Question - Schmidt Cassegrain or Dobsonian?

[yoda776]

If have the opportunity to buy a telescope after saving for a bit. If a person has the money to either buy a Schmidt-Cassegrain (Meade LX200 8" ACF, Celestron 9.25" CPC) or a truss dobsonian (Orion Skyquest XX16g) which would you choose? :question:I have narrowed my focus to these options (or a Celestron CPC 800).

I do not have aperture fever, however the 16" dobsonian is attractive. I am more concerned about owning a telescope I will use, rather than the biggest which may collect dust. My only concern about the Orion dob is it being unwieldy in terms of weight and dimensions (although I know you can break it down to the baseboard if need be for transport). I will be quite frank and say weight is an issue of concern for me. So for instance a Meade LX90 10" or LX200 10" would likely be a little too weighty for me.

I like the idea of larger aperture to view the night sky, but I also like the idea of being able to take images of the night sky. I have had no experience imaging so I am not going to even try to say I want to do this right away. I have however been learning goto and the night sky with my Meade ETX105EC which I do really like. The idea is viewing first and then gradually start looking into imaging ad there is an arm within the astronomy club that looks at this specifically I could talk to later on.

I always assumed you could not take any images through a dobsonian, but have been told by local club members otherwise. I guess this relates to the newer dobsonians that have goto on them, whereas manual movement versions it would not be possible.

If anyone has any comments to choice it would be great to hear from you.:)

[casstony]

I'd advise you to buy the scope you think you might like best second hand, so that you can sell it without losing a lot of value if you change your mind. An 8" computerized SCT is super convenient, a 16" dob gives much brighter images. Portability reduces considerably once you go larger than a 12" truss dob.

I've owned all sorts including a 16" Lightbridge: in the end portability and storage issues led me back to a C11 Edge as the best compromise large scope for my circumstances and preferences but everyone is different.

[The Mekon]

If my 18" dob did not have wheels, I would only use it 1/10th as much. As it does have wheels I find it just as convenient as setting up my 4" refractor. It wheels out the back door of the garage onto the lawn.
So, if you cannot move the 16" easily then get the SCT.

[rrussell1962]

I'm with John B and casstony on this. If my 18 inch dob did not have wheels I cannot imagine how I would move it about. Having said that I expect that some of the newer ultra compacts are a lot lighter. It's easy to forget that lugging equipment about is not only done in the shop, it is often done at 3am on a cold winter night when we are knackered!

[doug mc]

Another thing to consider is what you are mainly interested in viewing. Different horses for different courses. For high power viewing, a motorised eq mount. If deep sky is going to be your thing, then the biggest dob you can handle. On wheels if your home setup allows it. As for me, I have ended up with an eq mounted C8. Just terrific. Moon, planet, double star man.

[Camelopardalis]

If you're interested in starting to get into some imaging sooner rather than later I'd recommend an equatorial mount like an AZ-EQ6 and work from there. You could load it up with a C11 or fast 10" newt (at least) or just your camera and lens for wide field.

I'm probably going to get flamed for saying this, but with a few exceptions the (limited number of) objects I've seen through much larger scopes than 10-12" tend to be erm underwhelming given the additional cost, size, weight, etc that they entail, especially if you mostly observe from the city. Maybe I live a sheltered life :shrug:

[Amaranthus]

Dunk, I tend to agree. Especially if you start imaging, and realise that a 30sec to 1min exposure with a CCD through an 80mm apo already shows waaaay more detail than a 'live eye' through an 18" Dob...:rundog:

[yoda776]

That is a good point and usually the dark site I go to is a paddock / field that I can drive on and drop the scope right out of the back of the car. mind you I do not have a big scope yet - Meade ETX 105EC at the moment.

[yoda776]

Thanks for your input - certainly the sort of answer I can think about. The only thing would be the EQ mount, although a Meade / Celestron can have an wedge for that I guess or would you suggest a different tripod altogether that has an EQ mount?

I think my problem is I like deep sky objects, but I also like the planets as well. Imaging is a thought but I think that will be later, so probably not so much a consideration unless a scope has that as a package secondhand.

Wheels has come up a lot for moving a dob so will look in that. I have seen a 16" and I think an 18" dob at the club nights and they seemed ok, disassembling a truss dob and packing into a small car. Plus when you break up a truss dob the weight is also broken down into more manageable chunks. I just found the Schmidt Cassegrains essentially have been telescope tube and tripod is the main breakup of the package and that is why going to a 10" Schmidt-Cassegrain is not really an option in terms of overall weight. That is a consideration for the Schmidt-Cassegrain and the dob I am looking at. Love to be able to buy both but can only afford one!

[yoda776]

Yes I can agree from helping my friend with his 10" Schmidt-Cassegrain (SC). It did impress because I have a 4" scope however having seen a dob that I can break down show more. The 10" SC my friend has just cost a lot, can be bulky to handle and lift the tube and fork mount up on to the tripod and was quite heavy to move.

I will have a look at the newt options and the eq mount options. Thanks.

[yoda776]

I have considered that and content with viewing at the moment. If imaging I would be going an APO refractor most likely - I agree. Thanks for you comments. So viewing tends to be more in favour of a dob for DSOs at this point it seems.

[yoda776]

Certainly a good point about secondhand. Have given that some thought and have my eye on a couple of secondhand scopes that have a lot of extras and selling for less than the cost of a new one. Certainly worth a thought. Thanks for the input.

I guess by portability above a 12" truss dob you mean weight and dimensions to fit in your storage location and / or your car. Any other issues with portability for a large dob?

A SCT 8" or 9.25" in a Celestron would be my SCT choices. An 11" might be stretching the budget and the weight side of things for me.

[rrussell1962]

Hi Matt, my experience with my truss tube dob is that the single difficulty with portability relates to the weight of the mirror box including the primary mirror. All the other parts break down to a few kg each. Most of the weight in a large dob will be in the mirror. I bought a couple of cheap ramps to avoid having to lift the mirror box. Set up time, including collimation, is less than 10 minutes.

[Camelopardalis]

A mass produced Dob is winner for aperture for $ no contest, but be sure it is what you want. The lines between visual astronomy and imaging have been somewhat blurred in recent years by video astronomy, which enables you to see much fainter stuff with much less telescope.

Regarding the weight of SCTs...if your mate has a Meade LX then it includes the weight of the fork mount and motors which are necessary but increase the weight by quite a bit over the tube itself. I use a Celestron C11 for visual and the tube itself is 13kg, which is lifted onto an equatorial mount. The equivalent Celestron CPC tube + fork is 29kg! A wedge on a LX or CPC only adds more weight...

I still wouldn't use one as a FIRST choice for anything other than planetary imaging due to the longer focal lengths. A small doublet or apo refractor is an inexpensive place to start imaging if you already have an equatorial mount, as I have been learning this year ;)

[rustigsmed]

i have a goto 12" dob and love it - so would easily recommend one.
I've also had a dabble in astrophotography with it ..
i personally wouldn't get a cassegrain simply from a FL perspective i do enjoy having the ability to go 'wide' with the dob and powermating up for planets.


here is a couple of links to some deep space pics I've taken:

https://www.flickr.com/photos/80336656@N07/14167021549/in/photostream/lightbox/

https://www.flickr.com/photos/80336656@N07/14167104588/in/photostream/lightbox/

https://www.flickr.com/photos/80336656@N07/9672645018/in/photostream/lightbox/

https://www.flickr.com/photos/80336656@N07/8260374701/in/photostream/lightbox/

best of luck

rusty

[sn1987a]

No dob is too big, photograph by iphone

[Xtjohn]

WOW! These are taken with your goto dob? Could you please give a few details on how to achieve shots like this? When the time arrives to buy a scope I'm fairly certain It will be a goto dob and would love to be able to get a shot or two of this quality.
Thanks.

[yoda776]

I have noticed the weight can be an issue with the mirror box. Thanks for the comments and confirming about the weight break down which really helps. Certainly on the orion skyquest XX16g I found some specs on the weight of different components (not sure how reliable the figures are as I cannot find too many places that give weights and dimensions). this is what I have on the weights and dimensions (sorry in pounds and inches but can convert in google easily enough):

Assembled weight (including accessories): 195 lbs. Assembled optical tube, 68" long, 69 lbs., including six counterweights, 1.25" eyepiece, and EZ Finder II. Bottom tube section without counterweights: 49.7 lbs. Upper tube section without accessories: 11.4 lbs. Truss pole assemblies: 7.9 lbs. Counterweights (9 x 2.2 lbs): 19.8 lbs. Base groundplate assembly: 61.4 lbs. Base left side panel: 26.4 lbs. Base right side panel: 12.3 lbs. Base front panel: 4.8 lbs. Assembled base dimensions: diameter 33.25", height 32.5". EZ finder and 2" DeepView 28mm eyepiece: 1.0 lbs.

I saw a video from the rep here - https://www.youtube.com/watch?v=iHqSN3uMjvg and found some others by people that own them and one even showed how quickly they can assemble the dob - a little over 11 minutes while talking to people as well. I am leaning towards a dob by the looks of it.

[Poita]

For deep sky, find someone with a video astronomy setup. It might convert you.
You can use a little ED80 and see amazing detail *and colour* in effectively realtime. I love viewing this way, the setup is ultra portable and you really get great views, for a pretty low investment cost.

As for SCTs, I loved my C8, had it for over 20 years, and regretted selling it when it finally went. I found it to be very portable, and had many a night of planetary viewing with it.

If I was starting out again, I'd probably go a C8, forget the Edge or Meade ACF, the difference in views in minimal over the standard C8, and an ED80 piggybacked with a video astronomy setup.
Get planetary and high mag views, and full colour deep sky in a portable setup.

[yoda776]

I have to agree with xtjohn on this in saying well done on those photos, they are brilliant. That pretty much helps me into buying a dob with goto. Thank you, sometimes we all need a little push in a direction ;)

May I ask the astrophotography set up (what equipment) you used?

[yoda776]

Thank you I will keep that in mind for my next telescope. Thinking of ED80 or similar. Might check out video astronomy as that sounds intriguing in what you can view and achieve.

[yoda776]

Well my limit is 16" and I think I am going to get one of those judging by forum posts in general and I am pretty impressed with the:) reviews of the scope I am looking to grab.

[yoda776]

Thanks for the advice. I will look into video astronomy but believe with research and everything I have seen and heard I will go with a dob. If I wish to go down the path of something else, I will just need to save.

I made the mistake of saying at a club meet I will only grab one telescope ... they all laughed and said we have all heard that before ... from ourselves and we each have at 5 telescopes each! :P well, I have my Meade ETX105EC, which I need to fix with an issue it has with tracking and will go for the dob. Good balance I think and if imaging is really going to be something I wish to pursue I will consider the APO refractor and investigate the video astronomy route. Appreciate everyone's comments as they have all been helpful to arrive to a decision.

:thanx: Everyone

[rrussell1962]

Matt, I've had a quick look at the specs on the Optcorp website and the weights they quote for the Orion 16 inch GoTo are: Tube 89.8lbs, Mount 105lbs, Total weight 195lbs. These tie into the weights you gave as follows

Upper Tube 11.4, Truss 7.9 Weights 19.8 Bottom tube assembly 49.7, Eyepiece etc 1 gives Total 89.8lbs.

Left side of mount 26.4 (I assume with alt motor and encoder), Right side 12.3, Front 4.8 Bottom (I assume with motor and encoder) 61.4 gives Total 104.9 lbs.

I gather the telescope is assembled in situ, so if you assemble it in full each time you use it the heaviest items you will lift about are the bottom tube assembly 49.7 lbs = 22.6kg and the baseboard assembly 61.4lbs = 27.9kg.

[rustigsmed]

Hi, thanks john, yes those shots were taken with my goto dob. if you click on the top right of the picture there is a arrow thingy it will 'zoom out' and have some details of each individual photo. my 'general rule' was 20 seconds subs at iso 3200. 25 seconds is doable even 30 in some instances but I just obtained more consistent results at 20 seconds. after 25/30 seconds field rotation is introduced. I would also take darks, process in DSS and photoshop and that was it. I call it the 'lazy man's astrophotography' as you don't need a laptop, polar alignment etc. I have been meaning to write up an article for this website on imaging deep sky on an alt-azimuth mount. I'm sure someone with a cooled camera or perhaps something like the sony a7s could do way better than what Ive squeezed from the dob.



hi, thanks very much :) equipment wise, it was a 12" skywatcher goto dob, a canon 600d and a MPCC (coma corrector).

I will add that while you can definitely get nice deep sky results on a goto dob it is limited to the brighter deep sky objects.

personally I've more recently purchased an EQ8 and 12" f4 newt for my imaging rig but still bust out the dob often for planetary (slightly more focal length) and of course visual use. I think having an imaging rig doing its thing in the back ground while visually on a goto dob complements each other perfectly.

the goto dob however, is really an undervalued all-rounder as it has the aperture for good planetary (viewing and capture), can dabble in some deep space and is awesome for visual. :thumbsup:

[Xtjohn]

Thank you for the photographic info Russell. They are beautiful shots! I don't intend to go heavily into astro photography but knowing that shots such as yours are possible through a goto dob with a dslr has certainly pushed me further towards a 12" unit (just have to get my house built first).
And Matt, sorry to muscle in on your thread!

[yoda776]

No worries. Just thought to let everyone know I went with the Orion XX16g and is currently on order. So when some clear skies decide to turn up will be going for a test drive. Imaging for me will be a away off. Just do not have the funds (now :P) but will need to save up in the future. My wife has indicated telescopes will not take over the house (apart from the two I have) ... so I guess the backyard is not off limits :lol: Shed may be incoming at some stage ...

On another note the Pentax 10x50 whitetails I got from the US were a great buy approximately $50 US + postage. Was amazing to view through them and see stars I had not seen with the naked eye.

[sn1987a]

http://www.astro-video.com/ I've got a Mark III on order but you can start cheaper $99 US for the Mark I, they look alright.

[rustigsmed]

no worries best of luck John and congrats on the purchase matt, you won't be disappointed with that scope! 'shed' ... observatory same same :D