GSO / AT RC Prelim Reviews & Images.

netwolf · #1 16-03-2009, 06:24 PM

Hi All,

After looking around on CN, i came accross this.

http://www.cloudynights.com/ubbthrea.../1#Post2982925

8" RC images by John Oneill.
http://www.oneilladvertising.com/Resources/hobby2.html

6" RC Review and one Image by Adrian Vergot
http://www.mathcs.duq.edu/~vergot/as...yard/at6rc.htm

Some pretty pictures. Looking good so far.

marki · #2 17-03-2009, 11:47 PM

Looking very promising indeed. I wonder if Alex has seen them yet?

Mighty_oz (Marcus) · #3 18-03-2009, 09:50 AM

There has been a long discussion going on about them

http://www.cloudynights.com/ubbthrea.../o/all/fpart/1
More info in about a month i'd say, and if someone would buy Alex's C11 then he could get one as well

If u are considering getting the rc6" be aware of backfocus issuesas indicated here http://www.cloudynights.com/ubbthrea...rt/1#Post29887

Satchmo · #4 18-03-2009, 07:42 PM

Here's the translation of optical tests on two GSO 8" RC .

Scroll down for interferogram and star tests, ronchi and phase contrast photos ( to see surface roughness ) on two different instruments .

Strehl ratio of 0.56 and scary level of surface roughness on these instruments proves the old adage " you get what you pay for". Compare the smoothness of the ronchi bands ,phase contrast test and star test , with the refractors on this page. How much this effects prime focus photography I can't say but it is not desirable.

http://tiny.cc/XSmyf

Mark

jase (Jason) · #5 18-03-2009, 08:46 PM

Quote:

Originally Posted by Satchmo

Strehl ratio of 0.56 and scary level of surface roughness on these instruments proves the old adage " you get what you pay for".

http://tiny.cc/XSmyf

Mark

No free cut lunches today folks. Ouch, so much for the marketing hype. Not one but two of these tested badly. Strehl ratio of .56! I think if I rubbed my bathroom mirror hard enough with 180 grit and windex, I might get a better ratio! Very scary. Thanks for this info Mark. The proof is in the optical stats not the pretty pictures as you can partly improvise in processing, but only to a limit.

marki · #6 18-03-2009, 09:14 PM

Not too good is it.

gregbradley · #7 18-03-2009, 09:22 PM

I wonder if you can use those optics companies who say they can refigure your mirror to get a boost. (Wooden Optics on Astromart).

There is also a company in the NSW Central Coast that grinds mirrors. Perhaps he could be of assistance there as well.

Greg.

AlexN · #8 18-03-2009, 09:22 PM

hrmmm ....

The pics look promising, the optical report does not...

Its food for thought... Im still getting one..

I'll be very interested to see for myself what its like... I'll break out my ronchi tester and let everyone know what the surface smoothness is like etc...

Satchmo · #9 18-03-2009, 09:25 PM

To be fair the Strehl ratio given from the interefometric analysis is of dubious value as the person conducting the test has removed from the final analysis the Spherical aberration term ( which could be a significant error ) but left in the Coma term , which could just be due to optical misalignment . Not sure about that logic . However the star test pictures in good seeing of the optical lab, are pretty poor. The fresnel rings are blurry.Definately not a scope for planetary imaging.

Still lets see how peoples pictures look once enough are out there. I don't have much feel for the realistic optical tolerances for deep sky photography. The pictures I've seen so far look a bit soft with a lack of faint background stars.

Mark

AlexN · #10 18-03-2009, 09:36 PM

I've still not seen any real "deep" images from one.. some of the images I've seen consist of only 1 or 2 minutes of data with 15~30sec subs... Hardly showing off what the scope is capable of...

AstroJunk (Jonathan) · #11 18-03-2009, 10:14 PM

It is a little surprising that the first available versions of this scope have such seemingly poor optics given that reputations are built on these tests. Normally the initial production run is as near perfect as possible...

Those star images do look a bit suspect though - that workshop must have terrible seeing.

Terry B · #12 18-03-2009, 10:38 PM

I'm sticking to my VC200L

AlexN · #13 18-03-2009, 10:42 PM

if the VC200L's spider was thinner I'd love one...

Mighty_oz (Marcus) · #14 19-03-2009, 12:12 AM

Just found this forum with some more info and pics on the 6" rc

, only hassle is u have to register to see the pics. Part of Andy's Shotglass site.

http://www.telescopejunkies.com/foru...d=2518&start=1
Speaking of that Vixen how would that perform on a heq5 pro for AP, with maybe st80 as guider for AP ??

marki · #15 19-03-2009, 01:07 AM

Hurry up Alex

.

I will probably wait and see what the 10" is like before I commit. Should be lots of pics around by then.

Mark

AlexN · #16 19-03-2009, 06:21 AM

Mighty_oz ; Robin (Tandum) off the forums used to run his VC200L with a meade 80 or 90mm refractor guide scope on a HEQ5.. Produced great pics. Though he since moved to an EQ6 Pro for a little extra stability...

Mark, Im negotiating the sale of my C11 as I write this... with any luck, 8" RC mid next week!

Cheers.
Alex.

madwayne (Wayne) · #17 19-03-2009, 07:33 AM

Go for it Alex, be interesting to see how you go with it.

Wayne

netwolf · #18 19-03-2009, 09:22 AM

Ouch those optical reports are not very good at all. I wonder if AT will be implementing any local quality control on these. And from the optimistic point of view these few maybe the exception rather than the rule. I recall similar discussions on the quality of Synta and GSO mirrors for dob's in the past. And arguably a GSO dob are now carying mirrors that are far better than what this test reports show for an RC from same companies. I think it would overall still be wiser to wait and see results before jumping in.

But someone has to go first.. Alex...

I have always liked the Vixen scopes, especially there Japan made stuff. The VC200L has been modified by at least one user to remove the thick vanes, I think he filed them down. The R200 Newt is also very nice, but I am not sure how much better it would be than a GSO 8" F4. I think perhaps the corrected Newtonian is often overlooked.

AlexN · #19 19-03-2009, 01:53 PM

c11 sold today. Calling andrews to place an order for the gso 8 inch as i type this.

Kal (Andrew) · #20 19-03-2009, 07:21 PM

Quote:

Originally Posted by Satchmo

Here's the translation of optical tests on two GSO 8" RC .

Scroll down for interferogram and star tests, ronchi and phase contrast photos ( to see surface roughness ) on two different instruments .

Strehl ratio of 0.56 and scary level of surface roughness on these instruments proves the old adage " you get what you pay for". Compare the smoothness of the ronchi bands ,phase contrast test and star test , with the refractors on this page. How much this effects prime focus photography I can't say but it is not desirable.

http://tiny.cc/XSmyf

Mark

Mark,

For such a low strehl ratio I'm assuming they did not take into consideration the large CO. I have no idea of how large the CO is on this scope, but hypothetically if it were say 35%, then the maximum strehl you can get is 65%, so 56/65 = 86 strehl, which would put the two mirrors as diffraction limited. Apart from that I have to agree that the star test in the lab looks terrible, and the optics appear to have pretty rough surfaces.