10 vs. 12 dob dilemma

[N1 (Mirko)]

Hi all, I am looking to complement my 60mm refractor with a dob. While I love the idea of making one myself one day, I would also like something for this coming winter to set up in OZ that is all ready to go.

I am about to pull the trigger on a GSO dob. The decision needs to be made between the 10 and the 12 inch, both f/5, solid tude. I have not, and probably won't have the opportunity to compare them side-by-side. I like the thought of the 10 being much more portable and car friendly than the 12, but there may be a tradeoff in terms of what they show.

I have read numerous threads and comments on the 10 vs 12 dilemma, most reach the conclusion that "aperture rules", buy the biggest you can afford. I can afford both, they are very reasonably priced. I suspect though that the 10 might be the better package because of its better portability. That may be a greater advantage than the extra detail the 12 would show - which leads me to my question.

I'm a tangible-evidence guy: can anyone name an object or feature that the 12 would show but the 10 wouldn't? That could be some nebular or planetary detail, a colour hue, a faint galaxy using averted vision, anything? I understand the image that the 12 shows is 1.2 times larger than the 10's at the same exit pupil and therefore brightness. That difference appears laughable, a bit like the moon at perigee vs. apogee. I'm a bit lost here.

Thanks

Mirko

[AG Hybrid (Adrian)]

Get the 10". As much as I enjoy my 12" you can pretty much see everything a 12" can in a 10". Just a bit dimmer. You will however notice the size and weight difference. Which is actually quite substantial.
Apart from wide field observing. The 10" will eat your 60mm alive. The 10" is such a substantial size gain in light gathering power its views will amaze you anyway. You don't need the 12".

Your back will thank me when your unloading your 10" from your car.


Some may argue. And they are right of course, that objects with high surface brightness like globular clusters and faint open star clusters resolve better. There's a number globs in Winter sky where this is the case. But, the view in the 10 is still great.

[N1 (Mirko)]

Adrian, thanks for your quick reply. It confirms what I suspected. Yes the difference to the 60mm will be huge in terms of resolution, although I do see the 2 scopes as complementing each other quite nicely. The frac for example shows the Carina Nebula and the Football cluster in one view at ideal exit pupils, or the full Veil complex - those are sights not to be forgotten. Not to mention the airline hand-luggage factor. Luna at average powers may also work better in the smaller scope, because it may simply be too bright in the dob. Anyway - some interesting observing happening soon me thinks.

[michaellxv (Michael)]

I don't know what sort of car you have but if you are getting a solid tube then a 10" will fit across the back seat of an average car a 12" won't.

I currently have a 10" Lightbridge and for me it's the right size to pick up the assembled tube and move around. If/when I go any bigger it would definitely be collapsable not a solid tube.

[N1 (Mirko)]

It's a sedan with collapsible back seats. So putting it across the back seat without further ado sounds great.

[michaellxv (Michael)]

Originally Posted by N1

It's a sedan with collapsible back seats. So putting it across the back seat without further ado sounds great.

Just check how far your doors open. I have a van so it's straight in with no gymnastics .

[The Mekon (John Briggs)]

Get the 10". Ease of setup and carrying is a big part of use. I am continually amazed at what my smaller refractors will show when pushed. You will not see that much more in the 12" if any. For instance a couple of months ago I observed NGC1079 in my 106mm refractor. It was faint but seen nicely between two stars. The next night I used my 18' to check this observation, sure enough the galaxy was brighter and more easily visible, but the thrill of the observation was the main thing. This galaxy is mag 11.3 and seen in a 4" scope. Think what the 10" will do!

[astro_nutt]

Hi Mirko. Yes, do check how far the doors will open. I've made a transport box which measures 1200mm L x 420mm W x 200mm H out of the original packaging but minimized with only about 20mm clearance around the tube. This should give an idea of it's size. Weight wise, carrying the tube is like carrying a 15 kilo bag of spuds around.
The 254mm primary mirror's surface area is 20,546 square mm. This will allow you to see the envelope around Eta Carina, the cloud features on Saturn, the diamond sparkle appearance of Omega Centauri. I hope this helps. Cheers!

[N1 (Mirko)]

Thanks guys, mind is made up. 10" it is.
Great to be able to ask some people who know their stuff.

[Profiler (Profiler)]

I am sure you have considered this for yourself but as a potential compromise to get the best of both worlds why not get a 12' collapsible dob - thus you get the larger aperture and still portable - this is assuming price is not an issue

[N1 (Mirko)]

Yes I have considered a collapsible 12". While the cost of that would probably not be a major, it would mean that other endeavours would have to wait longer. The inexpensive solid tubes from China are a great way around that. Most observing will be done from home and will involve some carrying. Again the solid 10 seems ideal for that.And if it can be put in the car easily for that occasional expedition - all the better. Who knows - I might just end up with a larger dob one day, which is bound to be a truss structure and unlikely to be a 12 if I already have a 10. At this stage I have neither so I´ll just wait & see.

I can also see what The Mekon is saying - a good refractor around 4" to fill the gap would be great too, since I enjoy the lensed tubes immensely. Apos have a way of making you forget their limitations, regardless of aperture. They literally become transparent, placing you out amongst the stars no matter what the power is. But that´s another story...