Yeah carbon fibre fixes that constant refocus need. I find my CDK17 and the RCOS 12 I had hold focus extremely well once the mirror is close to ambient.''
This is an interesting thread as it highlights the decision making process a lot would be going through for this type of scope. It inevitably winds up with GSO because of the value and the high quality optics. That's probably exactly why DSI switched markets.
I have had a DSI RC10C for about 5 years and have really only had one successful image (my fault, not the 'scope). A 4 frame mosaic of Omega Cen. http://www.astrobin.com/full/80259/0/ I haven't used it for 3 years or so since I set it up imaging on a forecasted clear night and went inside for a cuppa. Came out again and it was raining and the primary was like a half-full soup bowl! When I eventually removed the primary mirror, cleaned and very accurately replaced it, I had managed to put it out of collimation. Having no experience there I struggled along until Paul published his work in that area and now I might have finally fixed it. Haven't had a suitable night for > 3 months to test it but here's hoping. One of my favourites, NGC 300, is now rising and it fills my QSI638 perfectly with the RC10C.
Probably my only change, if I had my 'druthers, is to get a CF tube rather than what it currently has. The RC10C seems to require an awful lot of focusing and I would think a CF tube would reduce that.
Cheers
If you like Charles I can come out one afternoon soon and check the collimation with my tak scope Charles. What type of focusor do you have? Is it a 2" or a 3" and does it have a 2" adapter?
Quote:
Originally Posted by gregbradley
Yeah carbon fibre fixes that constant refocus need. I find my CDK17 and the RCOS 12 I had hold focus extremely well once the mirror is close to ambient.''
This is an interesting thread as it highlights the decision making process a lot would be going through for this type of scope. It inevitably winds up with GSO because of the value and the high quality optics. That's probably exactly why DSI switched markets.
Greg.
I refocus via automation every 90 minutes or so but the change is barely worth mentioning and more to do with seeing conditions and altitude I think. I found the RC12 quite stable too since I put the mirrors in a truss. In the steel tube is moved around like a wobbly custard.
Further to your question re the truss employed. I have found no issues with this design at all. The 12" is using a Serrurier truss and it exhibits no flexure as described by Peter. I am not saying it is not a relevant concern; just that I have not seen anything in my long subs to demonstrate there would be a problem.
I guarantee it's flexing....but probably not much at all.
The original design by Serrurier was based on the telescope weighting tonnes, hence no material on the planet was not going to sag...and Serrurier solution was indeed elegant. The instrument load was trivial in comparison.
Barnes Wallis employed a similar principle when he designed the 64meter Parked radio dish. Keeping a rigid hyperbolic shape on a dish that large, is nigh impossible...unless you work with gravity...which he did and employed a twin spiral structure that in bending under load, kept a hyperbolic shape but changed the focal point! Clever stuff!! (the receiver cage is easily moved in/out)
With amateur equipment loads, it's a moot point...well...up to a point. Instrument loads on amateur telescopes however are often not trivial when compared to the weight of the telescope...as is evident by having to toss the GSO focuser.
I'd suspect with modestly heavy cameras (STX16803+FW7+AOX or a similar FLI16803 system) it would be detectable.
My point being...it works, but it's not optimum.
Last edited by Peter Ward; 29-08-2015 at 12:01 PM.
Reason: typo
I am not saying that there is no sag. The concept of that type of truss is to cancel out flex and sagging in multiple directions. It should not matter how big the system is, gravity will act in a corresponding way. Besides I am simply reporting I don't see any evidence of sag in my images and that is what really matters.
...........The concept of that type of truss is to cancel out flex and sagging in multiple directions. It should not matter how big the system is, gravity will act in a corresponding way......
Yes...but the Serrurier only works correctly if you know what the long and short arm masses are.
Given amateur cameras can weigh from a few grams, to a few kilograms...it's
not possible to design a "one truss fits all"
Last edited by Peter Ward; 29-08-2015 at 12:11 PM.
Yes...but the Serrurier only works correctly if you know what the long and short arm masses are.
Given amateur cameras can weigh from a few grams, to a few kilograms...it's
not possible to design a "one truss fits all"
So is that why you bought a truss in the Alluna Optics scope? Some of the spiel you used looks very much like that on your site and on the Alluna Optics site. They claim that sag is eliminated and that many lesser brand names would have sag in them. Sounds a little bit like marketing hype to me. Is your scope designed specifically for your payload? Or are they simply designed to take any payload commercially available. The difference might be very miniscule.
I suppose if you are looking at absolute necessity for precision, then the bells and whistles stuff is great. Though no point in having such a fine scope stuff in a light polluted environment in my opinion. Might as well use a lesser scope.
So is that why you bought a truss in the Alluna Optics scope? Some of the spiel you used looks very much like that on your site and on the Alluna Optics site. They claim that sag is eliminated and that many lesser brand names would have sag in them. Sounds a little bit like marketing hype to me...........
Err....I don't see the point you are trying to make..... the instrument end of the Alluna's is not a truss.
The load bearing (up to 50kg instrument loads) is taken up in quite a different way to ensure optical alignment is preserved.
The secondary supports are a truss system that have little commonality with Serrurier's design.
Last edited by Peter Ward; 29-08-2015 at 04:15 PM.
Reason: clarification
If you like Charles I can come out one afternoon soon and check the collimation with my tak scope Charles. What type of focusor do you have? Is it a 2" or a 3" and does it have a 2" adapter?
Thanks for the offer, Paul. your expertise would be very much appreciated. The RC10C focuses by moving the Secondary mirror so there is just a solid connection at the back-end. I have a Tak. collimation scope but, I hesitate to say, I think it is out of collimation! It would be good to compare with another. I will make a new set of adapters when it stops raining up here. My machinery uses 3-phase power and my generator is outside and rain + 415v is not particularly good. I'll get back to you soon.
Thanks again.
Charles
I have had a DSI RC10C for about 5 years and have really only had one successful image (my fault, not the 'scope). A 4 frame mosaic of Omega Cen. http://www.astrobin.com/full/80259/0/ I haven't used it for 3 years or so since I set it up imaging on a forecasted clear night and went inside for a cuppa. Came out again and it was raining and the primary was like a half-full soup bowl! When I eventually removed the primary mirror, cleaned and very accurately replaced it, I had managed to put it out of collimation. Having no experience there I struggled along until Paul published his work in that area and now I might have finally fixed it. Haven't had a suitable night for > 3 months to test it but here's hoping. One of my favourites, NGC 300, is now rising and it fills my QSI638 perfectly with the RC10C.
Probably my only change, if I had my 'druthers, is to get a CF tube rather than what it currently has. The RC10C seems to require an awful lot of focusing and I would think a CF tube would reduce that.
Cheers
Well worth getting Paul to have a look. I bought their first one and it is a great instrument.
Response as follows. Not unexpected but worth a punt.
We've been considering this opportunity and have decided that it does not
warrant our time and effort at this time. I wish we could help but we are
extremely busy and need to be selective of which projects we invest in. I
hope you understand our position. Good luck with your scope.
Hi H. I love my GSO 12" CF truss RC. Some fiddling is required, but I enjoy that part I got it strictly to use as a galaxy scope and it really delivers. To my untrained eyes, I'm well pleased with the results from GSO optics.
H don't make it sound like your being forced to settle for something second rate, as properly tuned they turn out wonderful images. Since I have sorted out the 'issues' that I had with the collimation on my RC08 I am impressed with what it is now producing with my DSLR. I am so impressed I am now considering upgrading to a RC10 - but the CF tube version to keep the cost within my reach. Just do it.
Might be worth PM'ing RickS too H about 10" RCs. He was using one in the past and I seem to recall found the focal length challenging in terms of time to gather sufficient light/data. Basically was tough to get sufficient data on a single galaxy in 2 nights.
May not be an issue for you as I understand you run on auto in the backyard over many nights from reasonable skies.
Might be worth PM'ing RickS too H about 10" RCs. He was using one in the past and I seem to recall found the focal length challenging in terms of time to gather sufficient light/data. Basically was tough to get sufficient data on a single galaxy in 2 nights.
May not be an issue for you as I understand you run on auto in the backyard over many nights from reasonable skies.
I was using the RC10 with a KAF-8300 and the combination was slowish. It's also a little oversampled for the seeing that most of us get (0.56 arcsec/pixel.) That system would collect signal at about half the rate of my most recent combo of Ceravolo 300 @ f/9 with a KAF-16803.
It was usable but a sensor with larger pixels would be a better match. I think H has a STL11K? That would be a decent match for a RC10 wrt imaging speed although I would expect it to need a flattener and the vignetting would be significant.
Some of the spiel you used looks very much like that on your site and on the Alluna Optics site. They claim that sag is eliminated and that many lesser brand names would have sag in them. Sounds a little bit like marketing hype to me. Is your scope designed specifically for your payload? Or are they simply designed to take any payload commercially available. The difference might be very miniscule.
, how often do you focus Paul, more than once a week?.
I got it strictly to use as a galaxy scope and it really delivers. To my untrained eyes, I'm well pleased with the results from GSO optics.
