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sharkmelley

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About sharkmelley

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  1. For diagnostic purposes, I've boosted the saturation in your image: Notice that the rings are much more like polygons than circles. Those polygons are a sure sign this is caused by the lens correction issue on Sony cameras. Mark
  2. As others have said, the dark patches are caused by dust. The concentric coloured rings are most likely caused by Sony's crude lens vignetting ("shading") correction. There are lots of threads about this e.g. https://www.dpreview.com/forums/post/62199570 It helps to switch off lens corrections but even so, you can't totally get rid of it because there are remaining "corrections" that cannot be switched off. Mark
  3. I've never seen the Cocoon so deep! Fabulous image! Helped by the fast optics of the Tak Epsilon of course Mark
  4. That is a stunner! It looks like a very interesting area of sky. It's certainly up to your usual standards. Mark
  5. Thanks. The master calibration files do show the PDAF (focusing pixel) banding. The trick seems to be to use dithering to prevent it becoming a problem in the stacked image. I'm currently using 14bit lossless compression but experiments with silent shutter look very promising. There's a lot more info over on my Cloudy Nights thread: Nikon Z6 Testing I think the Nikon Z6 will be a better match for my Tak Epsilon and is likely to become my main imaging camera. But I'll continue to use the A7S on the Celestron C11 - the large pixel size is better suited to a long focal length. Thanks. I agree that there are further things I could do to improve it.
  6. This is one of the first images from my new (unmodified) Nikon Z6 mirrorless camera. Full size version is here: http://www.astrobin.com/422848/ Imaging details: Unmodified Nikon Z6 on Takahashi Epsilon 180ED (f/2.8 500mm focal length) 60 x 2min dithered exposures at ISO 800 (Total integration time 2 hours) Sky quality over imaging period averaged SQM 20.87 Back-of-camera histogram peak was 1/5 from the left-hand-side The processing goal was to achieve a natural colour image using a traditional astro-imaging workflow, the main steps being: Raw file calibration with darks, bias, flats Debayering & stacking Apply Nikon Z6 white balance Apply Nikon Z6 colour correction matrix (Adobe RGB version) Background Subtraction to remove light pollution (but no gradient removal was required) Apply gamma 2.2 for AdobeRGB colour space Colour preserving ArcsinhStretch Convert to sRGB The blue haze at the top right is glare from the nearby Deneb - one of the perils of imaging near a bright star. I deliberately chose a well-known subject because it makes comparisons easier - particularly regarding H-alpha response. Mark
  7. Thanks for the additional explanation. I now understand what you are doing and the method makes complete sense. Mark
  8. From your description, my understanding is that you are calibrating the right white balance for your data but you are not applying the compromise colour correction matrix for your ASI178MCC camera. Unlike the DSLR world, I'm not sure anyone has ever generated them for dedicated astro-cameras. As an aside, I'm seriously thinking about writing a PixInsight script that will generate one from the image of a ColourChecker chart. The colour matrix reverses the mixing of colours caused by the response curves of the colour filters in the Bayer colour filter array. Without applying this matrix, colours will look washed out and unsaturated even though the white balance and gamma are correct. To understand more about its role, take a look at web pages linked below: https://www.strollswithmydog.com/raw-file-conversion-steps/ http://www.odelama.com/photo/Developing-a-RAW-Photo-by-hand/Developing-a-RAW-Photo-by-hand_Part-2/ Mark
  9. Natural colour is something that really interests me and I'm refining a workflow to do this. But your image looks unusually dull for a natural colour image so I'm intrigued to know why. What camera are you using - is it a OSC? If OSC, are you using the appropriate colour correction matrix after performing the white balancing? If the camera is not OSC how are you transforming the RGB data to the colour space you are using? Are you also applying the gamma transfer function appropriate to the colour space? By the way which colour space are you using? In my opinion, Adobe RGB is easiest to use because it has constant gamma which means you can scale the RGB values up and down within the colour space without altering chromaticity/saturation. Scaling data whilst preserving natural colour is a big problem in sRGB, for instance. How good was your background subtraction? You need to get that pretty accurate before applying the colour space gamma transfer function. If you are stretching the data in any way, after applying the colour space gamma, is this a colour preserving operation? I ask this because most "curves" type stretching operations that people use will bleach the colour from the data. Also, I would start with the RGB data alone. Experiment and get this right before attempting to blend with luminance data. Mark
  10. Sorry, I don't know of anyone in the UK who modifies the A7S. It doesn't mean they don't exist, just that I don't know. My own A7S was self-modified. Mark
  11. Typically sensors are designed with all the AF pixels using pixels of a single colour. Clearly in this case the sensor uses the blue pixels. As for the clip-in filter, it can't be completely ruled out but I honestly can't see how it could aggravate the issue. Mark
  12. You can see the problem in a single CR2 raw file. There's no way DSS settings can affect that. Mark
  13. M51 taken on Wed 10 April including the supernova imposter designated AT2019abn which It was discovered on 22-Jan by ATLAS (Asteroid Terrestrial-impact Last Alert System). Further info on AT 2019abn here: http://www.rochesterastronomy.org/sn2019/sn2019abn.html Some references call it a luminous blue variable (LBV) but it's definitely not blue! Others call it an intermediate luminosity red transient (ILRT). Imaged with modified Sony A7S on Celestron C11 with Starizona 0.72x LF reducer/corrector. 345 x 30sec subs at ISO 10000 giving nearly 3 hours of data. Mark
  14. It's normal. At least it's normal for certain Canon models. It's not a faulty camera. For example, here are some similar threads: https://stargazerslounge.com/topic/315126-lines-across-image/ https://www.cloudynights.com/topic/512886-canon-banding-help/page-3 https://www.cloudynights.com/topic/413422-examining-the-650dt4i-hybrid-cmos-af-pixels/ I haven't yet come across someone saying they solved the issue. It doesn't mean there is no solution - it just means I haven't come across anyone giving the solution. Mark
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