What is the biggest sensible aperture for the UK?

[osbourne one-nil]

I'm sure this will have been asked before, so I apologise now; I can't find anything relevant though so...

Considering I live in Cumbria, what is the biggest sensible aperture for general use in the UK? Do seeing conditions ever really allow extra aperture to give the theoretical benefit they're designed to? Right now, my largest scope is a 10" dobsonian with a (apparently) a top-notch mirror so would a 12" or 14" actually ever really be worthwhile?

[Stephen]

As big as you can get There's nothing theoretical (nor dependent on seeing) about a larger aperture. More light grasp is more light grasp

[sbooder]

I would also add that aperture is preferable to magnification.  Remember, whatever is bad about your view will only get worse with more magnification, but the benefit of aperture is more image for less magnification because you get more light.

[ronin]

Whatever diameter that you will use on a regular basis.

Having Mega-Mirror scope is fine but if you do not ever use it then you will see more through a Tasco 60mm that you do use.

If you look carefully you see a lot of big scopes go round and round the for-sale areas.

Is 12" sensible ?

Deepends, if you are 5' 2" of slight build and live with 4 flights of stairs to negotiate then probably not. If 6' 2" build like the proverbial outhouse and live with a dark garden and ground floor storage then likely yes.

Biggest sensible aperture can be different if you re married or not. The words "What the hell is that?" and "You are not keeping that in here!!" make a significant difference on the scope size. :grin:

[Mike73]

You live in Cumbria with some great dark skies so go with the biggest scope you can manage and afford.

[Tinker1947]

The bigger the better......

http://www.obsessiontelescopes.com/

[chiltonstar]

One scope is a poor compromise - get two! One for quick portability and sharp optics (small 'frac or SCT/Mak), and a light bucket for those nights that justify. Comments above about wives apply though, so you might need to build the light bucket into a wheelie bin to disguise it....

Chris

[osbourne one-nil]

Well, wouldn't one of those be lovely. Unfortunately, I was thinking more along the lines of a Lightbridge or Skyliner (not interested in drives or computers) but it would be lovely!

The words "What the hell is that?" and "You are not keeping that in here!!" make a significant difference on the scope size. :grin:

To which I would respond "perhaps you'd like to go back to work now darling?"...and then hide.

This all sounds very promising...I think I've looked at Cloudy Nights too much where people go on about seeing and scope size and benefits. Oh to have some of their desert skies!

[jnb]

There's probably no realistic upper limit. If you are into spectroscopy then sheer light gathering power matters even though your scope's resolution may well exceed any plausible seeing conditions so there is no practical limit. If it's AP then focal ratio matters more than aperture and above 1m focal length you won't get any better resolution (maybe 2m with binning) but even that could justify something like a 16" f4.

The aperture limits are more to do with practicalities than the fact that even a 6" scope will reach the limit of seeing in the UK.

[John]

Last year I moved from a 10" to a 12" as my largest scope. While thats not a big step I can certainly notice the difference in terms of both planetary / lunar detail and contrast and deep sky objects. My back garden has moderate light pollution but the difference is still there. The folks with 14", 16" and 18" scopes seem to see more than my 12" scope does, on deep sky objects at least.

[Mike73]

The Skywatchers/ Lightbridges are great scopes but they are quite big and bulky to move around. About 18 months ago I decided to go for an increase in aperture (I was using a 12") but for me both the Skywatcher and Lightbridge would have been too much hassle, you can add wheel barrow handles but as I've got steps at home and at my local dark site that just wouldn't work.

If you are serious about 14"+ scopes then make sure you see one in the flesh before you buy.

It does look like there are some portable big aperture scopes coming onto the market though (by Skywatcher and possibly ES) so it may be worth waiting to see what they release.

[Naemeth]

I used to think there was a sensible limit for aperture, however, as has been stated previously this is only really for high magnification. For low magnification deep sky observing, aperture is aperture so the only limits are the eyepiece height, what you are willing to carry and/or what you can fit in your car / van to transport it to a dark site .

By the way, I just assumed you were talking about a dobsonian, a large newtonian mounted equatorially would be a beast requiring an incredibly expensive mount and a large refractor, even one with an achromatic lens would be ludicrously expensive - unless someone has a cheap good quality ~20" lens for sale, I wouldn't say no .

[ollypenrice]

There are two reasons for having more aperture and only one of them will be effectively realized in UK skies most of the time.

1) Increased resolution. This is the one that will probably disappoint. Smaller apertures often see through 'cells of bad seeing' better than larger ones and premium quality optics are, in the real world, likely to be found in our amateur hands at smaller apertures. My 140 refractor has far better optics than my 20 inch, though that doesn't have to be the case. It just is!

2) Increased light grasp. This will work for you and make faint things brighter. I must say, though, that when you look at the giant Dobsonians the effect is more startling than the effect when you look through them. Yes, there is a benefit, of course there is, but the reality at the eyepiece is not quite proportional to the astonishing spectacle presented by the scope itself!

Conclusion, big but keep the F ratio fast or your diminshed FOV begins to defeat the object of seeing wider outlying faint stuff around old friends.

Olly

[osbourne one-nil]

But I wonder if the bulk of those models also equates to some added stability? My Sumerian Optics 10" Dob is feather-weight...about 10kg. But it does cause some problems in terms of retaining collimation and coping with heavy eyepieces. I'd even consider a solid tube 14" like Orion Optics make as I do think I'd only be talking about 10yds to pull it out of my old stable onto the driveway. I've seen quite a few in the flesh and they are beasts, but no more so than an equivalent SCT on a mount. I know Green Witch had a large dob set up in their Leeds showroom...maybe it's time for another trip.

I also absolutely love my TV85, but its limitations are very apparent on deep sky stuff and I am only interested in visual astronomy really.

[Naemeth]

But I wonder if the bulk of those models also equates to some added stability? My Sumerian Optics 10" Dob is feather-weight...about 10kg. But it does cause some problems in terms of retaining collimation and coping with heavy eyepieces. I'd even consider a solid tube 14" like Orion Optics make as I do think I'd only be talking about 10yds to pull it out of my old stable onto the driveway. I've seen quite a few in the flesh and they are beasts, but no more so than an equivalent SCT on a mount. I know Green Witch had a large dob set up in their Leeds showroom...maybe it's time for another trip.

I'd see them first. The Skywatcher ones really are pretty heavy when you compare them to their Orion Optics (UK) equivalents. John's 12" F/5.3 OO Dob is around 2.5kg lighter than my 10" dob (both including dobsonian mount).

[osbourne one-nil]

By the way, I just assumed you were talking about a dobsonian, a large newtonian mounted equatorially would be a beast requiring an incredibly expensive mount and a large refractor, even one with an achromatic lens would be ludicrously expensive - unless someone has a cheap good quality ~20" lens for sale, I wouldn't say no .

Good point - and yeah...dobsonian!

[LeeB]

I too have just moved to a 12 from a 10 like an earlier comment and it does make more of a difference than expected. As to weight and portability, the OO tubes are far lighter to move around than other makes. As an example my 10 without rings weighs 6.1kg and 11ishkg with rings , long bar, finder and dove. The 12 weighs just over 15kg with rings etc. While other makes of 12s can be over  25kg with steel tubes. and fittings. What that means for me is the 10 is kept on the eq6 as standard and I can lift it out of the consevatory in one unit (45kg), if I need the 12, I need three trips (Mount, weights(battery) and tube),(only just over 50kg but difficult to control). But still if I only have 30 mins its the dob.

[Mike73]

But I wonder if the bulk of those models also equates to some added stability? My Sumerian Optics 10" Dob is feather-weight...about 10kg. But it does cause some problems in terms of retaining collimation and coping with heavy eyepieces. 

I have the 16" Sumerian Canopus and its steady as a rock, I think the Propus/Alkaids were really aimed at being super light weight and transportable which brings on its own problems as you mention.

[Naemeth]

Good point - and yeah...dobsonian!

That's what I thought .

One of these would be great, but I just need to find a spare £800k, just for the OTA :Envy:

[brantuk]

If budget is no option and portability is important - then you can go large with Sumerian. Beautifully built scopes with large apertures that pack down to a size you can carry like a suitcase. And you can get the missus to carry it lol.

But there's no practical limit other than what the weather allows - large as possible/practical is the way to go with dobs.

I recently got a 16" Lightbridge - it's so heavy I couldn't move it from the garage till I'd done the "wheelbarrow mod". And I had to get ramps to pop it in the car for dark site visits. But the 12" Flextube was much easier to move around by hand cos it breaks down in two main bits.

Hope that helps guage it for you - but yes - do get a look at whatever you buy before you buy - it's sound advice.

[Naemeth]

If budget is no option and portability is important - then you can go large with Sumerian. Beautifully built scopes with large apertures that pack down to a size you can carry like a suitcase. And you can get the missus to carry it lol.

But there's no practical limit other than what the weather allows - large as possible/practical is the way to go with dobs.

I recently got a 16" Lightbridge - it's so heavy I couldn't move it from the garage till I'd done the "wheelbarrow mod". And I had to get ramps to pop it in the car for dark site visits. But the 12" Flextube was much easier to move around by hand cos it breaks down in two main bits.

Hope that helps guage it for you - but yes - do get a look at whatever you buy before you buy - it's sound advice.

+1

One of the major things that put me off the Skywatcher and Meade offerings was the weight of the larger dobs. When I get my big dob it will have to be a very light version, as a big mirror can weigh close to 25kg on it's own - Rich's (crashtestdummy) 22" mirror weighs 22kg.

[osbourne one-nil]

That's what I thought .

One of these would be great, but I just need to find a spare £800k, just for the OTA :Envy:

Does it come with a dual-speed focuser?

[Naemeth]

Does it come with a dual-speed focuser?

Fully customizable, I'd want a Feathertouch if I was ever that rich.

[ollypenrice]

Does it come with a dual-speed focuser?

At 795 grand it wouldn't harm to throw in the Paramount as well...

Olly

[John]

There are two reasons for having more aperture and only one of them will be effectively realized in UK skies most of the time.

1) Increased resolution. This is the one that will probably disappoint. Smaller apertures often see through 'cells of bad seeing' better than larger ones and premium quality optics are, in the real world, likely to be found in our amateur hands at smaller apertures. My 140 refractor has far better optics than my 20 inch, though that doesn't have to be the case. It just is!

2) Increased light grasp. This will work for you and make faint things brighter. I must say, though, that when you look at the giant Dobsonians the effect is more startling than the effect when you look through them. Yes, there is a benefit, of course there is, but the reality at the eyepiece is not quite proportional to the astonishing spectacle presented by the scope itself!

Conclusion, big but keep the F ratio fast or your diminshed FOV begins to defeat the object of seeing wider outlying faint stuff around old friends.

Olly

Yes, this makes sense to me too.

There is absolutely no contest between my 12" dob and my ED120 refractor on deep sky objects, with the exception of those that benefit from the wider field of view that the shorter focal length 120 gives. 

On lunar and planetary viewing, the ED120 does get surprisingly close to the 12" and can better it if the seeing is unstable. The "moments of best clarity" can be fewer with the 12" scope but when they come you can see what the aperture and quality optics can do. The ED120 presents a more consistent image of the planets quite often though, if that makes any sense.