EDGE HD 11 VS GSO 10" RC

[SirPeterWeyland]

what do you guys think im thinking of going for the edge hd more

but their are many who say get the gso RC one is better for imaging

the other is an inch bigger and can do both very good.

[ollypenrice]

Neither of these scopes can be called plug and play. They are the starting point for a project. What is your project? What do you want to achieve and what mount are you aiming to use?

Olly

[SirPeterWeyland]

i have a cgem dx i like imaging im looking for the edge hd if the price go,s down.

[ollypenrice]

You are sure you want to image at those focal lengths? You know the difficulties? And you are up for the slow F ratios? Lots of issues...

Olly

[RobH]

I have both an Edge 11HD and the Ian King 10 inch RC, which uses the GSO mirrors and cell.

They both have excellent optics, but the HD is hard to use a focal reducer with and still get a decent flat field, and its native F10 is very slow.

The RC is F8 and is easy to reduce to F5.3, making it pretty fast.

Of the two, for certain small targets requiring a large image scale, the HD is possibly fractionally ahead and doesn't have diffraction spikes having no spider, but the 10 is much more useable generally.

I can't directly comment on the build quality of the RC, having the beautifully engineered Ian King one which has a CF truss construction and not having used the GSO model, but the Edge is very nicely made.

Of the 2 though, if I had to choose, I would go for the RC any time.

HTH

Rob

[pete_l]

what do you guys think im thinking of going for the edge hd more

but their are many who say get the gso RC one is better for imaging

the other is an inch bigger and can do both very good.

Swings and roundabouts.

Price-wise they're similar unless Celestron pulls their special offer and the EdgeHD goes up by £2k - but see later.

The EdgeHD has a n aluminium tube, whereas the GSO can be got with a carbon fibre tube, so temperature sensitivity favours the RC - though it weighs a little more.

The Starbright XLT coatings on the Celestron are shinier than the GSO's. If you believe the Celestron figures, that could be worth nearly an inch of aperture (on top of its larger size), in terms of number of photons delivered to your CCD.

Saunders [link, PDF] says that the EdgeHD contains a built in corrector/flattener, which is why the range of scopes doesn't work with a normal SCT-type reducer. But Celestron have a 0.7 reducer available for an extra £750

That's all I can think of so far.

[ollypenrice]

The reducer is a game-changer for the Edge scopes but do we know the size of image circle it will illuminate? The advert I found for it was deafeningly silent on the matter and this made me suspicious.

I take Celestron's reflectivity claim with a large pinch of salt.

Olly

[ampleamp]

Ian King recommended an Astro Physics CCDT667 reducer for my 11" Edge. I have to say that I haven't used it as yet but it is only a reducer, not a flattener, so no effect on the flat field. I bought mine from the US, but I see TS do it as well.

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p4955_Astro-Physics-CCDT67-0-67x-Reducer-2----e-g--for-GSO-RC.html

It is quite a bit cheaper than the new Celestron option.

[RobH]

I've tried the AP CCD67 reducer with my Edge scope, and even with a small 285 chip, the edge of the field was unusable.

Also, re. the GSO carbon tube, the fact that the CF isn't affected in the same way by thermal issues as the aluminium celestron tube is negated by the fact that the CF tube has a full length Ali dovetail bar both on the top and bottom....this is affected and to some extent negates the thermal stability of the CF.

From what I've heard, the new Edge reducers won't give as large a flat field as the scope without a reducer, and they are horribly expensive.

Rob

[pete_l]

... the CF tube has a full length Ali dovetail bar both on the top and bottom....this is affected and to some extent negates the thermal stability of the CF

:)

That is an *extremely* good point. Presumably the reason they had to put a dovetail on the top as well, was to stop the OTA bending into a banana shape as the bar expanded and the CF tube did not.

[RobH]

Ian King recommended an Astro Physics CCDT667 reducer for my 11" Edge. I have to say that I haven't used it as yet but it is only a reducer, not a flattener, so no effect on the flat field. I bought mine from the US, but I see TS do it as well.

Astro Physics CCDT67 0.67x Reducer 2' - e.g. for GSO RC

It is quite a bit cheaper than the new Celestron option.

The distance between the reducer and rear flattening element in the edge has to be as close as possible in oreder to get a flat field. This means ditching any moonlite/feathertouch focuser if you use one as this will put the reducer too far back (which is why I only got a small useable area).

The result of this is that you have to use the coarse focuser to focus, and if you want to use the system remotely with automated focusing, then you can't engage the mirror locks, leaving you open to mirror flop.

The new reducer that's designed for these scopes also has to be attached before any third party focuser, although it looksd like it's threaded properly and will accept one.

The way to use one of these would be to attach your reducer, then your focuser, rack the focuser drawtube out a bit so you can have a bit of movement both in and out and then focus with the coarse focuser.

The engage the mirror locks and fine tune with your rear focuser.

In theory, this should worrk.....but that's oinly in theory remember, and £750 is a lot to spend if it doesn't.

Rob

[ollypenrice]

So the Edge is still a troubled telescope, it seems. No one has mentioned the Meade ACFs. Martin B and Peter Vasey get good results from these and Chris Suddell likes his 8 inch.

The point about the alloy dovetails and the carbon is very interesitng. I'm a wally for not having thought about this. Almost every night, often around midnight, Yves' ODK has a benny and loses its guide star. We don't suspect the mount. Also when you move it around it sometimes lets out mild 'crack.' I may have sorted it by slightly slackening the front tube ring. (There isn't a rear one, the back of the scope bolts to the dovetail.) I've assumed this was movement induced by gravity and tension but maybe thermal expansion plays a part. As Rob implies, it is downright daft to have a carbon tube and alloy dovetails top and bottom.

Olly