AweSIM

Hi, I recently purchased a ZWO ASI294MC Pro and was very happy with the results till a few days ago when all my processed images started turning up horrible. I've narrowed the problem to calibration frames not being correct. I've listed all problems with the calibration frames in this post, in hopes someone here can help me sort them out: PS. For all frames, I kept the camera temperature at 0C, gain and offset at 10. (And while we're at it, what gain/offset values do you guys use and why? Is it just a personal preference or is there a way to determine what gain/offset should I use? Does it depend on target, visibility conditions, narrowband filters, etc?) Also, I used the following exposure times for different calibration frames: BIAS (0s), DARKS (300s), FLATS (5s), LIGHTS (300s), DARK FLATS (5s). Also, the frames were captured in SGP and processed in PI. 1. The bias frames are wierd, to say the least. Being a DSLR user till recently, I'm used to seeing the raw, bayered, stretched BIAS frame to be an image full of random noise with no discernible patterns. When I look at the ZWO ASI294MC Pro's BIAS frames, and stretch it, I can see the bayer grid pattern very clearly. The GREEN pixels have the lowest brightness while the BLUE pixels have the highest brightness. I took BIAS frames by detaching the camera from the OTA and putting its cap back on and turning off all lights in the room (to ensure no stray light leaked in).In the first attachment, you can see auto-stretched image of a BIAS i took with my earlier NIKON. The image is bayered but still the noise is random. In the same image, you can also see the auto-stretched image of the BIAS i took with ASI294. The bayer pattern is clearly visible. If I split the CFA based on each CFA channel (1, 2, 3, 4), and auto-stretch them, the noise is random. However, the clearly different bias of each channel in the CFA raw file is what's bothering me. I haven't been able to find samples of a BIAS frame online taken from this camera, so I'm hoping that someone here with the same camera can tell me what I'm doing or understanding wrong here. 2. I took 20 darks of 5m each. The uncalibrated DARKS show the same bayer pattern and auto-stretch barely shows any amp glow. However, when I calibrate them against the MASTER_BIAS and integrate them into a MASTER_DARK, and look at it after auto-stretching, I can see no bayer pattern and the amp glow is clearly visible. This tells me that what I'm doing is right so far. However, when I calibrate flat frames against the MASTER_BIAS and MASTER_DARK and integrate them, I see a grainy result that shows the vignetting clearly but the amp glow is visible as a dark patch in one corner. This is wrong, I think. The exact steps I'm doing are listed in the guide that I'm following: https://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html If it helps, I've uploaded 5 files of each type of frame (due to space constraints) on google drive that are available at https://drive.google.com/open?id=1fsxw_LIDH7B-DqJrN7WBXQQhOwB-ezKz if you want to take a closer look at the data. So far, I've tried a lot of combinations of settings in PI but haven't been able to find or come up with a workflow that reliably works for me. I would be really really really grateful if someone could help me out or point me in the right direction. Finally, is it possible that I might've damaged the camera and that's why its not giving me good results now? I took superb images of the Orion and Rosette just days earlier and only now I am facing these issues. I lost raw frames for those targets so I cannot compare BIAS/DARKS of those images. I haven't dropped the camera, haven't gotten it wet (except when its cold and dew forms outside the casing. I cool it down via SGP down to 0C from 10C in about 4-5 mins. When warming it up, I sometimes ask SGP to warm it up to 15C in 5 mins but most of the time just stop the cooling aid so it warms up by itself. Is that the right way or a recipe for a disaster already happened or waiting to happen? Thanks, A very anxious member who's dreading something's massively wrong with his very expensive gear that he cannot afford again. =( Asim

Hi John. Thank you so much for your response. I'll try that configuration again and let you know how it goes. Your point regarding seating of the elements is a good point. I'll double check that too. I'll also try to post an image of what the finderscope shows. Thanks. 🙂

Hi, I have a SkyWatcher 9x50 finderscope that came with my SkyWatcher 200 DS OTA. The other day, I was disassembling the eyepiece of the finderscope to clean its lenses and I kind of messed up. When I unscrewed the crosshair retainer ring, I flipped it over to pop out the lens, expecting it to have only a single lens. Contrary to my expectations, two lenses and two spacers popped out. Since it happened very quickly, I don't know the order these lenses are supposed to go back. Although I have tried assembling back a couple of possible combinations of these elements, I am unable to properly focus my finderscope. The eyepiece of the finderscope has the following elements inside it: 1. A retainer ring with crosshair stretched across it with a screw thread to lock everything in place. I know this is the last element in the assembly. I'll denote this with [ # ]. 2. A small spacer (maybe 2mm), denoted by [ = ] 3. A large spacer (maybe 10mm), denoted by [ === ] 4. Two double-element lenses with one side flat and the other side convex, denoted by [ |) ] I've tried the following combinations without success: A. [ # === |) = (| ] B. [ # === (| = |) ] C. [ # . === = (| |) ] But none of these combinations are working. I remember how much I had to screw the objective lens in or out to reach visual focus for the finderscope, but now the focus is occurring near or just outside the limits of the primary lens threads. Also, the view through the finderscope show strange halos which aren't centered. I'm hoping that someone here might possess the same finderscope and can tell me what order do these elements go inside the eyepiece assembly. Thanks a lot! Asim

Hi! Thanks a lot for that information mate! I had thought that I would've needed to buy extra extension rings or adapters. But you're right, the camera itself comes with all the required accessories. That is impressive. 🙂

Any advice from anyone here? 🙂

Hi, I have a SkyWatcher 200 PDS OTA and a Nikon D90 camera for imaging. A friend of mine is coming to Pakistan from Australia and I'm planning to have him purchase and bring over some gear for me. I'm ordering a SkyWatcher Coma Corrector for F5 scopesscopes, and perhaps a ZWO ASI294MC ProPro camera as well. I want to ensure that when he comes, I will have everything I need and not some missing items. In particular, I'm worried about back focus distances and spacers required. I want to ensure that I be able to use both my D90 and ASI294 MC Pro with the coma corrector. But I'm not sure what spacers I will need. The coma corrector manual states it requires a back focus distance of 55mm. The ZWO manual states it has a back focus distance of 6.5mm with the 11mm T2 extender taken off. There are some spacers included in the package but I'm not sure what they are for and if they will fit my setup as I'm not really well versed in the science of thread types. I don't know what is the back focus distance of D90. Can you guys please help me identify what adapters and spacers I'll need to ensure that both my D90 and ZWO can be coupled to my scope? Since we don't have any astronomy shops in Pakistan, and my friends don't come frequently from abroad, I want to avoid the situation where I have the cameras and the coma corrector but can't use it since I don't have the proper spacers or adapters. Thanks and best regards, Asim Sohail Pakistan

Hi Earling! Thanks a lot for sharing those images. Seeing that you have the same setup as myself, the images you shared are so much insightful! Just recently, I managed to go to a dark sky site and had the chance to photograph the Andromeda myself. I was constrained on time so took 5 minute stacks of 30s exposures each and there's a good chance my focus wasn't perfect as I bring my Bahnitov mask along. I've shared my final stack below. I can immediately see a few things: The coma in my pic is noticeable clearly even though I haven't cropped any part of the frame. In your pic, I cannot see any coma and certainly not even close to what I have in my stack. Your image processing skills are way better than mine as I've blown the core of Andromeda and you've managed to keep it intact. To me, #1 is a clear indication that I NEED to be get my hands on a Coma Corrector now. It should get me much better stars across the field. Even then, I have a lot more to learn. Can you share how long your Andromeda stack was? When you say "unguided", I'm assuming you meant tracked but not auto-guided. At the moment, I'm also thinking about getting an auto-guider setup for myself. Seeing how better your pics are than mine, I'm getting doubtful if I'm overspending and that I simply need to get a CC and not invest in an guider scope/camera and a dedicated astronomy camera. What would your thoughts be about it? I live under VERY light-polluted urban skies, so much so that my city images suffer from a massive pink/brown overcast. What sort of skies did you take these images of yours? If you live under as light-polluted skies, then that's a reason for me to stop doubting my equipment and work on my skills, instead of investing in a dedicated cooled camera and auto-guider setup and narrow-band filters to allow me to cut light pollution and be able to take longer, tracked exposures that will allow me to see more detail in my images.

Hi! Thanks for your advice. Yes you're right. Whereas the coma is not problematic for visual work, but it is for imaging. The second image I uploaded was the same image but at 100% zoom. Since most galaxies and nebula appear quite small on the camera frame, I usually have to crop an image to allow more detail to be seen. This is where coma becomes a lot apparent. When I initially got my OTA, I didn't know that much about coma and I frankly didn't get it why would so many people settle for high quality, small aperture refractors when you could have an 8" newtonian for far less cost. But I have learnt my lesson. 😃 =P In Pakistan, hardly any company sells high quality astronomy equipment so I'm stuck with my newtonian (which is an impressive instrument in its own). Over the years I've learnt the importance of having a small setup that is easy to transport to dark sky sites than having a big setup that stays stranded under my light-polluted urban skies. Maybe in the future, I would invest in a fast high quality refractor. But at this point in time, I'm wondering if a coma corrector can bring me peace and satisfaction of having crisp stars. Judging by so many comments on this post, I'm actually very hopeful that I won't be disappointed. So most certainly, I will invest in a CC very very soon. 😃

Thanks @Ronclarke and @Grimbles for sharing your coma corrector details. I'll be putting in my order shortly. Thanks a lot guys. You have all been a great help!

@JamesF thanks for that valuable insight. I'll look into skywatcher coma corrector. :-) @Ronclarke and @Grimbles. Would you be kind enough to post a link to the coma corrector you're using? Perhaps if you could share pics that could show the difference your coma corrector makes to an image vs one without it. And if I understand you correctly... You're saying that my images would be s lot better if I invested in a coma corrector and that I don't need to switch to a different scope, right? Finally, I see that coma correctors have very different prices, some cheap, some expensive. What would you recommend for my scope? My scope has a 2" focuser. And would I need focus extension tubes to attach my dslr? Perhaps if you would kind enough to share a picture which shows how the CC fits into your optical train... :-) Thank you so much for your responses. :-)

Hi, I am a very proud owner of SkyWatcher PDS-200 F5 newtonian reflector and I've been using it for many years now. I think I understand the process of collimation well enough. However, even with my best efforts, I still can't get crisp stars. I've tried to ensure that my collimation is good. I've tried to ensure that my focus is good. But even then, my images suffer loads of coma. One of the best images I've been able to snap is the following. If you zoom the image up to 100%, you'll be able to see how bad coma is at the edges of the frame. I am aware that newtonian scopes suffer from coma, but is it really as bad as in this image? For a long time, I've been mulling over whether I should get a coma corrector (how is it different from a field flattener, btw?) or a different scope that doesn't suffer from coma. But I don't have answers to the following questions that pop up in my head: Should I get a coma corrector? If so, how should I go about choosing one for my scope? Can you recommend a suitable coma corrector for my scope? Should I also get extension tubes for the scope's focuser? Or should I get a different scope altogether? If a good coma corrector is gonna cost as much as a scope, I'll probably be better off getting a more portable scope. If so, which type of scope should I be looking at? I know any discussion about possibilities for a scope is very open-ended, but I really just wanna get your perspectives on this problem of mine. Is my current scope good and am I using it wrong? Or is it bad but can be improved to perfection with a coma corrector? Or is it a lost cause and I should rather invest in a better (and more portable) scope? Also, I would really appreciate if any of you guys can guide me how could I improve this image I've shot. This is one of my best attempts but it is nowhere near the awesome images I've seen elsewhere on this forum. I took this image from a really really really dark sky site. I shot it with a Nikon D5100 attached to my SkyWatcher PDS200 F5 mounted on an NEQ6 Pro mount which was polar aligned and tracked but without any PHD autoguiding (cuz I'm not very learned on the subject with regards to hardware required). The image is a stack of 10 images, each 30 seconds long (cuz my DSLR doesn't support computer controlled exposures longer than 30s). Any tips and guidance is most welcome. I would love to be shown how can I improve my skills. Thanks, Asim Sohail

Thank you everyone for responding to my query and sharing your thoughts on this issue. You guys have given me a lot more to think about, and well as raised more questions in my mind. I have updated the topic question in the first post to list these questions, as I didn't want to start a new thread for follow-up questions. If you have time to spare, please go through the edit I made to the question and share your thoughts. Thank you for your invaluable advice. Asim

Thank you for responding Roland. I have gained new insight and knowledge from your reply. Thank you.

Hi Olly. Thank you for that in-depth explanation. I clearly have to learn and understand a lot more than I currently do. As per your advice and Carole's and Roland's, I think I will settle for now on a Mono camera with fixed filters, then upgrade to having a guidescope and guide camera, and finally get a filter wheel. Does this sound like a logical order? Also, would you mind if I pm you some follow-up questions? Thanks a lot. 😃

Hi Roland. i appreciate that you do seem to understand my confusion and thought process. Thank you for your valuable suggestion. I do believe that I should save for a mono cam and filter wheel. If I have some more funds, I would even try to save for a guidescope and a guide camera as well. From what I've read on Carole's blog, a mono camera and filter should work quite well even in light polluted areas due to the fact that they let in such a narrowband. Thank you once again. 😃

Hi. Thanks for your take. Your suggestion will definitely help me make an informed decision. 😃

Hi Carole. Thanks a ton for your valuable advice. I had a look at your site as well and have bookmarked it to go thru it all. I found an in-depth blogpost you shared there too titled "Why change from DSLR imaging to CCD camera". I will be taking a closer look at your equipment to refine my selection of cameras. Thank you for sharing your views. And thank you for taking time out to explain all this in-depth to a novice like myself. 😃

Hi, I have a SkyWatcher P-DS 200 telescope and an NEQ6 Pro SynScan mount to go with it. I've done plenty of astrophotography over the past year or so using my Nikon D90. My D90 recently suffered hardware failure and is no longer usable for imaging. So I'm trying to build up my knowledge of what to look for to replace and improve my setup as far as astrophotography is concerned. I've tried using my google skills to gather knowledge but it hasn't proved very fruitful so far. Thus I am turning to you guys to share your wisdom. I love doing photography of deep sky objects and planets equally. 1. I understand I need to invest in a CCD imaging camera, but there are so many options in so many different price ranges. I've read about using web cameras for imaging. But from what I've read, web cameras usually have a resolution of just 640x480. Isn't this too low in order to get a good quality astrophoto? Also, I believe web cameras are not capable of taking long exposures (say, over a few seconds). Instead they take video which is processed in registax or iris or a similar software to work with individual images. On the other hand, I've seen really expensive CCD cameras like those from Altair that are not even color. Should I invest in a web camera capable of taking poor resolution video or invest in a decent camera from (say Altair), or I should abandon this route completely and have my D90 repaired? I would love to be able to image in color. How should I decide which of the 3 routes should I go? And what should I look for in choosing a camera? Sensor size? Megapixels? Brand? Color or black and white? 2. I don't have an auto guider, and don't know much about its limitations. Till now, I've constrained my exposure to less than 30 seconds. Should I save my money by not getting a CCD for primary imaging and repair my D90 instead, and instead invest in an auto guider scope and camera instead? If I don't invest in an autoguider, will a CCD camera (like Altair) not be an improvement over my existing D90 at all? I am aware that most of us here have taken small steps in this hobby: incrementally updating our kits. I don't have that luxury partly because I live in a country where astronomy equipment is of nobody's interest. So I have to have a friend bring it back from a trip abroad, which isn't very frequently. Also, there is no second-hand market here that I can sell my old gear to before upgrading incrementally. So I would prefer to future-proof my investment by getting gear that I will not have to replace/upgrade anytime soon. Even my SkyWatch PDS 200 and NEQ6 were brought many many years ago and are still serving me well. I know these are very subjective questions and there might not be a definitive answer. But I would love to hear your thoughts as to how you would solve this conundrum if you were in my place. Thanks everyone! Asim ------------------------------------- Edit: After going through all the responses posted to this topic, I have realized that guiding is a must if you're using narrow-band filters since they let in so little light that very long exposures are required. On the other hand, I have some follow-up questions: Why is it that mono cameras are more expensive than color cameras? Technically, color camera is giving you three channels worth of data whereas mono is giving you three times as long an exposure. But I fail to understand why is there such a cost difference. It's possible to use a color camera without any filters. But is it possible to use a mono camera without filters too? Would it see all visible wavelengths and render them as a greyscale image? If so, technically, I can get a mono or color camera first, and then get a filter wheel + filter set. Am I correct in assuming this? Carole, you mentioned in her blog that filter wheel caused a headache for you due to light leakage. Which is why I thought a better way might be to simply use individual filters when needed. But the lovely people in this thread seem to believe that this is not a big issue. Should I try to save more and get a camera with built-in filter wheel, or should a separate filter wheel be just fine too? I understand that for planetary astrophtography, I would benefit from the camera having a smaller pixel size since planets appear so small on the sensor in the first place. On the other hand, DSO photography might not benefit as much from small pixel size. Is my understanding correct? Where does pixel count become relevant? I've seen cameras having 2 million pixels cost more than ones having 20 million pixels. Why would this be? I believe that small pixel count (sensor size) cameras are more suitable as guide cameras while larger pixel count cameras are suitable as main cameras. Is my understanding correct? Finally, consider the following cooled cameras: ZWO ASI183MC | Color | 15.9mm sensor | 20 mega pixels | 2.40µm | EUR 960 Altair 183C | Color | 20 mega pixels | 2.40µm | EUR 980 Altair 183M | Mono | 16mm sensor | 20 mega pixels | 2.40µm | EUR 1129 ZWO ASI183MM | Mono | 15.9mm sensor | 20 mega pixels | 2.40µm | EUR 1149 ZWO ASI294MCPro | Color | 23.2mm sensor | 11 mega pixels | 4.63µm | EUR 1197 ATIK Horizon Color | Color | 21.9mm sensor | 16 mega pixels | 3.80µm | EUR 1399 ZWO ASI1600MM | Mono | 21.9mm sensor | 16 mega pixels | 3.80µm | EUR 1499 ZWO ASI1600MMPro | Mono | 21.9mm sensor | 16 mega pixels| 3.80µm | EUR 1533 ZWO ASI071MCPro | Color | 28.4mm sensor | 16 mega pixels | 4.78µm | EUR 1779 ATIK Horizon Mono | Mono | 21.9mm | 16 mega pixels | 3.80µm | EUR 1789 Should I aim for [Altair 183M Mono] camera from this list? It's the cheapest out of this lot, is mono, has very small pixels, and has a high pixel count. Thanks, Asim