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sharkmelley

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About sharkmelley

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    Tenterden, Kent
  1. sharkmelley

    Asking too much of a Sensor??

    Unfortunately, the read noise is higher with lower ISO and banding artifacts will also be more intrusive. Mark
  2. sharkmelley

    Asking too much of a Sensor??

    The crucial thing is to work out what is the dominant source of noise in your image. Is it read noise, thermal noise or shot noise from the light pollution? If light pollution is your main issue then you don't have a sensor problem. When calibrating using darks, make sure you have PixInsight's dark optimisation switched on - it does an excellent job of scaling the darks to match the lights, despite any temperature differences between the two. Mark
  3. sharkmelley

    IDAS D2 halos

    I have no experience with the Esprit range, so I can't tell if that is normal or not. Mark
  4. sharkmelley

    IDAS D2 halos

    Let's say 70 pixels. The pixel pitch of the Canon 6D is 6.5microns. You said your scope is f/7. Then given the refractive index of glass as 1.5 and assuming the cause of the halo is a double reflection within the filter glass then that would give a filter thickness of just over 2mm. 2mm thickness sounds about right for a filter. So your halo size is consistent with an internal reflection within the filter. But I can't explain why you don't see a halo with your other scope. Mark
  5. sharkmelley

    IDAS D2 halos

    Do you have an estimate for the halo diameter (in pixels) on the Canon 6D? Preferably a halo near the image centre. Mark
  6. sharkmelley

    IDAS D2 halos

    You have a new D2 filter? What is the second scope? Where have you mounted the D2 filter on the second scope? By the way, what camera are you using (so we can work out the pixel pitch). Mark
  7. I created a timelapse of the lunar eclipse after spending 4 hours in a subzero observatory taking bracketed exposures every minute. Sony A7S on Celestron C11 with Starizona LF Corrector 0.7x This is created from 220 frames. Mark
  8. Nice mod! But I'm worried you keep the tube outside in the UK. Don't you worry about the effects of humidity on the optics? Mark
  9. sharkmelley

    Are Nikon DSLR darks a waste of time?

    That's right, you've got it now! The Nikon long exposure noise reduction (LENR) will be subtracting an unfiltered dark from an unfiltered light, which is why it works fine. Mark
  10. sharkmelley

    IDAS D2 halos

    It would almost certainly mean that the halo is caused by a double reflection within the filter glass causing those rays to travel extra distance to the sensor and arrive out of focus - the halo being the out of focus version of the star. These double reflections are usually prevented by the anti-reflective coatings. It might be worth contacting the supplier/manufacturer to see if it is normal for this filter. The fact that you see the halo with the D2 filter but not the D1 could be an indication that something is not quite right. Mark
  11. sharkmelley

    Are Nikon DSLR darks a waste of time?

    I took long exposures for over an hour to let the camera thermally stabilise beforehand and only used the exposures after that point. It was all done in a single imaging run. I don't have details about the D5100 and 880E spatial filtering so I can't tell if they will behave the same way as the D5300. Mark
  12. sharkmelley

    Are Nikon DSLR darks a waste of time?

    The reason is subtle. The point of the spatial filter is to remove hot pixels. On the D5300 the spatial filter works by capping pixels whose value is more than twice that of their (same colour neighbours). In a dark frame the pixel values average out to zero so almost every bright pixel has its value capped unless it has a bright neighbour. In a light frame, the bright pixels are "protected" by the non-zero sky-glow level. That's why the bright pixels are obvious in the light frame but have been removed from the dark frame. Not all Nikon spatial filter algorithms work the same way. So its a fruitful area for further investigation. By the way, in-camera noise reduction works by subtracting a dark, not a flat. Mark
  13. sharkmelley

    IDAS D2 halos

    You've ruled out everything I can think of. You've changed the position of the filter and you still get the problem so it's not reflections between the filter and the reducer. The other obvious cause of halos is internal reflections within the filter glass itself. But that causes halos of the same size whereas you say yours have different diameters. It would be informative to see an example of the different diameter halos because that might provide further clues. Mark
  14. sharkmelley

    Are Nikon DSLR darks a waste of time?

    How do you expect the standard deviation to help? If you are unable to see visually that the thermal fixed pattern noise has not been removed then what do you expect standard deviation to tell you? By the way, no STF was applied. This is linear data scaled by the same multiplier in all 4 panels to brighten it sufficiently for screen display. Mark
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