First telescope advice 10" dob

[Crushellon (Tim)]

As stated in the title, I am looking to make my first purchase of a telescope. Astronomy has long been an interest of mine, but I am only now (at the age of 30) looking to actually make a telescope purchase of my own. I have made a fair amount of research into what type of telescope I should be looking for and have decided on something along the lines of a 10" dob (http://www.skywatcher.com/product.php?cat=6&id=60) in particular. The purpose of the scope is for viewing of galaxies and nebulae under conditions with low to moderate light polloution. I am looking for more experienced opinions on a couple of matters regarding this.

1: Opinions on whether this is the right type of telescope for my purpose.

2: I am a fairly intelligent engineering minded person. Will tracking galaxies and such targets be something that I will be able to do easily enough with patience and persistence (over time with practice of course) using a dob mount design, or should I go for a goto type design.

3: Filters. Do I need them? I realize that from the start I should refrain from buying accessories until my personal experiences tell me what it is that I myself from astronomy. But other than waiting until I know exactly what I want from astronomy, are there any "must haves" for this type of viewing?

[wavelandscott (Scott)]

A 10 inch Dobsonian mounted reflecting telescope is a good choice for what you are considering and a "large" first telescope.

It should be able to meet your stated requirements in terms of viewing targets.

When properly "optimized" I would expect that you will be able to hand guide your scope with few difficulties...getting the movement right for your tastes may take a little tweaking but it is not difficult.

GoTo scopes are nice but add a few potential areas of unneeded complexity (something else to go wrong) and while there are many advantages one of the biggest disadvantages is that in my opinion, they make the observer less educated (myself included) about the night sky. I find that outside of a few alignment stars I am not as savvy about what is where in the sky as I would like to be.

With respect to filters, I would start out without them and use your scope for a while...same goes for additional eyepieces...get some night sky under your belt and build an appreciation about what you are looking at and what you like. Go to some viewing nights with others and try out some of their gear and then after you know what you like, buy away.

In summary, a 10 inch reflector mounted Dob style is a very good entry point to the hobby...and if you use it regularly, aperture fever will kick in and you will soon be lusting after the 18+ inch scopes that will open up even more of the night sky.

Clear Dark Skies to you!

[Allan_L (Allan)]

Hi Tim,
Firstly Welcome to IceInSpace .

Secondly, I commend you on your research.
The scope you mention is a beauty, I had one for several years and it performed beautifully.
I currently have its bigger brother, the 12" GoTo model.

Finally, I completely agree with everything Scott has advised.
Having said that, ... The goto adds about $1,000 to the price, but if you can afford it I say why not. That scope can be used with or without the goto function.
And it can also be used just in an auto tracking mode.
Very versatile.

If you can't afford the extra $$$ I recommend you consider attaching setting circles (for Az) and inclinometer (for Alt) to help you locate those faint fuzzies.

Do a search for setting circles on this site.
This thread contains the file I used with my 10" Skywatcher (around post 68 I think)
http://www.iceinspace.com.au/forum/s...circles&page=4

And do try to get to an observing night where you can see others gear and discuss. We love to share our experiences with interested newcomers!

Clear skies

[mental4astro (Alexander)]

Hi Tim,

to ISS, where we LOVE to spend other people's money,

As Scott and Allan have mentioned, a 10" dob is a sensational first scope.

To answer your questions,

1, A 10" instrument has plenty of aperture grunt for galaxies and nebulae. But there is one thing to be aware of with galaxies and nebulae - you won't see the lovely spiral arms or the wonderful colours like you do in photos. Instead, things through a scope are much more subtle and faint, and require patience and a training of one's eyes to both see more and pick up detail.

With a 10" scope, there are only a handful of galaxies that will begin to reveal their spiral structure. And what you will see is not very pronounced, but more of a tease. Nebulae will show a how lot more structure, and the more time you spend on them, and understanding the forces and structures at play, the more you will see. Nebulae can have tremendous forces at play, but you wouldn't know it as things appear static, but only because of the vast distances involved. Visual astronomy is all about subtlety of detail and keenness of eye.

2, Tracking is certainly not essential. Yes things move across the field of view in a non-motorized instrument, and this movement is faster as the magnification is increased. But one can use a technique called 'drift' where one puts the object to be viewed at the edge of the field of view, or just outside it, and allows the object to drift across the field of view without shaking. Here, wider apparent field of view eyepieces help with the length of time that drift happens.

GO-TO is also not a magic pill. It can be useful but by no means essential. I have various go-to and push to systems available to me at home, but when it comes to my own personal scope time, I only use good old paper charts and star-hop to a target. Push-to systems are a step between push-pull manual moving, and totally automated go-to system. They use electronic encoders to determine the place the scope is pointed to and give a 'countdown' guide to how far to manually move the scope in order to acquire the desired object. These systems are great as after market add-ons to dobs that will be difficult, if not impossible to convert to a go-to instrument without a total overhaul of the scope and mount. When accurately aligned (a process that both push-to and go-to systems require), other than tracking, push-to systems can be faster to use than go-to systems. These push-to systems are better known as Digital Setting Circles.

There are two excellent systems available that are made in Australia, Argo Navis made by Wildcard Innovations, and the various Nexus systems by Astro Devices. Both are easy to retro-fit to most instruments. Other systems include Sky Commander and JMI MAX.

3, Filters, like go-to, are not a magic solution, but a damn fine help in the right instance. Astro filters, like all filters, work by transmitting only the required frequencies of light that are of interest to us. Filters for deep sky objects are designed to transmit a very select set of frequencies, and absorb everything else. For this reason they are good for nebulae, but not good for galaxies or stars as these glow across the entire spectrum. Nebulae glow at very exact frequencies.

This following link will take you to a great source of information relating to filters of all types for astro. Understanding what each filter does will help you make the best decision for yourself. One word of caution - don't go overboard with colour filters for the planets. You won't use these very much - really you won't. If you do want to get colour filters, try to limit your choice to two, three, no more than four. The types of features that these filters can show on the planets can actually be surprisingly difficult to see, and require experience and time to make out. Most of these features will not stand out like the proverbial doggie's:

http://www.lumicon.com/pdf/3filterspec_prnt.pdf


If you can before you make a purchase, try to get to a star party, organized by a club or an informal one, and see scopes of all types, and the many different types of accessories actually in use. You don't buy a car without seeing it in the flesh and driving it. Scopes come in many different sizes, capabilities, ease of transport and applications, not just price. If you buy a scope that in the end is too big to store or transport, it doesn't really matter how much of a bargain it is as you just won't use it. The BEST scope is the one that actually gets used.

Happy viewing,

Mental.

[ausastronomer (John Bambury)]

Originally Posted by mental4astro

But one can use a technique called 'drift' where one puts the object to be viewed at the edge of the field of view, or just outside it, and allows the object to drift across the field of view without shaking. Here, wider apparent field of view eyepieces help with the length of time that drift happens.

Mental.

I agree with everyone else's comments that a 10"/F5 dob is a great first scope that will see you good for a couple of years at least and more than likely 3 yrs to 5 yrs. The critical thing is "DARK SKIES". If your skies are dark enough you can see quite a bit of detail in many DSO's including Galaxies, Nebula, Clusters and Planetaries.

In regard to Alex's comments I have quoted above regarding observing using the drift method, I wanted to expand on that.

Let me say that probably well in excess of 50% of dob owners observe using their dobs in this fashion. I am not one of them and I never will be.

This graph on the Televue Website shows how the spotsize increases as you move off axis in some common F-ratio reflectors.

I think many people who observe in this manner are not aware (or don't care) about the image degradation and reduced limiting magnitude that occurs at and near the edge of the field of view in Newtonians with an F ratio faster than about F5.5 due to comatic blur. In a 10" F5 Newtonian using a fairly standard 12mm eyepiece the field of view is only diffraction limited across about the inner 40%. Whilst the view at and near the edge of field is not horrendous, it is not diffraction limited and it is blatantly obvious to most observers that it is not quite as sharp as the view in the centre of the FOV. What is important however is that due to the increased spot size (from 10 microns at 30% to 30 microns near the edge) and the fact the light is spread over a larger area and thus diffused, the ability to see dimmer targets and features near the edge of the field is much less than it is near the centre. This is easy to test. Find a dim star that is on the verge of visibility in the centre of the FOV, push it to near the edge of the FOV and it will more than likely not be visible if you have in fact chosen a star on the verge of visibility in the centre of the FOV. HN40 the multiple star complex at the centre of M20 (Triffid nebula) is a good target to test this on in with a 10" scope. In a decent 10" scope under good seeing conditions and dark skies you should be able to see the A,B,C and D stars in HN40. Push them to near the edge and you will not get D.

I recommend spending some time tinkering with your scope to get good smooth movement with both the altitude and azimuth bearings, then spending the time learning to hand track at high powers. Whilst 3 of my 4 Newtonians have a servocat fitted (one of them doesn't) I can still hand track every single one of my scopes at 500X plus. Most 10" Newtonians will be flat out getting to 500x. If this is the way you want to go there are lots of things you can do to the bearings to get the scope tracking smoothly and just for the record putting armour all or beeswax on one or all of the bearing surfaces isn't how you do it. Plenty of on line articles on re doing the bearing surfaces with ebony star laminate and virgin Teflon bearings. I spent a bit of time working on my 10" GSO dob to get it to track nicely, but it now tracks as well as any premium built dob. I put extra bracing on the base so that it couldn't flex outwards, used ebony star and virgin Teflon on all the bearing surfaces and actually shimmed all the sides of the bearing surfaces with virgin Teflon. If your 1/2 handy as a woodworker you could even build a new base and if you used the right design paramaters (read larger altitude bearings for starters) you could build a scope base that hand tracks beautifully at 500X plus.

Cheers,
John B

[dreamstation (James)]

Originally Posted by ausastronomer

Plenty of on line articles on re doing the bearing surfaces with ebony star laminate and virgin Teflon bearings. I spent a bit of time working on my 10" GSO dob to get it to track nicely, but it now tracks as well as any premium built dob. I put extra bracing on the base so that it couldn't flex outwards, used ebony star and virgin Teflon on all the bearing surfaces and actually shimmed all the sides of the bearing surfaces with virgin Teflon.

Getting the true "ebony star" at least in my experience was damn near impossible. The local kitchen and cabinet makers said it was discontinued and there were no offcuts at all around where I live. I was given some other textured laminate which I've since made a ring out of but haven't finished putting it back together to test yet. I have a feeling it's not going to be that great though so I may end up trying the lazy susan method. Probably not ideal but if I can't get a good enough ebony star replacement I have no other option.

[mental4astro (Alexander)]

Ebony Star is available. I get it directly from the importer here in Sydney and requires a minimum purchase amount of a full sheet at a time. Wilson Craft makes it, but the supply of it is small here in Oz as the dimpled style of the material is not considered fashionable. Laminex and Formica made similar products, and these were discontinued a few years ago.

[Crushellon (Tim)]

Thanks for all the great replies guys I think I will end up going with a manual mount. I like the idea of the digital setting circles and modifying the mount for smooth movement will be easy enough for me, as I am an engineering tradesperson. I think that if I am going to spend the extra money I would spend it on a larger aperture (I think it will be hard to resist getting the 12" model but you have to draw a line somewhere for my first scope I suppose...)

[Atmos (Colin)]

Originally Posted by Crushellon

Thanks for all the great replies guys I think I will end up going with a manual mount. I like the idea of the digital setting circles and modifying the mount for smooth movement will be easy enough for me, as I am an engineering tradesperson. I think that if I am going to spend the extra money I would spend it on a larger aperture (I think it will be hard to resist getting the 12" model but you have to draw a line somewhere for my first scope I suppose...)

Why stop there when you can go straight for the GSO 16"

[dreamstation (James)]

Originally Posted by mental4astro

Ebony Star is available. I get it directly from the importer here in Sydney and requires a minimum purchase amount of a full sheet at a time. Wilson Craft makes it, but the supply of it is small here in Oz as the dimpled style of the material is not considered fashionable. Laminex and Formica made similar products, and these were discontinued a few years ago.

So you are still able to get the original 4552-50 ebony star then? I was told by more than one shop here that it was discontinued. I was able to get 4552-90 though which from my understanding is no good. Will see how the stuff I have turns out first but if it's no good, do you offer pieces for sale to fellow members? Thanks.

I apologise for derailing the thread Tim, I should have taken it to private messages. Hope you can forgive us!

[mental4astro (Alexander)]

James, I don't want to hijack this thread into a discussion of Ebony Star, and I should have been a little more cautious about this. My apology Tim.

But I need to clarify the situation now that is up.

Ebony Star CAME in two textures, as you pointed out James. 4552-50 is the more textured one, 4552-90 is not as textured. BOTH work, though 4552-50 has been preferred for scope bearings. The textured laminates that were produced by Laminex and Formica were also recommended, and again if 4552-50 was not available, these were considered close to equal to 4552-90.

Now, 4552-50 has not being in production for close to ten years (from my understanding). The textured laminates by Formica and Laminex were also discontinued soon after. The ONLY textured laminate that is still produced is by Wilsoart, and of the textured laminates they produce, 4552-90 is still the most highly textured, and it is still more textured than the laminates produced by Formica and Laminex.

HOW GOOD IS THE REMAINING EBONY STAR 4552-90?

Best way I have is to give my own personal scope building experience.

In the first scope I built, I used Ebony Star on the az. bearing. As it happened, it was 4552-50. I did not know any better of the texture differences 20 years ago, but the piece I got did surprise me at how textured it was. But for the altitude bearing I used an iron-on laminate that was no where as textured. Both axis also use Teflon pads. The scope works beautifully (I still have this scope, and it happens to also be a 10" dob). The scope was designed to follow John Dobson's principles of large diameter bearings, a balanced OTA and careful material selection. When the bearing surfaces are clean and waxed, I cannot say I notice a difference in the action of both axis.

Scopes I have built since that instrument (and prior to starting Gondwana Telescopes), I have used a few different laminates on the bearings, none of which was Ebony Star of either type. What they all had in common was a textured surface. The action of all these scopes is not just governed by the laminate. Bearing design is also a major part of the action. All these scopes I have built all work very smoothly in their action. I have had many experienced dob users exclaim to me how lovely the action of these instruments is, all far better than mass production instruments. Remember, I had not used Ebony Star with these scopes, only laminates that were as textured as I could get my hands on.

When I started Gondwana Telescopes, I knew that the type of laminate I used would be judged upon, wrongly or rightly. What I always wanted to offer is the best materials I could offer. My sourcing of Ebony Star led me to situation as I understand it now on textured laminates. So as things stand for my production capacity, 4552-90 is the only textured laminate that is still available. Is it any good? Please ask anyone who has handled my scopes. Better still if you can handle them yourself to judge for yourself. Jason, I will be at Astrofest over the second weekend of its running. I will have there three Gondwana scopes, two of which have Ebony Star 4552-90, the other scope has a non-Ebony Star textured laminate. You, and everyone else too for that matter, are always welcome to come and have a feel of the action of these instruments. It is the only way you can actually understand what a dobsonian scope can actually feel like.

Laminate quality is only one part of the dob equation. Above this actually is bearing design! Design the bearings properly, and work with the centre of gravity of the OTA, and as long as the laminate is textured and you keep it clean and waxed, it will work like a charm.

~x.X.x~

Yes, I can supply fellow scope builders with Ebony Star. I can also cut to size. Price depends on the size sought as this also affects packing (a strip can be coiled, a sheet needs to be sent flat and padded) and postage.

I will need to address this in a more formal way in IIS, probably as an article, shortly. I will speak to the Iceman about this.

Again, Tim, my apology for the hijacking of your thread.

[Crushellon (Tim)]

So after discussions with my wife, we decided to go with a Goto... Lol. She wants her and the kids to be able to view things as well and I think they might have trouble with tracking as they are very young. Might have to keep my eye out for a second hand one I think.

[JoelyE95 (Joel)]

Tim,

Friday and Saturday nights, a group of us hang out in Mt Gravatt. There are usually at least 3 of us there with 10" dobs showing the public. At the moment, we can pull a few things out in the city (Carina before it sets, Blue Planetary, maybe Lagoon and Trifid Nebulas), but the others are more "dark sky" objects to see without filters.

If you are free, PM me and I can give you some details if you want to come along and get some advice and time on a scope to get a feel for it.

Joel

[SkyWatch (Dean)]

Originally Posted by Crushellon

So after discussions with my wife, we decided to go with a Goto... Lol. She wants her and the kids to be able to view things as well and I think they might have trouble with tracking as they are very young. Might have to keep my eye out for a second hand one I think.

Hi Tim, and welcome! Lots of good advice here already, and a 10" dob is a really nice scope to see all sorts of objects. A 12" isn't that much of a jump in terms of what you can see- so when you develop aperture fever you will probably want to go to 16" or above to make a real difference!
Just a couple of comments: I show children the sky all the time, and you are right, a stable tracking scope is a great idea, especially if your wife is on board with it! Very young children have a lot of trouble looking through an eyepiece, so don't expect too much if they are under about 6.
With regard to filters: I support "Mental" in his comment about colour filters for planets. I have tried several, and very rarely use them.
I do find that a "deep sky" broadband filter is great in the city for emission nebulae in particular, and even helps a bit with galaxies as it gets rid of some of the light pollution, darkens the background sky and doesn't remove the stars in the same way a narrowband filter does. If you want to go down the filter route, make sure you look through a range of them first- perhaps with your local astronomy club.

All the best with your search for a scope.

- Dean