Help me choose the best starter Dob

[ptrduffy]

Hi all,

I have been lurking for a while, and reading as much as I can, and now have some questions about getting started with observing.  I am asking for some help in choosing between a few options that I have narrowed down so far.

Background:

• I did a bit of observing many years ago, when I lived in Northern California after being gifted a 70mm Meade (I think) refractor with a GoTo.  The experience was at best okay - finding objects was reasonably easy, but images were not great, and the system was very flimsy (susceptible to wobbles and knocks).
• Fast forward 20+ years and my 16yo daughter has been expressing an interest for a while now in astronomy, and is thinking of pursuing a degree in Physics with Astronomy.  She is interested in a telescope for Christmas.
• I would like to get something that makes it easy to find objects, but is more robust and provides better viewing than my previous experience.
• I know that most responses to this type of query start with "what do you want to view" - but it's difficult to answer this question until you have some idea of what is possible.  If we could get good planetary views, by which I mean see Saturn's rings or Jupiter's cloud bands, then I would be happy with that.  If we would be better going for views of DSOs, then I'd be equally happy with that, just not sure until we know what we know.

Constraints:

• Budget is around £500 - could go a bit higher, would prefer not to.
• We now live back in Glasgow (Scotland) which obviously has more viewing challenges than California (weather and light pollution).
• We are in a ground floor flat with limited storage space, and a shared back garden - but there are numerous parks nearby and I have a car if we need/want to travel to better viewing locations.  This does put a bit of an emphasis on size and portability.
• We also regularly visit family in the rural west of Ireland, which offers more viewing options, but would require the telescope to fit in a family car alongside luggage.

My thoughts so far:

• A Dobsonian reflector seems to be the general recommendation for stability, ease of use and light-gathering
• The Celestron Starsense Explorer range seems to offer a good balance between electronic support and ability to go completely manual
• The Skywatcher GTi range also offers automatic GoTo, with the added option of tracking, and the ability to go manual (if I understand it correctly)

My current list of options:

• I was initially sorely tempted by the Celestron Starsense Explorer 8".  It's a bit beyond my preferred budget, but I could stretch. 
• I was then looking at the same brand 6" tabletop
• And then I was looking at the Skywatcher Heritage 150P GTi

My questions (or at least some of them!):

1. Is the 8" to bulky to store and move easily?  I'm finding it difficult to visualise how much space it would take up in the flat and in the car.
2. Regarding both of the 6" scopes, I would need to sit them on a table or similar, which presumably needs to be fairly solid and level or we lose the benefit of the Dobsonian mount?
3. From what I've been reading I would need 200x magnification to get the planetary views I would like.  I think all of the above scopes are capable of this with additional eyepieces.  The 8" has a much longer focal length than the 6"s (1200mm vs 750mm), meaning I could get this with 5mm eyepieces vs 3mm - does this have any impact in real-world viewing?  (I've read that about 200x is the best that I can expect in UK skies anyway).
4. Related to the above, if I was viewing a planet at 200x how quickly would an object move through the field of view on thes scopes?  And how possible is it to keep up with that without automatic tracking?
5. The 6" Skywatcher is the most compact and portable.  I would be quite happy making a shroud for it, but I notice its focuser also gets a lot of criticism - is this just because it relies on a screw mechanism which takes more effort/time to focus?
6. What am I not thinking about that I should be?

Thanks to all contributors for what I've read here to date, and I'll try to reciprocate with updates on whatever we evebtually go for

 

 

[Spile]

Everything points to an 8” Dobsonian in my opinion and I would recommend the StellaLyra. It will fit comfortably on the back seat of a car including the base.

[Carbon Brush]

A 6" or 8" dob reflector sounds like a good choice.

If you want aperture, but are competing for space (length or height) on the back seat, consider the Skywatcher Flextube scopes.
You have just as bulky base as other dobs, but the tube collapses a little.
I used to own a flextube 250 and was very happy with it holding collimation between outings.

My own take on lifting and carrying a dob is that for 8" you carry the base and tube separately for security.
For 10" the weight starts to show, supporting the decision to carry separately.
Consider fitting a handle on the tube if it doesn't have one.

Keeping an object in the eyepiece is easier if the dob base is well set up. Nice smooth action.
Spend a bit of time adjusting stiffness (springs/locknuts) and maybe lubrication - depending on the base materials.
Alternatively if you spend on expensive eyepieces with a wide field of view, time before nudge is increased.

Many low cost (a relative term) scopes benefit from better tube blackening. Simple flocking works wonders.
The great thing about a simple reflector is that you can improve it for little spend and no great skills needed.

My first 'proper' scope 20 years ago was an 8" reflector on a manual EQ mount. A great scope.
Since then I have always owned reflectors of this sort, sometimes on EQ, sometimes on Alt-az, and dobs.

HTH, David.

[Mr H in Yorkshire]

1 hour ago, Carbon Brush said:

My own take on lifting and carrying a dob is that for 8" you carry the base and tube separately for security.
For 10" the weight starts to show, supporting the decision to carry separately.

My son has a 12", I had to make a dolly, makes hauling the beast much easier. Lifting the OTA and base is possible, even I can do it at 70 (still strong and fairly fit) but it is a struggle limited to a short distance.

[dweller25]

Hell @ptrduffy and welcome to SGL.

The 8” Starsense Dobsonian would be an excellent choice, not too heavy but very capable optically. A 16 year old should have no problems moving it as the main optical tube assembly separates from the base.

Saturns rings, detail within the rings and the major belts on the planet surface will be visible. Jupiter will show a wealth of detail, Mars too not to mention the Moon.

The brighter DSO’s will look good, but fainter ones will look like dull grey smudges.

Also the optical tube assembly can be mounted on a motorised GOTO mount at a later date if you wish.

8” Newtonians are excellent all rounders 👍

 

Edited December 1, 2023 by dweller25

[ptrduffy]

Thanks for all the responses so far - everyone seems to be leaning towards the 8" Dob, which is kind of what I expected.  I think I need to find somewhere nearby to have a look at just how big and heavy this will be.

In the meantime, if I was to go with the 8" Starsense, it has a focal length of 1200mm - should I be looking to add a 6mm eyepiece to get 200x magnification for planetary viewing?

[Ricochet]

I think an 8" dob is a great scope. Reading through the "background" the 8" Celestron Starsense immediately comes to mind but having read further this size of scope may not be the best for your circumstances.

 

On 30/11/2023 at 23:07, ptrduffy said:

We are in a ground floor flat with limited storage space, and a shared back garden - but there are numerous parks nearby and I have a car if we need/want to travel to better viewing locations.  This does put a bit of an emphasis on size and portability.

...

Is the 8" to bulky to store and move easily?  I'm finding it difficult to visualise how much space it would take up in the flat and in the car.

A full size 6/8/10" Dob is best stored assembled on the base, pointing upwards. The circular base board is the widest part and is a bit under 2ft in diameter. You need about an inch clearance between the mirror and inside wall of the OTA so whichever size mirror you go for the OTA will be about 2" wider. The OTA is about 4ft long so adding in the base height and clearance you are going to need a storage space 2ft square and 4.5ft high in your flat. 

In the car I always found that the OTA would fit across all three back seats and would be almost touching the doors either side and so the base went in the boot. This limits you to only being able to drive with yourself and one passenger unless you have enough space to be able to put one or two seats down and have the OTA pointing forwards from the boot into the rear seat space. It is definitely not a scope that will fit in the car for the holidays unless all your other luggage fits in a roof box.

With regards to moving it to your observing locations, as you live in a ground floor flat and don't have to carry it down stairs, it will be suitable to be used from your communal garden. However, how much surrounding buildings obstruct the skies may dictate whether this is a suitable observing location. If your block of flats is a two storey house-height building surrounded by other house-height buildings then it is probably fine, but if these are high rise flats surrounded by other similar buildings then you are probably better off planning to transport your chosen scope elsewhere when possible. An 8" dob is not a scope that I would suggest you can carry down to the local park or take on public transport. You can carry it a short distance from your flat to the car, drive to a location, and then carry it a short distance from the car to the set up spot. In addition to the scope itself you will require a height adjustable chair and probably end up with a case full of eyepieces so taking it to and from the car is at least a two trip process if you're on your own, unless you can devise a way to take it in one trip using a trolley or carrying some items on your back.

On 30/11/2023 at 23:07, ptrduffy said:

Regarding both of the 6" scopes, I would need to sit them on a table or similar, which presumably needs to be fairly solid and level or we lose the benefit of the Dobsonian mount?

You would lose the benefit of the stability, but not the cheapness of the mount. I suspect you would be looking at a way of converting the mount to sit on top of a tripod, or buying a whole new mount, after a few sessions.

On 30/11/2023 at 23:07, ptrduffy said:

From what I've been reading I would need 200x magnification to get the planetary views I would like.  I think all of the above scopes are capable of this with additional eyepieces.  The 8" has a much longer focal length than the 6"s (1200mm vs 750mm), meaning I could get this with 5mm eyepieces vs 3mm - does this have any impact in real-world viewing?  (I've read that about 200x is the best that I can expect in UK skies anyway).

Personally, I would say anything from 150X up is a good ballpark figure to aim for. Two important criteria for planetary performance are aperture (bigger is better) and % secondary obstruction size (smaller is better). The 8" is f6 whilst the 6" is f5 so it is likely that the 8" is better on planets due to both aperture and secondary obstruction. The slightly longer focal ratio also means that the coma free (sharpest) area in the centre of the view is also bigger. When it comes to the eyepieces the f5 scope will be slightly harder for the eyepieces to correct so the image will be slightly worse as you move from the centre to the edge of the field of view.

In terms of 3mm vs 5mm eyepiece if you go for a simple design like a Plossl or Ortho then eye relief is a function of eyepiece focal length and so shorter eyepieces are more difficult to use (so barlowing a longer focal length is more comfortable). If you go for something more complex like the BST Starguider then it's picking up the knowledge that in that particular line the 3.2mm isn't as good an eyepiece as the 5/8/12mm so again barlowing a longer focal length is preferable, but at the top end there is no difference in performance as far as I am aware between the 3 and 5mm Delites.

The 200X limit is again a ballpark and highly dependant on atmospheric conditions on the night. This very much includes the atmosphere inside the telescope and so ensuring any telescope is sufficiently cooled before high power use. Bigger scopes take longer to reach equilibrium and so this could also be a consideration where you're having to take any scope out from your warm flat into the cold night.

On 30/11/2023 at 23:07, ptrduffy said:

Related to the above, if I was viewing a planet at 200x how quickly would an object move through the field of view on thes scopes?  And how possible is it to keep up with that without automatic tracking?

About a minute edge to edge of the field of view. You will probably want to keep it a bit more centred so on an unpowered scope you might want to move it every 30s or so. With a bit of practice and possibly fettling the mount this isn't an issue. I don't even think about it with my 8". Some (tripod based) mounts have slow motion cables which makes tracking easy, and the long flexible cables are good for preventing vibrations being transmitted to the scope (this isn't an issue with dob mounts).

On 30/11/2023 at 23:07, ptrduffy said:

The 6" Skywatcher is the most compact and portable.  I would be quite happy making a shroud for it, but I notice its focuser also gets a lot of criticism - is this just because it relies on a screw mechanism which takes more effort/time to focus?

It isn't the screw mechanism per se. There are some high quality micro focusers that work in a similar way. The issues arise from it being made from plastic and having some play in the threads. PTFE tape is usually used to tighten up the slack and it will be happier with lightweight eyepieces.

16 hours ago, ptrduffy said:

In the meantime, if I was to go with the 8" Starsense, it has a focal length of 1200mm - should I be looking to add a 6mm eyepiece to get 200x magnification for planetary viewing?

You could do, but depending on conditions it might be too much. 5/6/7/8 might all be useful, but if there is only the budget for one I'd probably go for a 7mm.

On 30/11/2023 at 23:07, ptrduffy said:

What am I not thinking about that I should be?

Proper winter clothing. It is so much colder at night so you need more substantial clothing than if you go out during the day.

On 30/11/2023 at 23:07, ptrduffy said:

my 16yo daughter has been expressing an interest for a while now in astronomy, and is thinking of pursuing a degree in Physics with Astronomy.

There are two similar sounding degrees, Physics with Astronomy and Physics with Astrophysics. Astronomy is more what we observe and why whilst Astrophysics is the complex mathematical equations that govern how things work. If choosing the latter being really on top of her game in terms of A level maths and, if possible, Further Maths is going to being to be a massive advantage throughout the whole degree.

[Jules Tohpipi]

To perhaps overly simplify things (rather than getting wrapped up in some of the deeper details).

For visual astronomy only (i.e. putting your own eye to the telescope rather than a camera) then an 8" dob is without doubt a fantastic choice. It gathers lots of light for seeing dimmer objects and has the resolution for great planetary views. In order to find objects quickly - particularly if under city light pollution - then the Celestron StarSense version becomes the self-recommending choice. Otherwise you could lose hours/days finding individual DSOs under light polluted skies - if inexperienced.

So far so good then, job done. Except... it's not exactly a small telescope to store. Nor would it be a first-choice telescope for moving around in a car, especially if other luggage is coming along for the journey. I promised myself I would take my dob out and about but never did. Well once actually and it seemed like too much of an expedition all things considered. And perhaps the worst of it, the vast majority of DSOs will still look like tiny grey smudges even through an 8" dob. I hesitate to use the word disappointing on general DSOs, but only because I've got very very well adjusted expectations of what's possible.

Let me make you aware of a possible alternative path for consideration. My daughter is also interested in astronomy and has just begun the GCSE course. Our main equipment is now focussed around the AZ-GTi mount bearing smaller and lighter telescopes. The first is the Sky-Watcher 127 Mak which offers similar focal length/FOV/magnification as the 8" dob but in a much more compact package - it's great for planetary views, but not so good on dimmer objects. We also have the Sky-Watcher Startravel 102T for the AZ-GTi. This gives good wide-field views at lower magnifications. But here's the rub, with the Startravel 102, I have recently added a camera to it for astrophotography. I use the word 'astrophotography' but what I specifically mean is EAA or EEVA as it's also know as. It's a simpler, cheaper, faster form of astrophotography that yields quick results by using less lengthy exposure times and doesn't require an equatorial mount. The results of which are closer to astronomy internet photos than grey smudges - and so much more than I've ever seen through my 10" dob, and could be much more inspiring as a hobby to a science-orientated young person.  Of course, that full path is slightly more costly but it's a path that can be trodden in stages by adding equipment to the AZ-GTi (rather than replacing equipment). For example, you could just start with either the refractor or the Mak on an AZ-GTi for visual use only at around £500 and build onwards from there if the bug bites. Check out the EEVA sub-forums here to see members posting their own nightly images, made possible by just adding a camera to a tracking GOTO system. Plus it's all easier to store away and transport.

 

Edited December 2, 2023 by Jules Tohpipi

[ptrduffy]

Further thanks to @Ricochet and @Jules Tohpipi for your detailed responses - you both raise some interesting points.

I'm now fairly certain that the 8" Dob is not going to work for us.  The primary issue is that I think we will need to regularly go further afield than the back garden due to visibility from there (thanks to @Ricochet for making me think about this).  Basically, we are at a corner position of two blocks of 4-storey tenements, around 17-20m high.  Due South we are not obstructed by buildings for about 150m; North and East we have buildings within 10m of any viewing point in our back garden; and West we have additional buildings around 20m away.  So South and SW are the only directions where we have reasonably unoibstructed viewing, and even then there are numerous trees around.

So, I think we need something that is relatively easy to transport both by hand to nearby parks (a good number of open spaces within a 10-minute walk) and by car to darker skies (Glasgow University has an observatory site a 20-minute drive away, and I gather a local astronomy club has monthly meet-ups there).

So, I'm now going back into research mode with a better idea of what the priorities are - and I do like @Jules Tohpipi's idea of a GoTo mount that could potentially have an imaging device added at a later date.

[Starfazed]

Had a similar dilemma to you and similar reason for getting a scope. Wow what's possible for £500 now is another universe from what was around in my childhood.

I narrowed down the options to a really big "pure" Dob like 10 inch, a push to like the 8 inch Starsense, or a 6 inch GOTO. 

After trying out some Dobs at a public observatory the two things I realised were 1. I couldn't find a thing up there and the kids would get really frustrated waiting ages for me to find anything. So it's got to be pushto or GOTO. 2. Having found things it was frustrating to find them disappear at high power after less than a minute and search for them again.

Combine that with living in a Bortle 8 city where options are carry everything to the nearest park or drive 40 mins to a decent sky and it became a choice between the Heritage GTI (tabletop 6 inch) or Star Discovery 6(tripod 6 inch ) reflectors. As the former had sold out I got the latter. 

So far (limited by very few clear nights this year) I've been happy enough - I can see the bands of Jupiter at 250x using a cheap 6mm and Barlow. I've seen Uranus and Neptune! But I also know they would have been brighter in a bigger scope and my son is developing aperture fever. But dead easy to carry in two modest bags I found on Amazon, so truly grab and go.

I guess you need to think how you will be using the scope - how transportable it should be, how much work you want to put into finding things manually versus goto, and if you want it to just latch onto and follow whatever you find, especially if most viewing is done under city skies.

My next scope meets all the needs my first scope has highlighted in use and will be a 12 inch Starsense on an equatorial platform, though we'll need to move house to find the space for it. Just don't tell my wife.

[bosun21]

6 minutes ago, Starfazed said:

My next scope meets all the needs my first scope has highlighted in use and will be a 12 inch Starsense on an equatorial platform, though we'll need to move house to find the space for it. Just don't tell my wife.

I'm afraid the largest Starsense is 10".

[Mandy D]

12 minutes ago, bosun21 said:

I'm afraid the largest Starsense is 10".

Yes, but it matters not, as you can transfer the Starsense unit to other telescopes, so can have a 12" Starsense equipped one if you so desire. Many are choosing to buy the cheapest Starsense refractor for this purpose and is something I am considering for my telescopes, which include a 12".

[Starfazed]

1 hour ago, bosun21 said:

I'm afraid the largest Starsense is 10".

Not for much longer, 12 inchers are being advertised:-)

[bosun21]

2 hours ago, Starfazed said:

Not for much longer, 12 inchers are being advertised:-)

That's good news.

[bosun21]

3 hours ago, Mandy D said:

Yes, but it matters not, as you can transfer the Starsense unit to other telescopes, so can have a 12" Starsense equipped one if you so desire. Many are choosing to buy the cheapest Starsense refractor for this purpose and is something I am considering for my telescopes, which include a 12".

That's exactly what I did with my Stella Lyra 12" dobsonian. I bought the Celestron LT70 and transferred the Starsense unit.