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Need advice on choosing a Dobsonian

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#1 MKuhn

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Posted 13 December 2012 - 07:03 PM

Hello all ....
I'm a new member here. Looks like a great forum!
I'm thinking about getting back into observing after being away for a while. I used to own a Meade 8 inch Schmidt Cass but I got tired of lugging it 50 miles to dark skies and sold it about 10 years ago.
Now I live in an area that's pretty decent as far as dark skies go.
This time around I'm thinking about a Dobsonian.
Skywatcher? Meade? Orion? Zhumell? Which brand seems to be the best?

Also, 8 inch or 10 inch? Is there much of a difference in what I'd be able to see between the 2 sizes?
Thanks all! I look forward to chatting with everyone here.

Mark

#2 starrancher

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Posted 13 December 2012 - 07:56 PM

Get a 12 " and be done with it .

#3 star drop

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Posted 13 December 2012 - 08:02 PM

Hi Mark and welcome to Cloudy Nights. There is a definite difference between the two sizes.

#4 Jon Isaacs

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Posted 13 December 2012 - 08:57 PM

Mark:

First, let me say hello and Welcome to Cloudy Nights.. :jump:

Dobsonians, I like 'em a lot.

Deciding on the right size is not so easy. The 10 inch is a little heavier than the 8 inch but easily fits in most cars. I have a 10 inch GSO... It's a good size.

A 12 inch is about a foot longer than the 10 inch and about 15 lbs heavier. At nearly 60 inches long, the 12 inches are a challenge to fit in many cars and more awkward. My 12.5 inch is a truss style, if you are considering a 12 inch, I would think seriously about a truss dob.

As far as which brand to buy. There are two manufacturers, Guan Sheng Optical (GSO) in Taiwan. They make the Meade Lightbridges, the Zhumells, the Astrotechs and the Apertura's. Generally these scopes are nicely outfitted with a solid two speed focuser, a nice finder and better eyepieces than the competition.

The other manufacturer is Synta Optical located in China. Synta owns Celestron, their house brand is Skywatcher and they manufacture the Orion Scopes. If you want the Intelliscope Digital setting circles or a GOTO Dob, Orion is the choice.

In general, these scopes are very similar. The original Orion XT Dobsonians were manufactured by GSO, it was not until about 2002 that Synta began making the Orion Dobs, all these scope share the same heritage. It's hard to go wrong with any of them, they are good scopes with generally good optics at very affordable prices.

Jon Isaacs

#5 pdfermat

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Posted 13 December 2012 - 09:12 PM

Welcome!! IMHO, if you can swing the extra weight and size of a 12", go for it. 12" is a great aperture to be at, it shows noticeably brighter and more detailed images on a wide range of targets vs. an 8" or 10".

#6 kfiscus

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Posted 13 December 2012 - 11:11 PM

I moved up from a 10" to 12". I never use the 10" anymore. I'm only 5'8" and can move my Z12 around without problem. It fits in my Honda Odyssey without problem when the back seat is down and one middle seat is removed.

I own both Orion and Zhumell and like the Zhumell adjustable bearings a lot. Everything else is about even between the brands but the bearings are extremely important and useful.

#7 Starman81

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Posted 14 December 2012 - 02:37 AM

Whether you go with an 8, 10 or 12 I already know that it is going to be a winner because you have something money can't buy--dark skies! Enjoy.

#8 nicknacknock

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Posted 14 December 2012 - 03:13 AM

Mark,

What is your budget first of all?
Any thoughts on Truss Vs Solid Tube?
How is your eyepiece collection doing these days?
Do you have O III or UHC filters at least?
How comfortable are you with collimation?

It's important that you budget for all the items you will need. On the eyepiece front, do consider for any potential dob a 30mm eyepiece and a 20mm eyepiece, plus a 2x barlow to get the equivalent of 30mm, 20mm, 15mm and 10mm. I recommend going for the widest field you can get to offset the narrow field of view inherent in Dobs. Also consider some planetary eyepieces if you are into that. And definitely a nebula filter. O III best choice.

Remember that to get the best out of a Dob, you will need collimation tools. A laser and cheshire collimator or a barlowed collimator is a must!

If cost is a consideration, a lot of fellow forum members have awesome eyepieces for sale. Same goes for Dobs on sale and filters as well and anything you may need :)

Finally, yes, there is a major difference between an 8", 10" and 12". The larger the diameter, the bigger the surface area of the mirror to collect light. Ignoring the secondary's impact (which is small anyway) see below:

8" = 200 cm diameter with surface area of 31,416
10" = 250 cm diameter with surface area of 49,087
12" = 300 cm diameter with surface area of 70,686

Of course, weight does go up as well as size. Be sure that you are comfortable with both aspects prior to parting with your money!

#9 CounterWeight

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Posted 14 December 2012 - 07:18 AM

Mark,

Welcome to the forum here. Lots of great posts about Dob's in the reflector forums. I envy you have pretty dark skies, that's a huge plus whatever aperture you choose.

#10 coopman

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Posted 14 December 2012 - 07:57 AM

Make sure that you're aware of how big & bulky these Dobs are. See this video.
http://www.opticsmar...a-ad10-dobso...

#11 MKuhn

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Posted 14 December 2012 - 07:57 AM

Mark,

Welcome to the forum here. Lots of great posts about Dob's in the reflector forums. I envy you have pretty dark skies, that's a huge plus whatever aperture you choose.

The skies are much darker than where I used to live in New Jersey, just on the other side of the Hudson River from Manhattan.
Was out last night watching the Geminids. Moonless night. Once again I was able to see 7 stars in the Pleides and fuzzy M42 (using averted vision trick) in Orion, all with unaided eye.

#12 MKuhn

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Posted 14 December 2012 - 08:01 AM

Mark,

What is your budget first of all?
Any thoughts on Truss Vs Solid Tube?
How is your eyepiece collection doing these days?
Do you have O III or UHC filters at least?
How comfortable are you with collimation?

It's important that you budget for all the items you will need. On the eyepiece front, do consider for any potential dob a 30mm eyepiece and a 20mm eyepiece, plus a 2x barlow to get the equivalent of 30mm, 20mm, 15mm and 10mm. I recommend going for the widest field you can get to offset the narrow field of view inherent in Dobs. Also consider some planetary eyepieces if you are into that. And definitely a nebula filter. O III best choice.

Remember that to get the best out of a Dob, you will need collimation tools. A laser and cheshire collimator or a barlowed collimator is a must!

If cost is a consideration, a lot of fellow forum members have awesome eyepieces for sale. Same goes for Dobs on sale and filters as well and anything you may need :)

Finally, yes, there is a major difference between an 8", 10" and 12". The larger the diameter, the bigger the surface area of the mirror to collect light. Ignoring the secondary's impact (which is small anyway) see below:

8" = 200 cm diameter with surface area of 31,416
10" = 250 cm diameter with surface area of 49,087
12" = 300 cm diameter with surface area of 70,686

Of course, weight does go up as well as size. Be sure that you are comfortable with both aspects prior to parting with your money!

Would truss tube cause me to collimate every time I set up?
I have never collimated a telescope before. My prior scope was a Scmidt Cass. 95% of the scope's use will be in my yard. Budget? Not sure yet.

#13 MKuhn

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Posted 14 December 2012 - 08:31 AM

Mark:

First, let me say hello and Welcome to Cloudy Nights.. :jump:

Dobsonians, I like 'em a lot.

Deciding on the right size is not so easy. The 10 inch is a little heavier than the 8 inch but easily fits in most cars. I have a 10 inch GSO... It's a good size.

A 12 inch is about a foot longer than the 10 inch and about 15 lbs heavier. At nearly 60 inches long, the 12 inches are a challenge to fit in many cars and more awkward. My 12.5 inch is a truss style, if you are considering a 12 inch, I would think seriously about a truss dob.

As far as which brand to buy. There are two manufacturers, Guan Sheng Optical (GSO) in Taiwan. They make the Meade Lightbridges, the Zhumells, the Astrotechs and the Apertura's. Generally these scopes are nicely outfitted with a solid two speed focuser, a nice finder and better eyepieces than the competition.

The other manufacturer is Synta Optical located in China. Synta owns Celestron, their house brand is Skywatcher and they manufacture the Orion Scopes. If you want the Intelliscope Digital setting circles or a GOTO Dob, Orion is the choice.

In general, these scopes are very similar. The original Orion XT Dobsonians were manufactured by GSO, it was not until about 2002 that Synta began making the Orion Dobs, all these scope share the same heritage. It's hard to go wrong with any of them, they are good scopes with generally good optics at very affordable prices.

Jon Isaacs


This is VERY informative. Thanks for your help!

#14 csrlice12

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Posted 14 December 2012 - 08:37 AM

You should check the collimation on a dob every time you set it up. It may need some slight tweeking, maybe not (the bigger the scope, the more likely it will need adjusting). A lot will depend on how jostled around it got between viewings. However, collimation is not hard to do, especially if all you need to do is collimate the primary (once collimated, the secondary usually holds its collimation pretty well). All you will need for collimation is a Cheshire sight tube and a collimation cap/eyepiece. These will collimate a dob just fine. If you're really into "perfection", I'd go the Glatter Laser and Tublug. You'll never have to buy another laser again...unlike the cheap lasers, Glatters keep their collimation (who want's to collimate your collimater?). The Glatter/Tublug system makes collimating your scope a breeze. Another good laser system is the Catseye, however, I have not used it, but others here love it too. The main thing you will find is that the 10" and above will require premium eyepieces (and what those are is an entirely other thread, but I like the ES82* series). While you won't need it up front, a Paracorr (used, type 1s are in the CN Classifieds all the time) would be nice to clear up the coma from the mirror. The 8" is a little easier on less premium eyepieces and collimation, while always critical, is a little less critical with the 8". There would not be a "great" difference between the 8" and 10" views (noticible, but not great), but there definitely would be between the 8 - 12. The 10" is about all I care to lug around, +1 on the truss if you go larger then 10", but truss dobs do take more setup time. For a truss dob, I'd definitely get a laser collimation system. You'll also need a shroud, especially in winter as you don't want your body heat creating thermals in your light path.

If finances allow, you might want to get a nice 8-10" dob and a smaller (4"/102mm) wide field refractor to supplement the Dob. Between the two, you'll have the full range of viewing for everything from the Veil nebula to finding those deep space fuzzies.....

Clear Skies....

#15 Jon Isaacs

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Posted 14 December 2012 - 09:39 AM

Would truss tube cause me to collimate every time I set up?
I have never collimated a telescope before. My prior scope was a Scmidt Cass. 95% of the scope's use will be in my yard. Budget? Not sure yet.



You should check the collimation each and every time any reflector or SCT is used. SCTs may stay in collimation better than Newtonians but collimation is critical in an SCT because of the two curved mirrors. Many SCTs under-perform because their owners are not careful about collimation. Collimation is something to learn, not something to fear.

Jon

#16 Bob Griffiths

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Posted 14 December 2012 - 10:46 AM

Would truss tube cause me to collimate every time I set up?
I have never collimated a telescope before. My prior scope was a Scmidt Cass. 95% of the scope's use will be in my yard. Budget? Not sure yet.



You should check the collimation each and every time any reflector or SCT is used. SCTs may stay in collimation better than Newtonians but collimation is critical in an SCT because of the two curved mirrors. Many SCTs under-perform because their owners are not careful about collimation. Collimation is something to learn, not something to fear.

Jon


OH SO TRUE....
I am NOT a dob guy (but I sure agree that they deliver fantastic views)... I prefer Scts and I have staed many times that half to the darn things I see onthe star field at both of my locals clubs star parties are NOT COLLIMATED well enough..

Now that i said that..if you are going to use it in your own backyard I'd get a 12 inch solid tube ..IF I had to transport it allot I would get an 8 inch Solid tube If only occasionally a 10 inch ..

Personally I do not see all that much of a difference between an 8 or a 10 nor do I see much of a difference between a 10 and a 12... The wow factory is quite apparent between the 8 and 12 however

Brands.. ??? I'll let that up to use..as a guy who has not owned a Dob in years I can't say for sure if it is 6 of one and half dozen of the other is true or not..

Bottom line...BUY a scope and enjoy it !

Bob G.

#17 tecmage

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Posted 14 December 2012 - 12:55 PM

The comments about a 12" scope are something to consider. The difference between a 8" and 12" are big. This page shows the difference. I am not endorsing the vendor, but the page is a great comparison of views different sized Dobs.

#18 stratocaster

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Posted 14 December 2012 - 01:19 PM

The GSO dobs are great values. Similar to a previous post, I also went with the GSO/Zhumell dob because I liked the adjustable clutch azimuth bearings. Plus the GSOs are a little less expensive than the Orions. As Jon has mentioned, the two speed focusers are very nice.

The Apertura dobs are exactly like the Zhumell's, except they offer a few upgrades, such as interior flocking and such. The eyepiece extension tube appears to be standard on the Aperturas. I did not get one with the Zhumell. As it turned out I could have used an extension tube to utilize my Naglar 12 T4 in 2" mode, but other than for that eyepiece an extension tube wasn't necessary.

Determining the primary's size will be a very personal decision based on your circumstances, personal preferences, and viewing habits. Most, but not all, comments I've seen on going from a 10" to 12" solid tube have suggested it is much larger, bulkier, and heavier than the 10" - and surprisingly so. This may not be a big deal if you typically plan on observing from your backyard and you leave your scope protected outside when not in use.

I personally would recommend against an 8" unless you have a physical condition that requires a smaller, lighter scope. 10" seems to be the price of admission nowadays for dobs.

If you plan on keeping the scope inside and you can keep it in a convenient location, e.g. next to the door, the 12" may still be fine. If you have to keep yours stored - say in a interior closet like me - I'd go with the 10".

If you typically plan on taking the scope to a dark sky site, consider the 12" truss (or maybe even a 16").

Then, of course, as has been mentioned you'd need to consider eyepieces, collimation tools, perhaps an adjustable observing chair (highly recommended), eyepiece case, etc. A 10" solid tube will allow your budget to go further.

Possibly a longer term consideration is that if you find the dob appealing and you want to squeeze the most out of your viewing experience by selectively upgrading the scope, e.g. getting a Zambuto mirror, the larger mirrors will be more expensive to upgrade. The standard mirrors are generally pretty good, though, and can provide years of satisfaction. So this may be a factor at some level depending on your financial resources.

#19 Eddgie

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Posted 14 December 2012 - 01:39 PM

My advice would be to get a Go-To dob from Orion.

And if you have a ground floor based place to keep it, I would recommend a 12" if you can afford it. The reason is that it is easy to fit a dob with wheelbarrow style handles which makes it rather easy to roll out.

The 10" only comes in a closed tube, but this is not a bad thing if you don't intend to transport it, but it really isn't all that big.

The 12" comes in either truss or closed tube, and if you think you would ever want to move it, the truss starts to make a lot more sense in this size. If you don't think you will transport it, the closed tube may hold collimation better, and will perhaps be easier to seal up.

Go-to to me is a slam dunk. Many people put dobs on tracking platforms, but if you ever decide to do this, it adds cost and raises the eyepeice height.

The Go-To also makes changing eyepeices easy because the scope is locked into position and won't move when you change eyepeices.

And while you may yawn about having "Go-To," remember that it is not "Just" Go-To. It is motorized slow motion slewing, and a computer in your hand to help you see what objects are in the sky or identify objects that you stumble across when you are sweeping.

And it is invaluable for doing double stars and of course high power observing (because of the tracking).

I would go one size smaller to get Go-To. It just makes observing far more productive and removes a lot of the hassles associated with regular dobs.

My next scope will be a Go-To dob. Not sure if it will be 12" closed tube or 14" truss, but I know it will be a Go-To dob!

Anyway, my advice is to seriously consider getting an Orion Go-To dob! It just makes observing so much easier.

#20 Jarad

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Posted 14 December 2012 - 01:50 PM

Truss vs. Tube: The main advantage of a truss is transportability. You can fit a much larger aperture in your car. You will need to check and tweak collimation each time you re-assemble a truss scope - it usually is close, but off enough to be worth checking. If you leave it assembled, it should hold pretty well, but then you are losing the advantage the truss gives of breaking down into a compact package.

Solid tubes usually hold collimation pretty well, but I still check it every time I set up, especially if you have driven over a bumpy dirt road.

With a decent set of tools, collimation is pretty quick and easy. After a bit of practice, it becomes second nature.

Jarad

#21 killdabuddha

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Posted 14 December 2012 - 03:28 PM

Get a 12 " and be done with it .


And as a 95% home scope you needn't worry about disassembly affectin collimation. And by the time you do pack it off to somewhere, collimation (tweaking) will have become second nature and even pleasurable.

#22 JohnMurphyRN

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Posted 14 December 2012 - 03:41 PM

Get a 12 " and be done with it .


And as a 95% home scope you needn't worry about dis-assembly affectin collimation. And by the time you do pack it off to somewhere, collimation (tweaking) will have become second nature and even pleasurable.


Collimation isn't as big of a deal to do as it's made out to be. I have a 12.5" solid tube that will require a tweak here and there but freqently is spot on from one use to the next. My 17.5" truss dob needs tweaked after each assembly/dissassembly. Takes MAYBE 3 minutes.

I'm in roughly the position you're in. I got back into astronomy fairly recently after about 10 years of not. My scope the first time around was a 9.25" SCT. This time it's dobs. If your expectations are set by your previous SCT experience you'll like the newtonian even better, BUT you will want a paracorr at F5 and below.

#23 tecmage

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Posted 14 December 2012 - 03:42 PM

If you don't mind a used scope, the used market has some of everything available- mass market scopes like Orion, Zhumell, etc, and custom house scopes like Obsession, Dobstuff, etc. The upside is you cam usually get a little more for less money. The downside is waiting for the right scope to be available near you.

#24 JohnMurphyRN

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Posted 14 December 2012 - 03:43 PM

If you don't mind a used scope, the used market has some of everything available- mass market scopes like Orion, Zhumell, etc, and custom house scopes like Obsession, Dobstuff, etc. The upside is you cam usually get a little more for less money. The downside is waiting for the right scope to be available near you.


Another upside is you can get high-end custom stuff without the wait or cost of ordering it new.

#25 TexasRed

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Posted 15 December 2012 - 03:45 AM

+1 on the suggestion to consider one of Orion's GoTo Dobs with automatic tracking. The convenience and ease of us make observing a dream!

I'll also second the comment that above 8", 2 more inches of aperture provide a noticable improvement but not the "wow" factor you'll get from 4 more inches of aperture.






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