I thought others might be interested to see just how bad the internal reflections are in the GSO RCs from Andrews. These are images taken tonight of NGC4945 and 4976. They are 5 minute subs (5 in 4945 and 2 in 4976) at iso800 in a Canon 1000D with a master flat applied. The stacked elliptical bands are bad enough but note also the bright rays like sunlight through cloud, coming in from the mid left side.
I would be very interested to hear from other RC owners experiencing similar problems. It seems to me that these scopes, marketed as the imager's dream, are in fact a shocker; unfot for the purpose for which they were sold.
Peter
A guy in our Deep Space Imaging group-a special interest group in our society-purchased one of these with great delight. It went back to Andrews in the same week for a full refund. The reason it went back is exactly this fault. Andrews sent the scope up to his repairer-cant remember his name-and he was quite surprised with the problem and thought it was a serious one, however, we have heard no more. It seems if you get a good one-great!! I did see some where else on this site that some one did mention what they thought was a fix for them-focuser flocking of something??
It seems the optics are a bargin. Paul Haese (spelling) has nailed an easy fix, he is an IIS member but I can't find his post on fixing the problem. You get what you pay for however if it is an easy fix where else can you get an RC with CF tube and diaelectric coated primary for what you paid.
Pete Ward could probably explain more succinctly.
I have seen these scopes on the Andrews site and thought they'd be the ducks guts. Not too sure that you do get what you pay for anymore, I'm not restricting that comment to astronomical purchases (pun or not). It seems too often to be the case that you pay what they can get out of you. No disrespect to Andrews, they've always done right by me.
Check out the ATS website. Peter is selling them with the revised baffle tube (the cause of the problem in the original) and at a cheaper price then Andrews. All of the earlier models have displayed this fault so far but only in certain situations. There have been a number of posts about this very problem. I have seen some cracking images from the old version and Paul Haese posted a link to how he fixed the problem by flocking the baffle on his website. It is a comprehensive step by step guide. Peter Ward took a nice pic with the new version which does not seem to suffer from the reflection problem.
pretty much all of the early ones had the same problem, wait until they come out consistently producing good results.
better still buy a good refractor, far less problems...
ive used most styles of scopes. refractors win hands down for me. No mirrors needing recoating, no internal dew, no secondary to block light, no star spikes..... just expensive, but a pleasure to use.
1. Ask for a refund and try ATS as I doubt Peter would sell gear that did that.
2. Go the route of fixing up the manufacturer's product with flocking and a new focuser.
Perhaps the focuser is better also on the later model as Peter says the focsuer was solid yet Paul's one he replaced the focuser witha Feathertouch one as it had too much flex.
I know from experience how annoying it is to do the manufacturers job for them so I'd recommend 1) above. There's no guarantee mucking around with fixes will solve it and it willl probably void your warranty or ability to refund if you start modifying it.
Most modern scopes use a series of baffles to redcue reflections.
They also coat interior surfaces with a matt black paint that is absorbing.
RC's have curvature. You need a flattner to get rid of curvature.
Theo.
RCOS, and similar high end RC's keep field curvature to a minimum by adjusting the focus with both the secondary mirror position and the back focus. (The secondary mirror on RCOS scopes moves to change focus.)
Generally the RC design has a field that remains flat(ish) when the relationship between the primary to secondary remains proportional to the secondary to back focus position.
While I have not seen the GSO in the flesh, all focussing seems to be at the back plate. This does not matter much for visual observing, but may be the reason why the image showed curvature.
How did those 240v network adapters go ... did it work?
Hi Rob and thanks again for your thoughtfulness:
In answer to your question, one did but the other was a dud. Something in the power train. No sparkee, no lightee!
So I have the age-old dilemma of deciding what I can do with a single powerline ethernet adapter. It is like the philosophical question "what is the sound of one hand clapping?"
Peter
1. Ask for a refund and try ATS as I doubt Peter would sell gear that did that.
2. Go the route of fixing up the manufacturer's product with flocking and a new focuser.
Thanks everyone. I've read Paul's instructions on flocking now and am tempted. If Andrews care enough about their reputation, they'll take it back or at least arrange a replacement baffle. I'm going down there in a few weeks so we'll see. Failing that, it's flocking. Anyone klnow of a source for flocking material?
Peter
If you look very closely there is a dim off-axis reflection in that image.
The scope did need colimation and apart from a mild spherical error, had no other vices that I could see.
The focuser handled an SBIG STL11k with no problems.
A bright star, just off axis, may still throw some scattered light onto the focal plane. Sorry, that's the way most telescopes work.
As for the RC design, they have no off-axis coma. This is very different to field curvature which they do indeed have.
That said it is very low, and would be hard to pick with an APS sized chip.
Last edited by Peter Ward; 11-08-2009 at 01:24 PM.
Reason: additional info
I expect that these models are equally as bad from any distributer, 
however that is just not good enough.
