So, I'm a beginner too..
I settled for something smaller, a mak127 goto.
Very small, light, easy to use , easy to setup,
seems to get some good views.
The 6" would've been nicer but pricey here in Aus.
A 6" Newt seemed similar in views,
so for pure bucks, an 8" eq mount newt or
as I was told a 8" dob.
But I wanted the goto n something smallish.
The other day I visited a telescope store and compared the sizes of an 8 inch and a 10 inch SkyWatcher dobsonian. They both seem to have similar lengths, although the 10 inch is a little more wider/bulky. That aperature for the 10 inch looks really inviting. I guess it would bring in twice as much light at an 8 inch? That would be amazing!
I'd say that in terms of length both scopes are similar in the area needed in a car to move them around. Also, the weight is similar. 8 inch has 20kg, whilst 10 inch is 25 kg. Interesting. Would there be much of a difference in the effort required to move around a 10 inch compared to an 8 inch? Perhaps not much if you had a good little trolley? The main requirement may be the heavy lifting.
The main difference is price. 10 inch seems to be 200-300 buck more in price. Maybe I should consider saving up more dosh going for it???
I notice that on a 10 inch the focal length (1200) is the same as on an 8 inch. Is that bad or good?
Hi Jowel, just coming in with my 2 centavos, the 8 brings in 64 sq. in. the 10 brings in 100 sq. in.. Certainly a noticeable difference but is it worth the extra money? your choice.
The f/l of @ 1200 is pretty much the standard for the 8 / 10.
Now here comes my 2 centavos worth... I own an 8" LB and I am very happy with the performance. I would undoubtedly be just as happy with the 10 or a 12.5 or an 18 but I have the 8 and I am happy.
Unless you are one of the very few who hit upon just the right scope for their niche first time, you are going to buy another scope down the road. So I would suggest to you that the 8 is a great place to start but then again so would be the 10.
Brian
The other day I visited a telescope store and compared the sizes of an 8 inch and a 10 inch SkyWatcher dobsonian.
The 10" gathers about 56% more light than the 8", I think you are correct about their portability being fairly similar, though that depends a lot on the individual lifting the scope, will the salesman let you test lift them in the shop . If the price per square inch seems fair, and you are happy to pay extra for it, it's probably a good idea to go for the 10".
The differences in focal length won't mean a lot in practice (at least to most people) The 8" would be f6 and the 10" f5. This means that for any given eyepiece the magnification would be a bit higher on the 8" scope, but the brightness would be lower. The scopes probably come with eyepieces to match their focal lengths.
The 10" gathers about 56% more light than the 8", I think you are correct about their portability being fairly similar, though that depends a lot on the individual lifting the scope, will the salesman let you test lift them in the shop . If the price per square inch seems fair, and you are happy to pay extra for it, it's probably a good idea to go for the 10".
The differences in focal length won't mean a lot in practice (at least to most people) The 8" would be f6 and the 10" f5. This means that for any given eyepiece the magnification would be a bit higher on the 8" scope, but the brightness would be lower. The scopes probably come with eyepieces to match their focal lengths.
Apologies if i have this wrong, but the magnification from the eyepieces on both scopes will be the same, as :
Magnification = Focal Length / eyepiece (mm)
As they both have a Focal Length of 1200mm Mag remains the same
The speed will be different (F Ratio)
As the 8" has a 200mm mirror 1200/200 = F6
The 10" has a 250mm mirror 1200/250 = F5
Both 1200mm FL scopes would have the same magnification factor on any given eyepiece. The F5 MAY be brighter than the F6 but it would be hard to pick at the eyepiece.
Woops your right, I crossed that up. Sorry for the confusion.
I have been doing numbers for a 10" f5 vs. a 12" f5 lately and my brain cross-wired the results.
Unless you are one of the very few who hit upon just the right scope for their niche first time, you are going to buy another scope down the road. So I would suggest to you that the 8 is a great place to start but then again so would be the 10.
Brian
Brian has hit the nail on the head here. Well said.
Go the 10" dob Jowel! The 10" should keep you happier for longer!
Though having said that, whether you have a 6" (which I used to have), 8", or 10", you won't be disappointed, you will see plenty. A few people that I know of on here upgraded from 8" to 10". I upgraded from 6" to 10" within 6 months. An example in the difference going up to 10" would be say, the Jewel box cluster. The gold star in it is much more noticeable in the 10". I was nearly going to go for an 8", and I very much wanted to see the colour in this star (as I could barely make it out in 6"). When I viewed thru a 10" it was in your face there bright as can be. So next was to see what it was like through an 8". Liz did me a favour at one of her club get togethers. Side by side her old 8" dob she sold and her current 10". She reported back to me there was a big difference in the colour of this star, and told me I should go for the 10". And so this is the scope that will be with me for a long time (I have maxed out weight, size and bulk, for me to handle).
Jowel, I put wheels on my 10" dob. Four wheels attached to a base under the base of the stand. I pull the dob along using the tension handle on the stand. I have two large wheels and two smaller castor wheels which are lockable. Way easier than having to get the trolley out and loading the scope up on it everytime I wanted to change my viewing spot in the yard.
I was just wondering, comparing a 10 inch to an 8 inch, would there be a need for any other accessories for a 10 inch on top of the ones I've already identified I'd need for an 8 inch? For instance, does the mirror in a 10 inch fog up more than an 8 inch? Would I need a fan or something? Any other tips?
Just been thinking of possibly choosing a SkyWatcher black diamond 10 inch collapsible dobsonian. The main drawcard is that the long lenth, which I think is about 1.2-1.3m can be shrunk down considerably for transport and storage.
Does anyone have one of these? Can you tell me how long it is when it's open and also when its closed? Would be great to know how small it can get? I also notice that the highest practical power (508x) is less than the solid tube version (600x), and the focal ratio (F/4.7) is also less than the solid tube version (F/5). Is there are reason for this? Also, does this SkyWatcher collapsible dob come in a standard, non-black diamond version? Or is "black diamond" the code word for collapsible? i.e. are there different types of SkyWatcher collapsibles or is there just one model?
Ofcourse, the main drawback is that I can't attach it to an equatorial mount later in life for astrophotography. It's quite a big decision to make here - do I stick purely with observational astronomy, or do I allow also for astrophotography? As I see it, observational astronomy is astronomy in its purest form, the way it's been done for thousands of years where you see and wonder at the marvels in the sky. Whilst astrophotography, if you get into it, may actually corrupt the observational experience. i.e. astrophotography would take focus away from the experience of observing, and instead focus yourself on getting a good photo and fiddling much more with your equipment. Is that sort of correct? Would be good to hear from people on each side of this question.
Thanks
Last edited by Mountain_Wanderer; 11-09-2010 at 03:27 PM.
You will notice more coma in an f5 or lower ratio Newtonian than in an f6 system although it is still present in all. Most users can live with the coma at f6 but most users use a Paracorr at f4.5 to f5. f5 is the fence where some users fall one way and others the other with regards to whether the coma is objectionable or not. An f5 system too requires better corrected eyepieces than an f6 system although the difference is more noticeable from say f5 to f8.
With regards to better corrected eyepieces even Tele Vue (highly corrected and tested to f4) will show coma as it is a function of the primary mirror not the eyepiece. What they wont show is astigmatism which poorly corrected eyepieces are masters of. In fact seeing coma alone with no astigmatism is almost pleasing (until you put in a Paracorr and stars are pinpoint to the edge!).
You will notice more coma in an f5 or lower ratio Newtonian than in an f6 system although it is still present in all. Most users can live with the coma at f6 but most users use a Paracorr at f4.5 to f5. f5 is the fence where some users fall one way and others the other with regards to whether the coma is objectionable or not. An f5 system too requires better corrected eyepieces than an f6 system although the difference is more noticeable from say f5 to f8.
With regards to better corrected eyepieces even Tele Vue (highly corrected and tested to f4) will show coma as it is a function of the primary mirror not the eyepiece. What they wont show is astigmatism which poorly corrected eyepieces are masters of. In fact seeing coma alone with no astigmatism is almost pleasing (until you put in a Paracorr and stars are pinpoint to the edge!).
Thanks. Interesting stuff about coma. Would F/4.7 be acceptable? Providing the mirrors are quality (which I gather they are), and the scope is well collimated (which I'll have to check and make correct every time I use the scope), then is it fair to say that F/4.7 is something you can get away with, without the need for additional devices? From the reviews I've read, the 10 inch skywatcher collapsible dob is well regarded.
I have the 12" LB with a argo and have ordered to servo cat to add to the argo and I feel this is a great scope to learn on. It has good power and a solid base to start from. It can start to have some complication, that I feel adds to the experience. My humble opinion.
Hi Jowel. the scope on my buggy fits in my car! a friend sent me the photo of the 10" on an eq6.
Go to a club night first, it will stop your head going round and round!
Andy.
I too had difficulty choosing between the 8" and 10" SW collapsible. I overcame this by upping the stakes to the 12" SW collapsible (F5 too), but this morning I awoke to the beckoning of a 14" SW collapsible, so hang it all, I've now settled on a 16" SW collapsible. Fortunately, I don't think they come in any bigger sizes. Hope this helps.
Bern
. If the price per square inch seems fair, and you are happy to pay extra for it, it's probably a good idea to go for the 10".
