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Hi Trace, My first question is what mount do you have? That is most important part of the entire rig. These OTA's are little heavy. In theory you want a mount that can support double the weight of your imaging rig. Also it needs to track fairly well with low PE and backlash. Long focal lengths can be nasty to you especially if you find your self chasing seeing conditions. My recommendation is to get the best mount you can afford and build from there! To quote Alessio Pariani Alessio Pariani: I agree with him 100% I have lost track of how many OTA's I have had getting frustrated for one reason or another and it really had nothing to do with the equipment. Just my technique. And believe me when I tell you I am still learning!!! CS/Bob |
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Bob J:I'm starting to shift my focus and money away from two scopes to cover the wide FOV and the FL. Ultimately that's where I want to be. I need to upgrade all of my equipment. Everything I have is 40yrs old and pure manaul, so in addition to the scopes I was planning to purchase the CEM60 mount. However, after viewing Lazy Astronomy's video I realized it was probably undersized. So I've decided to put more funds into the mount, and get the CEM120. If you have any more to share about your experience with this mount, that would be appreciated. |
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Alessio Pariani:Hi Alessio. I appreciate your comments very much, and I agree. And yes, I'm still manually guiding. Honestly, I kind of like it and will miss it once automated. That old school method just has a more intimate connection with the imaging, I think. Kind of like driving a stick (literally  ) vs. an automatic...funny that I mention it, my Infinity G35 sedan is a 6 speed manual, not many of them around. Guess I like sticks . For sure I will need to get my mount and all of the automation hardware, and then gain some experience with it and my 8"f/6 newt. I will move toward the scope purchases only after I have confidence that I understand their strengths and weaknesses for what I want to achieve.
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Bob J:YEP, 100% agree on the mount. My current mount is pretty much irrelevant to this discussion, it has to go. It is the original Meade GEM I bought 40 years ago, modified with a 7" Byers worm drive that runs very nicely, albeit manually under my guiding joystick and eyeball glued to the illuminated reticle for what feels like hours . Not really possible in cold winter weather, that's why I have no winter targets in my collection.
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Trace, As far as the CEM 120 is concerned I am quite pleased now. The 120 and the 120 EC and the 120EC2 are identical except for the encoders. The fit and finish is excellent. The many amenities that they have are fantastic. Through the mount wiring is real nice. Built in 4 port USB hub. Ample power connections, USB3.0 connection, an extra DIN connection just for what ever you want it to be. And all mounted on the saddle plate so there are no wires hanging to snag or sag your imaging train. It has built in GPS. Multiple ways to connect to the mount via USB, Wifi, ethernet, and the old standard RS232 serial port. It has the capability of installing a Pole Master internally so it is only exposed when needed. The hand controller is well laid out and very intuitive. Honestly I never use my hand controller as I completely control it with my PC through ASCOM. That is all I can say about the 120 as I have only had encoder models. I know the 120s have PEC training but how it performs I can not say. I am an early adopter of the 120 EC and EC2 mounts. I originally got the 120EC on the first shipment in to the US. Serial #5. That mount worked extremely well. Right after I received it they announced the 120EC2. I actually got iOptron to trade mine in for the EC2 at the NEAF show. This is serial #3. This was the only one in the US at the time. 1 and 2 went to a friend of mine in Mexico. I can honestly tell you I was sorry I did get it and did not keep the EC model. The firmware was still in development for the EC2 and it was performing poorly. Many beta releases and 1.5 years later it finally is performing as it should. I am getting total guiding errors around .35 This mount is really heavy and is really not too portable. It is mainly meant for a permanent pier although they do have a tri-pier that is really nice. There are some images on my gallery CEM120 Loaded of my mount. I have loaded it down to over 100 lbs of payload and it worked just fine! There are not too many other mounts in this weight class with all of these features at the price that you won't have to sell a kidney for. LOL Bob |
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Bob J:Wow, what a setup! Geez, I can't see the mount  . Well, I'm going to have to figure out a strategy for porting mine around. I'm too hooked on dark sky sites, which is not my backyard. I don't mind hauling heavy as long as I can lift it...pretty sure this mount is at my limit though.I'm not clear on the use cases for the non-EC vs the EC (EC2 is just getting in the $$ozone). I know it's an encoder on the RA, but not really sure what the in-practice implications are for a mobile setup using PPEC with the non-EC vs. have the EC. Isn't the EC mainly a benefit for observatory setups. This is what OPT explained to me, but I'm not convinced they knew what the use case differences were. |
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| I have the Orion 10 RC Truss. I love it, I replaced the stock focuser with a Moonlite. I chose it over the closed tube - I believe that the closed tube has the focuser attached to the primary, whereas the Truss has the focuser physically separated from the primary. |
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Trace: Here is a better image to see the mount CEM 120 EC As far as the encoders I would agree that the EC2 may be better served in an Observatory. The dual encoders allow it to be manually slewed by loosing the clutches and still knowing where it is in the sky. The EC obviously has a single RA encoder which improves the tracking and constantly is correcting any PE that may exist in the worm drive. Ultimately that is what we are trying to achieve with any imaging mount. Like I said I don't know how well the PEC is on a non-EC model and how well it can be trained out. I had a CGE Pro prior and I had to run several PEC training curves and build a PEC model that would help. It worked fairly well. I am not sure if you can write a PEC curve from outside software such as PEM Pro to the 120. I think it runs a single worm cycle and that is what is used for your correction. I am getting old and I could not imagine lugging this mount around to dark sky sites! May hats off to you if you do!!! Cheers Bob |
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Trace: A couple of things - if you are going to be portable, the CEM120 might be difficult for you to use. A new CEM120 is $4K. If you want a portable mount, you may want to look at a used AP900. That breaks up in to 2 parts which can be transported very easily (or even an AP1200 - there's an AP1200 for $5K on AM). Setting up those mounts is a breeze. They are "older" technology, but they are amazing instruments. I have 2 AP1200s in my remote observatory and they just work. And Astro-Physics will answer all calls - regardless of how old the mount is. Very minimal maintenance as well - I haven't re-greased any of my mounts since purchase. With regards to encoders - if you are going to be mobile, encoders may not mean that much for you. Encoders still help with guiding and tracking assuming you create a decent point model (it does not take too long to create a point model, meaning, even for portable use, you can do it fairly quickly), but most of these mounts are good that they give you consistent tracking errors that can be easily guided out without the use of encoders. Some may say, the encoders may help in slight wind. The question though would be, is that worth spending another $3K? CS! |
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Hi Jim, Thanks for your comments. Good point on the separation of the focuser for colimation. Bob shared that point as well, and I think that's a considerable benefit. Orion's marketing spiel on the focuser makes it sound top notch: "The focuser is a CNC-machined 3.3" dual-speed (10:1) linear bearing Crayford focuser features a stainless steel rail on the drawtube that provides extra support up to 9 lbs. of imaging gear without flexure or slippage." There's clearly a consensus they are garbage  .Trace |
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Bob J:Impressive!...as Darth Vader once said. Sort of resembles him actually .Thanks for your follow up on the encoder. Unless I learn that it will improve my long duration autoguiding, I'll spend the funds on other stuff.
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Dhaval Brahmbhatt:Appreciate that input Dhaval, the AP looks like a fabulous mount. But I've decided to go with the CEM120. It's got about twice the rated load capacity, and my 8"f/6 has a lot of sail surface. When I travel to remote sites, there's nothing worse than a breeze ruining the travels and the setup time. I need it to be as stiff as possible. My existing mount is 50 pounds, so I'll just have to get used to an extra 10 pounds. Thanks and CS Trace |
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To everyone who joined in the discussion here, I would like to say thanks again for sharing your opinions on this and giving me guidance. I've learned a lot from it, and have more to learn before making a new scope purchase. I will probably not purchase two scopes in the near term. As I mentioned, I decided to focus some of my funds onto the mount, upgrading my plans from a CEM60 to a CEM120, which I purchased today. I'm really looking forward to moving into the modern age of AP  . No more manual guiding and needing to stay glued to the scope through the night. My plan is to get my 8"f/6 newt mounted on the 120 and learn the ropes of autoguiding, and in the meantime continue my learning on the various OTA's.Cheers and CS Trace |
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Chris Sullivan:Chris, which scope may I ask, at f/2.8? Have you seen the amazing results of Erik Pirtala using a 6"f/4 imaging Newt? |
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Trace: The Sharpstar HNT f/2.8 hyperbolic Newtonian. I actually already own it, but I'm waiting until galaxy season is over before I start using it. I might end up mounting it earlier because my 8" Newtonian has been giving me a ton of headaches. It got destroyed by a storm (we had a tornado a few towns over) and the replacement arrived with just about every screw loose and the focuser not even completely attached. I've really been having a tough time getting it collimated - never had an issue before. |
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Sounds like the replacement got the tornado treatment also . Thanks for sharing the info on the SharpStar, I have not come across that in searching for wide field alternatives to the RASA. Erik's images give me hope there's a fast and wide reflector that can perform very well. Just too concerned about the reflections in RASA bright star images.
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Jim Miller: Similar to you I have the GSO 10” RC Truss and love it, mounted on my 120EC, combined they are fantastic and on still clear nights I am doing about 0.22rms, took a while to get there but the firmware is now really good. |
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| Hope I can do well with the non-EC 120. Still not entirely clear on the tracking differences. Clear that the encoders remember position, but don't understand their impact on tracking. |
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Is an RC really better than a F/6 Newtonian with a coma corrector? I see no reason why. The RC is coma free, but needs a field flattener/reducer. The Newt has very little field curvature, but coma. Not much at F/6. Even a simple coma corrector would work perfectly at f/6, even if it is a bit soft at F/4. These things are not linear. An F/6 newtonian is very easy to collimate, and the tolerances are not nearly as tight as the fast primary of an RC. |
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| Indeed, my thinking has been how to get to longer focal lengths and reasonable speeds. Of course aperture is key here, and I started the long FL scope planning around an RC10. One aspect of the newt is wrestling with the back focus issue and having the imaging train far out the side of the tube. The RC does better with this I think. |
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Erlend Langsrud: An RC does not not a field Flattener, I have had 3 RC's and my current 10"GSO RC Truss, produces a perfectly flat field. An F6 Newt is not going to have any advantage over an RC apart from less than 1 stop of difference, now an F4/F3.6/F2.8 to my mind really does have any advantage, they are just so damn fast at gathering images. As for a Coma corrector, I went through about 3 months research and you get what you pay for, just have a look at some of the images uploaded here and you will see coma in most Newts apart for those like Lacerta, Orion UK, who really do employ the very best coma correctors. Trace: Trace as for back focus issues, the RC indeed doesn't have a problem, whereas a Newt with a corrector will have, but they are issues that can be fixed so easily with adapters and a little bit of thought. |
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John Kulin:Erlend Langsrud:An RC does not not a field Flattener, I have had 3 RC's and my current 10"GSO RC Truss, produces a perfectly flat field. The focal plane of an RC is strongly curved. The radius of the plane is 199mm for a 8" f/8 RC (M=3). It is similar to a 70mm rafractor with a focal length of 560mm, but the RC will produce round stars, so the cievature is much less visible.. I guess the curvature is hard to spot unless you use a large CCD on a small RC. Also, if you can spot coma in an f/6 scope with coma corrector, something must be very wrong. The weak spot is that simple CCs introduce some SA that would soften an f/4 newt, but Even that would be negligible at f/6. |
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A truss RC is likely in my future, to serve for long FL imaging of smaller targets. It's the front runner based on what I've learned from this thread. I already use an 8"f/6 Newt for mid range size targets (1200mm FL). So the RC would not compete with the Newt. And to keep the RC relatively fast, I would like to go with a 12" f/8 and a .67x reducer (f/5.3 and 1633mm FL). So, returning to the goals of my opening post, here's where I am after all the great feedback:
Trace |
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Trace: Great plan. I think an f/4 photo newt (FL 600-800) is more versatile than a FL400 RASA. F/2 is only beneficial when you actually want the entire field. The Rasa is actually a competitor to small f400 refractors and telelenses. At a given focal length, f/2 reaaly is 9x faster than f/6. At a given aparture, it is more complicated. I also like RCs because they produce round stars and you dont have to deal with dew on the corrector plate (which is a real pain). For full format sensor you will still need a corrector, like this for instance: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4006_TS-Optics-RC-1-0x-Flattener-Bildfeldkorrektor-fuer-Ritchey-Chretien---2--Anschluss.html |
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| Thanks Erlend. My camera senser is APS-C...would the image be flat in a 12" RC with .67x reducer? |
