Scope info - SW 8" & 10" Newts

[Gina]

250PX with finder, tube rings and dovetail 1120 x 288mm 12.7kg

Edit: ha ha...almost cross posted.

Thank you

[Gina]

Actually the OD of the tube rings from hinge to fastening bolt is 330m. Don't know if that's important to you?

Ah yes - I thought it would be a good foot (in old money). Thanks Big beasty, isn't it

[JamesF]

There's always the C11 and Hyperstar option to cover both planetary and DSO imaging. Not exactly cheap, mind, and allegedly something of a pig to set up.

James

[Gina]

A C11 would be very nice but way way out of my price bracket I'm afraid. I might be able to save up for a C6 I had thought of the possibility of a Mak or SCT - definitely good for planetary but rather long exposures on DSOs. Nice and compact

[Whippy]

A C8 in theory would be a good option. Use a 6.3 reducer for DSO's still with a long-ish focal length and a barlow for lunar/planetary. They're not without their own issues though. Mak-Casses offer the same kind on flexibility but the availability of the right kind of scope and their reducers don't make them a budget concious option unfortunately .

Tony..

[Chris]

have you considered a 6- 8" Ritchey Cretien OTA, they are light and compact and have a long focal length of about 1.5m so would be a good counterpart to your wide field ED80 especially with your guiding setup. check out Altair astro's site I would be pretty tempted if there 6" fully loaded RC came back in stock (399 pounds), I'm looking at getting a 150pds as the counterpart to my zs66 for the time being:)

This is an affordable RC, alas temp out of stock:(

http://www.altairastro.com/product.php?productid=16420&cat=268&page=1

[Gina]

Now that looks a very good option - thank you

[Chris]

your welcome:), as soon as I read all the info at the bottom of the page about the advantages of RC scopes I vowed to one day own one, and they look great too:D

[Gina]

The 8" looks nice but too much for me - nearly twice the price of the 6".

Strangely they don't seem all that popular.

[Chris]

snap, I'm wondering if this is why the 6" is out of stock? I check the site every couple of weeks or so and they have been out of stock for while, I don't know if anyone else stocks 6" RC's I'm sure I've looked before and not found anywhere:(

[JamesF]

It's odd, isn't it? On the face of it the RC design looks far better than a Mak or SCT... No corrector lens to make, no internal focuser mechanism, no mirror shift or flop. I believe the image plane is not flat with an RCT, so that may be a problem, but otherwise the only obvious thing about them that I don't like is the spider.

James

[Gina]

The sellers quote a flat field as one of the advantages. Must admit, I don't like the spider either. But focussing by moving the primary mirror, I like even less - strikes me as ridiculous.

[Chris]

From what I've read you don't need a coma corrector for them which helps a little with how expensive the 8" is, still out my league though, I might email Altair about the 6" to find out if they are coming back in stock at any point. I too wonder why they are not more popular, maybe its just that most poeple have 200pds kind of money to spend rather than 8"RC money:D

I'm going to look at the spider again I must admit I didn't notice anything about it?

[Chris]

Just Emailed Altair Astro to find out if there coming back in stock in the next couple of months, if so then I'm going to hold out for one.

Gina- I'll let you know what they say just in case your interested in one:)

I've looked at the spider, is it the amount of obstruction thats not liked?

edit: you can get them form here http://compare.ebay.co.uk/like/370511963481?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&adtype=pla

[Whippy]

FWIW, the 'affordable' RC's aren't without their problems either.

As far as I know GSO don't make the 6" any more and they never made a flattener/reducer for it either (it doesn't have a flat field). They are pretty sensitive to collimation and the stock focuser is passable at best.

Tony..

[Gina]

Just Emailed Altair Astro to find out if there coming back in stock in the next couple of months, if so then I'm going to hold out for one.

Gina- I'll let you know what they say just in case your interested in one:)

I've looked at the spider, is it the amount of obstruction thats not liked?

edit: you can get them form here http://compare.ebay.co.uk/like/370511963481?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&adtype=pla

Thank you Yes, I am interested. I did see the ebay one when I did a search - £30 more plus carriage.

It's not that I can see anything particularly bad about the spider - it's spiders in general I'm not keen on with their spiky stars.

One thing that is apparent is that the secondary mirror is bigger than with a Newt and also the hole in the middle of the primary, which must reduce the amount of light compared with a Newt of the same size primary mirror and focal length. That will reduce the effective focal ratio I would have thought. So it would seem that f9 as quoted for the 6" version is rather misleading for the light gathering property.

[johninderby]

I had heard the GSO 6" RC did have some design problems and had been "dumped" by GSO at a heavy discount to clear stock, hence the price difference between the 6" and the 8" being a lot more than you would expect.

It's still available though.

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p2445_GSO-6--f-9-Ritchey-Chr-tien---152-1370mm-RC---limited-offer---.html

John

Now this is what I call a central obstruction.

[Gina]

FWIW, the 'affordable' RC's aren't without their problems either.

As far as I know GSO don't make the 6" any more and they never made a flattener/reducer for it either (it doesn't have a flat field). They are pretty sensitive to collimation and the stock focuser is passable at best.

Tony..

To quote Alair Astro from their website :-

A flattener is available separately however most users of this telescope do not consider this necessary.

They also say their focuser is better than the regular one.

There doesn't seem to be a "perfect" scope design - they all have their faults.

[Gina]

They say this design has a rapid cool down but if the scope is permanently set up on pier in obsy, does this make any difference?

[Whippy]

One thing that is apparent is that the secondary mirror is bigger than with a Newt and also the hole in the middle of the primary, which must reduce the amount of light compared with a Newt of the same size primary mirror and focal length. That will reduce the effective focal ratio I would have thought. So it would seem that f9 as quoted for the 6" version is rather misleading for the light gathering property.

There's a hole in the primary so the light can get down the focuser . As it happens, the centre spot on primaries don't get used anyway. I had an Orion/Intes Mak-Newt that had a hole in the primary, didn't make a scrap of difference.

To quote Alair Astro from their website :-

Quote:

A flattener is available separately however most users of this telescope do not consider this necessary.

They also say their focuser is better than the regular one.

There doesn't seem to be a "perfect" scope design - they all have their faults.

I know it has field curvature, I owned one for a while. While it's fine on smaller chips like the one on the Atik 314/SX H9, DSLR's do show some curvature, IIRC the smaller the aperture on RC's, the more pronounced the curvature is. That focuser looks identical to the one on the one I owned (I bought mine from Telescope Service) and as I say, it's passable.

What they don't tell you is that the thread on the focuser is non-standard and it needs an adapter to make any other one fit, plus those extension tubes you need to reach focus can be a right pain to change about with in the dark.

While on paper it looks like an excellent scope for the money, as Johninderby has mentioned, there's a reason while it's so much cheaper than the 8".

But yes, you're right. There's no such thing as a 'perfect' scope. The closest I found was an ED120, if you had a small chipped CCD like the 314, the Intes MN56 would probably be the same too.

They say this design has a rapid cool down but if the scope is permanently set up on pier in obsy, does this make any difference?

Yes it does and no it doesn't .

Tony..

[Gina]

Looks like the 6" RC is not really such a good idea then. I can't really afford an 8" RC and if the field isn't flat I can't see it being worth the money. Nice not to have coma or CA. A coma corrector has to be counted in when pricing a Newt.

I think I have the wider DSOs covered with the ED80 and later with a field flattener. So I'm looking for a scope with a longer focal length to cover the narrower DSOs and planets. I'm thinking a folded light path to give longer focal length without a hugely long tube. I'm not keen on focussing by moving the primary mirror - I would have thought that would cause collimation errors unless an accurate and very expensive mechanism was used. Are there any folded light path scopes other than RCs that don't use primary mirror focussing?

[JamesF]

Mak or SCT with an after-market focuser, so you never need to move the primary mirror? You're still making compromises though

I think this one is going to be a tricky one to solve well.

James

[Gina]

The MN190 looks interesting - a fully corrected Newt sort of thing but at a price! No diffraction spikes but big and heavy - twice the price of 8" Newt plus coma corrector.

I don't really think it's for me.

[Whippy]

FWIW, once you start getting above about 750-800mm in focal length, DSO imaging gets a bit more complicated as any little error tends to show up more. I never went beyond about 8-9 minutes with my ED120 as I started getting errors, 10 mins+ with my ZS66 or ED80 was relatively easy.

Tony..

[JamesF]

I'd discounted suggesting the MN190 for specifically those reasons, Gina

I do wonder if something like a C6 might work. Ok, it is f/10 rather than f/7 or whatever the 80ED is, but you have got probably five times the area of aperture even allowing for the central obstruction. I agree that having a moving primary is not the most desirable of features, but it would perhaps be possible to add an external focuser over time? There may be a focal reducer that could work with the C6 too. No idea on that one.

James