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drjolo

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Everything posted by drjolo

  1. I think it can be tricky. However if you control the camera from the computer you may still use plate solving to pinpoint the target. I have done this when imaging with SW Adventurer. You take a few seconds shot, plate solve it (there are many software that do it, like PlateSolve 2 for example) and then you will get the actual position. Then move the scope manually, capture another image and plate solve again till the position error will be small enough. You only need to provide your setup pixel scale and approximate coordinates to plate solve software, so the process will be faster. Approx. coordinates may be the coordinates you want to achieve.
  2. I have not been imaging in the medium range focal length for a long time, and I decided to go back to the 600mm setup. The selection in this FL is very large, but I decided to go and check for second-hand ED doublet, and I picked William Optics ZenithStar II ED 80 f/6.8. It is FPL-51 based doublet, about 15 years old as far as I know. I equipped it with adjustable 0.8x FF/FR from Teleskop-Express, added QHY247C camera, guider with ASI290MM attached to MC Sonnar 135 lens, put it all on CEM26 and made some first shots. Conditions were poor - some light fog, rising Moon and significant light pollution, so most of the processing time I spent on balancing the colors and removing gradients. I did not expect top notch quality from FPL-51 doublet, but the results are promising in my opinion and I will keep that setup for some time for sure. Here is the setup ready for capturing: M1 Crab - 60x2 minutes Perseus Double Cluster - 60x2 minutes M35 cluster, 30x2 minutes Cocoon nebula, 100x2 minutes Some galaxies nearby Cocoon Defocused star (omicron Gem) - inside focus, in focus and outside focus. Collimation looks good, but some chromatic aberration is present (I guess, because I have not much experience in analyzing that). Now I am looking forward to better nights
  3. I think you may miss the frame area - it is not a "cropped a little". Nikon's APS-C has 370mm2, 533 area is 128mm2 - that is a significant difference. You may check ASI294, that is 247mm2.
  4. That also depends on the pixel scale of your setup. Simplifying a bit - seeing blurs point image (star) to some finite diameter (FWHM, HFD). At my location average seeing is about 2.3-2.4". Good seeing is 2.0", best is 1.8" sometimes. That is for exposures 10s or longer. My Samyang 135 travel setup has 6"/px scale, and I never care about seeing conditions. My 80 mm scope setup has 2"/px scale, and I almost never care about seeing here. My 10" telescope has 0.45"/px scale, and I can always tell what the seeing is Once it is over 2.6-2.7" I give up on imaging with this scope. Sometimes there is a light fog and the atmosphere is stable, although the transparency is poor. But these conditions are often connected with very good seeing and I am capturing then Ha narrowband data in the targets that have features in this band. Like for this M16 image The nebula was quite low at my location, and the transparency was also poor, but atmosphere was stable and I managed to collect 115 minutes of good quality subframes.
  5. I would consider longer subframes - your setup is around f/6, so if you do not have tracking/guiding issues you can easily go to 2-3 minutes if you plan to collect many hours in total. It may require some gain adjustments. With regards to performance I have processed a few times 300-400 subframes (16Mpx) of one target using PixInsight and that took about 1 hour of processing time on i7 / 16GB machine - aligning and stacking, I do not calibrate in Pix. PS - I did some time ago a small comparison of the performance - you may check at https://astrojolo.com/gears/astro-applications-cpu-hunger/ , but that was for a small amount of frames.
  6. Thank you for comments. I am also quite happy about that clouds in Perseus image, but that was captured under pretty dark sky, and is not possible at my home location, where I have 5mag NELM (far away from the horizon only) when the transparency is good.
  7. I do not remember now for sure, but I think for this telephoto lens I did not use any counterweight at all. The mount was a little overweighted to the telephoto size, but that did not make much difference to EQ6-R sized mount.
  8. Not really, I have used EQ6-R with telephoto lens and Canon 550D several times, like this 40x3 minutes: However for such light load even single 5kg counterweight may be too much.
  9. So, correct me if I am wrong, now we agree that the problem exists, but the question is if it is visible or not, right? So the conclusion could be at that point, that when we switch from dark flats to synthetic bias method, we exchange dark flat random noise problem to synthetic bias uncorrected fixed pattern noise problem. Both can be visible or not, but in dark flat case we can minimize random noise by increasing the calibration frames number. FPN cannot be reduced by synthetic bias, because FPN information is lost in that method.
  10. Was it a CCD sensor? It looks similar to Kodak equipped CCD cameras I had. This fixed pattern noise was pretty significant, however it was 100% repetitive, so it was easy to remove. Repeatability and predictability it is something that I miss the most in CMOS cameras.
  11. This is not only ZWO, but also QHY case for sure. Some value is subtracted (probably not constant over frame, so it can minimize AG), that makes average ADU lower for longer exposures. As I mentioned before but of course the SD is higher for longer exposures. And we should also remember that calibration is not only specific for eye catching images. We use calibration for example for photometry, and for this application it is not enough just not to see a difference in the image. We need to be as accurate as possible, plus we need to be able to determine the error.
  12. If that problem persists with different computer, cables, PSU and drivers I would say that is camera fault, because it should not work that way. Friend of mine returned some time ago two ASI294MC and recently QHY294M, but probably some faulty 294 chips still may exist somewhere
  13. Year 2021 was not very good in images captured for me, however I collected a few frames that are maybe worth to share. Wizard nebula - that is composite of RGB, Ha and Oiii data. 12 hours total made with QHY163M, Meade ACF 10" f/10 and EQ6 mount in my backyard. Mars and Pleiades in March, 2021. QHY247C and Samyang 135 on SW Adventurer at my backyard. M42 area made with QHY247C, Samyang 135 and SW Adventurer in my backyard. 4 hours of exposure. Coma cluster imaged with Meade ACF 10", QHY163M and EQ6 in my backyard. 10 hours total with L filter. Molecular clouds in Perseus. Imaged with Samyang 135, QHY247C on SW Adventurer. At the star party in Zatom. 220 minutes total exposure. Soul nebula fragment. Imaged with QHY163M, Meade ACF 10" on EQ6. From my backyard. 10 hours of total exposure with RGB, Ha and Oiii filters. Thanks for watching!
  14. I totally agree for this camera and masterflat case the difference may be not visible in the final image. The same as the amount of noise introduced with dark flat may not be visible. My only concern is that fight against the dark flats as useless method of calibration. I know many amateurs who do not feel comfortable with ADU readings and plots. And they really prefer to shot dark flats that takes a few minutes, than taking bias frame and analyze that. That will not be useless at all, and the final outcome of both methods will also not be useless, but the same in most cases.
  15. That is not correct by definition. AG is a area with different ADU values than other frame parts. And how do you want to replace value that changes over frame with some constant? It may be more or less accurate, may be not visible at some stretch level, or become visible, but will never be 100% covered.
  16. What is really misleading in this thread and the linked article, is calling calibrating with dark flats "useless" - in my opinion it is 100% correct way of calibrating images. Synthetic bias or synthetic offset can be used, but in all cases it will be a workaround. How much inaccurate workaround? It only depends on the data from the camera. When you have ampglow - you should have dark flats. Many CMOS cameras have AG. Some of them uses kind of "AG reduction" that basically subtracts AG signal from the frame. It leads to another CMOS problem - dark signal is not linear with exposure time, and may decrease with increase of the exposure time. For my QHY163M we have 733ADU for 100ms dark, and 710ADU for 180s dark. At some point I could go below zero. Another thing is that data from CMOS depends on gain, offset, USB traffic, temperature and driver version. If anything changes, there is a good chance you need to update your calibration library, but also need to take care of determining new bias offsets. And how much noise is introduced into the final image by dark flat? My 40x100ms dark flat has 3.8ADU noise. My 120s light frame has 168ADU noise. With dark flat added it will be 168.04 ADU (noise does not add linearly, it is square root of sum of squares). I do not see a real benefit here. My 180s Ha frame has 29.7ADU noise. With dark flat added it will be 29.9ADU. Still not too impressive difference, plus 180s is pretty short for narrowband and f/7 optics. So, I would definitely avoid calling dark flat calibration useless. It is 100% correct, but introduces some noise. I would rather call master bias or bias offset calibration useful in some cases, and never 100% correct.
  17. I have been doing biases when I imaged with CCD cameras. The only reason I did bias frames was, that CCD dark signal scaled well with time, and it was possible to "synthesize" dark signal for different dark time having bias frame and dark frame of the different time. At least Maxim did that in the reasonable way. But that was a workaround of course. Since the time I switched to CMOS cameras I never did bias frames, I use only dark flats. For me it is the only way to have proper flat calibration of the frames. The higher background signal (LP) is and the longer exposure for flat frame is required, the more useless bias is for flat calibration. As vlaiv mentioned - this is a simple math, and to have proper flat signal to calibrate, it must be subtracted with dark flat. I prefer to fight with noise with more data captured, because removing of dust donuts caused by bad flat calibration is for me a much more pain.
  18. Thanks! I forgot about the challenge, but still hope to catch it a little bit better - waiting for optimal conditions It is just a processed stack, I did not align separately on comet and starfield. Then processed a little bit in Pix, and mostly in Photoshop.
  19. Two nights ago I captured the comet in the Cancer. There are significant LP in the eastern part of the sky at my location, but I could not wait longer, because clouds were coming, so the image is not as deep as I wanted it to be. Comet was about 65 mln km away at this image and is currently making a fancy loop at the sky Imaged with WO Zenithstar II 80ED, Flat3, QHY247C, CEM26. 30x2 minutes.
  20. I suspect that this flattener probably does not cover APS-C size sensor. This is quite old model (as well as Zenithstar II ED 80 refractor), so maybe some newer flattener could help. I have asked WO for some recommendations. Here is sample image captured last night. Setup: WO Zenithstar II ED 80, WO Flat3, CEM26, QHY247C camera, suburban sky, 15x2 minutes About 5% cropped.
  21. Recently I purchased second hand setup WO Zenithstar doublet ED 80 II with WO Flattener III 0.8x and I have some problems with setting the right distance between sensor and flattener. The camera is APSC size QHY247C. In all tests stars in the frame center are perfectly OK: Frame corner without flattener shows curvature: When the flattener is added there are always cross shaped stars in the corners. I have checked the distances in the range 48 to 58mm. The smallest stars in the corners are at the distance to the flattener 52mm: At shorter distance the stars are more elongated radially: and at longer distance there are more elongated in the other direction: They are pretty much symmetrical to the frame center. I suspect that maybe the flattener is tighten too much and I plan to try to loosen it a little - is it something worth doing? Do you have any experience with that flattener? Maybe it is not designed to cover the APSC size sensor at all, and I should look for some other model? This Flat3 looks like very simple flattener, basing on its dimensions it is probably a doublet only.
  22. I do not hunt specifically for quasars, but quite often scan my existing images for distant objects. I have found objects over 12 billion light years away three times already. First one is in the M105 galaxy trio area. It is SDSS J104718.26+130318.6 quasar 12 billion years http://skyserver.sdss.org/dr9/en/tools/explore/obj.asp?id=1237661068716474941 : Another one is close to NGC4244 galaxy - SDSS J121510.36+375811.2 - http://skyserver.sdss.org/dr13/en/tools/explore/Summary.aspx?id=1237664338792350092 - 12.4 billion years: And another 12.4 billion years target - http://skyserver.sdss.org/dr14/en/tools/explore/Summary.aspx?id=1237661417138094494 - next to M101: First image was captured with 8" newtonian and Atik383, another two with 130mm refractor and QHY163M camera under suburban sky.
  23. Yes, dithering must be performed between the shots (or between the shots group). Then is usually requires some time to stabilize guiding after dither command.
  24. It may, but it does need to interfere - depends on camera behavior. In my estimation most probably it will not cause any problems. I just wanted to point out the root cause of some problems, because many astrophotographers are not aware of it and trying to replace cables, USB hubs, power supplies, and the ground loop is still present in the system.
  25. Yes, because you have two paths for the ground signal: first: power supply cable -> DC hub -> 5V power cable -> USB hub -> USB cable -> camera second: power supply cable -> DC hub -> 12V power cable -> camera The 5V voltage is of course separated from the 12V voltage, but they share the same minus (ground), unless the DC converter inside the hub is isolated, but as I mentioned it is not probable. But in your setup it will be easy to detect. If any problems with camera signal or connection occurs, you may just power the USB hub with separate 5V supply. If the problem will disappear, then it was a ground loop.
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