Questions about a Dobsonian...

[Tom25]

I've had my first telescope (Nexstar 4SE) for about a year now but I'm saving up a much bigger one - I'm looking at a 12" Dob - possibly the Orion XT12i. Ive been reading up on these for a couple of weeks now and I just have a couple of questions...

My 4SE has a Goto function which tracks the sky and a variable-speed motor which allows for fine-positioning. I know most Dobs aren't motorised but from what I've read (unless I'm missing something), most don't have fine-positioning knobs either, meaning they have to be 'pushed' into place. I would imagine this makes fine-positioning and tracking very difficult, especially at higher magnifications (500x or more for planets for example) although I haven't read anyone complaining about it on forums/reviews etc, so is this the case?

Lastly, my budget is around £1200. Would my money be better invested in a larger aperture telescope  instead of an intelliscope with a computer? I have enough car-space for a larger scope but bear in mind I have only a years' experience and have yet to properly find many DSOs (most are too faint for my 4SE)

Thanks for your help

Tom

[Owmuchonomy]

There are plenty of Goto Dobs.  I used to own one, the SW 300P Flextube.  It was more than capable of finding the object of your choice and also then tracking it and fine adjustment is via the handset.  Just a note on your expectations of magnification.  Under our skies and with a 12" or less scope you are unlikely to get good views at anywhere approaching 500x.  More achievable is about 260 maybe a bit more in my view.  Also, the major and favourite planetary targets are poorly placed for the next few years.

[alanjgreen]

With a dob you ideally need wide angle eyepieces, this combined with the shorter focal length (when compared to an SCT) means that you would be viewing a big piece of sky.

as the previous poster says, usually magnification in the 90-200 range is useable in U.K. Skies.

if you buy eyepieces giving 100 degree views in these low to mid magnifications you will be able to hold an object in view for a few minutes while you do nothing, just stand there and let the object drift across the view.

you are buying a 12 inch scope for its light gathering power rather than huge magnifications. It is this extra light that makes more objects visible

[John]

I find that manually tracking at 300x or more quite possible with my 12" dob. I do use wide angle eyepieces which help and I've been doing it for a while so I have a "feel" for the scope and how it moves which helps but this is soon acquired.

The seeing conditions are the final arbiter on what power is useful be but on suitable targets I find 250x frequently used.

 

[D4N]

So the XT12i is a push-to dob, it has encoders and can tell you where to point it but won't track on its own.

It is priced very similarly to the SW250P goto dob which at under £1000 is still within your budget but obviously smaller aperture.

I don't think there is anything bigger than 12" that will fit your budget, the 350P is just outside of it.

 

Personally I got a goto dob for the tracking, the goto bit is nice but it was the tracking that made me want it.  I tried it manually when I first got it and found the moon went past pretty fast at high magnification, at lower magnifications it is fine though and wide angle eyepieces are really nice in it.

 

[ronin]

You can get a goto dobsonian but the standard dobsonian was as you say a push/pull system where you pointed it at the desired object. Simply you find it, you center it, you track it. Couple of aspects is that it is a learnt skill, so do not head off the first night and expect to get everything, or maybe get anything. But iot should come in time. Guess at 2 to 4 weeks of learning.

Being honest some never get it, simply not everyone can do everything. You also really need to have a fair idea of where things are and I would say need to have a bit of a plan. You could simply select from the handset menu of a goto, but dobsonian = no handset unless goto.

I see you mention Intelliscope, that is the Orion. It sits sort of half way. It will direct you on how to find something but is not (as far as I am aware) a goto. This means to the prejusice that it is more costly then a manual, and does not have the features of a goto. Or is it more features then a manual and less cost then a goto. Interesting arguement.

Forget magnification, you are collecting light to enable the fainter things become more apparent. If magnification is the over riding aspect then a 925CPC is likely a better option.

[Paul73]

Don't worry about the tracking. I spent weeks trying to work out how I could modify my 10" dob to track. Now it doesn't cross my mind. Manual tracking is easy with good eyepieces.

Paul

 

[Tom25]

Thanks for the replies!

I have read somewhere on a review of a 12" that it was being used at magnifications of 500 and greater so I naively assumed this was the norm... I'm more interested now in viewing DSOs than planets anyway - and my 4SE performs poorly with these.

Will i need to invest in very high quality eyepieces for a 12"? And would a ~£30 eyepiece generally be considered high quality? Or will I end up spending much more? (I know this is a vague question, im just searching for a price range)

thanks

[Timebandit]

20 minutes ago, Tom25 said:

Thanks for the replies!

I have read somewhere on a review of a 12" that it was being used at magnifications of 500 and greater so I naively assumed this was the norm... I'm more interested now in viewing DSOs than planets anyway - and my 4SE performs poorly with these.

Will i need to invest in very high quality eyepieces for a 12"? And would a ~£30 eyepiece generally be considered high quality? Or will I end up spending much more? (I know this is a vague question, im just searching for a price range)

thanks

 

Hi. Magnification is limited by aperture and seeing conditions in the main. In the states with the big dobs 20" + and there great seeing conditions then very high magnifications are within the realms of easily possible. I have on occasions pushed between 400+ In this country on very good atmosphere conditions with viewing lunar , so it is possible.

With eyepiece. In my opinion there is no point getting a quality 12" dob and then putting in cheap poor quality eyepieces. The scope is 50% of the set up and the eyepieces the other 50% ( we will leave atmosphere, dark site conditions out of this equation for the moment). But eyepieces can make all the difference. Also with faster scopes at f/ 4 , F/5 the quality of the eyepieces are more important. As fast scopes really test eyepieces and therefore the eyepieces that can handle fast scopes are more than often more expensive. You then have wide field , long eyerelief eyepieces again more money. But do not be tempted to look through an ethos or you may get hooked on big expensive eyepieces?.  A scope at around f/5 will work well with some Explore scientific 82 d eyepieces, or William optics uwan or skywatcher Nirvana, these eyepieces are quality and will work well without busting the bank with televues when you are starting out.

I hope you like the above and it helps☺

[Phil Fargaze]

I have been more than happy with my 10" `push to` dob over the years. It is the 10" Orion Intelliscope, and with a good wide field eyepiece it provides a decent amount

of time before a deep sky object will drift out of view. I used the stock supplied ep`s for a long while but when I invested in a 24mm Nagler and a Meade 8.8 ultra wide angle ep

it really made a huge difference. The Nagler is great with galaxies, whilst the 8.8 does a good job on smaller objects such as planetary nebula. However these ep`s and similar others might not come cheap, but once you have the scope, you can always upgrade the eye pieces as and when the budget allows.

[Charic]

Nudging, pushing,  moving the scope on a basic dobsonian  becomes  intuitive with  a little  practice. I can pickup and track any satellite that moves through my field of view with ease.

For DSO's  a good aperture, low power, and a  wide field of view eyepiece and NO terrestrial lighting helps big time! If the light pollution is an issue, consider the size of your dobsonian, should you need to travel to get the best/better results.

I use my aperture as my  guide to magnification. 200 = 200x  with  6mm EP. The image gets smaller but sharper at half the aperture,  giving 100x  from a 12mm EP but going the other way, less than 6mm the image degrades the more maginification I use  on the smaller targets, but its  fine for my Moon craters, where I can use my 3.2mm!

I have three Delos EP's for my 12" ( its  a virtual 12" at present? the EP's  arrived before the scope! but like you. I thought I was going to upgrade?  but  seems like I'll be staying with the  8" scope for much longer ) but I would just try the  new scope with the eyepieces you already have.  A coma corrector is maybe all you need, if coma becomes an issue!

[brantuk]

31 minutes ago, Tom25 said:

would a ~£30 eyepiece generally be considered high quality?

The type of eyepieces being described as high quality start at over £150. Top quality ones are over £300 second hand - just to give you some idea. But you have to be quite experienced to appreciate the differences, which are less and more subtle the more you spend.

You can still achieve a lot though once you go over £50 per eyepiece - you start to get significantly better pieces where the difference from supplied eyepieces is highly noticeable. The good news is that you really don't need much more than three or four good quality eyepieces for most types of viewing.

[Scooot]

I think you'd really enjoy using a push-to scope, and won't find the lack of tracking an issue.  If I want to track I put my dob on an Equatorial Platform but I only tend to use it if I'm dedicating a session to viewing the moon or planets.

The Orion Xti 12 does seem to be quite big and heavy, 37kg according to the spec, whereas by way of comparison an Orion Optics 12" is only about 28kg, (and with these you can carry the mount & OTA separately). So You might want to look at an XTi in the flesh so to speak to check you're OK with its size before committing?  

[laudropb]

You soon become proficient in manual tracking of objects, but I do also use an equatorial platform. This keeps a target in view for about 1/2 an hour and I find this very helpful when sketching the Moon etc.

[Charic]

2 hours ago, Tom25 said:

would a ~£30 eyepiece generally be considered high quality?

1 hour ago, brantuk said:

you have to be quite experienced to appreciate the differences

High quality is dependent  on materials, branding and pricing,  but also in the eye of the beholder!

I believe my  Revelations, are of  high quality? one of them was less than £9 if I recall. Their not made of exotic materials, they just work and very well too.  I've  tried other premium Plössl eyepieces  but found the Revelations to have the  extended focal length  in the range that suited my requirement, they actually feel more comfortable, are extremely affordable,  so great value,  high quality, all on an f/6 scope with my old eyes?

I know from a better site, I may  see things differently/critically if I looked properly  ( or not-eyes!)  through the Delos in comparison to my  Starguiders,  but like  brantuk mentions..........I may need more experience/time to assess!
At present my  preference are still for. the  Starguiders

[niallk]

2 hours ago, Scooot said:

I think you'd really enjoy using a push-to scope, and won't find the lack of tracking an issue.  If I want to track I put my dob on an Equatorial Platform but I only tend to use it if I'm dedicating a session to viewing the moon or planets.

The Orion Xti 12 does seem to be quite big and heavy, 37kg according to the spec, whereas by way of comparison an Orion Optics 12" is only about 28kg, (and with these you can carry the mount & OTA separately). So You might want to look at an XTi in the flesh so to speak to check you're OK with its size before committing?  

As Scooot says, tracking can be achieved with a platform.  This is the route I took too.

Push-To is also the route I took: as a later user add-on.

I just mention this as you could invest in good optics and mechanics (rigid but portable aperture), then build on it over time.  This might allow one or two good EPs to start with, plus a great scope within the budget - particularly for ease of use if you travel to dark skies

250x to 380x represents the typical mag I use on planets, and on planetary nebulae. Often lower mags are used on many different types of DSOs.

[brantuk]

Charic's quite correct - just occasionally you can stumble across a combination of telescope and dirt cheap eyepiece that just seem to gel and produce amazingly high quality views. Same with barlows - the Tal 2x and Orion Shorty Plus are incredible performers for the price (under £40).

A good sign to look for in an eyepiece is to see how close to the edge the stars stay sharp and pinpoint with no obvious warping - this can be anywhere from 50% to 95% of the view - the lower the percentage the more you have to move the scope to keep the object central and sharp. Another good general guide is - the lower the scope f-ratio - the more you have to spend to achieve good quality views across more area of the eyepiece - low cost eyepieces mostly just don't cut the mustard.

Then you get the 100 degree and more eyepieces - you can easily blow £500 on a new one of those lol - but it's like looking round the corner and still seeing a perfect view. I've often had a shoot out during a session with a buddy between two scopes or two eyepieces - it's fun and you learn a lot about how to compare and discover differences.

[Tom25]

I guess I've never had a good enough scope to worry about high quality EPs. I hadn't really considered the cost of them in my budget... but from what you guys are saying I'd be a fool to blow loads of cash on a high tech scope and service it with cheap EPs.

This in mind, ive been doing a little more research into non-computerised Dobs and spending the extra cash on EPs. I've found the 12" Revelation @ £550 which has good reviews but is considerably cheaper than other brands of 12" Dob (seem to average around £700), which makes me wary... is this a good scope? Or have you guys got any suggestions?

[faulksy]

high power viewing of around 400x+ is easy with a dob, you will get used to it and love it.

best bet in my opinion is keep your money and wait for a second hand orion optics uk dob. they are so light and small compared to others on the market. there was one for sale on ebay

also check astronomy buy and sell

[Timebandit]

1 hour ago, Tom25 said:

I guess I've never had a good enough scope to worry about high quality EPs. I hadn't really considered the cost of them in my budget... but from what you guys are saying I'd be a fool to blow loads of cash on a high tech scope and service it with cheap EPs.

This in mind, ive been doing a little more research into non-computerised Dobs and spending the extra cash on EPs. I've found the 12" Revelation @ £550 which has good reviews but is considerably cheaper than other brands of 12" Dob (seem to average around £700), which makes me wary... is this a good scope? Or have you guys got any suggestions?

 

1 hour ago, faulksy said:

high power viewing of around 400x+ is easy with a dob, you will get used to it and love it.

best bet in my opinion is keep your money and wait for a second hand orion optics uk dob. they are so light and small compared to others on the market. there was one for sale on ebay

also check astronomy buy and sell

 

Yes Mike has a good point here about a second hand scopes. You could go for a new revelation telescope at 12" and in all fairness they are supposed to be pretty good in the performance aspect, Mark Beaufort on SGL has one of these and I understand is very happy with it.

But second hand you will get a lot more for your money. The Orion Optics Uk(not to be confused with the standard Orion, with syna mirror) . The OOuk have aluminium tube so are much lighter that it's equivalents made from steel. Also the OOuk have superior mirrors options with up to 1/10pv. The revelation I understand are around 1/4 pv . So a 1/10pv mirror would be far superior in performance (when conditions allow, atmosphere ect) . So you could get a lot more for your money in buying a second hand OOuk scope with superior specs than a new standard scope (so to speak). What I have said about the above is just not theory as this is the route I took and brought a second hand OOuk VX scope and very happy with the bank for buck scope I now own☺ 

[Mark at Beaufort]

Tom as Simon (TImebandit)  mentioned above I have the 12" Revelation which I have used for the past 12 months. I previously had a 10" Skywatcher Flextube Dob and I still own a Orion (UK) VX8 Reflector which is a quality OTA.

I have made several modifications to improve the Revelation - secondary collimation screws, new primary springs, 3 large carrying handles (the photo does not show the one lower down the OTA and 3 lockable wheels (again these are slightly different than the ones shown in the photo).

I have 3 100 degree EPs - 9mm Myraid, 13mm TeleVue Ethos and a 20mm Myraid. I also use a 4.7mm, 6.7mm, 11mm ES82 EPs + a 24mm ES68. This gives me a range of 63X to 323X.

You only need to see my recent observing posts to get an idea of the Revelation performance. As Simon mentioned the advertised wave is 1/4pv although chatting with the guys at Telescope House they believe in some cases it can be higher. I think my primary mirror is pretty good.

I have no problem finding objects and staying with them by simply moving the scope.