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Hi, just looking for feedbacks from astrophotographers who currently use a coma corrector on their Newton 8 to 10 inches (200 to 254mm) with FD of 4 or 5, and with large sensors (full frame, maybe APS C, but not the small ones). What brand do you use ? Are you happy with it on the corners of your images with large sensors ? Do you have proofs !? :-) Link to images are welcome to be able to judge (before cropping if possible :-) ) Thanks |
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I used to use the Baader one. It's OK but not up to APS-C. This one below is definitely better: https://www.ebay.co.uk/itm/TS-Optics-MaxField-2-Newtonian-Coma-Corrector-3-element-TSKomakorr/372432064320?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l9372 |
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Hi, just looking for feedbacks from astrophotographers who currently use a coma corrector on their Newton 8 to 10 inches (200 to 254mm) with FD of 4 or 5, and with large sensors (full frame, maybe APS C, but not the small ones). My opinion tele vue big paracorr type 2 is the best, 52mm diagonal should work with a full frame camera. |
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For full frame to work you'll need 3" focuser and coma corrector. Anyone that will tell you that it's not so is fooling himself. While Paracorr-2 or GPU can give OK-ish stars at the corner of 43.3mm diagonal, they are far from being perfect. As for the smaller sensors, GPU is good since it doesn't add 15% of Paracorr-2 to the focus. But vignetting is quite strong with this coma corrector. I did side-by-side comparison of these two correctors and both were good at APS-C. |
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| Thanks @Nadir Astro ! |
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Nadir Astro: Hi Nadir, I am curious whether your comment only applies to the small version of Paracorr-2 or both the small and large versions of them? In your opinion, for FF (or even bigger), which coma corrector can outperform the big Paracorr-2? Thanks. |
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Nadir Astro: Big paracorr’s diagonal 52-53 mm and works with 3” focusers, if paracorr is not perfect, which one is perfect I don’t know. |
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Wei-Hao Wang:Nadir Astro: Hi. My comment was about standard 2" version of Paracorr-2. There's also large 3" version which will require 3" focuser, larger secondary mirror, etc. I personally haven't used 3" Paracorr yet, but I know that there's also ASA Wynne 3" corrector. Before larger Paracorr 3" came out it was a standard for imaging with 24x36 and 36x36 sensors on newtonians. |
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 Hi Jérémy, Here is a flat taken with Baader RCC1 , on a 200/800 newton (UNTC) . So that you can get an idea of vignetting on a large sensor (ASI071) at F/D 4 . RCC1 is not the best corrector there is but has a "good" price/performance ratio . Backfocus is 91,5 mm (on its M42 connector) or 94,5 mm (on its M48 connector) : it leaves a long lenght (space) for a filter wheel, or a filter box, an OAG, a rotativ ring ... Adjusting Backfocus will require precision at F/D 4 (or less) , and must be done by trial and error, depending on the optical assembly and telescope focal , you will not have to reach exactly 91,5 mm/94,5mm but may be less or more from time to time : stars will give the answer ... RCC1 must be fully inserted in the crayford (eyepiece holder) + at least 20 mm (i would say 22mm in UNTC) for focusing : 91,5 - 20 mm = 71,5 mm long for other accessories in fact (the rest is inside the eyepiece holder) A long backfocus can be advantageous , it is a little bit (may be) more sensitive to tilt too : provide good quality rings of fitting and mechanical accessories to avoid tilt "as much as possible", OAG , rotative rings etc ... ). Few elements before choosing a corrector : - size of camera sensor (as you said in your first post) - F/D (as you said) - total optical assembly with desired accessories : Filter wheel or not, filter box, filter screwed at the front corrector or not, rotativ ring or not, OAG or not ... (all this can be put in a short backfocus too ) - capabilty to make a good collimation in a short F/D ratio (good quality laser already collimated for exemple, or middle quality that you can colimate yourself) - and of course, budget ;-) Here is the link on my last picture https://www.astrobin.com/bsk0jz/C/?nc=user with RCC1 . I still have a small tilt ptoblem to solve I think (right sides) , and also will have to reduce a little bit the backfocus distance (may be 0,5 mm ) in the same time , once the tilt problem will be solved (or better) For the time being , I would say that RCC1 makes the job, I have to make mine  before evaluating wether it is necessary to choose the higher quality .Hoping it can help you to choose a corrector Clear Skies ! |
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| Thanks a lot for this in depth feedback ! |
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Hi Jeremy, here is (bad) single shoot 360" EOS 100D APS-C 22,2mm X14,8 mm at F/D 4 . Do not take care of noise , just have a look on stars at corners : baader Rcc1 200/800 UNTC . I took this picture in mars 2020. (no flats, no darks, nos bias offset ... and of course, no star reduction and no crop ;-) , just a basic post processing of a single light ) It gives a better idea of what baader RCC1 can do when backfocus is Ok on large sensor Clear Skies !  |
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 Hi Jeremy, here is Capella B&W picture quickly taken tonight (UNTC 200/800 ASI071 Baader RCC1) . Backfocus is Ok now, no tilt any more  . Stars are not so bad in corners ;-) . The small default we can see, from time to time, is because the "chanfer mask" is not 100% regular, this is not a corrector artifact (This chanfer mask was also quickly hand made and I will manage for installing a new one : we can see on shiny stars the "beginning" of the spider from time to time ).Of course, no deconvolution and no crop on this picture CS |
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I'm very happy with my Explore Scientific. Perfectly round stars with a Canon 600D (aps-c) and a skywtcher quattro f/4. Now I have a zwo 1600mm cooled and since it's heavier it introduces some flexure and the stars aren't any more as perfectly pin point as they used to be, but obviously is not CC's fault I based my choice of buying the Explore Scientific CC on this beautiful comparison bewteen 4 different coma correctors here: https://www.astrofotoblog.eu/?p=856 |
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For full frame cameras: Some people here use skywatcher's TSGPHU or F4 komacorrector SW in full frame, which are the same, with different labels (users Sky-watcher Johny and Christoph Lichtblau, for example),. There will be a small vignette, easily removable at pixinsight. It's not ideal, as it does not give full field luminance, but they work well and they take great pictures. The common paracoor will not work anyway in a full frame (diagonal of just 29mm, up to aps-c formats), the vignette is very big violent (half of the photo). The 3-inch Paracoor would be the ideal, if it weren't for the price. But there's a new, very good one, a little cheaper, that some people here are using well (Arnauld Peel) , it's is a 2.5 inch full frame, the Winne Comma Corrector. A new focaliser would be necessary. Regards Ricardo |
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Michele Vonci: Thanks @Michele Vonci ! Very useful. Thanks as well @Joel85 . Pictures are definitely worthy in chosing the right setup ! |
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Thanks @ricardo leite ! I have seen the work of some of them but didn’t notice what they were using. Nice references ! Thanks for your help. |
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Hey. Here in Germany, the most professionals recommend the GPU Optics Comakorrektor from Hungary for a 8" / 10" Newton. I am waiting my selve for it. Because of Corona you have to wait for every little screw for months. CS Christian |
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Hi Jeremi ! I have spent several month on : - Tilt problem - backfocus setting ( + filter ...) --> Between 92 mm and 92,5 mm ( for F/D 4 : it depends on telescope focal, like the GPU ...) I have also cleaned primary and secondary few days ago, and changed the chanfer mask on primary ( a better one) Here is a single shot 360" (HEQ5) gain 90 ASI071 taken with RCC1 UNTC F/D 4 : now it's OK / I do not think a can get better stars CS  |
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For big sensors and coma correctors (3" inchs, for example), one interesting questions is: how can we handle with 2" filters (once they wil, problably, decrease the full illuminination) ? |
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ricardo leite: Depends how big is your sensor. If it's 24x36, then 50mm round unmounted in most cases. For 36x36 only 50mm square. There are also a larger size filters like 65mm square. You can always run calculator here: http://astronomy.tools/calculators/ccd_filter_size |
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Hi Jeremi ! |
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I have some experience with both the TV big paracorr and the ASA Wynne Corrector. Both were used on a 15" F/4 and SBIG 11000 full format CCD. The 3" TV corrector worked nicely straight out of the Box. The Wynne corrector had some centering issues, which were resolved after some hassle. So, in my opinion the 3" TV is a safe bet if the 1.15x increase of FL is acceptable. |
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I always a RCC corrector from Baader, mostly with F 4 with my Boren Simon Astrograph. No vignetting, stars are pinpoint in the corner. The most important issue is that you have been coilimated your telescope carefully and the distance to the corrector to the chip is 91,5 mm. IUf you work with a Newtonian telescope you must made flat field images, and when you use a DSLR camera use a light pollution filter of Hutech or so if you use a CCD mono camera do not forget to take dark Frames and bias frames, the same is always needed if you use a DSLR camera and take many images as you can. With a DSLR I use ISO 400 with my Canon EOS 6 D . About the corrector: you can buy this item at Teleskop Service in Germany. There are other correctors such as from Baader but they are very expensive. |
