Read consumer reports for sure.

You definetely want one that hooks into your computer with hardware that it comes with.

Real telescopes don't have viewpieces.

You want one with advanced hardware and software that will tell it to move based on input data you give it. This way you can see objects just by knowing their position. The software will tell you where everything is at every moment in everyday.

4. May 26, 2003

### chroot

Staff Emeritus
Interesting, isn't it -- that Labguy admonishes that good optics on a simple mount, along with a chart and a Telrad, are all you need.

Then comes LogicalAthiest, who assures us that what we need are not optics, but a computer-equipped techno-scope that finds things before you know you want to look at them.

You really couldn't have gotten more anthithetical responses!

The best scope for you really comes down to a few simple questions:

1) Where will you be using it?
a) Can you comfortably carry it to this destination?
b) Is this primary location light polluted?

a) Are you planning on learning the sky like the back of your hand?
c) Are you planning on looking at mostly the easy-to-find, impressive, bright objects, or on trying to find the dimmest, fuzziest fuzzy your eye can see?

3) Will you be using the telescope to introduce others to the hobby?

Choices based on these questions:

1a) Pick something that you can easily drag to and setup at your primary location. What doesn't seem so heavy in the store might be unmanageable in the dark in a remote location.
1b) If the primary location is light-polluted, it might make good sense to follow LogicalAthiest's advice and get a computer-controlled telescope. Orion does not sell these; Celestron and Meade are your best bets. The computer system will allow you to find objects even when manual star-hopping is impossible due to light pollution. If the primary location is reasonably dark, the computer system may well be a nuisance -- depending on your goals....

2a) If your goal is to really thoroughly learn the sky, most people will stick with Labguy and tell you a copy of Uranometria, a nice 10" Dob, and some good gloves will set you up nicely. The satisfaction of being able to swing your 'scope around and point directly at hundreds of objects is very alluring. A computer-controlled scope will generally help you establish one of two observing habits: either you will rely on it for everything, and never have the motivation to learn anything about how to find things on your own, or you will use it as a backup -- the world's most patient teacher. If you want to learn the sky, but think you can't resist the temptation to throw up your hands in frustration and press the Go-To button, you might want to skip the computer. The best thing about telescope computers, IMO, is that they can all be turned off!
2b) If you're a gadget hound (like LogicalAthiest ), you may want the latest-n-greatest technological wonder. Please don't skimp on the optics, however. Also be aware that many of the low-end computerized scopes are really pretty poor in the electromechanical department -- they don't track well, or really find things all that well, have shoddy plastic internals, etc. If you're looking at a low-end (sub-$1000) scope, my honest opinion is that the electromechanicals in that price range are not worth buying. Spend the money on better (or larger) optics instead. 2c) This is just a question of aperture. If you're the fuzzy-hunter type, sacrifice all else for larger aperture. No amount of gadgetry will make up for the fact that your small aperture scope can't show you the dim galaxy you want to see. 3) This is really a catch-all question. If you think you'll be showing lots of people things, your priorities shift a bit. Having a telescope that can track (generally an EQ) is a godsend if you're showing 10 people what Jupiter looks like -- with a Dob mount, you'll have to keep recentering it for each viewer. If you plan on doing public star parties, it can be frustrating to spend 20 minutes trying to find your favorite planetary nebula while 20 kids wait impatiently on you. Having a computer system will allow you to instantly find the objects, even in those light polluted school-parking-lot skies, and make everyone enjoy the experience more. My two all-time favorite 'scope types are: 1) The 8" computerized altazimuth Meade and Celestron Schmidt-Cassegrain scopes. They may be too expensive for you, but they have the ease of use, features, and aperture to make them fine scopes for almost anyone. Normally priced around$1500-$2000. 2) The 8-10" newtonians on Dobsonian mounts. Generally priced around$600-$800. They're both very different instruments, but both instant classics in their own rights. Good luck in your decision! - Warren 5. May 26, 2003 ### chroot Staff Emeritus Also, I just have to ask -- what do you mean by "viewpiece?" - Warren 6. May 26, 2003 ### chroot Staff Emeritus Oh, and don't forget Astromart! www.astromart.com It's a classified system for astro gear -- sometimes you can pick up an awesome scope at very good prices. Keep in mind that simple scopes, like those Dobs, never go out of style. If it's maintained well, one of these scopes will work just as well when it's 50 years old as it did on its first night out. - Warren 7. May 26, 2003 ### Labguy I mainly recommended the "Dob" (more simple) over the GO-TO (computerized) scopes for just a few reasons. (1) Cost: If you get a go-to scope, well over 1/2 of the cost will be for electronics, and I will guarantee that once you get your hands on a new scope, you will discover dozens of accessories (better eyepieces, dew shield, heating strip, etc.) that will cost another small fortune. Most amateurs I know have far more$ in their eyepiece box than in the entire telescope and mount. But this (eyepieces) also applies to all scope owners, but at least some didn't pay $1500 for just the mounting and elecs. on an 8" scope. (2) Quality: As chroot mentioned, any but the finest, high-end (=$4,000 to 10,000) go-to mounts are made with poor quality control, plastic gears, motors that fail often, boards that burn-out often, etc. You wouldn't believe the number of "failures" I see every month at our observatory weekend. Many of these folks spend hours just trying to align and "program" their mount, while other folks are looking at things. (3) Quality-2: With only a rare exception, almost every scope sold to amateurs on go-to mounts is a Meade or Celestron Schmidt Cassegrain telescope (SCT). Just by the original optical design, an SCT has the lowest contrast, light throughput and image quality of any other design still in use. An SCT has a minimum "spot-size" (pinpoint stars) of 30 microns, while a Maksutov Cassegrain can get to 9 microns, as can a well-made Newtonian reflector. Only an "Apochromatic" refractor (APO) can beat these, but a 4" APO starts at over2,000 for just the tube, no mount, no eyepieces. A decent 5" APO can be had for ~$5,000 for just the tube. You don't even want to know what a larger one costs. (4) Amateur astronomy and a telescope: If you are interested in astronomy as a science-only, and not to do any observing, then you wouldn't be planning to buy a telescope. The scope means that you want to actually see some of the neat objects you have been hearing about. You will "see" more objects, and see them better, with a Newtonian reflector, whether on a Dob mount or even an equatorial mount, and for less$ than any of the go-to SCT's or Maksutovs.

(5) Extras: With any scope you buy, you will always want to add upgraded eyepieces, Barlow lens, and many other "goodies". So, if you need extra $for accessories, you will have it if you start with a lower-cost scope in the first place. I have far more$ in eyepieces, filters, etc. than my telescope cost, and my scope has very "high-end", custom made optics.

There are, of course, many exceptions to this as chroot mentioned, but the main ones in using your scope, instead of storing it, would be portability and astrophotography. But, the location you mentioned rules out any successful photography unless you can sometimes travel to a real "dark-sky" site. I would always choose quality of optics over any other features; you will see more and see it better. All of this is just my $2.07 worth... Last edited: May 26, 2003 8. May 26, 2003 ### chroot Staff Emeritus What's with the distate of the SCT Labguy? They (can be) great scopes. :) - Warren 9. May 26, 2003 ### Labguy They can be, but I have never seen one yet, out of at least 200 attempts, probably more. The first thing is inherent in the design itself. The primary mirror is spherical, the secondary mirror is spherical, and only the front "corrector lens" is curved, in a very odd shape, to try to correct for the otherwise awful spherical aberration. This has the possibility of giving a sharp image, but this design was intended to get a long effective focal length (EFL) into a short and light weight tube. Today, almost all SCT's have a primary mirror with a very steep curve to make it an f/2 primary. Any optician will tell you that the extremely short f/ratio mirrors (deep curve) are much harder to polish to a fine (accurate) surface than a longer f/ratio mirror like an f/6 or f/8 used in many Newtonian designs. Therefore, a mass-produced f/2 mirror is much more likely to have a poorer surface accuracy than a longer f/ratio mirror made with the same tools and care. Next, the convex, spherical secondary is also a steep convex curve to provide an "amplification" of the light curve to become the final f/10 EFL. Again, a steep curve is likely to be less accurate than a more shallow curve. Then they have to make a full-aperture corrector plate covering the entire diameter of the telescope. The design (shape) of the corrector is hard to put in type, but a search would show its complex shape. This is, again, harder to make with a fine surface accuracy than a simple parabola or flat as are used in a Newtonian reflector. And, the secondary mirror has to be made very large to "gather" the light cone from the primary. A typical SCT has a secondary with a diameter of 33% to 40% of the entire primary mirror. This causes (a) a lot of light-loss by obstructing how much light can reach the main mirror, and (b) a large obstruction in any telescope design causes more diffraction, which results in much lower contrast than a smaller obstruction would cause. So, in an SCT we have hard-to produce deep curves and a large secondary obstruction. There are four optical surfaces that all have to be very good to get the original light entering the scope to the rear of the scope, where an eyepiece can be placed. These are: (1) The front surface of the corrector plate. (2) The rear surface of the corrector plate. (3) The primary mirror front surface. (4) The secondary mirror front surface. I know that you would agree that any surface errors (no surface can be "perfect") would compound the total error in the entire optical path, and in the SCT, we have at least four surfaces to try to make a perfect as possible final image. I say at least four, because it is rare, and hard, to use an SCT without adding a "star diagonal" to send the light at 90 degrees from the back of the scope to be able to mount and reach the eyepiece. So in most all SCT configurations, we have five, yes five, optical surfaces for the light to encounter before it can ever even reach an eyepiece! Look at the fork-mount design of most SCT's, and you can see that the star diagonal is necessary ot be able to observe anything higher than just a few degrees above the horizon. The best viewing is, of course, high in altitude where there is less atmospheric obscuration. Then, it only gets worse! We already know that five optical surfaces with any error at all will compound the error of the final image (wavefront accuracy) of the light reaching the eyepiece. Then, we have to realize how much of the light entering the telescope will be available to the eyepiece, regardless of the accuracy. As you know, every optical surface (air-to glass, glass-to air or reflection) will cause some light-loss of the total incoming light. I won't go through all of the refractive and reflective percentages, but until just recently, the total light reaching the eyepiece in an SCT was 70 to 74% maximum! Lately, Meade has introduced their UHTC (enhanced) coatings that bring that number to about 85%. Celestron improved their "Starbright" coatings to about the same 85%. That helps quite a bit, but each optical surface also introduces what is called "scatter" in the image. With 5 surfaces in an SCT, before the eyepiece, the scatter can and does also decrease contrast, along with the too-large secondary mirror obstruction. Add it all up, and you get a hell of a lot of contrast loss, and contrast makes the difference between seeing good detail (like in Jupiter's belts and Red Spot) or just seeing them as "there". It also makes a huge difference in being able to see finer detail such a splitting very close visual binaries. Compare the light-loss and scatter to a well made Newtonian. One enhanced primary mirror and one enhanced secondary flat, at 96% to 98% reflectivity each, gets at least 92% of the light to the eyepiece. Also, there is a total of only two optical surfaces to introduce scatter. I could go on a bit about "mirror shift" and other SCT problems, but I have already typed too long. Maksutov Cassegrains are better than SCT's, but they cost more. Don't ask!.... 10. May 26, 2003 ### chroot Staff Emeritus It would seem that you'd dislike Maksutovs as well. You also seem to be missing the rest of the terms in telescope choice equation: portability, features, etc. SCTs clearly have some advantages over your precious Newts. Besides, most of your post dealt with the number of optical surfaces in an SCT -- and it's the same in a Maksutov. I often use my SCT in "Fastar" mode, in which I remove the secondary mirror and install a CCD camera. According to your maths, then, there are only three optical surfaces -- not so bad. I can choose to operate the scope at f/2, f/3.3, f/6.3, and f/10. The versatility of SCTs is really just simply unmatched by any Newtonian. Also, to be honest, few of the optics found in normal 8" to 10" Dob newts are anything to be excited about. My Celestron C11 beats very nearly all the 'scopes most people have pretty handily. At some recent star parties, people were amazed by the crisp views through my C11 -- two people independently stated that the view was better through my C11 than through a neighboring Obession (which was, I believe, a 15"?). SCTs are very sensitive to collimation -- I have to tune up my SCT once every, say, five-six observing sessions. Many people don't collimate their instruments well, which may explain why my C11 is consistently able to outperform them. Most newts, of course, need collimation nearly every time you use them. You're right, you're not going to choose an SCT if your interests are contrasty, fine planetary work. Newts are also not the first choice for that kind of work either -- the persistent coma of most newts takes the fun out of it. If you want planets and double stars, BUY AN APO! There's no point in your attempt to say that Newts are better than SCTs for planetary work, because most people will say both pretty much suck (equally) for planetary work. On the other hand, my C11 can show me all of the Herschel 400 on a good night, and fits nicely in the passenger seat of my sports car! It seems to me that your observing goals are such that SCTs do not suit you -- but you're doing a disservice to the astronomical community when you go around telling everyone that they're not good for anything! - Warren 11. May 26, 2003 ### enigma Staff Emeritus kleinma, this could be a dumb question, but I've got to ask (personal experience here)... Is this your first telescope? If yes, then you are looking at one which is waaaay to big for you. I took an astronomy class a few years ago. Afterwards, I went out looking for telescopes. I'm glad I got a small one, because it's sitting in a corner collecting dust right now. The light conditions where I live are crummy, and I just don't have enough nighttime availability to actually enjoy it to the fullest. Before you go spending an arm and a leg on a huge telescope (which I'll say is bigger than 3 or 4"), make sure you are willing and able to devote yourself to the hobby. 12. May 26, 2003 ### chroot Staff Emeritus That's exactly Labguy's point (and mine too) -- a good dob-mounted newt will cost less than half of what that eq-mounted scope costs, and really will do nearly everything just as well (except photography, of course). - Warren 13. May 26, 2003 ### Labguy Chroot: Of course, buy an APO if you can afford a good one. My emphasis was mainly optical quality, or at least the chance of acheiving optical quality. In that catagory alone, SCT's come in at last place. Also, a "good" Maksutov has quite a few advantages over an SCT, but that is another story. The SCT is easily the most portable, but I still would opt for image quality over portability unless we get to BIG scopes, and any of these would be permanantly mounted in an observatory. BTW, several makers sell Newtonians labeled as "Apo Eaters". These would be long f/ratio scopes with a very small secondary, low-profile focuser and several contrast-enhancing things that can be done (mechanically) to a Newtonian that cannot be done to an SCT. I guess I am spoiled by having my newtonians made by me (I did everything but the mirrors), and having "custom" optics made for me by one of the finest in the US. My little 8", f/6 can and does always knock over the C-11's and 12" Meade SCT's as far as resolution, contrast and razor-sharp images on any object within the magnitude limits of even the 12" scopes. Even from average-at-best skies, showing 6 stars in the Trapezium seems to be a task for the 11" Celestron GPS models at any power, and I check and get all 6 with ease at only ~80x as a test to see how good the sky is that night. I will honestly say that from very dark-sky sites, the 8" I use most beat the heck on every object viewed with an Astro-Physics 6", f/12 APO refractor on a$3000 mount. Why could this happen? The answer is that both scopes had superb optics, but 8" is bigger than 6", period. You don't even want to know what my 10", same mirror-maker, will do.

As far as versatility, you use positive lens combinations to get different f/ratios. A Newt. can do the same with quality Barlows, or TeleVue Powermates. I can use them for f/6, f/12, f/15, f/18 and even f/30 with the 5x Powermate. Versatility goes both ways. My 10", f/6.25 is tight, but I can get the whole thing in a smallish Mitsubishi Gallant with enough spare room for a can of Coke...

But, it is always said that the best scope you have is the one you use the most, and I see forrests of SCT's all over the field along with a few of the big Dobs (14 inch to 20 inch). Some of the worst views I encounter come from the biggest Newtonians. See:

http://www.rfroyce.com/standards.htm and
http://www.rfroyce.com/mirror_performance.htm

for some reasons why the big, short f/ratio Dobs (any Newtonian) are over-rated, over-priced and under-performers. Don't even consider most "commercial" Newtonians, but who is going to make you a "custom" SCT?? Royce did not make my optics, but you may note on his site that he even advertises that he will make replacement mirrors for Obsessions and other biggies. What does this tell you about even the so-called high-end commercial scopes?

You know, if you would sell your SCT's, then I would give you the name of the custom optician who made my optics, and optics for even some universities... ... ... ...

14. May 26, 2003

### chroot

Staff Emeritus
You must be looking through some SCTs tuned by complete idiots, man. I have not once looked at the trapezium through my C11 and not seen E&F -- even on nights of really ****ty transparency. Really, seeing E&F should not be a challenge for ANY reasonable telescope. You're stretching your credibility by making it sound like an 11" SCT can't show you E&F -- that's just stupid, I'm sorry. I'm disappointed you're actually spewing this kind of trash at me now.
This is incorrect. The Fastar system on the SCTs permits a wide variety of effective focal ratios -- and a barlow is NEVER used. Perhaps you should do some reading before making these kinds of comments?

- Warren

15. May 26, 2003

### Labguy

Do you always have Mag 6.5 skies? Don't forget how humid and hot it can be where I am located. The C-11's just can't do it. We rarely get good seeing. It isn't trash, it comes from quite a few years of testing every type of scope imaginable, from crap-skies to working in great sky at Mc Donald observatory. If you are going to get pissed-off because you are limited to a commercial SCT, then send it back and buy a real telescope.

I don't think I mentioned a Barlow at all with SCT's, just Newtonians. A lot of SCT owners do use the so-called "focal reducers" which are positive lenses, not negative like Barlows. That's real great too, because now you add about four more optical surfaces to the 4 to 5 already there. Re-read it if you didn't get it the first time. I do read all the time, and a lot of reading has led me to decide that if I ever got an SCT, I would sell it quickly and buy some expensive eyepieces.

Since you do all the reading / research, why don't you tell all of us the many advantages of a good Maksutov Cassegrain over an SCT? Maybe you could toss in some of the reasonable upper and lower exit pupil limits for anyone, depending on age, what design and size of scope they use, and where they observe from? Maybe you could fill us in on figuring the true field of view based on measuring the field-stop on eyepieces, instead of the more common method of dividing AFOV by the power?