GSO / AT RC Prelim Reviews & Images.

[netwolf]

Hi All,

After looking around on CN, i came accross this.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2879276/page/0/view/collapsed/sb/5/o/all/fpart/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/astronomy/backyard/at6rc.htm

Some pretty pictures. Looking good so far.

[marki]

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

[Mighty_oz]

There has been a long discussion going on about them :)
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Board/cat/Number/2870680/page/0/view/collapsed/sb/5/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/ubbthreads/showflat.php/Cat/0/Number/2986775/page/0/view/collapsed/sb/5/o/all/fpart/1#Post29887

[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

[jase]

:eek: 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]

Not too good is it.

[gregbradley]

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]

hrmmm ....

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

Its food for thought... Im still getting one.. :P 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]

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]

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]

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]

I'm sticking to my VC200L

[AlexN]

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

[Mighty_oz]

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/forums/thread-view.asp?tid=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]

Hurry up Alex:D.

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

Mark

[AlexN]

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]

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

Wayne

[netwolf]

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]

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

[Kal]

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.

[AlexN]

the average CO for a RC design is usually between 40~50%....

[Kal]

Best of luck with that Alex, I hope you can prove that the tested scopes listed above are just a couple of bad apples, because these will become a hot scope to have if they live up to their potential!

[AlexN]

Thanks Andrew... Overwhelmed with excitement at this stage... Should it live up to its potential I dare say you're right, they will become very popular.. I hope to prove that the tested scopes are simply bad apples..

I'll give it a good run when the weather it brings clears. :) Will test it with a APS-C sized chip and with the SBIG to test both resolution and field flatness! :)

[marki]

Onya Alex. I will be very interested in how you go with it all. I am just being very patient and will wait for the 10" version.

Ciao Mark

[AlexN]

Yeah. 10" is tempting thats for sure, however, patients is definitely not my strong suite! :D I am a "I want it now" kind of guy! :)

Alex.

[marki]

I kinda noticed that Alex . One only has to read this thread to work that out:D. I will wait, I will I will .........

Ciao Mark

[Tilt]

Alex, I knew you would come good :) well done on the purchase (you did order one right?)

Michael

[AlexN]

Oh yes... Ordered and paid for :) Should be here monday/tuesday next week! :D

[Mighty_oz]

Oh No ! Stop asking him guys he keeps putting the arrival date back a day each time !
Hehehe
Nice one Alex :) Oh and by the way. Don't u dare get clouds next week !

[AlexN]

hah... I dare say that the clouds will smell an RC and come down like a million tons of bricks... :)

I figured, If I order it now while its already cloudy, then the clouds should be dissipating by the time it gets here... I'll be heading to a dark site the on the 28th, so that might be the official first light night.. :)

[mldee]

Good on you Alex, this should be all we need to bring next week's forecast cyclone all the way to Brisbane.

Seriously, looking forward to hearing how the RC goes.

(I'm the guy who bought your Dob)

[AlexN]

How is the dob going Mike??
Hah, yeah I figured I may as well buy it when theres already a cyclone on the go.. that way its not exactly my fault! :) and what are the chances of 2 cyclones at once?? :D :D

[mldee]

Like you, we all move on. The dob is snoozing in my garage at the moment. Soon to be in a garage sale on IIS.

I've almost finished my RO observatoy, and now have an EQ6 with refractor and C8 SCT mounted on a hefty pier. One of these days I might actually have to start looking though them:whistle:

Just bought a 1000d, so liveview is now reshaping my viewing plans.

Great fun, anyway.

I'm also intrigued by the RC's, so look forward to reading your experiences.

Cheers,

[telecasterguru]

Alex,
I too am very interested to se how the RC goes.
I started a thread here on the pros and cons of the RC and an APO and got some good feedback.
Still haven't made my mind up yet so eagerly looking forward to your reports.
Thanks
Frank