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Hello everyone, Please share your opinion. I'm looking to buy a scope or scopes to add wide field imaging and also long FL imaging for galaxies. I currently use an 8"f/6 newt with a Canon M50 mirrorless, which I'm very happy with. For the new scope (or scopes), I'm thinking about a RASA 8 and a Ritchey Chretien 10". Another approach I've considered is a Celestron Edge HD 11 + Hyperstar to reach both ends of the spectrum with a single scope. The cost of the RASA + RC and the Edge HD + Hyperstar are about the same. My goal is to choose based on the best imaging quality and speed, not the most versatile. I'm leaning towards the RASA and the RC, mostly because of the faster RC at f/8 vs. the f/10 of the Celestron. Also, buying the two scopes seems analogous to choosing two prime lenses in photography instead of a zoom lens. For image quality, that's usually the best route. But with the Edge HD, I'm not sure that's a valid analogy (being more like two prime lenses in one). Another issue I see with the Edge, but I'm not sure it's true, is switching between F/1.9 and F/10 during a single night's imaging. Wouldn't that risk the need for recollimation? Switching out the RASA for the RC onto my mount seems simpler. Thanks much |
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I'm not sure I can add anything worthwhile to this question, other than that I've been consistently impressed with the optics of my 8" carbon fiber RC. That's no knock on the EdgeHD scopes - I've been very impressed with the images from them as well, but I would definitely choose an 8" RC over an 8" EdgeHD again and would probably choose a 10" RC over an 11" EdgeHD. The only things worth criticizing are that the stock GSO focuser is pretty terrible and the dust cap is annoyingly bad. Also, I still find f/8 too slow, so I use it now with the Astrophysics CCDT67 - a very inexpensive reducer considering how well it performs. It puts me at about f/5.75, which certainly beats f/7 (and the price for the EdgeHD reducer). The focus stability from the carbon fiber tube is awesome - I can image all night without needing to adjust at all, I never have to worry about mirror flop (of course, you won't with an EdgeHD either), and I have no issues with dew and don't require a dew solution. I don't have any first-hand experience with SCTs, RASAs, etc., but I have seen people post images with odd reflections due to the front corrector or with bloated stars from the RASA's corrective elements (the ones in front of the camera). I know that some people even put an empty Newtonian spider in their dew shield on their RASA to distract from the effect. But they are amazing scopes! Speed really is key - and because I've seen so many amazing RASA images over the past year, I'm actually planning on incorporating an f/2.8 scope into my arsenal soon. |
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| RC telescopes have good reputations and for good reasons but I am a huge RASA fan! The RASA 8 is only 400mm and while I wish it was a bit more, imaging at F2 with great optics is a true pleasure. You will need different filters because of the speed, even your light pollution filter should be rated for f2. With regard to your question about recollimation of the Edge HD when switching configurations; typically recollimation is not necessary because the Hyperstar camera mount screws onto the threaded receptacle of the secondary mirror. The keyed design of the mirror receptable ensures that the mirror is returned to its original position leaving collimation undisturbed. At least that is how it has been working on my Celestron SCT. |
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| I'm interested in this topic too. I would like to hear from those who use RC in portable imaging, about whether it holds collimation well, how frequent you have to re-collimate, and how hard it is to collimate. |
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Chris Sullivan: Hi Chris, I can see why. Your images are amazing! If I go with the RC, not the Edge HD 11, I'm leaning towards the TPO RC 10 Truss. Do you have any thoughts on that type of scope? Chris Sullivan: Yes, I've seen the large light circles around bright stars in some of the RASA images. I understand it is the reflection of the main mirror in the image. I'm not sure what RASA users are doing to avoid that. Definitely need to understand that better before investing in a RASA. Roman Pierce: Hi Roman, thanks for that confirmation, I'm very glad to hear that. Of course the need for recollimation after switching configs would be a non-starter. Wei-Hao Wang: Hi Wei-Hao, great questions, thank you! By the way, probably a topic for a separate forum post, I found one of your posts regarding asin stretching to be very helpful in finishing my Lagoon Nebula image. After consulting with Roger Clark regarding the use of his rnc-color-stretch (by the way I think Roger and his website are an absolute treasure), I was not able to successfully stretch with full image size. I had to reduce the image size for the rnc-color stretch to work. It was then that I found your comments about asin stretch for linear stretching of the image, and it is that stretch that I used to finish the image. Trace |
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Trace: Just that I'd be jealous? I'd definitely recommend getting the shroud and highly recommend replacing the focuser to either a Moonlite or Feathertouch. I think that's the only thing that would cause me to get rid of my 8" RC: Getting a bigger one. Clear skies! |
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Chris Sullivan: ;) well that will make two of us. 10" RC or not, I think I'll be frustrated for a while trying to capture & process to the level of the images in your bin! |
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Chris Sullivan: Chris, my plan for the RC is at the long focal length, to image smaller targets. I think your galaxy work is direct, no reducer, is that right? Does the RC need a field flattener for galaxy work? My 8"f/6 newt with coma corrector is my plan for the mid scale imaging. Trace |
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You're far too kind. I used it at the native focal length from February 2018 (first light) until August 2018 (even though I bought the reducer with the scope) and I vowed never to use it again without the reducer. Because my light pollution (Bortle 7-8-ish) is so bad, I need to gather a lot of data to get a decent SNR. I just found f/8 to be painstakingly slow. F/5.75 feels a lot more manageable - I haven't changed my camera angle since this past March. As far as needing a flattener - it might depend on how large your sensor is. I do recall reading some people use a Hotech SCA with the scope, but I'm not sure if it's really needed. I might ask on Cloudy Nights. |
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| I will add one small thing that I haven’t seen anyone else mention, and I’m not advocating for one over the other in saying this. If you ever want to do planetary imaging as well you would be better served by the 11” EdgeHD. They’re very versatile instruments. |
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Chris Sullivan: Well may be Chris but your Imaging with an 8" is remarkable. I've been browsing and admiring your images for a few days now since deciding that an RC was a strong contender for my next scope. Regarding f/8, I hope I'll be ok since I'll be Imaging mostly in dark sky locations, Bortle 1-3. My sensor is an APS-C, don't know if that's going to need the flattener with the 10"f/6 RC. |
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If you ever want to do planetary imaging as well you would be better served by the 11” EdgeHD. They’re very versatile instruments. Hi Arringar, this is great feedback, thank you! I haven't planned to do planetary, but it does interested me some and I suspect in time I'll give it a try. Besides the Hyperstar, are there good options to configure the Edge HD at mid scale speeds such as f/6 or f/8? The f/10 is just too slow for me, I'm not getting any younger  .Trace |
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Wei-Hao Wang: I used my RC for years in portable imaging. I have not collimated it. Now, it's in an observatory. But, I should mention, it has a reasonable build quality, and that makes a difference. Regards, |
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The biggest reason why folks don't like a RC scope is collimation. That being said, RCs do stay collimated for a long time. I am not sure if you intend to place these scopes in an observatory, but if you do, then the question of collimation should not arise (with either scope) for a very long period of time. The other thing with a RC scope, as compared to one of the EdgeHD scopes, is that there are quite a few after market reducers/flatteners available. With the Celestron EdgeHD scopes, you are pretty much tied to the reducers that they sell, which are on the expensive side. One last thing that I personally like with a RC scope are the star spikes - I know a lot of people don't like spikes, but what it sometimes does is, it covers some star bloat. This was very true when I was shooting with an RC and a very small pixel camera. Without the star spikes, the star would seem bloated (which is what it does now with the Celestron EdgeHD paired with the small pixel camera and I don't get star spikes with the EHD scope). Hope this helps! CS! |
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Thanks Dhaval, very helpful points going both ways. Clearly these are both great setups. I was not aware of the difference in cost/availability of reducers for RC vs EHD. Again this is great info and I'm learning a lot through this thread. I'm a very long time newt user, and I would definitely miss the star spikes. One real joy of this hobby for me is sharing pictures with friends and family, and in almost every case, the first comment I get is "look at those stars!, referring to the brighter spiked ones. I guess if I go with the EHD, I can always add some vanes to the dew shield if that's the result I'm after. Trace |
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Trace: And you could add Optec's FastFocus Secondary Mirror Focusing System. You split the wires out on the cardinal points like the vanes in a RC or Newt and get the spikes, and no image shift while focusing.  |
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| Interesting. I assume the resulting spikes are not super straight and sharp. |
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Im Just gjetting started with my Rasa 8,. There is a circle/disc around vert bright stars, but vey faint with my setup. You can look at my Rosette nebula image to get the idea. The post processing is pretty basic, so what you see is what you get. My understanding is that the front element itself will create å rather dim "Schmidt ghost". Filters can create really strong circular reflections at F2, unless they are designed for fast optics. I therefore bought the original (and expensive...) Rasa 8 LPS filter. Maybe thats why I dont get very strong reflections. I think this "problem" with my setup is comparable to the diffraction spikes from a Newtonian or RC. I accept it as a inherent effect of the scope design. I will not try to fight it, except for coosing suitable filters. It is a sharp scope . The stars are not more bloated than with a Newtonian with coma corrector. My first impression is that the sharpness accross the field is better than budget APOs with correctors, but not quite on par with true premium scopes like TAK FSQ. (I have first hand experience with Takahashi FSQ, as well as WO APOS, SCTs, Newts etc). My rosette does not do 100% justice to the sharpness as the object was very low above the horizon and the exposures were unguided. It goes without saying that focusing and spacing is critical at f2. The one really huge drawback IMO is that you will not be able to use a filter wheel. You can use a filter drawer, but it makes narrowband imaging more of a hassle. I would go for the RC pluss RASA. I suspect that hyperstar is a hassle, and not quite as good as a RASA even if you get the collimation right. It is also hyper-expensive. I think the price of the f7 reducer is off-putting. That said: EdgeHD would be my first choise for long focal length scope is price was not an issue. |
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iHi Trace, Well I guess I can chime in whereas I have at one time owned all 3 of these OTA's, albeit my RASA is an 11". Edge 11" HD with Hyperstar...I had it a while back and found it to be an awesome and extremely versatile scope. I had a Hyperstar and a FR/FF from Celestron. At prime focus @ F10 I found it obviously slow and could not control star bloat. Also I had to buy a bigger capacity mount just to handle the weight. With the hyperstar I found it to be quite rewarding shooting at F/2. What I didn't care for was loosing the remote/automated capability as I had to manually change the filters. I found collimating the hyperstar to be a nightmare. I could not tame this for what ever reason. I can not say too much about using the FR/FF as I only had it for a short while and didn't get much usage. Never tried planetary either. Dew shield and heater is a must have! Celestron RASA...In my case I have an 11" and still own it. Overall the performance is ok. Once again you need a stout mount. I have been quite satisfied with my iOptron CEM 120 EC2. I found that using a Starizona filter slider worked for mono but vignetting was terrible. I have upgraded to the Baader UFC system and that solved the vignetting and it is a nice system to dial in the very critical back focus for the RASA. Also 2" filters are a must!!! Getting the back focus correct is a must with scope! I can't emphasize that enough!!! My problem with this scope is the focusing SUCKS!!! Mirror flop is terrible. So bad that after focusing I need to plate solve to get back to my position. Off by sometime thousands of pixels. Now to the mirror reflections on the stars... some people don't mind them. I personally think the ruin an otherwise great image. This is the deal breaker for me. I wasted many nights imaging as I found the reflections to be really bad after stacking.! Once again a dew shield and a heater is a must have! I do know that Celestron has admitted that the focus system sucks and have released a version 2 of the RASA 11". Unfortunately they will not allow a trade in or upgrade to this new model even though mine is only 6 months old. Also they lowered the price so much on the original version that I can't sell mine on the used market for what they want for it new. I guess I will be stuck with it sitting in my garage. Now for the RC...I have an iOptron 8" Photon and just recently got a GSO 10" Truss. First collimation...I was worried about this prior to purchasing an RC as I read too many bad reviews. I can say this. I have owned the 8" for 2 years now and I have NOT had to touch the collimation since I originally set it up. Now I do use it in my obs but I have had it on and off of my mount several times transporting it to my garage while using other OTA's. I have used in in high heat and extreme cold and the collimation is spot on! I bought a Howie Glatter Laser collimator for this but actually found a $15.00 Cheshire on Amazon that put me spot on!!! Diffraction Spikes!!! I love them....Main reason for wanting an RC. Dew is not an issue with either of these OTAs I do use a shroud on my truss. It also helps keep stray light out. As has been stated prior, the stock focusers are garbage. I have a Moonlite CSL on both with their mini V2 controller. Focusing is exact and repeatable over and over. These OTA's hold focus all night with little or no adjustment needed. I do use a Stellarvue FF/FR on both OTS . .8X reduction get s me to a manageable f/6.4. I can use my 1.25 " filters on both of these OTA with no vignetting. I have never tried visual observation on the RC but I have been told that is a no no as these are strictly an astrograph! I only have a short amount of time on the 10" truss up to now. I got it for Christmas this past year and the weather has been horrible. When I have had opportunity to use it the seeing has been dreadful. Collimation on this OTA was quick and spot on. The advantage the 10" truss has over the the 8" besides FL is the capability to center the focuser on the secondary with a separate adjustment unlike the 8". This can come into play if your focusing system has any sag or tilt. You can buy a separate tilt adjuster for the 8 from AstroTech. Always seems to be out of stock for some reason!!! I wonder Why? The RC is my favorite of all of these. Performance is awesome. After all, there is a reason the Hubble Space Telescope is an RC design. In conclusion: Versatility----Edge HD Speed- RASA High Performance- RC CS/ Bob |
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Bob J: My understanding is that the focuser on the RASA 8 is of a new and improved design. I havent noiced any mirror flop at all. Bob J: I am not able to spot this problem at all in your excellent images (M33, Pelican nebula) nor in my own Rosette image. I did notice this problem around a bright star in Orion Nebula, so it can certainly be an issue with bright stars. I'm guessing M45 with several bright stars would be affected by this problem. I guess Trace will have to look at the pictures and judge by himself. |
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Erlend Langsrud: You are correct about the focuser on the RASA 8. As I stated above I was talking about my RASA 11 which I believe the new version has the same focus system in it that the RASA 8 has. The fact that Celestron has admitted to a flawed focuser design with this model and they won't stand by it with a 6 month old OTA has me quite annoyed! Erlend Langsrud: Thank you very much for the compliment on my images. Yes the RASA's are capable of excellent quality images. I found that I just have to select my targets carefully to avoid any slightly bright stars. My Pelican for instance is in HA only because I had to throw the O3 data away. The stars had enormous mirror reflections around them in addition to the expected halos inherent with O3. Here is a link to an image of the Double Cluster. Double Cluster w RASA 11 I kept it because I am quite pleased with it, but if you look you will see the reflections and these stars are not what I consider all that bight! And yes I agree with you..Trace will definitely have to look at images and judge by himself. CS/Bob |
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Trace I appreciate you rose the discussion, but in my opinion, you should get more experience before spending so much money. I saw your images and, in details, I read you manually guide. That is amazing, but 20-30secs shots are very very short. You should get an autoguide camera, get experience on autoguiding system, adjust your mount and whole setup to achieve longer shots... meanwhile you may change your ideas multiple times, trust me (I did ;) ) |
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Wow! These are really fantastic responses. Thank you all very much for sharing your experiences, expertise and suggestions. This is turning into a reference, not just a topic thread. At least it is for me, I will be returning to it often to hone my understanding.Erlend Langsrud:Hi Erlend, your image looks fine, I see no obvious discs. I've seen some RASA images where it's very pronounced, and I must say I'm not a fan of them. Erlend Langsrud:I find them to be too distracting even if they are faint. But that's just me, of course everyone is different. I know some people really don't like the star spikes, but like Chris, they are an aspect of the RC that I like over a SCT. Erlend Langsrud:For now my interest lies with one shot color imaging and broadband. While I respect the amazing images (and extra work I must say) that comes with narrowband work, it's not for me at least not yet. I have used a 40 year old Lumicon Deep Sky Filter (Ha,Hb,OIII) in my backyard for the whirlpool galaxy, but the results were very poor (image has strong blue signal and no matter what I did in post I couldn't get natural color in the image). Erlend Langsrud:I think the Edge is an amazing scope and I will continue to keep it in mind, and having an 11" model + Hyperstar I'm sure would be fantastic. Equinoxx seems to do pretty well with it ;) (pure magic!!). However, the RC does appear to be lining up better with my interests. Erlend Langsrud:Well, long focal length is what I'm after, but f/10 is just too slow. Not sure if I can reduce the Edge 11" down to f/8, and how it would perform there compared to the 10"f/8 RC. I think that's a key question for me. |
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Bob J:Hi Bob! Perfect. Thank you so much for your detailed posting! Bob J:I hear a lot about star bloat in long focal length imaging. Is this because of the long subs needed for the faint target (galaxy) but stars are then over exposed? Very sorry to hear about your RASA 11" experiences. Sounds like early adopter blues. Again, very sorry to hear that. Maybe there's a skilled shop that can resolve the mirror flop and focuser issues at a reasonable cost? That's a serious piece of optic to gather dust in the garage. I hope that can be resolved for you some day. I really enjoyed your comments on your RC experiences. Wow, nice Christmas gift!! The Orion 10" truss comes with a 3.3" dual speed focuser. Is this one of the stock focusers you're referring to? From their marketing material at least, it sounds like a quality focuser. That said, I would never purchase any Orion product given their original owner only policy for parts. Thanks for your closing thoughts on the RC, and the other scopes. Makes sense. If you had a choice between 10" carbon fiber tube or a truss, what would you choose? |
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:Very much agree and second that, your images are fantastic. The only image that I see the disk in is the Double Cluster. It's very faint, but I agree it is not adding value and again I'm not a fan of this type of artifact from the optics. |
