aperture fever - big scope but no dark sky.

[Moonshane]

Hi all

I am thinking about getting a larger scope and going through all the usual pain and agony about which one to go for.

I have the gear below and live about 3 miles from Stockport and about 9 miles from Manchester - roughly on a line from one to the other. Thankfully Manchester is pretty much due north and Stockport due south so although light pollution is an issue, my garden points almost due east so I get the best views in a 'relatively' unpolluted bit of the sky.

I am delighted with the 120mm refractor I have and bought the 6" newt as a cheapie to see if I could get on with it and collimate etc. I think I have the hang of collimation etc and now I want to go for a bigger scope - maybe a 10" or 12" dob. I think first in line would appear to be a flex tube skywatcher for a number of reasons.

looking around though I see adverts/reviews of larger scopes for sale saying things like 'no good in my light polluted sky now I have moved house' or 'larger scopes suffer more in light polluted skies etc'

although I may travel occasionally to dark sites, the majority of watching will be a quick couple of hours in the back garden.

my query then is this.

will it be worth me getting a larger scope in my circumstances and if so, will a 10" or 12" be better in people's view?

I think the answer to the first bit will always be 'yes?' given more aperture and then even more aperture is always stated as so important, but is this always the case? ....leading me to my second half of the question

Thanks for any guidance offered

Shane

[johnh]

Hello Shane, I have a big scope and 'aperture is King' does really apply to dark sites without LP and good seeing but many have gone for 16" Lightridge even with LP. 2nd hand ones are doing the rounds at £1000-800 - you could try and then sell it if it isn't working and get your money back so look out in buy/sell section .

With LP many use LP filters to get the contrast for nebula cutting out the yellow/orange pollution. If you are not sure 16" or 12" best to buy 2nd hand and try but even in a city the Moon and planets will give good viewing but fainter stuff will be difficult even with a filter.

JohnH.

[brantuk]

The skywatcher flex tubes are great - the 10" is more portable than the 12" which may be more important if you have to go searching for dark skies - also depends on you car - my 12" just fits in a volvo estate when broken in two pieces and a rear seat removed. If you do go that route though get the "auto" version with tracking - it's a godsend.

[oceanheadted]

Is that a V40 or one of the big ones?

cheers

Alan

The skywatcher flex tubes are great - the 10" is more portable than the 12" which may be more important if you have to go searching for dark skies - also depends on you car - my 12" just fits in a volvo estate when broken in two pieces and a rear seat removed. If you do go that route though get the "auto" version with tracking - it's a godsend.

[jimhaleysscomet]

It is a myth that "big scopes are not any good in light pollution".

They may suffer more loss than a dark sky site than a little scope (which rarely shows much of anything either way) BUT aperture always rules and more aperture will show more for any given site. A 10" scope will blow the doors off any 6" scope not matter what the site.

I like the Skywatcher flex tube dobs. They are MUCH easier to transport.

[George Jones]

See

http://stargazerslounge.com/equipment-help/90395-12-inch-wasted-my-sky.html#post1313615.

[kniclander]

It is a myth that "big scopes are not any good in light pollution".

They may suffer more loss than a dark sky site than a little scope (which rarely shows much of anything either way) BUT aperture always rules and more aperture will show more for any given site. A 10" scope will blow the doors off any 6" scope not matter what the site.

I like the Skywatcher flex tube dobs. They are MUCH easier to transport.

I have a 10" and a 6" do and I would be inclined to agree but maybe not quite so enthusiastically. from my Lp'd site I can't see galaxies at all through either scope so one big benefit of aperture is lost. having said that, even at lowish powers, planets and moon and even some double stars are just much nicer in a bigger scope and last week I saw the trap stars E & f very clearly in the 10" which i never did in the 6" .

[George Jones]

I have a 10" and a 6" do and I would be inclined to agree but maybe not quite so enthusiastically. from my Lp'd site I can't see galaxies at all through either scope so one big benefit of aperture is lost. having said that, even at lowish powers, planets and moon and even some double stars are just much nicer in a bigger scope and last week I saw the trap stars E & f very clearly in the 10" which i never did in the 6" .

Yes, too much light pollution and galaxies are lost. Have you tried same-magnification comparisons with other deep sky objects like M42, planetaries (M27, M57, and others), and globulars (M13, M15, M92, and others)? I think that there should be a quite noticeable difference on stuff like this.

[acey]

A bigger scope will show you more, even in a light-polluted environment. But a dark sky is always better.

Increasing aperture by 50% allows you to see roughly 0.9 magnitude fainter (enough for anyone to notice, under any conditions). Increasing by 100% takes you 1.5 mag fainter.

My back garden has limiting mag 4.5, my dark site is mag 6. So an 8-inch at the dark site performs the same as a 16 inch in my back garden. Actually the garden views would be worse because sky contrast is poorer and ambient light prevents dark adaptation. But it gives an idea.

If you can drive somewhere that gives you an extra magnitude of darkness then you've effectively increased your aperture by 50%, like going from a 6" to a 9".

If you're always going to be viewing from your back garden then you might as well get the biggest scope you can afford and hope for the best. Personally, I feel that trying to do visual DSO observing at a site where I can't see the Milky Way naked eye is a bit like trying to go mountaineering in Holland. But that means a long drive every time I observe. I look at galaxies almost exclusively - the faintest I can see - but there are lots of clusters that stand up reasonably well to light pollution, not to mention nebulae where a filter can help.

So I wouldn't worry about whether you'll see more - you will. You should instead worry about ease of set-up, whether you'll feel like lugging it around, etc. I have no trouble taking my 12-inch flextube in the car to my dark-site, and I feel it's just right for me - but for some people it's too much to handle, and that's why you see a lot of them on the second-hand market. It's certainly a lot more effort and bulk than an 8-inch.

[Doc]

I'm one of these guys who have gone for a 16" scope under light polluted skies. Being such a light gatherer does mean you see alot of light pollution affects but you still go much deeper then you would otherwise with a smaller scope.

From a light polluted garden, globulars, open clusters and planetaries will not be a problem, seeing galaxies on the otherhand is very hard due to light pollution.

[acey]

Yes, thinking about it, there's the question of sky contrast in addition to magnitude gain. The figures I quoted are really for stars rather than extended non-stellar objects: i.e. galaxies, nebulae and the sky itself.

If the sky has the same surface brightness as the Milky Way then I guess you're not going to see the Milky Way with any aperture. Magnification does have the effect of darkening the sky background and enhancing contrast, but there has to be a limit.

Presumably you can only see galaxies down to a surface brightness roughly equal to that of the sky itself, as seen through the particular instrument at a given magnification. And for a light-polluted sky that's a pretty low magnitude. Hence you may find that you can only see the bright core of, say, M31, and not the fainter halo, which binoculars will show from a dark site.

That still leaves plenty of clusters and globs to look at, and emission nebulae where a filter does the job of cutting out the sky background.

[fmeireso]

Bigger aperture shows always more,i agree with Doc here and others. The reasoning that anything above 10" or 12" is lightpolluted skies is wasted is a myth..

Of course, get a scope that you can move to dark places. Better a 12" you can move to dark places then a 16" scope grounded in the lightpolluted backyard....

[Moonshane]

thanks so much everyone for your helpful comments and links.

I have decided on a 12" Dob and will try and get one used. anyone suggest a fair price for a solid tube 12" skywatcher? I thought about £300-350?

just need to 1) save some more money! (just spent up on eye pieces and a ED short barlow) 2) find one 3) get in there quick!

[kniclander]

Yes, too much light pollution and galaxies are lost. Have you tried same-magnification comparisons with other deep sky objects like M42, planetaries (M27, M57, and others), and globulars (M13, M15, M92, and others)? I think that there should be a quite noticeable difference on stuff like this.

the biggest difference is globs (where more stars can be resolved and higher mags can be used) and planetaries - the ring through a 6" is never more than a smudge with a hole in it; through the 10 there is a hint of shape, structure and (dare I say...) colour. Polaris, the diference is noticeable because the little blue one is so much brighter

[acey]

The Ring was one of the first things I looked at through my 8-inch, in my light polluted back garden. No filter, and just the generic eyepiece that came with the scope - but I could see the hole easily, and was amazed at how good it looked, having grown up seeing Palomar photos of it and assuming you needed a huge scope to see anything at all.

[Doc]

I agree Andrew the Ring Nebula is an awesome target to observe. A few months ago just for giggles I place the 4 Uwan into the 16" to give me x457, a little unsteady but I was almost inside the Ring Nebula, very strange sight and feeling.

[acey]

I just found this interesting site which has some relevant information:

Aperture versus Light Pollution