200p or 250px?

[spike95609]

Having spent an enjoyable six months learning to navigate my way across the night sky with a pair of 15x70 Helios Apollo's, I'm looking at buying my first scope and am stuck between the Skywatcher 200p and 250px dobs. I'll be using them to look at planets and just about anything else really, but my main interest is DSO's, above all galaxies and the many of them scattered across my Sky & Telescope's Pocket Sky Atlas which my binos don't have enough power to detect. The consensus seems to be that bigger is better for DSO's, which is fine because I'm going to spend any money at all I'd rather spend a bit extra and get something I'm satisfied with rather than save a few pennies and always feel like I cheated myself. 10" is the limit though, the financial leap to a 12" is a bit beyond me.

I'm a little confused about how much of an impact light pollution has on the issue though. I don't see myself going to a dark sky site very much at all, almost all my observing will be done from my not dreadfully light polluted semi-rural back garden. Under these conditions will I still see enough benefit from the extra two inches to justify the cost?

Also entering the debate is the question of an F/5.9 vs an F/4.7 scope, and all the implications this has for collimation problems and quality eyepieces. Although whatever choice I make, good eyepieces will follow in time - Televue's are probably a bit beyond my reach unless the plossls are good enough, mostly I'm looking at something in the range of the ES82s.

Overall I get the impression that the 8" is a good deal less hassle, but I'll go with the 10" if it gives a noticeably better view.

[Grotemobile]

I have gone from a C11 to a

CPC 800.I get a lot more use

out of this.No way would i go

back.A lot of people will tell you

to go as big as possible.The 8"

is a good size scope.You wont

notice a lot of difference.I would

pay around £80-£100 for a good

EP.Hope this helps a bit.

Steve.  

[ronin]

If it is faint objects that are primary then really the 10" is the one to consider. However the 10" will be a bit more "hassle". It is bigger and so a bit less easy to move (will say 10" seems not exactly big if you get a tape). The faster scope will cause a bit more work - collimation will be important, however should really be a case of check and adjust.

You will need good eyepieces for a f/4.7, TV plossls are rated down to f/4 - however people seem to want a physically big eyepiece in a big scope and TV plossl's don't deliver that impact. An f/4.7 will require a coma corrector, so add that cost in.

As a "cost guide" you will likely spend 2x or 3x on eyepieces (and eyepiece bits lkike the CC) then the cost of the scope.

If you think this is wrong then consider 5 nice eyepieces for the scope and then add the cost of them up.

If you had the will power then get thew BST Starguiders (all 6) and stick with them, however the lure of a nice green band is high, very high.

Need to be honest and ask yourself if you will easily ahd regularily take a 10" up and use it.

If you use it 1/3 the occasions of an 8" then get the smaller and use it more often.

Will a 10" show in reality more then the 8"? That small, faint, grey NGC galaxy in the 8" is not going to fill the eyepiece in the 10" and sparkle in assorted colours.

[Paul73]

You'll be happy with the 8". However, If you can store and easily carry the 10" to your viewing site. Then 10" is the only way to go.

Saving for reasons of portability, storage and £££, you will never ever hear a member of the Dobnosenti say "big Dob or little Dob? I'll take the little one please"!

As big as is easily practical is the key.

Paul

[Reeny]

The 250 will be a better scope, but I got myself the 8-inch 200p for the lighter size and weight.

Plus points =

- I can carry it outside on my own, in one piece (it is a perfect grab and go).

- the base is only 52cm wide = so it can stand in the corner of a room / and fit in the motorhome door

- The next step up to a bigger 12" or 14" scope will be achievable and worthwhile (10"-12" = not worth it)

Negative points = 

- you always wonder what if I had more aperture (faint galaxies like the Triangulum are slightly harder to find with the 8", but do-able)

- you are still going to need good optics around 200x magnification = expensive eyepieces (as mentioned above, they will be 3x cost of scope)

I bought my 8" scope because there were more pluses than minuses.

I suggest that you go to see both models side by side and decide what is right for you (bigger normally = better).

Pick them up to assess the weight, and judge the size for storage and transport logistics (a manageable size is a "must have").

Then choose the best compromise for your situation.

[Reeny]

PS - if you are considering the 250px for £530

You may also want to consider the ES 12-inch truss for £710, and go bigger/ better again (F5 scope).

http://www.explorescientific.co.uk/en/Telescope-optics/Explore-Scientific-Ultra-Light-Dobsonian-305mm.html?cur=1〈=1

[John]

If deep sky is where your interest lies then aperture really does matter and you will want as much as you can get. The focal ratio difference does create some issues for collimation and eyepiece choice but these can be dealt with.

Light pollution will affect scopes of all apertures but won't stop a 10" showing DSO's a bit better than an 8" under the same conditions.

Your back garden sounds like mine with regard to light pollution but my 12" dob still gives some great DSO views if I select the targets with some care and observe them when they are optimally placed.

I have owned the Skywatcher dobs in both the 8" and 10" sizes and they are both very good scopes for the outlay involved.

[swamp thing]

First off you can't really go wrong with either if I'm honest.

Both the 8"and the 10" skyliners are great scopes and both will serve anyone well for many years.

As it's your first scope I'd go with the 8" myself, I believe it's an easier scope to live with than it's slightly bigger cousin.

[Earl]

i have a 250 and its at my limit for managability the 300 is huge and there is no way i could move it unasisted.

Also the 250 fits through a door way with ease 300 is a squeeze bigger is impossible.

200 everything it that one level easier.

[estwing]

whichever you choose.....astro buy and sell is the way forward/second-hand.

[Paul73]

Also consider flex tube versions which make storage a bit easier. Mine lurks in the corner of my study until needed.

Paul

[Schorhr]

How about a 10" with f/5 instead of f/4.7?

That will make a difference if you choose to observe with cheap eyepieces at first.

Light pollution always plays a role, and a portable 8" may show more then a 10" right next to street lights or such. But at the same location, the 10" will show more, also on planets.

The 8" f/6 have the benefit of even working well with cheap eyepieces (18-30£ erfle).

Can you see the milky way from your location?

I live at the edge of a city and it's a bit faint, but there. And deepsky observations are possible.

Of course even bright DSO will vanish in light pollution;

http://www.perezmedia.net/beltofvenus/archives/001459.html

Faint galaxies might not even show at all.

Of course with a larger aperture you can magnify a bit higher, what can help with small DSO contrast as the exit pupil will be the same as the smaller telescope but the object area larger.

Deepsky really benefits from aperture ( http://clarkvision.com/visastro/m51-apert/ ) but I actually bought a 5" after getting my 10" to have a grab-and-go telescope that fits into a backpack. But then, I have no back yard :-)

[spike95609]

Thanks for all the replies, I've read them all twice (and will no doubt do so a few more times) as I like to ram as much information into my head as possible before I make a decision, especially where money is concerned! As I was writing out the question the thought did go through my head, and I think it's borne out by the replies, that there is no bad choice to be made here. It's just a case of weighing up the pros and cons of both and deciding which fits me best. This is something I'm going to have a long think about. Fortunately I know someone who owns a 200p dob, so I'm hopeful of having a good go on it whenever we can arrange a meet up and that should answer a lot of my questions. I do see myself leaning more towards the convenience end of the astronomy scale, which is why I like binoculars so much because it takes all of three minutes to set up my tripod and start flying around the sky.

No I can't see the milky way with the naked eye, and my eyesight is very good. I live about 3 miles outside Wolverhampton, the surrounding area is a little rural but the village I live in is very large and I think that makes the skies worse than they should be.

Thanks again for all the help!