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Hi, I have a question regarding the optical setup for planetary imaging. For my first tries I used my brand new 8-inch Meade AFC-SC with a 2x achromatic barlow lens with the filming mode of my DSLR. I upgraded to a astro camera with region of interest ROI for higher frame rates and smaller Pixel size. But to reach the common quality seen at Astrobin there must be something lacking. I searched for a 3x, 4x or even higher Barlow, maybe apochromatic for better details - but this is a very expensive den to explore, the Baader Fluorid Flatfield Converter at the top. Now I saw an especially detailed Jupiter Image also using an 8 inch SC somehow sporting a 7mm Ortho Ocular - without Barlow. So my Question is, how such a setup is working in detail (I know, it's working well 🙈 ) and what your experiences are in comparison to a Barlow based setup? (It could definitely have a better price tag) Or is the Barlow setup the better solution in the end? I'd be glad for your comments. CS, Hermann |
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Hello Hermann! Unfortunately I don't know the pixel size of your planetary camera. With an ASI290 you are already close to oversampling at a focal length of 2 metres. You need excellent seeing for a barlow to be of any use. Many greetings, Michael |
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Hi Michael, Thanks alot for your expertise. I really have to take a closer look at this fundamentals regarding optics, kamera resolution and oversampling - really didn't get this yet. My camera is a ToupTek ATR3-16000-KPA (3,8 μm Pix) with a nice region of interest-Feature. But framerates are still low - possibly due to the small tablet pc I'm using to capture. One known issue I'll have to address. Maybe I'm just too demanding for a single try capturing Jupiter in soso seeing conditions, without a filter. I've seen way better images based on an 8 inch SC telescope, and was sure it's a Problem with my setup. But seeing, framerates, oversampling, filters and (lack of) experience in postprocessing could equally be responsible for the quality of the result. (Jupiter Aufnahme) Best regards and always CSHermann |
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Hi, A camera with 3.8Micron pixels will reach critical sampling around f/20. So you 8”SCT with a 2x barlow should be fine. Don’t go higher, it will only lead to a smeared out image which will not contain any more detail. There are many things in image capture that affect quality. The most important ones are collimation, focusing and thermal equilibration. On top of that there’s the seeing, but thta last one is something you can’t do much about. processing for lunar or planetary involves a couple of steps. stacking and registration of the movie frames in autostakkert sharpening eg, wvaelts or deconvolution final processing in a photo editing software. to assist you Further I’d need to see the movieclip , that would help me asses the actual data. If you don’t have that the raw stack from autostakkert. Clear skies wouter. |
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Please allow me to throw in a few unordered thoughts without warranty. Though dependent on seeing, as a rule thumb, the maximum useful f-number is camera pixel size * 5. ATR3-16000-KPA = 3.8μm * 5 = ~f/20. There are no more details to tweak beyond. You may dismiss the flattener since the small planets, when centered, will not be affected by coma. A fast frame rate and short exposure time help freeze poor seeing and air turbulences. Even with a smaller ROI, your DSO camera may not be the fastest around. A favorable frame rate for lunar and planetary starts at 80fps. As frame rates increase you may wish to use a PC with a fast SSD disk to avoid frame dropping or buffering. A SCT has a long focal travel while its focal length varies as the primary mirror is moved (during focusing). You can insert an extension tube to obtain a little higher magnification instead of using a barlow. Since your camera has a large sensor you may try 2x2 binning = 7.6μm which may forgive the use of a say 3x barlow, but it needs to be a fine one and good seeing provided. Binning accelerates the frame rate. If you are after larger planets you can choose to 1.5x drizzle the image when stacking in Autostakkert!3. If you can afford it, I recommend a camera sporting the small IMX462 color sensor. It is highly sensitive to near-infrared in that high frame rates can be achieved even with an IR pass filter, say around 640nm. So equipped you can combine color (with IR-cut filter) and infrared images to achieve higher contrast. Since I could not get any more details with my ASI290MM (2.9μm), Celestron 8 and a 2x barlow, I purchased a low-cost 1.6x barlow (lens-unit only) that threads to a 1.25" nose piece. That way the f-number will be around f/13~f/14, since the barlow lens sits closer to the sensor without mechanical extension involved. Nevertheless, the less glass in the path the better. So far with the C8 and ASI290MM I obtained the best lunar images at native focal length, i.e., without a barlow, yet I still need to learn the ropes, if only clouds would permit experiments. Best luck! Robert |
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Dear wouter, dear Robert, thank your very much for those highly appreciated insights. They add some very valuable information. @wouter I'll have to find the used raw-data and get it to you somehow. If I still have it, I'll just send you (or anyone interested) a download-link or is it possible to upload the clip to Astrobin? There should be notes on the used postprocessing routines too. It would be very illuminating, what the differences are and how they add up in the resulting image. @Robert The ACF-Variant of the SCT delivers a flat image without the need of a flattner - so there is just a Schmidt-plate and the mirror in the optical pathway. The idea of lengething the path for -higher magnification is a new twist to me tough. I think i could use the 2x barlow with higher distance to the camera for a test with 2x2 binning or the higher distance alone for magnification with full resolution. How to achieve maximum framerate with the Touptek will be subject to some testing. In my case it could be a very slow drive implementation - some alternative hardware and some optimization should get the cam to 80 FPS (I was capturing at about 16-30 as far as I remember). I also have a 4 GB raspberry Pi on my desk, that to my regret also has a very bad USB-implementation, killing the advantages of its great processor performance. Regarding filters I understand, you recommend a combination of frames shot with IR filter and IR Pass filter for better contrast. Do you use a filter wheel or drawer for fast filter change? On Jupiter you would use a maximum of 2 Minute clips without derotation (that i really dont understand  ). What do you use to darken the image, so the brightness of the planet or Moon is not too high? A polarization filter or something else?Another camera with a smaller and faster sensor would come after such experimentals. Learn to work with what you got - is one of the rules I learned about astrophotography. You cant buy quality images with money, they need real effort  and clear skies  ... plus the energy to stay up and running, when the kids are asleep at last  So CS to you all, and thanks a lot for your thoughts. Best regards Hermann PS: but no one uses focal projection with an ortho ocular like he does. Thats really interesting. But the main principle could be the same: just a two-Lens construction for maximum magnification and clarity - calculated to f/20 |
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Hello Hermann, Oh good, the ACF is coma-corrected. That escaped me. Contributing factors to a high fps are short exposures and 8-bit data recording. I do not know the settings for the Touptek, but there should be some room to play with. A fast USB 3.x and an SSD would be future-proof. Yes, I am using the ZWO mechanical filter wheel, but there are alternatives. The wheel also serves as an extension while a barlow can be placed at either side to manipulate the magnification factor. When seeing is good I do not combine visual and IR images. Jupiter rotates fast around its axis in that longer videos will smear the clouds. Since I prefer simplicity I take videos below 2 minutes. Haven't tried it yet but the software "WinJupos" is capable of "de-rotating" longer videos. To avoid over-saturation I expose slightly shorter than the capture software would recommend. No filters other than IR-Cut or IR-pass used, rarely a quad band filter for Jupiter. Regarding another camera... with these wise words you are ahead of me. 👍 Now I have a question, what are you running on the Raspberry PI? Cheers, Robert |
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Hello Hermann! As Robert has already written, filters really make sense with the moon and planets! I also use a manual filter wheel, equipped with an IR pass, an IR / UV block, a green filter and a Venus UV filter.  With the frame rate I would always choose the maximum and if necessary increase the gain and, as Robert wrote, choose 8 bits. If the seeing is good enough, then I use an Antares 2x ED Barlow. I haven't tried eyepiece projection yet, but I think there are special projection eyepieces. Greetings, Michael |
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Thx Michael, I could sport a semi functional QHY filterwheel of a mono-setup I'm actually fiddling with. To reduce color depth to 8bit sounds like a big price to trade for framerate. In DSO imaging you use lots of (at first) invisible information in this 32 bit data, to lift contrast and colors from later. For anyone interested (e.g. @wouter), I uploaded the original dataset of my Jupiter shot Download here I analysed frame quality and exported best shots using Pipp, then stacked via Autostakkert. For postprocessing I used RegiStax 6 Wavelet filters and finalized with Photoshop CS2. After a long and cloudy winter and only punctual spring improvements it will take some time to find all equipment and relearn postprocessing details. I'm sure your generous information will help next planetary season. Thank you all, and please add to this thread if you have more to share. Best regards and CS Hermann |
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@Robert ... I did not forget the Raspberry part 🖖✨🤓 I got hand on a Raspberry Pi model 4 with 4GB Ram and installed Astroberry on a 32 GB SD card. The process is easy and it doesn't take longer than half an hour to have a completely preconfigured system up and running. Astroberry uses the apps kstars and Ekos and further relies on the lNDI database of hardware drivers. You can remotely tap into the desktop by a remote machine like a PC/Laptop, smartphone or tablet and remote control your equipment. I laid this project aside because i did not get my QHY mono camera working with the INDY drivers. Everything else is pretty stable and straightforward. but you have to learn a whole software platform from the very beginning and to check if your hardware is compatible. At last, I didn't see the point in trading in my PC platform that offers compatible drivers and software for all my hardware - and could easily be remotely controlled using windows remote desktop on my laptop. Additionally I have to build up (and down) my equipment every session anyway - to polar align, three star align and focus manually, set up guiding and do lights and darks by hand - so there's not much left to be remote controlled in the end. If you got any questions though, let me know and i'll be glad to help if I can. Always CS 🖖🤓 Hermann |
