dawson Posted March 3, 2013 Share Posted March 3, 2013 Having spent the afternoon with Ron and admiring his Ritchey-Chretien scope, and reading a little about these, why aren't they more common? It was the first time I think the name has ever registered in my head. The 6" RC is cheaper than the 6" Skywatcher Mak (£400 vs £520); how would the two compare with moon and planetry imaging, and for some DSO imaging? Thanks James RC scopes: http://www.telescopehouse.com/acatalog/Revelation-Ritchey-Chretiens.html Wiki link: http://en.wikipedia.org/wiki/Ritchey%E2%80%93Chr%C3%A9tien_telescope Link to comment Share on other sites More sharing options...
Tweedledee Posted March 3, 2013 Share Posted March 3, 2013 Very interesting question. I'm not sure of the answer. I know that RCs have a wide well corrected image plane. They are generally slightly shorter focal ratio than most SCTs (f8 or 9) and much shorter than MAKs. Better for imaging but slightly less easy to achieve higher power due to focal ratio. I have heard that they are generally more complicated to collimate, but I'm sure that as with anything, practice makes perfect. They are very compact and therefore convenient optical systems to transport in the smaller sizes. And as you say the prices are competitive in the 6" to 10" sizes. They certainly seem to have a lot of plus points. Will be very interested in any other comments on this. Link to comment Share on other sites More sharing options...
Brantuk Posted March 3, 2013 Share Posted March 3, 2013 The idea is to create optics that produce flat fields and give a true representation of the object on a flat camera chip - if that makes sense. RC designs attempt to eliminate off axis coma but fail on off axis field curvature and astigmatism. A read of this page comparing RC designs with CDK design optics is very interesting. They are very expensive scopes to produce: http://www.planewave.com/index.php?page=3 Have a look at the rest of the site - these are some of my favourite scopes but I'll never afford one without the help of Camelot lol Here's the one at Leicester Uni obsy for an idea of size: http://www2.le.ac.uk/departments/physics/news/news_items/the-university-of-leicester-opens-the-most-advanced-astronomical-teaching-facility-available-at-a-uk-university Link to comment Share on other sites More sharing options...
Doc Posted March 3, 2013 Share Posted March 3, 2013 Even the Hubble is a RC design. The single biggest advantage for the RC design over SCT's and Maks is that it does not suffer from coma. It does suffer from astigmatism, though, causing stars at the edge to assume an oval shape. Also the RC design produces a flatter field due to lower amplification factor of the secondary mirror which I think is about x2.5 compared to x5 for most SCT's. Another thing to take into consideration is that they have only two surfaces for reduced light loss. Most catadioptric types have four surfaces and triplet refractors have 6 surfaces. Each surface degrades the image, and the effect is cumulative. Link to comment Share on other sites More sharing options...
dawson Posted March 3, 2013 Author Share Posted March 3, 2013 Pat, yes that link does suggest they are labour intensive to run. I'm less interested in the tinkering side of things if I'm honest. I like the set up and go option, which is why I like my Skywatcher 127 Mak; no collimating to be done every time I set up. I've done some imaging with mine, but I'm still struggling with the tracking (though I've not had a good clear night yet to try my next steps in solving the issues). The synscan handset also still appears to be on version 1.7 of the firmware, which seems to be older than when I got it so goodness only knows how I managed that when I updated it. I am planning to try and update it again at work tomorrow, as it's the only computer I've found in Nottingham with a serial port! I've emailed the astronomiser to get a serial-usb adaptor. I'm going to get order an equatorial mount this week too, in preparation for a week off work. I am going to see how I get on with that and my 127mm Mak; I might try and go away somewhere dark for the week, but will need internet access to get help. You two have put me off the RC scopes. James Link to comment Share on other sites More sharing options...
catman161 Posted March 3, 2013 Share Posted March 3, 2013 you can get the serial to usb adapter fro maplins james for £20 Link to comment Share on other sites More sharing options...
+RonC Posted March 3, 2013 Share Posted March 3, 2013 James, I have collimated mine twice in a year, a simple 5 minute job with just a Cheshire Colli ! Link to comment Share on other sites More sharing options...
dawson Posted March 3, 2013 Author Share Posted March 3, 2013 you can get the serial to usb adapter fro maplins james for £20 I was a fool and got one off ebay for £5 or so, and none of my computers recognize it! The one on the astronomisers website is £13 I think. I'd be more confident that one will do the trick. I wouldn't have a clue how to colimate my Mak. I think that is another thread for another day...! James Link to comment Share on other sites More sharing options...
Tweedledee Posted March 3, 2013 Share Posted March 3, 2013 ****** James, I have collimated mine twice in a year, a simple 5 minute job with just a Cheshire Colli ! That's good Ron. Sounds pretty hassle free with yours. Someone somewhere is always going to have a problem with any scope and then post about it when there may be many more happy users. I see another plus point for the RC over the SCT, SNT and MAK - no big dew attracting corrector plate. Also important as Mick says fewer light loss surfaces. Thanks Mick and Kim, all very interesting info. Link to comment Share on other sites More sharing options...
Tweedledee Posted March 3, 2013 Share Posted March 3, 2013 I have a BC&F metal dew shield for my 10" SNT and in my opinion it is not long enough. My tube is 12" wide and the length of the dew shield when fitted only adds another 10.5" to the tube length. I think 1.5x the diameter is recommended. I have no dew control and sometimes have to resort to the 12v hairdrier. May have to mod it or sort out some wiring. Link to comment Share on other sites More sharing options...
Tweedledee Posted March 3, 2013 Share Posted March 3, 2013 Cheers Pat. I have two different types of 12v hairdriers, and even when switched to hot, they are probably only a couple of degrees above ambient. No good for warming fingers . I take your point about drying up the crud on the corrector. Wiring looks like the way to go. Thanks. Link to comment Share on other sites More sharing options...
andyboy1970 Posted March 5, 2013 Share Posted March 5, 2013 The Astronimiser serial cables work a treat As for RC's another issue that hasn't been mentioned is the mount really has to be up to the job and guiding is essential for DSO astrophotography, also at f8 or f9 the exposure lengths get a lot longer. Link to comment Share on other sites More sharing options...
Guest kirkster501 Posted March 27, 2013 Share Posted March 27, 2013 Hi, I have an Altair Astro 8" GSO version. Never used it for AP yet, the skies have not been fit for it. Have used it for visual a couple of times (not really intended for visual) and very nice. I am a bit nervous of collimation though.... I hear its a nightmare! Link to comment Share on other sites More sharing options...
Guest Ely Ellis Posted March 28, 2013 Share Posted March 28, 2013 Is that not just there version of a 200p. Extra's like slow mo, low profile focuser etc. The RC is actually a different scope. I was also considering the 8" GSO though, but decided I need to get more out of what I have before spending more money. Still waiting at some point to have ago with Ron's RC. Cheers Martin Link to comment Share on other sites More sharing options...
+RonC Posted March 28, 2013 Share Posted March 28, 2013 Collimating an RC is a quicker job then doing a Newt, only 1 mirror to adjust!! Ron Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now