Buying 1st telescope - Looking for advice

[jjplude]

I'm buying a telescope for my daughter to cultivate her interest in astronomy. I have taken advantage of the MAS loaner program and borrowed an 8" and 10" dobsonian and taught her how to align and find objects, but manually tracking can be a major pain after a while so I'm definitely looking for something with GOTO or the like. Also a good dobsonian would be too large to take places if we wanted to go out in the country to observe sometimes, so I'm leaning towards a Schmidt-Cassegrain or Newtonian.

So far she has really liked looking at planets, eventually I'm sure she will want to get into more distant objects. I liked what we saw with the dobsonians and am hoping to see even sharper magnifications if we can so I was thinking of getting something with a slightly bigger aperture. I'd also be interested in dabbling in imaging too.

In the looking around I've done, the scope I'm liking the most is the Celestron Advanced VX-11 Schmidt-Cassegrain. https://www.celestron.com/products/adv ... telescope .

I have a $3000 or so budget that I can spend and can add more accessories over time. I was thinking the best thing to do would be to get the best scope to build off of, since that can't be easily upgraded but eye pieces, lenses and imaging equipment can be added as we go.

I'm looking for general advice but also had a few questions for the experts:

1) Is the Advanced VX-11 a good choice for us?
2) What accessories and other equipment should I consider getting to start out?
3) What exactly are we getting with the 11" vs an 8"? My understanding is that the greater light collection would make sharper images when magnified with smaller eyepieces? Is that correct? Is there other advantages?
4) Once I decide, what is the best way to purchase? There aren't any telescope stores around I could find and I haven't had much luck finding decent scopes used anywhere. Is buying online from Celestron the best option?
5) Any other thoughts or general advice you have is appreciated.

Thank you!
JJ Plude

[rdavidjohnson63]

I purchased my first scope used off Craigslist. Just have to meet the person, setup the scope and see if it works for you. Walk away if there is anything wrong or you don't get the warm fuzzy feeling about it.

I have since purchased 2 more used scopes off the Marketplace/Exchange forum here. Again, I meet the seller, looked through the scope, tried out the go to and once satisfied all was as I expected, negotiated a price.

One of them did not come with a mount, so I got recommendations from fellow MAS members and settled on a brand new Celestron CGEM II mount for it. I went to the Celestron site, found the mount, clicked on the where to buy. I checked out the offer from all the vendors listed. They all offered the exact same price. One however included a SkyPortal WiFi Module and a Husky 25 gallon wheeled tool case for the mount, all at the same price.

I have bought from Woodland Hills, OPT, and Amazon, all with great luck.

Larger aperture means gathering more light, which means you can see dimmer objects, but also allows for more magnification assuming the same focal length. The down side is they get heavy, fast. I know a couple folks have 11" SCT's they cart around to star parties, but that is a rather heavy device. My 9.25 CPC is about 60lbs and is the max I'm willing to transport. I know several folks have truss dobs 12" and larger, some much larger. The advantage to a truss dob is it breaks down into much more manageable parts. Several collapse into what looks like a wheelbarrow. I built wooden folding ramps for one such person. She can load and unload a 14" truss dob all by herself. With a truss dob, you need to have a laser collimator as you have to perform that task every time you put it together.

Not every scope comes with a spotting scope. If what you decide on does not, many people like Telrads.

If you plan to get into imaging, going with some equatorial mount is almost required. It allows longer exposures with out the twisting effect Alt-Az mounts have. You need to make sure the mount can handle the weight of scope, camera, and any accessories you might want to add. I like to start at 2x the weight of the scope itself as a minimum.

Enjoy and clear skys,
-Dave J

[Dale Smith]

What is the best scope depends in part on what you want to look at. Viewing the moon and planets generally does not require much light gathering capability, so you could go with a smaller diameter scope. If you want to view faint objects (e.g. most galaxies) you want as big a mirror as possible. The type of target also affects eyepiece selection. If your tastes run toward wide angle targets (e.g. open clusters) then you might want to lean toward lower magnifications and wide FOV (Field Of View). If you are more interested in the moon and planets then you will want to lean toward higher magnifications.

A good eyepiece collection can cost as much as the scope itself. You basically want to fill the low, medium and high magnification niches (roughly 30-100X, 100 – 200X and 200-300X respectively). Which eyepieces will yield those magnifications depends on which scope you buy, so you will have to crunch the numbers specific to your scope. You will need the focal lengths (expressed in mm) of both the telescope mirror and eyepieces for running magnification calculations.
Magnification = Focal length primary mirror ÷ focal length eyepiece

In addition to the focal length of an eyepiece, the manufacturer will also give its apparent field of view (FOV). To find out the actual FOV that this will yield in your scope first figure out the magnification that focal length will yield in your scope and then divide the apparent FOV by that result. The prices of eyepieces correlate roughly to apparent FOV – the higher the apparent FOV the higher the price.
Actual field of view = Apparent field of view ÷ magnification

My advice is to buy the best quality you can afford. Cheap optics are not worth the aggravation. It is better to bite the bullet and pay the blackmail up front rather try to save money and then suffer the consequences until you finally break down and pay the blackmail anyway.

You should also run exit pupil calculations on the eyepieces.
f = focal length of primary mirror ÷ diameter of the primary mirror

Exit pupil = focal length of eyepiece ÷ f = Diameter of primary mirror ÷ Magnification
Exit pupil values greater than about 5 mm (for older people) or 7 mm (for younger people) will result in light being wasted by falling outside the diameter of the pupil of the eye.

You should also buy a Barlow lens. This will double or triple the magnification of any eyepiece it is used with. This can essentially halve the number of eyepieces you need to buy.

Another common purchase is collimating tools to make sure the mirrors remain properly aligned.

[Ron Schmit]

JJ:

I've just got to toss in, here. I've always told people that the best scope for them is the one they will get the most use out of. Dave's right that if you want to do imaging, you're going to want an equatorial mount, and that means counter weights and a strong pedestal. An 11" is already a lot of scope and a lot of weight and a GEM would mean tons more. I've seen a so many with a scope that size that can't get over the inertia of setting it up each night, and so there it sits.

Dobs are perfect for kids, but I've never seen a GOTO dob that can. They are awesome if you want to aim on your own, but if you're really set on GOTO, that's not going to get you there.

If you are trying to get your daughter to use it, make sure it's one SHE can set up. Since you want a GOTO, I would start with a smart 8" on a fork mount. I prefer forks on wedges (better accuracy) but they are becoming a rare breed. Good luck!

[FF2Rydia]

If you are trying to get your daughter to use it, make sure it's one SHE can set up.

I concur, if you are getting this for your daughter, SHE should be the driver for what you get, not what YOU MIGHT do. If YOU want a scope that could be used for imaging, get YOU a scope with that possibility, AND get her HER scope, that fits her style.

[SEmert]

I concur with most of the comments here already, but I'd like to add a bit.

I have an AVX mount, but with a C8. I like the AVX but I have a concern that this mount might be a bit light (i.e., short on load carrying capacity) for the heavier C11 OTA. It'll probably have longer settling times and a bit shakier views than I have with my C8. That also reduces its usefulness for imaging. Besides, you don't need huge aperture for imaging; shorter focal ratios (obtained on SCTs by using the Hyperstar adapter) and smaller apertures work just fine.

Ron mentioned the weight, and whether she could easily attach the OTA to the mount. Don't discount this! From what I've seen, Celestron SCT OTA's are a little lighter for a given aperture than Meade SCT OTAs, but they are still significant. My 8" C8 OTA, when lifted to the height of the extended tripod takes some work to get clamped to the EQ head by one person.

The Dobs from the loaner program you have used are bulky, but because the tube is largely empty, are relatively lightweight in comparison to SCT OTAs. That may have misled you in thinking how easily an 11" SCT OTA can be handled.

By the way, although most of the respondents to this thread have succumbed to aperture fever, many amateur astronomers have been happy throughout their entire "career" as amateur astronomers with an 8" scope, whether it's a Newtonian/Dob or a SCT. Yes, you'll get brighter views and a bit better theoretical angular resolution with an 11", but for the resolution Minnesota skies and seeing is probably more the limiting factor than the difference in aperture between an 8" and 11" SCT OTA.

One thing I miss when using my C8 on AVX is the fact that, once having done the two-star alignment (actually most of the time 3- or 4-star to get good accuracy in my case), you have to use the hand paddle for all scope movements. You can't unlock the clutches and even move it a little bit or you'll lose alignment. You have to use the goto capability or use the direction keys on the hand paddle to move it. With my Dob, I can just push it and even just pan through the Milky Way when I want. Dobs equipped with encoders but not the motors to give you a "push-to" capability still let you do this, and generally are just as accurate in their finding capability. However, no more than "snapshot" through the eyepiece imaging.

Accessories for an SCT setup.
Good portable battery, including jacks for dew heaters.
Dew shield (recommend heated one), dew heater for eyepieces, dew heater for finder.
Telrad or Rigel QuikFinder or red dot unity finder.
If the OTA has a 1.25" visual back (C8 does, don't know about the C11), a 2" visual back so you can use a 2" diagonal and 2" eyepieces. SCT's are long focal length, and she'll often use longer focal length eyepieces for lower power viewing, and good longer focal length eyepieces are usually 2". Also, the adapter will let you use a refractor diagonal rather than a SCT diagonal, and if you ever get a refractor, you can use the same diagonal for both. I did this for my C8 with a visual back from ScopeStuff.com.
Cases to store and transport the mount and OTA. You can go custom and expensive, or just work up something with plastic tubs from home stores. I went with the latter.

For more detail and thoughts on accessories, download my presentation from the February BSIG meeting. Suresh put a copy in the BSIG forum.

For purchasing, I'd go with OPT (I believe when saying you're a member of a club you can get a 5% or 10% discount), or Astronomics or Starizona. Especially Starizona if you're really planning on imaging. They can give you some good advice. Amazon and eBay are only providing prices, no customer service. Big photo shops like Adorama and B&H specialize in cameras, not astronomy. OPT, Astronomics and Starizona specialize in astronomy.

[SEmert]

... Dobs are perfect for kids, but I've never seen a GOTO dob that can. They are awesome if you want to aim on your own, but if you're really set on GOTO, that's not going to get you there. ...

That's correct for all the 6" - 12" or 14" Dobs. But an exception to that statement is every one of the large truss Dobs that are resident at the MAS observing sites! (The 24" Starmaster at CGO, the 20" Obsession at ELO, and the 25" and 30" Obsessions at LLCC.)

All these truss Dobs are equipped with encoders and Argo Navis digital setting circle (DSC) computers. (Less expensive alternatives to the Argo Navis are the SkyCommander and the Nexus DSC computers.) They are also equipped with ServoCAT servo drive systems which interoperate with the Argo Navis.

All of these scopes can accurately find and track objects. And one thing I love with the AN/SC system is that you can run it in any mode you want.
1. You can leave the AN off and servos disengaged and find and track things manually like any Dob.
2. You can do the two-star alignment and engage the servos and use it as a full go-to system with tracking.
3. You can just use the AN and leave the servos disengaged and use it as a "push-to" system.
4. You can manually find objects, but just use the servos to track the sky.
5. You can start out in full goto mode, then if you want to just disengage the servos and push it around a little bit to look at a nearby object or to just scan the skies, you can disengage the servos and push the scope around. When you are done, just re-engage the servo clutches and you are tracking again, without losing alignment of the sky. (The AN has its own encoders to keep track of where it is pointing in the sky, and they remain in place even when you disengage the drive servos.)

This gives the user the best of all worlds (except portability as these are big scopes, and of course, no imaging!)

Yes, this setup is expensive and requires a little more knowledge to own and maintain, but it takes no more expertise to run than the computerized GEQ mounts that are at the heart of the rest of this discussion thread. And this setup can be added to as small as a 12" truss Dob.

Of course, this is why we have them at the MAS observing sites - so members can use them without having to purchase this type of setup themselves!

[clayton]

JJ Plude

I think its great you are looking for telescope. Lot of good information in the replies. So I won't rehash it too much. You mentioned you borrowed dobs but if you have not borrowed the SCTs you might want to try one of those too.

First your Questions:

1) Is the Advanced VX-11 a good choice for us?

I would say weight is going to be an issue as it fairly heavy as mentioned previously. The VX mount is rated for 30 lbs the OTA weighs 27.5lb. For Visual you are OK. The extra aperature will make the images brighter. For astrophotography which adds more accessories ( and weight) you are pushing the mount. The normal rule of thumb for right sizing the mount is 50-75% of rated capacity for AP. You'll probably have some success with simple dslr AP if you don't add too much weight. A C-11 has a focal length of 2800mm which is really long to start learning deepsky AP. The local focal length will mean smaller field of view and tighter guiding requirements. Most suggest learning with 500 to 700mm small fast scope that are more forgivable with tracking until you learn the techniques. Also the F/10 of the SCT will mean you have to expose longer. There's a few ways to help with that , the hyperstar being one, but that is more $$. For Lunar/ Planetary AP the longer AP is what you want.

2) What accessories and other equipment should I consider getting to start out?

General: Red Flashlight, Portable power, observing table, Storage boxes. Eventually some type of Dew control
Visual: Eyepieces and Barlow as mentioned previously, Light Pollution filter if observing under city skys. Red light, Charts.
AP: Camera to Telescope adapter, Guide scope and Guide camera. DSLR to start assuming you have one. Software to capture images, software to process images. Probably a better focuser and mirror lock mechanism if you get really serious. There are some fairly good free programs but I would say 75% of serious imagers buy spendy software. Time, lots of Time. The imagers in our club spend a lot of hours learning the software and techniques to make good images. Still even without all the gizmos you can some results.

3) What exactly are we getting with the 11" vs an 8"? My understanding is that the greater light collection would make sharper images when magnified with smaller eyepieces? Is that correct? Is there other advantages?

Without going into a lot of detail the aperture jump is significant. Side by side the images will be brighter and in most cases you will see more faint detail. Under ideal conditions larger scopes show more but do deal with a few constraints. We live in minnesota at a relatively low elevation and have fairly turbulent local climate. Many nights the seeing is not that great. Most nights its not really possible to use the theoretical useful magnification of a telescope. The C-11 supposedly has a useable magnification of 660x. An 8" has 480x. There's only a handful of nights a year where the seeing good enough to use those higher magnifications. Most of Deep Sky observers for casual observing viewing max out at 250 or 300x Some extended objects just look better at lower magnifications and wider fields of view. I have observed only a few times in the 600x+ range observing planets or the moon on exceptional nights.

4) Once I decide, what is the best way to purchase? There aren't any telescope stores around I could find and I haven't had much luck finding decent scopes used anywhere. Is buying online from Celestron the best option?

Online stores mentioned previously. For used I give plus votes to Astromart and cloudynights but would probably not spend the big dollars on used unless I saw the scope first. Our Market Place is local. You can always try a wanted post.

5) Any other thoughts or general advice you have is appreciated.

Try a few more telescopes. Maybe explore the clubs options for getting started in AP.

[FF2Rydia]

By the way, although most of the respondents to this thread have succumbed to aperture fever, many amateur astronomers have been happy throughout their entire "career" as amateur astronomers with an 8" scope, whether it's a Newtonian/Dob or a SCT.

I'm still on a 4.5" Dob, or 10x50s. The Dob had first light 14 years ago in February down at CGO.

[Deane Clark]

Lots of good advice above.

I’d like to clear up one potential point of confusion. You don’t actually need a go-to mount to track objects in the sky. A German equatorial mount (GEM) or a fork mount set up equatorially on a wedge will track the sky just fine with a simple “clock” motor drive as long as the mount is aligned so that its right ascension (RA) axis is parallel to the Earth’s axis. There is also an equatorial solution for Dobs - it’s called an equatorial platform.

I’ll admit, however, that in practice, it is probably easier to just buy a go-to scope, and it may be easier to transport and set up.

Finally, another caution about go-to for beginners: They sound like the best way to easily start seeing lots of stuff with minimal effort, but they have a few disadvantages that can discourage people new to astronomy and astro-tech.

They don’t help you with learning your way around the sky.
If you lose (or don’t have access to) power, you’re toast.
They are another computer to deal with. They need things like software updates, and have more things that can break, or just be frustrating to deal with.

If you learn with a manual scope, you will understand what a go-to is really doing for you. So after finding and learning your way around manually for a while, you can decide to upgrade to a go-to save yourself some labor while understanding what’s going on. I have heard plenty of stories of people starting with go-tos that gave up because they couldn’t make it work right.

[jjplude]

Thanks for all the great advice, it's really helping.

To clarify, this would be for BOTH my daughter and I, not just for her alone. We have tried the dobs and while they are nice for simplicity, tracking and fine movement gets very frustrating and I don't think it would last long if that were our only option. I have taught her how to spot and locate objects in the dob at least so she has a leg up there. I plan to borrow a SCT loaner from MAS too to make sure that's what we want.

It sounds like the 11 is not the right size/weight for us or the mount so I am going to downshift to a 9.25 on the VX mount, which is only 20lbs, which will give a little more leeway on the 30lb capacity of the mount and will be easier to move around.

I'm also planning on getting the following accessories: Case, eyepieces (still undecided on which ones), filter for light pollution and nebular filter, Powermate (2.5x or 5x, not sure), smartphone adapter (I will wait to get a camera for imaging for now), dew shield and dew band, power block, flashlight, collimating laser and telrad.

Am I missing anything?

You mentioned a discount OPT, that would be very helpful. How do I take advantage of that?

On eyepieces, what is a good number/variety of eyepieces to have? I liked having the selection of eyepieces that come with the loaners (I think there are five), but am not sure how often we'd switch between them. As they can get expensive, I'd like to keep it down to a few good ones. How many do you use regularly?

Thanks again for all the great help! I really appreciate it!

[Deane Clark]

About filters:
The two I would recommend are a lunar filter and an OIII filter for nebulas. Unfortunately, light pollution filters were designed for use against mercury and sodium vapor lighting, and while sodium vapor is still common, most cities are changing their streetlights to LED which emit in a broad spectrum making them impossible to design a filter for.

As for eyepieces, that’s a huge question and has a lot to do with the telescope you have, what you like to view, and what is comfortable for you. If you prefer to wear glasses while observing, you would want eps with longer eye relief - at least 15mm, but 20 is better. When selecting the magnifications, you will want something that gives you a wide field without wasting aperture with a too-large exit pupil. Keep exit pupil to 7mm or less. I have found that a few magnifications cover the majority of objects and conditions. 50-75x for larger objects, 100-120x for smaller ones like globulars, planets, etc. 180-220 for use on things like planets and double stars when the seeing is nice and steady. It’s rare to be able to go 250x or higher under Minnesota skies. In practice, you’ll have to try out eyepieces and decide what you like. A Barlow or powermate will help cover more mags with fewer eps, but they can also be a bit of a pain and add weight. 2” eyepieces are great if your scope and budget can handle them. They are mostly of benefit for getting large apparent fields at low to medium powers. One warning - if your budget is limited, don’t go looking through a bunch of 2” Tele Vue Naglers or Ethos. You’ll be spoiled for anything else

[Dale Smith]

A worked example on eyepiece usage. My first telescope was a Dob with a 10 inch (254 mm) diameter mirror. The focal length of the mirror was 45 inches (1143 mm), so the f ratio was 4.5. I found I could do most of my viewing with just 3 eyepieces
a. 9 mm Nagler (apparent field of view 82°, fits into a 1.25 inch eyepiece holder)
magnification = 127X in this scope with actual field of view=0.65°
b. 26 mm Orion Q70 (app. field of view 70°. Fits into a 2 inch eyepiece holder)
mag. = 44X in this scope with actual field of view = 1.59°
c. 7 mm Nagler (app. field of view 82°, fits into a 1.25 inch eyepiece holder)
mag. = 163X in this scope with actual field of view = 0.50°
Using a 2X Barlow lens with these eyepieces doubled the magnification and halved the field of view (254X/0.32° , 88X/0.79° and 326X/0.25° respectively). The focusser on the telescope could handle 2 inch wide eyepieces and had an adapter for holding 1.25 inch eyepieces. The Barlow lens was 2 inch.

The 9 mm and 26 mm eyepieces saw heavier use than the 7 mm, which in turn saw heavier use than the rest of my eyepiece collection.

However, these same eyepieces used in another telescope with a different focal length mirror would yield different magnifications and fields of view. I briefly owned a 18.5 inch Dob. Its mirror had a focal length almost double that of the 10 inch, so all the eyepieces I had collected for the 10 inch scope suddenly had double the magnification and half the field of view. Whichever scope you end up buying, you will have to run calculations specific to that scope when trying to figure out the best eyepieces to fill the magnification niches.

Your scope will probably come with 1 or 2 cheap eyepieces. You might want to live with those for a little while and get a feel for their limitations. If you attend some of the star parties you can often borrow other peoples’ eyepieces for a few minutes to see how well they work in your scope.

[farroutman2003]

This is a month after your post, but if you haven't bought yet and aren't in a hurry, goto a star party. Usually a large variety of scopes at the star parties and generally everyone is more than willing to let another person view from their scopes.