[Mountain_Wanderer]

OK, after much research I find myself stuck with the decision on what dobsonian I should buy.

I've narrowed it down to 4 choices:

- Skywatcher 8 inch black diamond collapsible

- Skywatcher 8 inch solid tube

- Skywatcher 10 inch black diamond collapsible

- Skywatcher 10 inch solid tube

I'm a completely new beginner and so this will be my first scope. I require ease of transport, which means I favour the collapsible version which shrinks the length a little bit to make it easier to cart around in the car. It would be interesting to know how much the collapsible versions shrink by if someone has one.

I also am leaning towards observational astronomy and not astrophotography. A solid tube version would allow a potential upgrade onto an equatorial mount in the future if I ever get into astrophotography, but I think that for now observational astronomy will be my interest.

Both the 8 and 10 inch versions have 1200mm focal lengths. In terms of aperature, a 10 inch gathers twice as much light than an 8 inch. However, if I'm only to use it for observational astronomy and not astrophotography, would a 10 inch actually deliver much more benefit? Do deep sky objects in both scopes just appear as white whisps and no colour? I know that 8 inch dobs can deliver some great views so perhaps an 8 inch is more appropriate, particularly also because it is lighter in weight and less bulky for ease of transport.

Just comparing the 10 inch collapsible to the 10 inch solid tube, I notice that the collapsible has a focal ratio of F/4.7 compared to the solid tube version of F/5. I've heard anything below 5 can be a problem for the occurance of coma. Does anyone have a 10 inch collapsible version and is the focal ratio a problem? I also notice the highest practical power is 508x in the 10 inch collapsible compared to 600x in the solid tube version. Why the drop? Can this be overcome by the choice of eyepiece?

Now looking at the 8 inch, I notice that the focal ratio of F/6 is the same in the collapsible and the solid tube versions. But, the highest practical power is 406x in the collapsible and 480x in the solid tube version. Is this a concern? Can the issue be fixed with an appropriate choice of eyepiece?

Looking at the 8 and 10 inch collapsible versions, it seems to me that they're not quite up to the same quality as the equivalent solid tube versions. Yes, a 10 inch collapsible would be great for light collection, but does the focal ratio (F/4.7) screw up the optics? Therefore would an 8 inch collapsible with a better forcal ratio (F/6) be more appropriate?

Hope someone can help me here?

Cheers
Jowel