I did my preliminary tests last night on the GSO RC 8". Several things need attention to make this OTA perform at its best.
I am awaiting a feather touch focusor and adapter. This will ensure rigidity.
Next this image is totally unguided. I am awaiting vixen guide rings from ADM. Guiding will reduce the star bloat and increase the sharpness of the images.
Finally, I am looking for a RC flattener. RCOS sells them but not on their website. I guess I will need to speak to Peter Ward about this. I used a Tak Flattener for this image and it has caused some defects in the stars.
However, this image does give me promise. It looks reasonably sharp with plenty of good contrast. This image is comprised of 120 second subs at ISO800. Flats applied, darks and biases.
Feel free to comment on this. It is not one of my better images but I put it up for a bit of analysis.
Well, so much for the stars will be blobs post from Valery.
Quite impressive. Looks as good as just about any other image of that
area from different scopes.
Are you sure your Tak flattener isn't working as the stars are odd only in the top left hand corner that I can see at that image size. That would seem to indicate lack of squareness - so something is tilting. Loose connections or the focuser drawtube is a bit loose etc.
I got an RCOS flattener once. They are US$1500 + shipping + GST (ie. almost as much as you scope cost) - didn't fit and really really couldn't care less type customer service. The packaging was also very amateurish. You get a US$400 Tak flattener and it has beautifully machined aluminium caps, a nice box and it fits. Their flattener is actually made by Peter Ceravolo and you could even contact him direct
(Ceravolo Optics - he makes an astrograph).
I am not sure flatteners are that sensitive scope to scope. Perhaps I am wrong but the main thing with them is the metal back distance so you would need to know the exact metal back distance for your Tak flattener. They are often around 86mm or 106mm. Tak uncensored group is a good place to find out. Looking at your image it doesn't appear to be so much the flattener is a problem but flexure in the focuser as you mentioned.
For example my 4inch FS152 flattener works fine on my AstroPhysics 140mm triplet.
Are GSO planning on making a flattener for theirs?
Another potential source for a flattener is Deep Sky Instruments who make an 10 inch RC and a flattener.
Hey thanks for the info Greg. I was thinking along those lines with the focusor, meaning I thought that the flexure was causing the issue.
The metal back distance for the TSA flattener is a minimum of 106 I think from memory. I checked this some time ago and as I understand it so long as I don't go below that distance it should work. I think with the TSA I am usually 117mm and this seems to work all the time. What I did not know is that I might be able to use the same flattener. That will be good if I don't have to buy another piece of kit. I had thought that each flattener was independently made for each type of OTA.
Apparently GSO make a flattener for this OTA, well at least that is what I read on CN and even on Astronomics but so far I have not found it.
Thanks so much for the feed back Greg, much appreciated.
I got an RCOS flattener once. They are US$1500 + shipping + GST (ie. almost as much as you scope cost) - didn't fit and really really couldn't care less type customer service. The packaging was also very amateurish................ Their flattener is actually made by Peter Ceravolo and you could even contact him direct
(Ceravolo Optics - he makes an astrograph)....................
Greg.
I've got a RCOS flattner. Seems to fit just fine.
Cerevolo (a mate of mine) does make them. Not mass produced...Each are hand figured....but probably didn't have a clue (not!)
Packaging is important...goods need to arrive in one piece.
Nice Paul.. Real nice... Cant wait to get mine out... (How embarrassing, I was the first to buy one and will be the last to actually use one!! ) Such is life I guess.
Your image has strongly supported my original thoughts on the scope, and definitely makes me feel better about buying it... Now.... To get some images out of mine....
As you can see the stars look triangular and are a bit blobby with flares. The triangular comes from not guiding with the EM400 and the blobby and slightly flaring is from the focusor.
It is not pretty but once these issues are sorted I am sure it will produce fine images.
I wonder if the odd shaped star images could be caused by a very slight mis-collimation? Otherwise it looks pretty good.. resolution seems nice.. the finger is rather well defined thats for sure.
Well the collimation was fine when we did it on Hadar, but with the flop in the focusor it may have shifted collimation. This is the whole problem. These focusors should never have been placed on an OTA that demands such precision optics. The triangular shape comes from the way the EM400 works when not guided. I saw these in my images that I took unguided with the TSA at 10 minute exposures. With this focal length though I am lucky to go 3 minutes. I will need to address the polar alignment a little to improve that to 10 minutes with this scope. Time to break out Pempro I think.
Cant wait to see some 10min guided images from these scopes... Longest exposures i've seen yet are 2~3 mins... Hopefully I'll get mine out tonight this weekend, with some self guiding I should be able to manage 5 mins.... 5mins exposure with the ST9 seems to be PLENTY of light (well it was with the C11...) So i assume that it will do nicely with the 8" RC...
fantastic detail, star shapes aside , as you say tracking can improve.
the detail is as good as i can get out of the 12 inch and a bayer arrayed camera on a good night.
i am impressed !!!!!!!!
just in case i missed it , what camera did you use ? what is one of these scopes worth (provide link if you can ) aaaaand if you find a flattener ( which i find odd for a scope supposed to be an imaging scope that they dont have one) let us know.
edit... i had a quick squiz at your other thread and the review, couldnt find the camera info, do you also have a pic of it setup on your mount, im curious to see how much back focus is needed as somewhere i remember reading about this.
excellent work
clive
Last edited by Alchemy; 04-05-2009 at 06:10 PM.
Reason: why not !
Clive, The camera Paul used was a Cooled Canon 40D...
The scopes cost $2495 @ Andrews...
A flattener is in the works by a group called Astronomics in the USA. Its going to be a 0.75x Reducer/Flattener... No price has been mentioned yet on that...
Clive, The camera Paul used was a Cooled Canon 40D...
The scopes cost $2495 @ Andrews...
A flattener is in the works by a group called Astronomics in the USA. Its going to be a 0.75x Reducer/Flattener... No price has been mentioned yet on that...
Alex.
thanks alex... as you have one , what is the back focus..... do you have a pic showing the focuser as it seems to be a contention.
I dont have a pic, but can get you a shot showing what it looks like at the focus position with my SBIG. There are a lot of extension tubes involved the back focus is quite long... I dont have an exact measurement at hand, but it is quite long, as is generally the case with the RC design..
Paul,
try if you can the MPCC, it worked for a triplet refractor which most said it wouldn't. It "could" just do what you seek here. There are enough of them about that someone must be able to lend you one, otherwise I'll send mine across for a quick try (I use it often).
Gary
Scopes like this are so frustrating though for the potential buyer - the promised "virtually coma free images" have to be flattened with more expensive glass and the focuser flaps around like flares in the wind and needs replacing too!!!
Does it perform so poorly as a stock scope that it has to be "pimped" by at least another $1000-2000 to perform adequately!?
Would love to see an uncropped high res image from the scope that came out of the box.
No indictment on your image Paul - just moaning!!!!
) Such is life I guess. 
