What's a good dob for viewing?

[gregbradley]

I'd like to hear suggestions about a good dob for visual work.

I was thinking around the 12 inch size, that is portable and not super heavy, easy to setup, ideally go -to or some easy to use finding device.

I don't know where you get them from except the GSO/Skywatcher/Bintel types. How are they?

I know APO refractors well and CDK and compound scopes. SCTs.

SCTs are very convenient except for dew on the objective.

APO's give very pleasing views but limited in aperture and brightness so more wider views.

Some older reviews stick in my mind praising optics like Zambuto etc.

I don't see these exotic brands up for sale in the classifieds. Do people mostly hold on to them?

Greg.

[m11 (Mel)]

Hi Greg,

In terms of the scopes from a personal point of view, I have found the Skywatchers pretty consistent and the view is pretty good. I have used all three and I think the bang for buck you get for the Skywatcher is pretty good. I know you mentioned weight but a goto versions I view through of a 12inch and two 14inch were good.

I have 11" CPC SCT now on JMI wheeley bar to make it easier to move but I still need to be careful with it. I am no expect on SCTs but I do use them for planetary and eaa shots which work out well.

In terms of a APO - speaking to a few owners and having used some refractors - I use them for a session when I don't have much time or energy. They don't replace my larger scopes and if I go country its the largest dobsonian I can transport.

In terms of premium mirrors and scopes - its really a personal choice as to what you want to spend on this hobby. Zambuto is definitely the standard for mirrors and then you need a structure to put it in. Carl has mentioned on his website that there is now a 18 month wait for a mirror. Just be prepared for a lengthy wait and to factor that in.

Alot of these scopes are customised and treasured by the owners including myself and I don't think I would be selling any of my premium scopes, it would be my kids doing that

Take what I say from my perspective and it maybe bias.

Hope it helps,

Mel

[Hans Tucker (Hans)]

Originally Posted by gregbradley

I'd like to hear suggestions about a good dob for visual work.

I was thinking around the 12 inch size, that is portable and not super heavy, easy to setup, ideally go -to or some easy to use finding device.

I don't know where you get them from except the GSO/Skywatcher/Bintel types. How are they?

I know APO refractors well and CDK and compound scopes. SCTs.

SCTs are very convenient except for dew on the objective.

APO's give very pleasing views but limited in aperture and brightness so more wider views.

Some older reviews stick in my mind praising optics like Zambuto etc.

I don't see these exotic brands up for sale in the classifieds. Do people mostly hold on to them?

Greg.

They hold on to SDM's ... for good reason.

http://www.sdmtelescopes.com.au/

I think SDM uses Zambuto primary mirrors

[m11 (Mel)]

Originally Posted by Hans Tucker

They hold on to SDM's ... for good reason.

http://www.sdmtelescopes.com.au/

I think SDM uses Zambuto primary mirrors

Hey Hans,

You can pick pretty much any mirror you want with SDM (Pete).

Obviously Zambuto is the preferred choice for scopes 20inch and under and f/4 and above. You do pay alot more for f/4 as compared to f/4.5 which is his standard and quartz if you want it.

[wavelandscott (Scott)]

How serious do you want to be in your visual exercise?

A 10 inch dob is a glorious thing and could last you a lifetime. Once the aperture bug bites it is hard to resist. While certainly the bigger the mirror the deeper you can go, this can be offset by effort to use (with a bigger scope). Best size is the one you will use.

I loved my 8 inch until I got my 12.5 inch which I adored until the 15 inch arrived. I would love to go bigger but as I age I prefer to keep my feet on the ground so the 15 is likely as big as I will go.

Regardless of which size dob you get, save some money for (or get ready to build) an adjustable height chair…it is a thing I use every time I observe. It truly adds more to my viewing pleasure and capability than a high end eyepiece.

[rustigsmed (Russell)]

Hi Greg,

I have a 12"skywatcher goto dobsonian, I would recommend if you aren't going for an exotic option. Excellent value for money, I also have a 12" GSO f4 for imaging, while not a dobsonian, the build quality in the skywatcher is light years ahead. I also do my planetary imaging through the dob - they can track pretty well if you are level even for long FL planetary (I add a 5x televue).

I also assisted a friend setup his 8" version of the same SW and that too was giving surprising detail on Jupiter.

Cheers

Russell

[mura_gadi (Steve)]

Hello,

I'd be looking at your weight as the guiding limit, depending on that you can sort out your size to budget.

There is a huge difference between an ultra light 16" and an SW 16" in regards to weight, an UL 16" will weigh less than the OTA of the SW 16".

Just about all of the light weight dob's will have someone recommending after market changes though. Same for the SW if you want to pimp your scope...

The 16" was my cut off for size, mainly as I read that at some stage you get no real visible gain in aperture in light polluted areas past 16". Not having a permanent dark site or frequent access to one it made sense to look at 16" or less. (That also means that I can dismiss aperture fever in my backyard viewing, which was very appealing)

I saw a Hubble 16" at $2400 in Melbourne a few months ago, but couldn't get to it. So, ultra lights do come up but very rarely.

I'd look at the weight first, you want the biggest scope possible your going to look at and say "yeah I want to move that". The easier that is to say the more you'll use the Dob anyway...



Steve
Ps. There are after market kits for SW/Light bridges etc that look pretty schmick and cut a lot of weight out from the original designs. _ don't have the 16" yet, but that was my thinking on the Dob I want.

The point of a Dob is to be a light bucket, so, get the biggest light bucket you can move and use easily.

[Merlin66 (Ken)]

Greg,
Having used many Dobbies over the years I found, as do many others, that the 10" f5 (or thereabout) is a "sweet spot" - large enough to give light collection and resolution but still small enough to be moved and handled.
Certainly a great starting point.

[m11 (Mel)]

Originally Posted by Hans Tucker

Please don't, it wasn't intended to be sarcastic, apologies if it came across that way. There was an extensive list of Dobs in your signature block and not just SDM's so who better to ask but a Dobson owner.

Hi Hans,

All good, its hard to decipher tone and intention, I wasn't sure.

You are welcome to come and view through any of the scopes if you want, I see you are in Melbourne.

My long term plan was to collect and grab enough equipment to allow others to view without spending anything to view the night sky and hopefully give them a lifelong experience . A number of my 12" dobs I have lent out with no timeframe for return to allow others to view without needing to spend.

[astro744]

Highly recommend SDM Telescopes as Peter is a great guy to deal with. I don’t own one but was close once. Get the works in whatever size your comfortable with and your set.

Other than that I can think of a similar US offering at Obsession Telescopes. They have standard truss Dobs as well as ultra compact ones.

See https://www.obsessiontelescopes.com/

If you don’t want the ServoCAT you can get a quality EQ platform at

http://www.equatorialplatforms.com/

However I highly recommend you go to a few star parties first to see what size telescope you are comfortable with. (Covid rules allowing of course).

[mura_gadi (Steve)]

Orion in the UK will supply mirrors finished to varying levels, professional, research and ultra...

https://www.orionoptics.co.uk/produc...scope-mirrors/

Another good point, is chair/steps and ladders, consider the eyepiece height at close to zenith.

Depends on the pockets, but I'd say get a location system over a goto system and save some money if your not tracking planets. DSO's stay in field for ages and need little nudging.

[Startrek (Martin)]

Greg,
I’ve had my Skywatcher 12” Goto dob for 3 years now and it’s located down at my retirement getaway on the South Coast
It’s stored in the garage and I use a parcel trolley with a piece of packing foam and adjustable belt to transport it out to my car bay area next to the driveway ( about 12m away ) Very easy to move around on the parcel trolley (I’m 61 years old, light framed 70kgs with a history of lower back issues since I was in my late 20’s , regular Chiro and morning exercises keeps my lower back in check )
As far as Goto accuracy , its accuracy is dependent upon your initial set up and sky conditions but in most cases the object ends up in the FOV of most eye pieces, sometimes very close to centre.It has encoders so it remembers its position in the sky.
I added Dew control ( heater bands ) to the stalk of the secondary plus finder-scope and eye pieces if needed , but rarely have to use it
Collimation is really easy , I collimate every time I move it , only takes a few minutes
I use my full compliment of Televue eye pieces which covers DSO and Planetary observing plus Paracorr, Powermates , Lunar filters , planetary filters , UHC filters etc..,
Prior to the 12” Goto I used a 10” GSO dob ( manual nudge ) for about a year until I got sick of finding objects by star hopping around.
On some occasions I have my Nexdome in the backyard up and running , imaging, whilst I’m out the front Observing with the 12” Goto dob
The 12” has enough aperture and focal length ( 1500mm ) under my Bortle 3 skies to experience fantastic views , the 14” would have been too big for me to handle.
Thumbs up for the Skywatcher 12” Goto Dob

Cheers
Martin

[gregbradley]

Some great advice here, thanks to all that have responded so far.

I do have a CDK17 that I have not really used for visual beyond a quick look at home once when collimating it. It really showed up the bad seeing so hard to tell how good it is for visual or not.

Go to sounds handy or the Servo Cat sounds good too if its easy to use.

I did have a Celestron Nex 11 for a few years a long time ago and it was nice and bright but mostly only in a suburban location.

Greg.

[ausastronomer (John Bambury)]

If you don’t want the ServoCAT you can get a quality EQ platform at

http://www.equatorialplatforms.com/

However I highly recommend you go to a few star parties first to see what size telescope you are comfortable with. (Covid rules allowing of course).

In an astronomical world where everyone is going to faster and faster dobs, to reduce eyepiece height to eliminate the need for a ladder, or to allow seated observing, an equatorial platform is counter productive because it raises the height of the scope by quite a bit. You also have to lift the scope onto the platform and also reset it each time it goes through its travel range. Unless it was going to be used for photography (which I doubt, as Greg already has better imaging scopes) I wouldn't even consider an EQ platform. I've used both many times and have had 3 servocat equipped scopes for 15 years. IMO Servocat is a far better option in every respect.

Cheers
John B

[gregbradley]

Originally Posted by ausastronomer

In an astronomical world where everyone is going to faster and faster dobs, to reduce eyepiece height to eliminate the need for a ladder, or to allow seated observing, an equatorial platform is counter productive because it raises the height of the scope by quite a bit. You also have to lift the scope onto the platform and also reset it each time it goes through its travel range. Unless it was going to be used for photography (which I doubt, as Greg already has better imaging scopes) I wouldn't even consider an EQ platform. I've used both many times and have had 3 servocat equipped scopes for 15 years. IMO Servocat is a far better option in every respect.

Cheers
John B

Thanks John.

Good advice.

Greg.

[astro744]

Originally Posted by ausastronomer

In an astronomical world where everyone is going to faster and faster dobs, to reduce eyepiece height to eliminate the need for a ladder, or to allow seated observing, an equatorial platform is counter productive because it raises the height of the scope by quite a bit. You also have to lift the scope onto the platform and also reset it each time it goes through its travel range. Unless it was going to be used for photography (which I doubt, as Greg already has better imaging scopes) I wouldn't even consider an EQ platform. I've used both many times and have had 3 servocat equipped scopes for 15 years. IMO Servocat is a far better option in every respect.

Cheers
John B

ServoCAT is no doubt a better option especially for the large Dobs but the OP mentioned a 12” Dob. Get a quality f4 to f4.5 or perhaps shorter mirror on one of these and the 6” extra height of the platform is welcome especially if you prefer the eyepiece at eye level at zenith. The platform of the EQ mount can become the baseboard of the Dob as a permanent fixture. For a 12” or 14” it’s not a bad option but anything larger then you would want to consider all options carefully.

I consider perfect Dob to be 12.5” designed with focal ratio and EQ platform in mind such that eyepiece is at eye level when the telescope is pointing to zenith when standing up. I prefer to stand and move freely around the telescope from target to target. I personally don’t like GOTO but tracking is nice but I understand some people cannot be without GOTO for whatever reason.

A seat is OK at some angles but definitely not for all and that is the nature of the Dob. Anything low can be awkward standing but anything high just out of reach can be achieved with a $5 folding 8.5” step from Kmart.

[ausastronomer (John Bambury)]

Originally Posted by astro744

ServoCAT is no doubt a better option especially for the large Dobs but the OP mentioned a 12” Dob. Get a quality f4 to f4.5 or perhaps shorter mirror on one of these and the 6” extra height of the platform is welcome especially if you prefer the eyepiece at eye level at zenith. The platform of the EQ mount can become the baseboard of the Dob as a permanent fixture. For a 12” or 14” it’s not a bad option but anything larger then you would want to consider all options carefully.

I consider perfect Dob to be 12.5” designed with focal ratio and EQ platform in mind such that eyepiece is at eye level when the telescope is pointing to zenith when standing up. I prefer to stand and move freely around the telescope from target to target. I personally don’t like GOTO but tracking is nice but I understand some people cannot be without GOTO for whatever reason.

A seat is OK at some angles but definitely not for all and that is the nature of the Dob. Anything low can be awkward standing but anything high just out of reach can be achieved with a $5 folding 8.5” step from Kmart.

I always try to set my observing program for a night so that I am observing targets with reasonable elevation (above 45 deg). Below that, the image quality and light throughput is significantly reduced. Obviously there are a lot of targets that don't get above 45 degrees and you have to observe them down low, but those that I can observe at good altitude I do. A $250 Observing chair has enough height adjustment to allow for 90% targets to be observed seated with a compact dob. I use my 10"/F5.3 mostly seated. A taller person could use a slightly larger dob seated, like a 12"/F5. Observing seated effectively adds 10% to 15% to the aperture of the scope, at a minimum. I don't worry about sitting down if I am out doing a tour of bright globulars or the like, but if I am observing moon, planets, double stars, threshhold galaxies with the 10" scope I always observe seated. Without question, you extract more detail than you can standing.

Another thing to consider is that as the scope gets faster, the depth of focus reduces. This is the range that the image is in focus. With sub F4.5 dobs this is very shallow and in marginal seeing higher power images tend to continually phase in and out of focus. With slower scopes this is something that is a lot less noticeable due to the greater depth of focus. Notwithstanding that the Paracorr II has fixed the coma issue with sub F4 scopes, it hasn't and can't fix the depth of focus issue. This is the specific reason none of my scopes are faster than F4.5. Having observed with just about everything over the past 50 years including 36"/F5, 30"/F4.6, 25"/F5 and a 28"/F3.3; I will climb the ladder and take the 25"/F5 over the 28"/F3.3 every day, for high power work. With the scopes Greg has owned over a long period and the scopes he currently owns, he would probably not not have experienced a scope with very shallow depth of focus. On that basis I think he is better off looking at a 12"/F4.5 to 12"/F5 scope, which without an EQ platform, would be the perfect height to use seated, or standing and slightly bent over.

FWIW all my scopes have Servocat on them, including my 10"/F5.3, and I wouldn't have it any other way.

Cheers
John B

[astro744]

I absolutely agree with not going too fast despite this being the trend but get a master optician to make a quality mirror and the fast speed isn’t really a problem, (Paracorr is mandatory of course). Forgive me John but I thought from your earlier post you were endorsing fast ‘scopes to eliminate ladders yet you are happy to climb up to a 25” f5. Having only ever observed with 20” f5 (comfortably on ladder) I cannot compare with large very short focal ratios and I’d probably go the f5 too but 25” is getting tall at f5. My 16” is f4.5 and that is the fastest I have. My favourite is my 10.1” f6.4 but I do like to use my 6” f5.5 on the Losmandy AZ-8.

I fully understand the depth of focus issue and remember once mentioning it on CN after reading an article by Neil English only to be shot down in flames by ‘experts’ who are always right even when they are not. (I leave them to it now). I ground my 10.1” from a Coulter thing Pyrex blank to f6.3. I was never quite happy with the figure and got Mark Suchting to refigure it although he basically reground it first and it ended up f6.4. I thought that I got the f6.3 recommendation as the perfect f ratio between long and short in ATM (Ingalls) but it could have been another publication.

Anyway to he OP! if you want to enter the Dob world cheaply consider a used 10” f4.7 Skywatcher to see if you like how a Dob operates and make your second or third Dob a premium one if you like what you see. I picked up a Skywatcher 10 f4.7 a few years ago for the kids and it’s a joy to use. A bit low normally for me but put it on an EQ platform and it is perfect.

If you want GOTO or think your not going to enjoy finding objects yourself then don’t even consider a manual Dob and get the GOTO. If you enjoy the hunt or like to work off memory or printed (or electronic, not for me) charts, then get a manual dob. You’ll learn your way around the sky faster that way.

There is nothing wrong with mass produced telescope except less strict quality control to keep costs down, (you cannot expect a mass producer to individually inspect every telescope). In this regard you do get what you pay for with a premium mirror and overall dob package but the difference in price is considerable. Only you can decide if it is worth it.

[gaseous (Patrick)]

Lots of good advice here. The issue John raises about the focus in fast scopes is very interesting too.


If you have a trailer and little to no respect for your lower back, you could lash out and get a 20" dob. I only use mine once a month at a dark site, but once it's cooled the views are phenomenal. If you plan to use it more regularly in the back yard, then something in the 10" - 12" range is probably more feasible. As many others have said, it's whatever you can move/afford which will dictate the scope you get.

[ausastronomer (John Bambury)]

Originally Posted by astro744

Forgive me John but I thought from your earlier post you were endorsing fast ‘scopes to eliminate ladders yet you are happy to climb up to a 25” f5.

I think you read something there that I didn't actually say. My comment related to the general trend over the last 15 years amongst telescope purchasers and telescope makers. To give you some perspective of the trend, only 2 of the first 30 scopes Peter Read built, were faster than F4.5. Of the last 30 scopes Peter has built, only 3 have been slower than F4.5. Of the last 23 scopes he has built only 3 have been slower than F4. I didn't say anywhere that it was my preference, just that this was where just about everyone else was going. My comment related to the fact that just about everyone in the astronomical community was going to faster thus lower scopes, so why would you want to raise the scope several inches by using an EQ platform, as opposed to a Servocat, which also provides GOTO which an EQ platform can't do.

Cheers
John B