GSO RC testing review

[netwolf]

Paul, I belive the casue of the square pixels is said to be the thick vanes of the secondary spider. But recently Guy (in his VC200L carbon fiber modification thread) noted that not everyone gets this issue.
It will be interesting to see what Guy produces with his modified VC200L's.

[Paul Haese]

Fahim,

if that is the case then it is likely to be a production related issue. Maybe the Vixen mirrors are not all the same quality. Whether this is the case or not the RC design is supposed to be sharper but less contrast by virtue of the optical designs of each telescope.

Personally I think having a shoot out is meaningless exercise. One would have to use exactly the same equipment on several telescopes to get a meaningful comparison. That is never going to happen.

[AlexN]

Paul.. If I'm able to do it, it would be the same night, same mount, same guiding setup, same polar alignment, same camera... That would be pretty close... However I think that the RC will outperform the VC200L with regards to star sizes and resolution... Also, being F/8 rather than F/9, the RC will gather more data in equal length exposures... Maybe, as you say, meaningless... Definitely tedious... Maybe a go ahead, Maybe not.. We'll see...

I know this. I have owned quite a few scopes for deep sky imaging.. So far, I like the RC the most...

[mick pinner]

maybe Alex or Paul or anyone else can help me with this,
using the same mount, camera and processing style why would this scope be any better than a Meade ACF of the same aperature? l think this is a very interesting thread on this scope but going by images l have seen from not only your own scopes but also others posted on some US sites l'm not sure what you guys are chasing image wise compared to as l mentioned earlier say an ACF.

[AlexN]

At the risk of starting a flame war... The RC design is superior to the ACF/SCT design with regard to deep sky imaging in many ways. Yes, the ACF scope is a step ahead of the standard SCT with regard to coma. The ACF scopes, for starters, are a sealed tube.. This makes it very difficult to get the mirror to ambient temperatures, where as the open tubed RC cools to ambient relatively quickly.. A well designed and built RC will produce better star images than an equally well designed SCT, and the off-axis spot diagrams I've seen show RC's and CDK optical systems leaps and bounds ahead of SCT/ACF optics..

I'm sure many people will be able to give more reasons why an RC is better for deep sky imaging than an SCT/ACF...

This is sort of an unfair comparison, however I will say this, I've produced sharper images with my RC already than I achieved with my SCT.. Allbeit, it was with different cameras, and with my SCT my mount was fairly heavily loaded... But the RC has produced better images for me in the two nights I've used it than the SCT did in 8 months of use...

The biggest kicker for me with the RC is the lack of corrector plate... My SCT's corrector would fog up at the drop of a dime... Also, the corrector plate being a refractive element, can introduce some aberrations, the RC being a purely reflective optical design is free from such aberrations..

[Paul Haese]

Mick, I think it is purely the optical design. The tolerances for an RC are so much tighter than the manufacture of an SCT. This is not to say the ACF is a slouch. Indeed I have seen plenty of really nice images taken with them. That is most likely the result of the operator using it and the individual optics. However, the hyperbolic design of both surfaces in an RC requires very narrow tolerances and this is the reason for the sharper images. (well in Theory)

[mick pinner]

a legitimate question Alex, only the stirrers would turn it into a war, l'm not saying one is better than the other just exploring why one would or should be better.

[Bassnut (Fred)]

Originally Posted by mick pinner

maybe Alex or Paul or anyone else can help me with this,
using the same mount, camera and processing style why would this scope be any better than a Meade ACF of the same aperature? l think this is a very interesting thread on this scope but going by images l have seen from not only your own scopes but also others posted on some US sites l'm not sure what you guys are chasing image wise compared to as l mentioned earlier say an ACF.

Good point Mick, been wondering this myself, should have done this direct comparison long ago damb it . My 10" RCOS RC has an ST10XME, and my 12" LX200R (same as the ACF) also has an ST10XME, so even though there is an apature diff, its as near as were going to get it seems. Ill attempt now to get an image on the RCOS with the same object,exposure time, and processing as the LX and post results.

Ive already, some time ago, found the RC to give definitely give tighter stars, thats all I remember (while I had it at home for a short time), but also found back then that some deconvolute (on megadata) gave comparable end results. I suspected at the time that extra exposure time and carefull processing rendered the diff mute. Not to say that makes them the same (given the LX required more exposure time, to produce less noise with deconvolute), but there are many factors that influence the final image quality, not just the optics.

Another factor is offaxis performance, oft quoted as a definitive difference between optical designs. A smallish sensor uses a far smaller portion of the illumination circle than a 16meg monster, so maybe for narrow field, off axis performance is less important.

[bert (Brett)]

Just out of interest can't wait to see the difference between these scopes, both fred's and Alex's, just for curiosity not bragging rights.

I hope that I didn't infer that it will start a war in my earlier post, I own a VC200l and think that it will not be as sharp as the RC from what I have seen, and my VC definately has square star syndrome. So if a war is started, the vc is gonna come second.....

But I still love it to bits.

Brett

[netwolf]

I have no experience with either the VC or the RC. But I think it would be safest to say that there is no real allrounder telescope out there. I have high hopes for the GSO RC, but i do hope that they venture also into the CDK design. I am also looking forward to how these rate against the new EDGE HD SCT's from Celestron.

[Paul Haese]

That aside I have done a how to on the way to fix the reflections caused by the baffle.

Click here for the link.

[Satchmo]

All these designs ( VCL, RC, CDK ) would theoretically be as 'sharp' as each other on axis and with the appropriate field flatteners /correctors should be good off axis too on a flat field. It the actual implementation that is more at question in these low cost commercial intruments.

[Paul Haese]

Mark, I was of the understanding though that the hyperbolic mirror configuration required far less tolerances in the figure? Is that true and if so then to get a truly sharp image greater precision is required? Or is it simply a matter than some companies only work to 1/8 wave and others are working to 1/12th or better?

[Gama]

Paul, what Mark is saying, is that they are all capable of producing similar results, and of course they must be well collimated.

There is more involved in collimation with certain designs, and there is those that say that the RC can not be "Properly" aligned and so suffer a little loss. Either way, the results are in the final image, and as can be seen they are still capable of some great images.
Truly sharp image is just not going to happen if your seeing is always worse than the scopes ability. I dont see anywhere where a star in an images is only 9 microns wide. Add seeing, and the star is now 30 plus microns. So why piddle with either 9 micron, or 2 micron stars, as they will balloon up due to the current atmoshepic conditions.
This is just a rough example, you really need to see what it all means when put to practical use.
If you decide to put your telescope in a remote site with great seeing conditions, then what you say is going to have some impact.

Theo

[TrevorW]

Nice job of the instructions Paul

Thanks

[AlexN]

I agree with Trevor... Good job on the instructions regarding the internal baffle reflections... Dont mind me, but I'll wait untill I've seen testing before I perform the same on mine!

[leinad (Dan)]

Originally Posted by netwolf

Paul, I belive the casue of the square pixels is said to be the thick vanes of the secondary spider. But recently Guy (in his VC200L carbon fiber modification thread) noted that not everyone gets this issue.
It will be interesting to see what Guy produces with his modified VC200L's.

True. See Alan Smallbone's website, http://www.pbase.com/snowlep/vixenmod; other mods have been made also.

Nice Mod and Instructional work Paul.

[TrevorW]

I did it, I'll post some pictures later didn't have flocking material so gone for chalk board paint light multiple coats

[Paul Haese]

I have updated the baffle flocking page. No reflections at all now. Problem fixed. I will need to buy a Tak collimation scope though I am still not 100% happy with the collimation.

Click here

[TrevorW]

Thanks Paul actually quite straight forward and simple.

Checked collimation after it looked still OK but will need to wait for a star test.

Not impressed by the lack of feedback from GSO though.

Cheers