A bright star, just off axis, may still throw some scattered light onto the focal plane. Sorry, that's the way most telescopes work.
Hello Peter. Granted, but surely the pattern exhibited in the images attached to my initial post are well beyond anything that ought to be considered 'normal', 'acceptable', 'within tolerances'. Would you consider a scope you had bought to be accetable if it displayed those features?
Peter
Would you consider a scope you had bought to be accetable if it displayed those features?
Peter
Depends.
If the 'scope always showed said reflections, I would not be happy.
If it only happened with a bright star/object just off axis, then I have to say that is is nature of the (in this case, inexpensive) beast and look at a workaround....eg flocking to make it better.
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
Yeah I bought self adhesive backed flocking from Scopestuff. I think its scopestuuff.com
Its not very expensive and fairly easy to use. I flocked the interior of my RCOS 12.5 inch and it improved contrast a bit.
I also made a little ring out of black thin cardboard you can get from a newsagent to block the last 5mm of the primary mirro as
sometimes the primary mirror has a turned down edge right at the edge that causes unwanted effects although I don't know that it causes
large round reflections like that more extra haloes around stars.
The images I've seen suggest these blooms are light from a bright star just outside the field of view being reflected into the focal plane, but there are several candidate sources of the reflection. In particular I suspect it comes from something with a machined surface.
1. The central baffle - both outside and inside surfaces.
2. A machined edge around the perimeter of the secondary mirror cell, with the light reflected in much the same way as glancing incident light will be reflected off the sides of those lovely "handgrenade" eyepieces from Meade, Vixen and others.
3. Circular baffles inside the OTA - assuming there are some.
4. Could even be coming from a reflecton off the inside of the last bits of tubing coupling the camera to the scope, if any of them has a machined surface - even if its black anodised its still shiny enough.
I think the vanes supporting the secondary could be ruled out.
Mick, To my knowledge, this was the first GSO RC sold in australia... (according to the only person who stocked them at the time of purchase... As I said to you via PM Peter, Andrews will likely replace you baffle tube.. If not, flocking it yourself will be the go...
You could also try Astronomics in USA, they might be able to sell you a new baffle tube, ATS may be able to do it for you too.. All in all, these scopes are great despite a few shortcommings.. given the money, I would buy one again tomorrow..
I've asked Andrews to replace my baffle and confirm that the scope he sold me was an F/8 as advertised
These reflections did not appear in every image I've taken and were most apparent in an image I took off M83 but not apparent in anything else except maybe the recent shot I took of M30 which I'm still not convinced was an internal reflection caused by the scope.
As mentioned internal reflections as displayed are quite common in SCT's and the like.
The replacement of the focuser is a personal choice if your not happy with the rigidity of the stock one.
As far as I'm concerned they are a good scope for the price and will produce the results
ok first and foremost. It is likely you have a scope from the second batch and not the third batch. I found that on bright nebula the reflections were not present, however on this galaxy and M83 it was present.
The new baffles will not fit your scope so flocking is the only solution. The optics are fine you just need to make a few mods to get the most out of the scope. I only found two galaxies that this issue arose. I have seen plenty of other galaxies imaged with this scope and no reflections.
RC are coma corrected not flat fielded, use of a flattener is mandatory if you want to correct for field curvature.
For the price, this scope is a ball tearer, it just has some spots that is all.
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
The images I've seen suggest these blooms are light from a bright star just outside the field of view being reflected into the focal plane, but there are several candidate sources of the reflection. In particular I suspect it comes from something with a machined surface.
1. The central baffle - both outside and inside surfaces.
2. A machined edge around the perimeter of the secondary mirror cell, with the light reflected in much the same way as glancing incident light will be reflected off the sides of those lovely "handgrenade" eyepieces from Meade, Vixen and others.
3. Circular baffles inside the OTA - assuming there are some.
4. Could even be coming from a reflecton off the inside of the last bits of tubing coupling the camera to the scope, if any of them has a machined surface - even if its black anodised its still shiny enough.
I think the vanes supporting the secondary could be ruled out.
Thanks. That's helpful. It is a hunting list, at least.
I have identified the prime candidate for the just-out-of-image reflections. See attached image.
Peter
