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I will be correcting the problem in my RC as described here: https://www.youtube.com/watch?v=nHuLrYe-oik You may find this information usefull as well. |
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I am still trying to figure out if this was corrected or not in recent releases. I bought mine in late 2021 from TS and the baffle gas a small extension threaded into it. I probably should email TS and ask, maybe they sell them separately if someone doesn't want to 3D print their own. what kind of issues are you facing? |
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Wow. This leaves me feeling pretty stupid, as I have owned a GSO RC8 since September 2020 and never noticed a problem with it. Perhaps I am just not critical enough, but my flat fields have always worked (even in bright moon) and I don't notice an edge brightning effect from stray light as described. My baffle does have a screw-on extension, but it is not shaped in the way shown in the video. |
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I purchased the RC8 carbon from TS in September ‘21. It seems that they must have fixed the issue: The baffle tube’s front piece has a slight conic shape. From the front, there is no direct view onto the camera/end of the focuser possible. Also the center of the secondary can hardly be seen through reflection in the primary mirror as the baffle tube just blocks the view. In addition, I might have never noticed the issue as I always imaged with a dew shield attached to the tube. Björn |
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| I have older RC. I am getting reflections of strong stars into my images. I suspect that I also get some extra noise. |
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| Thanks for this one. The last few months i tried to figure out why my RC always shows big light blobs/reflections around brighter stars - i think i now know the answer. I wanted to order the light shade mentioned in the video but it seems that there is no one available for my smaller 8" scope. I just asked TS if there is one available. I'll report back if i have an answer from them. |
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Michael Timm: As expected, TS replied soon. They are currently designing the light shade for the 8" RC. They could not tell me exactly, when it will be released for production, but they promised that it WILL be released some day :-) |
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| I never had the problem on my old 8RC, but it is very apparent on the 10RC. |
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I have seen a problem with my TPO-branded truss RC10 which I acquired second-hand in May 2021. It's a late 2020 manufacture. I'm unclear if the problem with bright sky or moonlight is the same as when imaging close to bright stars, but imaging anywhere near Alnitak I've had a similar glare or flare problem to the one described in the video that couldn't be corrected with flats. I encountered this when imaging the Flame Nebula close up at f/8, especially with the Oiii filter. I did a lot of work to try to minimize this. https://astrob.in/synr4g/B/ I purchased and installed the TS Optics mask after encountering this video some time back. I haven't had (or noticed) an issue since, imaging on nights with at least a 50% illuminated Moon and my heavily light-polluted skies (Bortle 8). It's a nice, compact solution and the plastic primary mirror cell cover still fits over it which perhaps makes it preferable to a 3D-printed extension in that respect (despite the one down-side described in the video). However, I most recently imaged the Horsehead Nebula at f/8 with this mask in place and I experienced a severe diffraction artifact from Alnitak, again just outside the field of view. I believe this may have occurred due to one of the shiny, silver set screws on that baffle. You can see the effects of this artifact in my most recent image in my gallery, with rays coming in from the direction of that star. That can be seen here: https://astrob.in/9p4qo6/0/ I plan to cover the set screws with flat black gaffer tape in hopes of resolving that issue. I should have thought of that initially. In contrast, I also have a TPO-branded carbon fiber tube RC8 purchased in January 2021 which came with a screwed-in, slightly tapered extension to the baffle. I don't know if this was part of the original design or something added later, but it's definitely detachable from the main baffle tube. I've seen it depicted in drawings from GSO, however. I haven't seen the issue on the RC8 (also imaging the Horsehead nebula up close) that I have with the RC10 close to bright stars or on heavily moonlit nights. Here is almost the same shot of the Horsehead taken with the RC8 and a micro-4/3 sensor camera vs APS-C: https://astrob.in/s7mgvh/B/ I suppose it's also possible that the smaller scopes are less susceptible to this since I believe the central obstruction on the RC8 is ~47% vs 44-45% on the RC10. |
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| I would not try to diminish the quality or usability of such telescopes in any case but I have to say something about... The term RC is been abused for more than 20 years even for optics that are NOT true RC. Meade was the first to claim they produce an RC telescope causing the reaction of many manifacturer that makes REAL RC. They did a public cause to Meade and finally They had to remove the term RC and use "coma free" instead. Suche claimed RC optics made in China are still not true RC. The only way to produce such an optics is by hand since there are two optical sets (primary and secondary mirrors) that havo to be worked toghether as a pair. While the first paraboloidal shape could be obtained by machining de surfaces, the Hyperboloidal aspherization could be made only by hand, figuring the two pieces of optics toghether and one in relationship withthe other. Such a work imply the use of an interferometer to figure out the shapes in relation after each correction. It is quite clear that this process is not an industrial type one and it's very costy and time consuming. Suche so defined RC's from China are more a kind of aspherized classical cassegrain than RC's. If You buy a true RC flattener and place it on Your optical path it simply doesn't work. The baffles on such systems are crucial and, if You just introduce some sort of reducer or flattener, it could simply don't work anymore. In a real achromatic system such an only mirrors optic any introductions of glass elements destroy the advantages of having just two reflective optical elements so why an RC? Not only buffles but also materials and flocking it is very important on such telescopes, using a material that seems to be very dark and unreflective but is not in infrared i.e. could be an error causing unpredictable results when measuring. Typical obstruction of an RC is quite large for the fact they produce an aplanatic field (which means free of coma but not flat) so they can use this to cover very large illuminated fields but is not mandatorty, if don't need such big field You could use smaller secondary mirror to have less obstruction but, if You choose an RC is also for that big field right? In the end if You don't really need sucha a large illuminated field You can choose other optical shapes that are less complicated to do and so cheaper... RC is the most used scheme by professionals but in big diameter, the advantage of such a scheme in small aperture is really less evident, specially with the use of corrector/reducers/flatteners. |
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Giovanni Paglioli: Um, modern computer aided manufacturing can definitely provide matching primary and secondary mirrors without hand fitting. Finally, the use of a lens as the third element is part of RC design according to this extensive article on RC construction. https://en.wikipedia.org/wiki/Ritchey%E2%80%93Chr%C3%A9tien_telescope#Further_corrections_by_a_third_element |
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Giovanni Paglioli: We’ll this statement surprises me a bit. Since Meade’s “RC” case, some years have passed and industrial manufacturing has advanced, so I see no reason why these mirrors shouldn’t be producible through CNC machines as the previous post notes. Besides it: if a true RC can only be made by hand shaping, I am curious how Hubble, the VLTs and many other research grade telescopes came into existence? Björn |
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RC simply refers to the optical design, not the manufacturing process, and if these GSO RCs weren't true RCs you can bet that the same people who sued Meade would have went after them as well. While I wouldn't argue that the GSO RCs are made with the fit, finish, construction, etc. that ones from Planewave, Officina Stellare, ASA, etc. are, they are still a Ritchey Chretién telescope. You do get what you pay for, and with a GSO you can get some wonderful images, but you're going to need to mess with things, change focusers, curse at collimation and tilt if you run a heavy imaging train, and the like. Once you get them dialed in and any needed or desired changes made to them they are a pretty decent telescope, but when you can order a 16" for 7k and a 20" for 13k (according to Astronomics) and you compare them to the premium brands that is like comparing a base model Chevy hatchback with a high end BMW, Mercedes, or Porsche. Even with that said those GSO RCs do open up some of that faint and fuzzy astrophotography to people who couldn't afford it before. My old 8RC was what got me hooked more than anything. My wallet hasn't been happy since. |
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| I've never stated that a gso RC scope Is not good and can produce excellent images at good price point. I've gotvthe chance to have some of these scopes under test also with interferometer and I've found they'r Just not "true" RC. Machining a hyperboloidal shape It Is possibile actually but to "finish" the optics toghether You have to make a correction, look at the interference figure than correct again and so on until the final double shape Is obtained. It Is possibile to include glass elements in the system but you have to make it in the project and not as a standard external element. There are brand that produces specialized RC flatteners that, coupled with gso telescopes, simply doesn't work. I repeat these are very good telescopes but they are simply aspherized hyperboloids made in series. In fact You can Always buy just one optic (primary or secondary) for sostitution, It Is not possibile to do so on true RC 's, You have to send the optics to let the optician to figure out the other. Nobody cares anymore about true or not rc's since the marketplace is no more the same of 20/30 years ago and many new optical schemes are on the market nowdays. Big scopes are possible 'cos they are made by multiple panels and, even so, they are still finished using interpherography and corrections to the final shape. Many years are necessary to do so... Anyway I just think that the advantages given by the RC scheme are almost useless for nowdays astrophotography, the cost Is simply too high for the needings. If You make Just measures or spectral work It could worth the extra money but just with diameter from 12" up on my opinion. Choosing a gso for having a cassegrain/long FL telescope alternative to Newton it is very convenient and a good choice. Mine Is just a "technical" point of view... |
