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Found 15 results

  1. i am looking for a coma corrector for astrophotography, i have a skywatcher 254/1200 pds, a nikon d5100, and a skywatcher off axis guider, what would you recommend?
  2. Reason for sale: bought it intending to do imaging with my Dob, but have instead acquired a separate dedicted imaging setup. The Coma Corrector is AS NEW, having been used only once to test if it works visually (it does!). There is a full description at: http://bit.ly/1OPa6hu, but to summarise: * 4-element optics. * Incorporates helical focuser (so that, once it is optimally positioned, focusing does not move it). * T2 and 48mm adaptors included (unused) UK retail price (Telescope House) is £249 £200, to include insured UK mainland postage. Payment by transfer of funds (net of fees) or cash on collection, GBP only. (Also advertised at UKAstroB&S)
  3. Hello all Im just started in imaging and I have to say I'm pleased with the first result BUT on closer inspection I see I have slightly oblong stars. So people know what I've got and done here it is http://www.astrobin.com/full/271950/0/?nc=user I have a baader coma corrector that I'm using set to 55mm from canon sensor and I have tried short exposures and I notice that it's still there in short exposures. Could it be collimation? It's the only thing I didn't do that evening. I would appreciate your input! Thanks Gerry
  4. I have an Orion 8" astrograph f/3.9. I'm looking to purchase a Baader 2" Multi Purpose Coma Corrector - MK III, I'm currently imaging with a DSLR which the backfocus should be fine. My question pertains to looking into the future. If I purchase this coma corrector now, which says it has a backfocus of 55mm, and later upgrade to a different camera, say a ZWO ASI178MM, will I still be able to use this coma corrector with that camera when the ZWO camera says it needs a backfocus of 17.5mm. How does the backfocus of the coma corrector relate to what the camera wants for backfocus. Hopefully I've worded my question well enough. Any help would be appreciated. Thanks in advance.
  5. Baader 2" Newtonian x1.7 Glasspath & Coma Corrector for sale https://www.baader-planetarium.com/en/2"-glaspathcorrectorr-17x-for-newtons.html I used this corrector with my Baader MarkV binoviewer with my dobsonian reflector telescope. The corrector is supplied ready for the Baader MarkV Bino. - However, it can easily be adapted for T2 connection, you would need to buy the additional T2 Adaptor BA2456320. The corrector is in excellent condition and comes supplied with both original end caps, original box, allen key and thumbscrew. - You have the option of attaching to the MarkV via an (invisible) grub screw (or remove that with the allen key and use the thumbscrew instead) NOW SOLD
  6. Hi, guys i have a Opticstar ARX200 f/3.9 astrograph which came with a f/3.9 adjustable coma corrector and I am struggling to work out the back focus! I am using a Nikon D5100 DSLR which I know the the air gap is 48mm from sensor to imaging plane. When I use the corrector I can only gain focus with it when it is 0mm but still get major coma around edges of frame. I have tried at every point from 0-55mm and cant gain focus anywhere else?? Anyone any ideas what I am doing wrong??
  7. I am looking into getting a coma corrector at some point. It might be after I get a new OTA, as that one will likely have more coma, and that coma isn't the biggest of issues right now. BUT, I've been surfing around, trying to figure out how coma correctors actually work and what other effects they might have, and it has been a bit confusing to me, especially concerning focus. I've read several places that some CC's will either require in-focus or even out-focus, even out-focus in such a case where prime-focus, which wasn't possible before, actually can become possible. I'll quote what I read, but I'd like people to give some comments on how that would work out: "I've found that the GSO requires about 10mm of focuser in-travel when using the supplied eyepiece holder and an additional 25mm of spacing between that holder and the optics unit. For every additional 4mm of spacing, you save about 1mm of in-travel required. So I guess if you put 110mm of spacing in there, you wouldn't change the focus point at all. Of course, the correction would be awful. If you screw the same 70-75mm of spacing onto the back of your 2"-1.25" adapter, you'll need about 1.5 inches of out-travel to reach focus. Since my focuser won't go that far, I just pull the whole assembly up and out of the focuser about and inch or so. Thus, you'll always be able to reach focus with 1.25" eyepieces and possibly even with cameras setup for prime focus photography via the T-mount adapter that wouldn't be able to reach focus otherwise." Louis D - This was interesting to me, as I am actually not able to achieve prime-focus as of right now with my current OTA (Celestron 130SLT), and was wondering if acquiring a CC now instead of later, would be able to fix this for me? And if so, does the focal-length attributes of the CC determine this? Like some CC's acting as a 0.9x reducer or a 1.15x. And what CC's would you recommend that I eventually get? My current plan for the new OTA, is a Skywatcher 8'' Quattro CF, so I'll want a CC for it eventually, but if the CC can also "fix" focus issues with my current OTA, that would kill two birds with one stone as I currently have to use a barlow to focus my Nikon D5200. So any insight into this or general advice would be very welcome! -Mathias M. M.
  8. I recently tried imaging M7 with my 6" f/4 Newtonian. I had earlier commimated it with a Cheshire and Howie Glatter and was sure of the collimation. However, when I imaged using my DSLR with the coma corrector installed, I get focused stars off centre and not on the optical axis. Anyone experience anything similar before? What could this be? Tilt in the optical train? The focuser was drawn out only about 5mm to reach focus along with a 50mm extension tube. Any suggestion is welcome.
  9. Over the years I have done a lot of Excel calculation to solve my astronomy problem when I try to make parts work together. Most of them has been my private and only in Swedish, some of them I have published on a Swedish forum and I believe some people have found them useful. Now I decided to translate them into English and put them on my homepage for downloading. It's always hard to understand Excel sheets that others have put together, but I hope that these ones with a little help of the instructions on my homepage could be interesting and useful to some of you. http://astrofriend.eu/astronomy/astronomy-calculations/astronomy-calculations.html Beware that it could be something wrong in the calculations, if I find something I try to correct it. I don't take any responsible of it, you use them at your own risk ! /Lars
  10. Hello! I bought a GSO 2 inch Coma Corrector for my 8inch Newtonian. I'm still having terrible coma on one of the corners which is actually worse than without the coma. The rest of the corners look fine with proper guiding. Here are some details and what I've done to try and solve the issue: 1- Spacing is 75 mm just as recommended. 2- Used a Cheshire, laser collimator, and a webcam to check collimation. 3- Squared the focuser so that it's orthogonal to the optical axis. 4- Tried another DSLR Note that once I collimate and double check that I'm collimated with all the tools, I always try to do a star test and collimation appears off (the dark spot isn't in the middle). Last time I tried to collimate the primary using a star but it's really tough to fine tune since due to the focuser's sag, I can't be sure that the star is in the middle of the fov. My take on the problem is that when I'm using the DSLR with the coma corrector, the weight is moving the focuser away from the center of the optical axis but I'm not sure this if this is the case. I've tried everything and I'm out of ideas. Below is a test image I took for Lagoon Nebula. Notice the coma on the left top side mostly, while the right side usually appear to have no coma (not the case in the attached image though for some reason, but usually the right side is fine). One more thing I've noticed, the stars on the left corner appear to be out of focus while the rest of the image appears well in focus (used a Bahtinov mask with APT bahitnov focus tool) There's also another image I took for a distant light to check collimation (since clouds covered the sky as soon as I decided to do a star test). It appears to be fine and I was able to center it better but didn't capture the image. Please let me know if you have any idea what's causing this. My number one suspect is the focuser's sag preventing me from doing accurate collimation although everything appears to be normal while collimating. I'm giving this another 2 weeks of my time, if it doesn't work I might quit astrophotography till I'm able to afford an APO. One more thing that needs to be added, when using the GSO CC I had to move the primary mirror up the scope by around 2 cm to be able to achieve focus. Clear Skies!
  11. Funny thing - I have an ASI1600 + EFW and am connecting to SW coma corrector which requires 55mm spacing. The camera is 6.5mm the EFW is 20mm, total 26.5, so 28.5mm spacer required - sound correct hopefully? But the suppllied spacers are 21mm and 16.5mm which doesnt help (and doesnt seem correct even for a colour ASI1600 with no EFW) There is also a 11mm female/female adapter and a very short 1.5mm male/male adapter, so I guess I could use the 11mm F/F followed by the 1.5mm M/M + the 16.5 giving 29mm but this seems a bit complicated! Just wondering what other folk do - I cant be the only one with this problem. Any thoughts please?
  12. 650mm fl /130mm aperture reflector scopes are great for imaging with the fast focal ratio of 5, but they do suffer from coma aberration due to this. My scope is no exception and seems to have especially bad coma. As coma should reduce with increasing focal ratio, as an experiment I cut a 108mm circlular hole in a piece of card and placed it centrally across the front of the OTA, effectively changing the focal ratio to 6 with the reduction of the aperture from 130 to 108mm. Below are two single subs : one without the card(f5 at 120secs) and one with the card (f6 at 180secs). I was surprised by the great reduction in coma in the f6 image. (Almost full Moon so rather bright subs.) Of course the reduction in aperture means an approximate 50% increase in exposure time, but it could be useful for brighter targets.
  13. I am the happy owner of an ES 82 degree 18 mm eyepiece that I use together with a Baader MPCC coma corrector on my SW 200 mm f/5 Newtonian. Until now I have been using the CC directly attached to the filter thread of the eyepiece, which I know is not correct. I now wish to buy the corresponding spacers so to be able to use the optical system correctly, but this is seemingly more difficult than I first supposed. According to the CC specifications, the distance between the flat surface and the focal plane (camera or eyepiece) should be 55 mm. I have verified this when using the CC photographically and that worked fine. If one removes the T-2 adapter and uses the M48 thread instead, as I do for use with the eyepiece, this distance becomes 57.5 mm. Thanks to this table in a post in Cloudy Nights I was able to figure out that I need a spacing of 32.5 mm between the coma corrector and the eyepiece. The post includes some references to spacers, but aside from the Baader ones (28 and 14 mm, see here) I am having trouble to find suitable spacers in European retailers that would add up to 32.5 mm. This is why I would like to ask you for help. Has anyone solved this problem before? If so, how? Where can I buy spacers suitable for adding 4.5 mm optical path to a system with 2", M48 threads? Thanks in advance and clear skies!
  14. I have just gotten set up for the first time with astrophotography and have taken my first couple images. I have an Orion 8" Newtonian Astrograph F3.9. To the best of my knowledge I am collimated extremely well, I am still learning everything but I feel like my collimation is right on. The problem I am having is with the coma I am getting in my images. I am using a HighPoint Scientific coma corrector but it doesn't seem to be doing much, I wanted to take some photos without the coma corrector to see how it would compare but I don't have the proper adapters to attach my camera and get it to focus without the coma corrector. My question is, is my coma corrector insufficient and should I get a new one? My HighPoint Scientific coma corrector costs about $120, the description says that it is for newtonians with a focal range of F3 to F6 but optimized for F4.5. My telescope is definitely toward the lower end of that range and below what it is optimized for. I have attached a slightly edited image to give you an example of the issues I am having for your thoughts. You can see around the edges, and even when zoomed in on the stars in the center, they exhibit pretty bad coma. Just curious on what your thoughts might be.
  15. Hi everyone, really need some help as I can't get my head around this. I need a coma corrector as I'm using a Newtonian and coma is so bad so I'm getting the baader mpcc mark 3 coma corrector. I would also like to get a focal reducer of around 0.5x My question is can anyone suggest an item where these are built into one, or can a focal reducer be screwed into the coma corrector?
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