16inch dilemma

[astronymonkey]

After some time thinking about a new scope Ive narrowed it down to either a 12inch or 16inch skyliner or lightbridge. My main use will be visual DSO and I want the collapsable design so it can go in the car easily ... I have an estate car so Im not too restricted by size. Im wondering on a few points though , mainly to do with the 16inch versions of these scopes.

• Ive heard a lot about the f4.5 optics not being too kind on cheap lenses, Id be thinking of William optics UWAN range of eyepieces or maybe second hand naglers but in all honesty how bad is the image with the stock lens which comes with them?
  
• Ive also read about the coma at the edge of field, again how bad is this in real life with the stock lens and then with something like the UWAN.
  
• With the minimum mag I could go for being around 60x how difficult is it keeping an object in the eyepiece ?
  

and finally....

• How portable are these 16 inch beasts. I think the meade is easier to transport as if can be broken into a few pieces...this this correct ?
  

Thanks in anticipation of your comments and suggestions but for the past 15 years Ive been using a 6inch dob so Im ready to trade up !

Astronymonkey

[Daniel-K]

i tried the uwans in my old 16 not bad but could have been better

the image with the stock lens - pants

coma in a good EP is less than 10% on the edge of the FOV

very easy to keep the target in the EP

portability GREAT ! mine was just to big for me as im 5,6 i could manage it but it was a struggle

[crashtestdummy]

And there's a 16" lightbridge on ebay.

[umadog]

The size of the coma-free field depends on the magnification. You'll see plenty of coma in a low-power wide-field eyepiece: about the outer 30% of the field. At higher powers you'll see none at all. Coma is a product of the primary mirror. Good eyepieces won't get rid of it. Good eyepiece get rid of eyepiece induced astigmatism, which is worse at faster focal ratios. You can rid of coma with a coma-corrector. A good one isn't cheap, though. Either a 12" or a 16" will be a big, big difference over the 6".

[NGC 1502]

Good advice above.

However, with portability, what one person quite genuinely regards as portable, another will quite genuinely think is not.

I would urge you to see one of these scopes in the flesh, perhaps at a club or starparty, or maybe at a dealers.

Plenty of folk have had a nasty shock when the delivery van turned up

Regards, Ed.

[cs1cjc]

To get the best from a good f4.5 newtonian, you need a coma corrector, particularly if you intend to use wide angle eyepieces.

[umadog]

Ed is correct. Do not underestimate the amount of space taken up by a 16", particularly a Lightbridge-style Dob that has an overly large base. Did you know that the base will not fit through a standard doorway unless you pick it up and turn it on its side? IMHO if you're really keen on going >12" then at least consider going down the premium route. e.g. employing someone like Lukehurst. You'll end up with a 16" that's less bulky than a typical 12". Probably weigh less too, if it has a thin mirror. Alternatively there's this: http://www.hubbleoptics.com/UL16.html

[E621Keith]

Are you going to buy new or used? A new Meade lightbridge 16 costs £1928 form Telescope House

A Summarian Optics 16" Canopus with GSO mirrors seems to cost just a little bit more.

€1495 body, €924 GSO primary, €78 GSO secondary, €148 TS crayford focuser = €2666, that's about £2090 GBP and it comes fitted with secondary mirror heater, collimation hand knob, blacken trusses ...

http://www.sumerianoptics.com/products/canopus/

http://www.sumerianoptics.com/price-list/

[J_Archer]

I'm a newbie in all of this so don't buy in to what I say without reading further into what someone more experienced says.

I have an f4.8 250px Skyliner with the cheap eyepieces that came with it.

Coma is noticeable at the edges,far from it,but with big objects you won't even notice it,with little ones such as planets when they are at their furthest from the Earth you will notice it plenty when they start drifting to the edges.

It's nothing that I would dismiss buying the scope for but it is noticeable.

As for the portability part,a 10" dob is a mighty workout,it fits in the backseat of my '99 Volkswagen Bora(that would be Jetta in Brittish/American terms).

Honestly I don't bother to take it out for a quick glance,except for rare ocassions,but only take it out for looooong gazes at the sky.

But I tell you,after my neck is sore,and my arms hurt from carying the equipment,and I am in a poor mode,I come home ,take a wrench in my hand and start working around my bike,just to find out it seems pointless.

What I am trying to say is that I think you will be amazed with the 16",and that even with the portability issue,you will not regret your decision for a moment.

A thing to remember though is that mine isn't collapsable...

Good advice above.

However, with portability, what one person quite genuinely regards as portable, another will quite genuinely think is not.

I would urge you to see one of these scopes in the flesh, perhaps at a club or starparty, or maybe at a dealers.

Plenty of folk have had a nasty shock when the delivery van turned up

Regards, Ed.

Right you are Ed,imagine my face when the delievery truck came at an hour when i was not home,and I was later told that they don't re-deliever but that I would have to pick it up

Told the delivery guy that I would slip him a couple of quid extra and they came back soon enough lol.

Ah,one of the best days of my life...

[astronymonkey]

Thanks for all the replies. Ive considered a 12inch collapsible with a view to trading up to a 16inch at a later date but Im also thinking should I just go for it now and get the 16inch ..... I dont want aperture fever with the 12inch.

As for the size Im aware that the 16 inch is big but I have a large door into the utility room where it would be stored and this is much wider than a standard door. The skywatcher seems much heavier for the same size as it doesnt break down as much so I think that is off the list.

I am concerned about coma though with these fast optics, which is one of the reasons Im thinking of a 12 inch @ f5 which will hopefully not need the added expense of a Parracorr or something similar.

The Leukhurst dobs do look fantastic (but probably too dear for me ) but even with these optics would they not have a coma also, so despite the premium optics Id still need a coma corrector of some sort ?

Thanks,

Astronymonkey

[umadog]

You're right: coma is an inherent property of a parabolic mirror. All parabolic mirrors, good and bad quality, will exhibit coma. The degree to which you see it is inversely proportional to the square of the focal ratio. Don't be overly concerned about it, though: coma shouldn't put you off buying a 16" if that's what you want. The scope will be usable without the corrector and you can simply save up and buy one at a later date. Frankly, even at f/5 a corrector is nice. I didn't realise the Canopus from Sumerian were so competitively priced. It would seem to be a very viable alternative to a Lightbridge.

[glowjet]

Just for your interest one of our senior club members acquired a 16" mirror and had our friend Lukehurst build the scope for him. He demonstrated how easy it was to erect at a club meeting and it fits into his car with no problem, but you do have to carry round a small set of step ladders as part of your kit, I have used the scope on or two occasions and with an Ethos. I am not going to describe the views but suffice to say in my younger days I would not have hesitated in in raising the finances to buy one

John.

[Mike73]

Are you going to buy new or used? A new Meade lightbridge 16 costs £1928 form Telescope House

A Summarian Optics 16" Canopus with GSO mirrors seems to cost just a little bit more.

€1495 body, €924 GSO primary, €78 GSO secondary, €148 TS crayford focuser = €2666, that's about £2090 GBP and it comes fitted with secondary mirror heater, collimation hand knob, blacken trusses ...

http://www.sumeriano...oducts/canopus/

http://www.sumeriano...com/price-list/

I think this is a very good option.

Upgrade the optics to OOUK secondary with a GSO primary with Hi-Lux coating.

Only weighs 30kg!

All for £2230 (but thats without focuser.)