Buying a Used 'Scope - What to Look For; What to Avoid?

[rabbithutch]

Please note that this is a question, not a primer!

I've just begun trying to educate myself about 'scopes. I intend to buy a used unit to test the waters because I have a closet full of stuff from other enthusiasms that didn't last. Besides, I'm just a cheap sod!

I have decided that I want a reflector scope; and it must come with a good tripod and mount, but most importantly, I need automation for setting up, finding targets, and tracking them. I've found several Meade and Celestron (and 1 Orion) units that have my interest, but I don't know enough to trust my ability to inspect them and determine if they are seriously flawed.

I realize that any optical instrument can benefit from informed tuning if there are no physical defects. What I'm looking for is how to detect and identify those killing defects. Being retired, I can't afford to buy twice (at least not too soon) because " 'er indoors" will beat me if I waste money.

I've been searching SGL and have read many useful threads. Some I've bookmarked to go back to to reinforce my understanding. I have not found a thread that discusses buying used equipment. If someone can point me to one, I'd be very grateful.

[Chris H]

If your going to buy second hand then look for telescopes made my Celestron, Meade, Skywatcher, Orion optics or Orion USA don't be tempted by anything else. Avoid anything that claims to be able to magnify x500 or higher these are always spurious claims. As for defects too look out for check the primary (mirror as base of tube) and secondary (mirror set at 45 degrees at top of tube) for and signs of damage, scratches, chips etc if these mirrors are dusty then thats not a problem these can be cleaned. If the mirrors are wildly out of alignment this is also no problem as these can be adjusted follow this link to see how

Astro Babys Guide to Collimation

Check the tube for dents and check the tripod for correct operation. Also ckeck the focuser for smooth operation. Other than these things there is not much else if the scope has been owned by somebody who is upgrading or downsizing you could bet that the scope has been looked after especially if you bought one from the for sale section on this forum, also have a look at astro buy & sell.

You say you want a reflector scope on a tripod that tracks but you also say you are just testing the waters. Unless you drop lucky this sort of set up is not going to come cheap and can be heavy and time consuming to set up IMO the best scope for a beginner to use to test the water would be a Skywatcher Skyliner 200p this is a Dobsonian reflector, it is not on a tripod but the base is rock solid, takes seconds to set up and the telescope will be big enough to give you great views of planets and deep sky objects alike. It may not have finding and tracking but it will enable you too learn you way around the night sky.

[rabbithutch]

Thank you, Chris!

That is just the kind of information I was looking for. I was fearful that misaligned mirrors might be a permanent defect. Should I be concerned with any 'hidden' defects in mirrors - those not discernible to a critical eye?

Thanks for the hints to use the trading section. I'll look into that.

Thanks again for the help.

-rh

[Moonshane]

Chris has given excellent advice. in a way misaligned mirrors are a permanent defect in that collimation of a newtonian reflector is a constant requirement (at least before each session) a bit like tuning a guitar. once learned it takes a minute or two that's all and not something to worry about. I agree with the recommendation too - I love dobsonians and the 8" is a great all rounder.

generally, if the mirrors look in good condition they will be and ALL mirrors look dusty when you shine a light down the tube.

if looking at a dob then check the base is in good condition and not affected by damp or sticking and what have you - motion both up and down and left and right should be smooth.

you will no doubt buy further gear and eyepieces etc as you get into the hobby so again don't worry about this.

even modest dents in the tube really won't affect the view.

good luck with whatever you buy and welcome to SGL! I think the problem won't be convincing your wife that a scope's a good idea it will be that she wants prolonged looks through it!

[AWR]

If you hang around on the forum for a little while, you'll be able to use the For Sale section on here. Whilst it does not guarantee anything, buying from an established member of the forum should allow you to have a lot more confidence in your purchase.

You wont find any of the lemons that you get on ebay. (Ebay does have some good bargains but it also has an awful lot of overpriced rubbish).

I bought my Dob from the forum - a brilliant scope at a great price!

HTH

Andrew

[rabbithutch]

Thank you, Moonshane!

Your suggestions are well taken.

If I may, could you explain why you suggest a Dobsonian instead of a regular Newtonian? From the primers here in re 'scope selection, I've been confused. It seems that the gratification that the electronics and automation (while no substitute for learning the basics, I know) would bring a beginner would supersede any benefits I'm aware that a Dobsonian would bring. I have been to a sky party where a large dob was in use and was impressed with the visible images but the size was more than an old man would want to deal with, I think; and from using a refractor many years ago, tracking is going to be a problem for me.

As between a 200mm (~8") Newtonian with GOTO vs. Dobsonian without automation, what would I gain or lose? It seems that I'd have to have a table (at least) for a dob, if not a special tripod. Would the dob be larger and potentially more cumbersome?

I want to get started with something (8" reflector, automation) that will be capable enough to get me out often. If my interest is sustained, I expect I would next acquire a comparable refractor for planets and moon. If I really become enthused, no doubt I'd add a dob - and, likely, upgrades to my first purchases. I share these thoughts to let you know where my mental gymnastics are at the moment.

Finally, I can't seem to find the members trading section here at SGL. I found the retailers/sponsors page, but not one for members. I could certainly understand a decision not to dis-intermediate the business of sponsors, but I've seen several references to a buy/sell page that I can't seem to find.

Again, thank you very much for the guidance. I hope my questions are not too ill informed and boorish.

-rh

[rabbithutch]

Very good advice, Andrew. I will certainly entertain purchasing from a regular here; however, as I'm located in Texas and most of the members are in the UK (I think), shipping costs might be problematic (I don't know this; just projecting.)

[Tantalus]

Unfortunately Hutch, you need to have reached at least 50 posts before you can see the For Sale section. Just like to add though, If you find a scope for sale locally, ask if it's possible to see the scope working before you buy, this might help you assess how good the scope performs before you part with any money.

[Moonshane]

Thank you, Moonshane!

Your suggestions are well taken.

If I may, could you explain why you suggest a Dobsonian instead of a regular Newtonian? From the primers here in re 'scope selection, I've been confused. It seems that the gratification that the electronics and automation (while no substitute for learning the basics, I know) would bring a beginner would supersede any benefits I'm aware that a Dobsonian would bring. I have been to a sky party where a large dob was in use and was impressed with the visible images but the size was more than an old man would want to deal with, I think; and from using a refractor many years ago, tracking is going to be a problem for me.

As between a 200mm (~8") Newtonian with GOTO vs. Dobsonian without automation, what would I gain or lose? It seems that I'd have to have a table (at least) for a dob, if not a special tripod. Would the dob be larger and potentially more cumbersome?

I want to get started with something (8" reflector, automation) that will be capable enough to get me out often. If my interest is sustained, I expect I would next acquire a comparable refractor for planets and moon. If I really become enthused, no doubt I'd add a dob - and, likely, upgrades to my first purchases. I share these thoughts to let you know where my mental gymnastics are at the moment.

Finally, I can't seem to find the members trading section here at SGL. I found the retailers/sponsors page, but not one for members. I could certainly understand a decision not to dis-intermediate the business of sponsors, but I've seen several references to a buy/sell page that I can't seem to find.

Again, thank you very much for the guidance. I hope my questions are not too ill informed and boorish.

-rh

good to see you researching and getting to know your subject before buying - and asking questions on the right Forum too

you can see the for sale section on here after 50 valid posts so not too long and it will appear.

basically, the tube of a dobsonian is the same as a newtonian, in fact it IS a newtonian it's just the mount that differs. newtonians are usually mounted in two (or three ways). a dobsonian (named after the original designer of the style, John Dobson in the 70s I think it was) is the simplest and cheapest. due to the mount being simple and robust it offers a cheap route to a very stable platform and as a result, it costs much less to get more aperture (and more light gathering which equals more power) for your money.

you can of course buy a newtonian tube and mount this on a GOTO scope mount but this would need to be quite heavy and expensive to cope with eg an 8" tube.

as an example a new SW 8" dob is about £250. this is all you need to start observing. it's about 1.5 metres tall so you observe sitting down.

an 8" newtonian on a goto mount of adequate strength would be about £700. this would need a power pack, you'd need to regularly turn the tube as an equitorial mount gets in all sorts of weird positions and it would take a lot longer to set and and break down. I am guessing but it it would also weight about three times what the dob would weight and take up a lot more space.

you would be able to take some basic photos with it and it would find and track but at an obvious price.

personally, I love the challenge of finding things myself and also the fact that I can afford a larger scope for my money which allows me to see more. also tracking with a dob is easy due to the design. you basically get the target in the right and it drifts left (in a newt). I time Jupiter recently in a standard plossl with a relatively narrow field of 50 degrees and at 145x mag and it took a full minute for it to traverse the view.

I used to have a decent refractor (120mm) but sold it as it used to wind me up setting it up and breaking it down and it took up more space than my 12" dob which sees a lot more and takes about 2 minutes in total to set up including carrying the length of the house!

I stand by my 8" dob as a brilliant starter scope and used they are an even bigger bargain and you will love it.

obviously a good book (eg Turn left at orion) and some free software (eg Stellarium) and some star charts etc will help you find things (as will a Telrad finder and a right angled finder-scope but they are for a bit later).

if you can, attend a local group (although I note you attended a star party and presumably looked at a larger dob than the 8"!!) and see some scopes at first hand. you can go for a smaller GOTO scope but if you do it's likely to be less accurate and even though you are in the right spot, you cannot see the target as it requires more aperture than you have

hope this helps.

Shane

[Chris H]

You need 50 posts to enter the trading section. As a US based member have a look at cloudynights.com

[rabbithutch]

OK, Shane!

Let's see how much I understood. Both Newt's and Dob's use a tube mirror lens. A Dob is lighter weight but larger in dimension and has a simpler mount mechanism not normally employing a tripod but typically has no automation or tracking. These simplifications mean that one can purchase Dobs of greater diameter aperture for less money.

I am guessing but it it would also weight about three times what the dob would weight and take up a lot more space.

This part confuses me a bit. If a Dob is 1.5 meters for an 8" aperture, isn't that quite a bit larger than a non-Dob Newtonian? Or perhaps you were saying that while the Newt tube assembly would be smaller the whole kit you describe would take more storage space?

Am I close?

[rabbithutch]

Kris,

I will certainly check out the link.

(At this rate, I'm gonna cross the 50 post threshold pretty quickly.)

[earth titan]

Good discussions here.

Essentially dobs are lighter because a tripod mount is heavy. My 12" dob is just as easy to set up and use as my 6" eq3 mount and it takes up less space. It has a smaller footprint as the dob base is not too large and the tube lives in the upright position.

Can I canvas against buying goto software, etc. Although it is very clever, it has a massive catalogue of things to find which are way beyond the capability of the scope and the expense will restrict the size of primary mirror you can afford. In astronomy, size is VERY important.

[earth titan]

Good discussions here.

Essentially dobs are lighter because a tripod mount is heavy. My 12" dob is just as easy to set up and use as my 6" eq3 mount and it takes up less space. It has a smaller footprint as the dob base is not too large and the tube lives in the upright position.

Can I canvas against buying goto software, etc. Although it is very clever, it has a massive catalogue of things to find which are way beyond the capability of the scope and the expense will restrict the size of primary mirror you can afford. In astronomy, size is VERY important.

[Chris H]

In the 1970's a guy from California called John Dobson wanted to bring telescopes to the masses and he came up with the Dobsonian mount. He wanted to reduce the costs of getting into astronomy so by using 'chip board' (you may know this by another name in the US) he invented a simple but sturdy mount onto which a Newtonian reflector tube could be placed. This base enabled the scope to move up & down left & right which was all that was required and it works brilliantly.

It's not that the dobsnonian reflector weighs less than a Newtonian, for example an 8 inch Newtonian Reflector tube is 1200mm (sorry about mixing imperial with metric) and weighs 20 pounds place this on a dobsonian base weighing another 20 pounds and the total is 40 pounds. But put this on tripod and you need something pretty bulky to take the weight it would need to be around 40 pounds giving a total of 60 pounds.

Not only that but when using a Newtonian on a tripod the eye piece can end up in awkward positions which requires you to rotate the tube to get the ep where you want it (not impossible though, many folks do it) this does not happen with a Dobsonian base.

Hope this all makes sense.

Finally with regard to technology there is an answer a kind of half way house if you like and it comes in the form of the Orion (USA) XTi range. You get a dobsonian reflector telescope with a computerised object locater (COL) this runs of a single 9v battery and once aligned, which is a simple process taking no more than a couple of minutes, you key in what you want to see for example M1 and it will tell you how far left or right to push the scope and how far up or down you need to go and you end up with what you want in the eyepiece. Once located you have to track manually but it will finds stuff no problem. It works great check out this link Orion SkyQuest XT8i Computerized IntelliScope | Orion Telescopes

[AWR]

OK, Shane!

This part confuses me a bit. If a Dob is 1.5 meters for an 8" aperture, isn't that quite a bit larger than a non-Dob Newtonian? Or perhaps you were saying that while the Newt tube assembly would be smaller the whole kit you describe would take more storage space?

The two key parameters of a telecope are its aperture and its focal length. Simplifying somewhat: The aperture governs how much light the telescope collects whereas the focal length governs its magnification. The ratio of the focal length to the aperture is given by the focal ratio or f-number. (This becomes very important for astrophotographers but that's a whole new story.) High f-number means higher magnification/smaller field of view (for a given eye-piece) but more contrast and is more forgiving of eye-pieces.

Because a scope in a Dobsonian mount is held closer to the ground and it doesn't need motors to turn it; such a scope might have a longer focal length than one which has been designed to go on an equatorial mount. It takes a strong mount (and powerful motors if you want tracking/GOTO) to hold a large scope. (It's not just the weight of the scope but its size which matters!) Apart from these considerations, there is nothing to stop you changing how a scope is mounted.

As an example, the Orion Intelliscope Dob recommended above has a 1200mm focal length whereas Orion's Newtonian on a equatorial mount has a 1000mm focal length.

Andrew

[Ben Ritchie]

I bought my Dob from the forum - a brilliant scope at a great price!

Glad to hear it

[brantuk]

So to summarise and add a bit extra:

Scopes

There are two general types of scope available: refractors, reflectors.

Refractors can be: achromatic and apochromatic.

Reflectors can be: basic (eg Newtonian) or compound (eg Catadioptric).

Compound catadioptrics come in varieties like: Maksutov Cassegrain, Schmitt Cassegrain, Richie Cretien, and hybrids like schmitt newtionians.

There's also a special category for "solar scopes" here.

Mounts

There are two general types of mount: equatorial, alt/azimuth.

Varieties of alt/az mount include: "dobsonian" and "fork mounted".

Varieties of scope tube include: short tube, medium tube, long tube, and truss tube.

Principles of operation include: manual eq, "push to", motorised tracking, and "computerised goto with tracking".

Purpose

You can mix and match most of these depending on your personal criteria like: solar system only, deep sky only, combined solar system and deep sky, size, weight, portability, observational only, astro photography (or not), or combined AP and observing.

What you need to know before buying.

You need to know what you intend to do with a telescope before buying. Will you be observing only? Or will you want to do photography too? Will the scope be used primarilly in a light polluted area? Or will you be travelling mostly to a dark site? Are you physically fit enough to lift a heavy scope in/out of a car boot? Will your scope have a permanent location? (e.g. in the garden/observatory). Are you interested mostly in the Sun and Planets? Or does it include deep sky objects.

Perhaps the biggest criteria for most is budget. How much can you afford? Will budget need to include extras: like power, collimators, eye pieces, dew systems, shrouds, electronics, covers, computer control, filters, finders, books, software like planetaria and picture processing etc. And will you buy new or used?

I'm sure I haven't covered everything above, but spend a few months exploring/understanding the hobby and it will soon all fall into place and you'll be in a much better position to choose. Hope that helps

[Sirius_Starseed]

OK, Shane!

Let's see how much I understood. Both Newt's and Dob's use a tube mirror lens. A Dob is lighter weight but larger in dimension and has a simpler mount mechanism not normally employing a tripod but typically has no automation or tracking. These simplifications mean that one can purchase Dobs of greater diameter aperture for less money.

This part confuses me a bit. If a Dob is 1.5 meters for an 8" aperture, isn't that quite a bit larger than a non-Dob Newtonian? Or perhaps you were saying that while the Newt tube assembly would be smaller the whole kit you describe would take more storage space?

Am I close?

I'm new myself so I don't want to answer your questions just in case I get them wrong However, here's the 8" Dob - http://www.firstlightoptics.com/proddetail.php?prod=dobsky200

As the guys have already stated, stick with known/trusted brands i.e. Skywatcher, Orion (good choice as you're in the US), Celestron and Meade. Steer clear of eBay rubbish such as Seben, Tasco and other crappy makes which make ludicrous claims. Apparently the guys tell me they're made of plastic and are no better than toy 'scopes I nearly got suckered in myself

My opinion on a first 'scope would either be the Skywatcher 130P SynScan AZ GOTO - Reflectors - Skywatcher Explorer 130P SynScan AZ GOTO

You'll get good views of the Planets and also some deep sky objects, and obviously you've got the GOTO feature which you wanted. As a newbie myself this is what I also wanted. I'm glad I went for it Some folk would say get more aperture with your money and leave the GOTO for a later date. I'd rather compromise on the aperture (not by a lot) but get the GOTO feature.

Another to look at is the Skywatcher Skymax 127 SynScan AZ GOTO - Maksutov - Skywatcher Skymax 127 SynScan AZ GOTO

Apparently it's excellent on planets, and again as with the 130P you'll also see some deep sky objects (DSO). Your field of view is narrower than the 130P but it's got a longer focal length (I think this is right anyway) I'm soon to find out as I have one of these coming It's also very portable, more so than the 130P (that's also portable though).

Another is the Skywatcher 150P EQ3-2 - Reflectors - Skywatcher Explorer 150P EQ3-2

This is on a equatorial (EQ) mount instead of the Alt AZ mount. It also doesn't have the GOTO feature like the 130P and the Skymax 127. However, it's bigger aperture so you'll get better views of DSO. It all depends on what you prefer and what your budget is...

If you want the best price then I'd stick with Skywatcher. You'll get more aperture for your money with these.

There are hundreds more 'scopes out there which are suitable for beginners but these are the 3 which I'd personally recommend for a newbie such as you and me. I've owned the 130P (even if it was only for a few weeks) and I like what I saw. Light, portable, looks good, and on the rare occasion I got to look through it I liked what I saw. Jupiter's Moons were a lovely sight! I'm also soooo glad I bought the GOTO handset and converted it to GOTO. Worth the extra money IMO. As for the Skymax 127, well I can tell you more next week when it arrives. From all the reviews I've read though I should be very happy. I don't know about the 150P personally but from the reviews I've read this is an awesome starter 'scope (definitely not just a starter 'scope either) and the views are meant to be spot-on! It's just if you want to compromise the GOTO feature.

As for the Dobs which others have mentioned, I can't say. I personally don't like the look of them but it's not about what a 'scope looks like it's about the views it gives. I'd personally rather use a tripod mount but that's just me. An 8" Dob would give you fab views though. Talk about swings and roundabouts lol.

Wow, this is getting long lol. I'll leave it at that.

Good luck in whatever 'scope you choose, and just be careful if you're getting off eBay as there are so many scams out there and cheap rubbish being sold as something amazing! Do your homework on brands first and always check sellers feedback.

[Moonshane]

hi RH

I see others have been busy and answered your points nicely

the main two things that came across to me in your original email are that 1) you don't want a really big telescope due weight etc and 2) your wife will give you grief if you keep buying different gear! (you develop new and very ingenious ways to justify new gear like the rest of us if you get into the hobby ).

For me the 8" f6 dobsonian is the sort of scope that you can move easily and will show you a lot more than scopes with lesser aperture. About 20 years ago, this was the scope of dreams of many amateur astronomer and now is affordable to all. It really is a scope that many will be happy with for life. Chris' idea about the USA Orion intelliscope is a good one as this satisfies your other wish which is some electronics, although I presume the price will be higher than a non electronic one.

As others have said the tube is really no different between the two, just the mount.

if you want a scope which you can readily pick up, set up in two minutes and then observe in comfort, albeit without being able to take photos, then the dob is the one for you.

if you want a scope that is somewhat heavier, takes longer to set up, costs a lot more and is less intuitive to use but allows you to follow a long list of targets electronically and possibly take basic photos then the newt on an EQ mount is for you.

it has to be said that although with the latter you'll get good shots of the moon, planets and possibly the very brightest DSOs you will have to spend a lot more to get good results of the majority of targets you will see visually.

good luck and let us know what you decide in the end.

[rabbithutch]

WOW !!!!

What generous folks! Thank you very much for taking the time to make your posts and for sharing your (presumably) hard won knowledge!

As I read your posts, I opened another tab to the glossary to improve my knowledge of the terms. I also opened a notepad and began taking notes but found myself mostly asking more questions.

I really appreciate your categorization (do I have to use British spelling here ) of topics, Brantuk. I had already begun a notebook with an outline of those components. I hope to fill out the sub-categories and variants until I gain familiarity with them all.

Shane, you are very perceptive. I must avoid the rolling pin; I won't use heavy cumbersome equipment as much, I fear; electronics for positioning and tracking are attractive because I think they will give me gratification faster thus incentive to use the gear more.

Now to some further questions that ask you to share your opinions as well as knowledge.

Light pollution: I'm very much aware of what this is. I've visited Davis Observatory in far southwest Texas and driven those rural roads by starlight; so I have some perception of what dark really means (though not so much as do deep sea sailors and deep sea aquanauts and spacemen). Quantitatively - or qualitatively for that matter - are there degrees of light pollution that should educate my choice of 'scope? I live in a small city (~60k) with all the lighting that entails in America; however, I can go to some parks that are relatively unlit at night. This means that the direct light is subdued but there remains the reflective ambient light. I wondered if there were a scale that someone had come up with based on lumens or some other comparative scale.

I have some understanding of aperture and f-number from experience with photography, but I'm a bit confused about field of view. I would assume that scopes of the same aperture and focal length would have virtually the same FOV. Similarly, 'scopes with smaller aperture have a smaller field of view given the same focal length. Now, then, does that mean that longer focal lengths decrease the FOV? And while I'm at it, how does the f-number affect these variables. In photography, I would expect a smaller aperture (higher number) to allow less light in and give greater depth of field; however I don't know if depth of field is a meaningful factor given the distances of space. Focus, yes; but depth of field? Also, I assume that stargazing is about gathering light so that more is better. No?

I promise. I'll only include this one additional question in this post. As between 6" and 8" reflectors (dob or newt) there seems to be a significant price differential. And I read that going to 10" means increasing mount sizing to handle the increased mass and dimensions which, combined, increase costs significantly. My web surfing seems to bear out the price info, but I'm unsure if I understand the underlying factors correctly. Then the question becomes, will a 6" newt or dob vs an 8" newt or dob make a material difference in how satisfied a noob would be with the smaller and for how long.

Sorry for the convoluted language but I was trying to demonstrate my understanding (or lack thereof) of the subject in order to frame the questions.

Thank you again for your generosity and tolerance.

-rh

[pvaz]

The 6" to 8" is regarded as an important barrier by many (or so I read when I was in your spot about 12 months ago). With an 8" you can aspire to complete the Herschel 400 list given a really dark sky. 8" almost doubles the light gathering ability of a 6" (8^2/6^2 = 177% ratio).

Regarding the Field of View(FoV) : A scope doesn't work alone. You need an eyepiece (EP) as well. You change EPs to get different magnifications, the more you magnify the smaller the FoV (which is the area of visible sky) gets.

So lets say you get yourself a 8" dob with 1200 FL and it comes with a 25mm plossl EP. That EP haves a FoV specification of 55 degrees. Now how much is the true FoV?

1st) Find the magnification: Scope FL / EP FL = 1200/25 = 48x

2nd) Find the true FoV = EP FoV / Magnification = 55 / 48 = 1.146 degrees, which means you'll see an area of sky equivalent to a 1.146 degrees diameter circle.

If then you used the same EP on a shorter 8" scope (which would have lower f/ratio), that combination would give you less magnification and a wider true field of view. That's why a lower focal ratio, when comparing scopes with the same aperture and using the same EP, gives you a wider FoV.

[rabbithutch]

My brain is beginning to knot up!

What happens if I substitute your 25mm plossi with a 7mm plossi EP? ( 1200/7 = ~ 171X) Therefore, I presume the much greater magnification with the 7mm EP gives a much smaller FOV with that same 8" dob. No?

If that's the case, then larger EPs would be used for finding broader areas of the sky and smaller EPs might then be substituted to view portions of what you find. That is probably not the way it works out in practice as spotters and automation probably put you in the right part of the sky and you choose an EP for reasons other than narrowing the view. Demonstrating my ignorance and inexperience here, I'm sure.

Is there a way to determine the FOV given a particular sized EP? You stated that the 25mm plossi has a 55 degree FOV, but that was stated after talking about an 8" x 1200mm scope. Is the FOV dependent on the plossi size and the 'scope aperture and or FL? (IT's been near 50 years since I took Physics.)

Your advice about 8" over 6" is exactly what I was looking for. I had been convinced by my reading thus far that a 10" would be much to large for my first scope which narrowed the choices to the 6" vs 8".

Now I have to decide if I'll be intelligent enough to use a dobsonian (ie, smart enough to find the right targets without automation) or spent the extra 200USD to get an Orion with automation. Or . . . do I hold out for an 8" newt with GOTO and plan to use my laptop and build a power tank before stepping out. Then . . . getting my brain around the pros and cons of of FL. (Hmmm, this might not be a hobby for an old brain like mine )

FWIW, I ordered a pair of the Skywatcher binocs which should be here about Thursday, and now I'm shopping around for a tripod.

Thanks for the reply, Paulo. You've helped me a great deal.

Did you buy a 'scope? 6" or 8"? Dob or newt?

[pvaz]

I went for the Orion XT8 with the intelliscope goto system as I feared I wouldn't find stuff. But when it arrived I did a quick test of the goto and paciently turned it off for over a month to learn how to star hop efficiently. I believe a good book such as turn left at orion can help you a lot. You will definitely need a red dot finder to easily point the scope where you want. I strongly recommend the telrad. A dobsonian telescope is in fact a Newtonian Reflector scope, sitting on a Dobson mount. It can later be mounted on another mount, say an Equatorial, in order to be used for astro photography.

Paying the extra money for the GOTO may come in handy if:

- you live under heavy light pollution so you can't see enough naked eye stars to star hop.

- you're not much into the hole star charts and "knowing your way around the sky" thing.

I use mine when I'm too tired to look at charts or when the conditions are so good that I don't want to waste time looking at charts. Otherwise star hoping is much more enjoyable.

You got it right, on how to use eyepieces. You work your way from low to high mag. This is how I (and many others) do it:

1) look at the chart, then locate the area naked eye using the brightest stars. Use a red torch to read the map so your eyes don't loose dark adaptation.

2) point your scope at it. This takes seconds with a zero magnification finder such as the telrad (it's like a gun sight). It can be a pain with a magnifying finder, setting you back a few minutes per target (the magnified view shows too much stars compared to the map, which is confusing, and it's not enough to show the DSO you're actualylooking for).

3) Pan the area at the lowest mag till you find it.

4) work your way from low to high mags till you can frame the target well.

Regarding the true FoV. You can find a 10mm EP with a 55º FoV and another 10mm EP with a 100º FoV. On the same 8" dob they provide 120x but one will show only 0.458 degrees of the sky while the other shows 0.833 (almost twice the diameter and 4x the area). Problem is the 100º one costs about 20 times as much as the 55º.

I would advise you to use the 2 EPs that come with the scope for a while, 10 sessions or so, before thinking of new ones. When you don't know what you like/need you easily make some inadequate purchases.

[rabbithutch]

I should have looked at your signature and seen what scope you bought.

Thanks for the clarification. I'm glad to learn that the EP's come with their own FoV stats. That makes it a bit clearer.

I think I'm getting closer to the decision on a first scope. An 8" dob looks like it might be my best first step. The Orion and the Skywatcher look good to me. The extra cost of the automation on the Orion doesn't look too much to pay - especially if I can find one in the used equipment market.

You say that you turned off the automation to force learning how to push to the right section of sky. Does that mean that now you have experience that you don't use the automation so much?

My problem is having such a large - no, vast - amount of ignorance of the subject. My motivation in looking at the automation is to gain gratification of finds faster and thus get me out more often. Is it possible to link the automation on the Orion to a PC in order to expand its utility for more difficult to find objects? If so, what software?

Thanks again for the help!