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About sharkmelley

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  1. It's a question of semantics. The Sony issue is well understood because of detailed investigation and it only affects pixels with outlying values - which of course is a type of visible noise. With these types of algorithm the problem comes when tightly focused stars are damaged along with the rest of the noise. The problem is that we don't yet know the effect of the R5/R6 raw data filtering on stars. From the reviews we know it probably doesn't affect untracked images with slightly trailed stars but the Sony raw data filtering didn't cause any issues for these types of images either.
  2. Sorry, I can't take those reviews seriously. Marco Nero (DPReview) is shooting untracked JPG images. Brent Hall (PetaPixel) is also shooting untracked and has star trails. Those reviews don't help us understand if accurately tracked long exposure astrophotography with good quality optics will have problems similar to the well known Sony star eater issues. Mark
  3. There are one or two DPReview threads relating to "noise reduction" on the R5 and R6, from the work done by Bill Claff. For example here: https://www.dpreview.com/forums/post/64403868 The Fourier transform of the raw data certainly shows that internal camera processing of the raw data is taking place but it's impossible to say whether or not it is a deliberate attempt at noise reduction. It's unusual to see such processing on short exposures. I have seen some of these raw files and I've confirmed what Bill is seeing. However, it is not possible to extrapolate from these results
  4. Yes, I'm absolutely certain that the CR2 file contains linear raw data. Mark
  5. I'm not sure what you mean. The values in the CR2 RAW are linear unstretched values, just like the values in the QHY raw file are linear unstretched values. Mark
  6. This site gives you the ISO for unity gain (i.e. 1e-/ADU): DxOMark Derived Sensor Characteristics (photonstophotos.net) The QHY268 gain setting for unity gain (1e-/ADU) will be available probably in the documentation. You can then adjust upwards and downwards from there. You will want to choose a gain where both DSLR and QHY268 are operating in the same mode i.e. high gain or low gain. Mark
  7. There will be a big advantage because the modern sensor has at least twice the QE of your 40D sensor. Also you have the advantages that mono gives you over one-shot-colour i.e. you can shoot luminance and narrowband is not impeded by the bayer matrix. Mark
  8. I purposely said modded DSLR/mirrorless i.e. the bare sensor without the filter stack which is removed during modification.
  9. The main difference is the noise reduction from the cooling. Otherwise a modded DSLR/mirrorless can produce very similar results because in many cases dedicated one-shot-colour astrocams use the same sensor as a modded DSLR/mirrorless camera. Mark
  10. The 40D is approx 14 years old! There have been huge advances since then. Look at this chart comparing the 40D to a more recent camera: https://www.photonstophotos.net/Charts/Sensor_Characteristics.htm#Canon EOS 40D_14,Canon EOS 7D Mark II_14 The 7DII has nearly twice the QE of the 40D. That means the sensor as a whole will capture twice as many photons from the same scene in the same exposure time. Mark
  11. The Canon 40D uses an old sensor with very low QE (quantum efficiency). A more recent camera will have vastly improved QE. You can choose either a modern consumer camera and have it modified or a dedicated OSC astro-camera because in many cases they use exactly the same sensor. Both will be a huge improvement over the modified 40D. Obviously the dedicated astro-camera will have much lower thermal noise because of cooling. Mark
  12. The Panasonic sensor in the ASI1600MM behaves differently for exposures shorter than around 0.1sec. So if the flats are longer than 0.1 sec (which they usually will be) then flat darks should be used. However this isn't a general rule for CMOS cameras. Mark
  13. You're right - sorry about that, I need to fix it! The Nikon D90 uses the exactly same compression scheme as the D5300, so in the meantime the earlier version, version 2 will work fine because it applies the Nikon D5300 correction which is identical to the required D90 correction. https://www.cloudynights.com/topic/746131-nikon-coloured-concentric-rings/?p=10860569 Mark
  14. There's been a lot of discussion in his thread about the walking noise but none about the coloured rings in the background. The coloured rings are almost certainly caused by Nikon's lossy data compression. It's a common problem when imaging with Nikons and it was discussed on a recent thread over on Cloudy Nights: Nikon Coloured Concentric Rings - DSLR, Mirrorless & General-Purpose Digital Camera DSO Imaging - Cloudy Nights Mark
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