Pics of GSO 8" F/9 RC scope...

[dugnsuz (Doug)]

Hello all,
Perhaps this is old news, but this is the first pic I've seen of this scope...

http://www.gs-telescope.com/content.asp?id=149

Cheers
Doug

[Tilt (Michael)]

Looks good, now how does it perform??

Are you going to buy one and do a review for us Doug

Michael

[Bassnut (Fred)]

Very interesting Doug, carbon tube,RC, mmm, obstruction is large, but it is 8", very interesting......

[Starkler (Geoff)]

How will this be any better than say a Vixen vc ?

[AlexN]

I'm with Geoff on that... I know its an RC not a SCT, but in pure english, whats the big difference?

Wonder if the bigger models they plan to release will be actively cooled?

[netwolf]

If it is the same as these
http://www.astronomics.com/main/prod...oduct_id/AT8RC
then the 1/12 wave optics maybe the difference to the Vixen. But the 1/12th figure stated is a bit vague is it peak or RMS is it overall etc etc.

[Garyh]

1/12 wave surface only amounts to 1/6 at the wavefront. That doesn`t sound that good to me. Also being a true Ritchey-Chrétien 2 mirror scope I always thought that they too suffer from coma unless there is some sort of corrective lense in the optic train? Correct me if I am wrong. A f/9 newtonian would have very little coma too, but it would be long!

[ving (David)]

Originally Posted by Starkler

How will this be any better than say a Vixen vc ?

probably price sir

looks that part

[Gama]

Originally Posted by Garyh

..... Also being a true Ritchey-Chrétien 2 mirror scope I always thought that they too suffer from coma unless there is some sort of corrective lense in the optic train? Correct me if I am wrong.....

The RC has no coma, but does have Field Curvature and Off Axis Astigmatism. But this can easily be removed by (As you said) placing corrective lens's in line. Then you would have a really good scope.

But, what is inherent with this design is the collimation. It needs to be dead on.
Some say its not that hard to collimate, and others say its extremely hard.

Not having one, i cant answer which is true, but i would assume people who are not familiar with scopes may find it hard, but others who tinker with their scopes, may find it easier.

Theo.

[AlexN]

GSO 8" RC-200SDX advertised at Bintel @ $2499..

Just thought I'd throw that in...

[Kal (Andrew)]

Originally Posted by Garyh

1/12 wave surface only amounts to 1/6 at the wavefront. That doesn`t sound that good to me. Also being a true Ritchey-Chrétien 2 mirror scope I always thought that they too suffer from coma unless there is some sort of corrective lense in the optic train? Correct me if I am wrong. A f/9 newtonian would have very little coma too, but it would be long!

1/6th wavefront is only marginally behind the expensive RC boys, RC Optical Systems list 1/24th wave RMS, or about 1/7th wave PV

[TrevorW]

It looks nice but how can they justify the 8" being nearly twice as expensive as the 6" also nearly twice as expensive in the US as an 8" Vixen SC.

Go figure

[toyos]

Why would someone choose an 8" f/9 RC with 40-45% central obstruction over say a 5" f/7 APO refractor with a field flattener & zero central obstruction??

[AlexN]

because with the apo they cant tell people they have a RC..

I think its all going to be about having an RC for the sake of having an RC...

[Kal (Andrew)]

Originally Posted by toyos

Why would someone choose an 8" f/9 RC with 40-45% central obstruction over say a 5" f/7 APO refractor with a field flattener & zero central obstruction??

The 8" RC with a 45% CO will have 200% the light gathering capability of a 5" APO. A Better comparison will be against a 7" APO.

[toyos]

Originally Posted by Kal

The 8" RC with a 45% CO will have 200% the light gathering capability of a 5" APO. A Better comparison will be against a 7" APO.

I have to disagree, but I guess it's just a matter of opinion. I tested my 5" refractor side by side with a near new well-collimated 8" Meade SCT (with less CO but plus the corrector plate compared to an RC), and the light gathering capability looked pretty much equal to my 20/20 eyes. But the refractor of course had more contrast and sharpness. When I put the 8" SCT against my 6" refractor, the 6" refractor clearly showed better definition.

I don't see a reason why an 8" RC with its larger secondary + its holder (adding diffraction spikes) should make any significant difference over an 8" SCT in terms of light-gathering capability. I'd rather test different equipment myself than just read what other people write when possible.

[g__day (Matthew)]

A really good 5" apo (versus ED or near APO or Chinese - still quality fluctuating apo series) is going to cost you more than $2,500 (Williams Optics around $4.8K, Takashi $7.5K and Televue around $9K). Secondly when you do an intensity test did you compare really bright star fields or really dim ones and did you have the same field of view so its an apples versus apples intensity test?

[Kal (Andrew)]

I was just going by the math, not side by side test, as I've never directly compared a 5" APO to an 8" Cat. 5" APO = 20" squared, compared to 8" RC = ~50" squared - CO of 10" squared = 40" squared, so it has 200% the light gain capability, so if you are imaging you get the same amount of photons in half the time. It will have alot less contrast though because of the CO, and to be honest, I have no idea of wether this affects DSO imaging performance (I know contrast affects planetary performance alot)

[toyos]

Also keep in mind that fully multi-coated lenses generally transmit more light than the combinations of mirrors used in reflecting scopes. So direct size comparisons without taking into account the other factors will not be accurate.

[mick pinner]

you also have to define what a true Apo really is as the glass varies quite markedly from one scope to another.