sharkmelley

I'm very late to this thread but it looked interesting. Did you find your problem? In any case I simulated this in a spreadsheet and found that 1.5x binning leads to a SNR reduction of 1.8x, which is what you expected. I generated 10,000 groups of 9 random values. Each group of 9 values was binned down to 4 values using your algorithm. This created 10,000 groups of 4 values. The SNR of the resulting 40,000 values was 1.8x lower than the SNR of the original 90,000 values. Mark

That's a very informative video and an interesting solution to the problem of using filters with the Nikon Z cameras. The approach probably works well for lenses but I think 1.25" filters will cause vignetting issues when attaching the camera to a scope. Mark

Drizzle works best on undersampled images. Standard (random offset) dithering is all that is required. I use Bayer Drizzle (sometimes called CFA Drizzle) as part of my standard processing workflow and it's especially beneficial for OSC cameras or DSLRs because it increases resolution by avoiding the interpolation that takes place during debayering. The other advantage it gives is a more finely grained noise structure than standard stacking, which helps with noise reduction. It's definitely well worth a try! Mark

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

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

I've never seen the Cocoon so deep! Fabulous image! Helped by the fast optics of the Tak Epsilon of course 😉 Mark

That is a stunner! It looks like a very interesting area of sky. It's certainly up to your usual standards. Mark

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.

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

Thanks for the additional explanation. I now understand what you are doing and the method makes complete sense. Mark

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

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

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

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

You have the usual ASI183 "starburst" amp-glow on the right hand side. This will calibrate out. The big oval shaped bright patch in the upper centre is probably some kind of light leak. Does it happen if you take darks with the lens cap on in a totally darkened room? If not then it's definitely a light leak. You will just have to experiment putting a black cloth over possible entry points until you narrow it down. Mark

Yesterday I was looking for another example that I've come across before. I have now found it. It's interesting example because this one is another microlens diffraction but it reflects back off the narrowband filter instead of the sensor protective coverslip. http://geoastro.co.uk/equipment/ghosts.htm The pattern is huge and the overlapping defocused star images are also huge. Mark

That is incorrect. The reflective surfaces of the filter contribute nothing to the microlens diffraction pattern. You can convince yourself of this fact by going away and performing a few experiments. Unfortunately I don't think there is anything more I can add that will help you. Mark

You have multiple things going on there! I think we're heading a bit off-topic but I'll play along. First of all, all the filters show a very large doughnut with spider vanes. The doughnut is the same size in each case and disappears when there is no filter. That indicates reflections off the filters. The extra length of the light path can be confirmed by using the Dust Donut Calculator (http://www.ccdware.com/resources/dust.cfm). and this will help confirm which other surface is implicated - either the chamber window or the sensor stack. The centres of those big halos have different offsets to the star causing them. Either the star is in a different position in each image or the filters are mounted with slightly different tilts to the optical axis. The H-alpha filter also has a series of increasing rings around the star. This is usually caused by internal reflections within the filter glass because the AR coatings (if any) aren't too effective at the wavelength of H-alpha. I'm guessing it's not an Astrodon filter otherwise you need to send it back and complain. Again the dust donut calculator will give you the additional optical path travelled within the filter glass (at least its equivalent in air). The refractive index of the glass is then required to calculate the actual filter thickness. As for the Laue Diffraction off the microlenses, I can't be 100% certain I'm seeing it in the H-alpha image but it is certainly there in the OIII image. The distance of the sensor protective cover can be implied from the geometry of this diffraction pattern. Mark

We assume it's the protective cover on the sensor itself because the reflection is from a surface less than 1mm above the microlenses. Yes we would expect the "halo" caused by this diffraction effect to be brighter with no narrowband filters. In very rough terms the star would be 50-100x brighter and its halo would also be 50-100x brighter. Mark

Unfortunately the sensor coverslip on the ASI1600 is not AR coated. This is why the ASI1600 is notorious for creating these patterns. I'll briefly explain the mechanism of the interference pattern. Wavefronts hitting the sensor are being scattered in all directions by the 2D array of microlenses. At certain angles (dependent on pixel spacing and wavelength) these scattered waves will interfere constructively. This is reflected back onto the sensor forming a regular grid of points where constructive interference is happening. This is the same as Laue Diffraction from a 2D lattice that occurs in X-ray crystallography (but scaled up enormously from an atomic lattice). At each point on this regular grid we see the image of a defocused star. Typically this forms a pattern of overlapping defocused stars. The diameter of each defocused star indicates the extra distance that the light has travelled and shows beyond doubt that the reflection is off the coverslip and not off any filter. If you want to understand more then take a read of the Cloudy Nights thread that Carole linked earlier (ignoring the post about the Talbot effect which is another very fascinating diffraction effect but is not what we are seeing here). There you can also find some PixInsight code I wrote that allows you to reproduce the geometry. Mark

The key word here is diffraction. The exact geometry of the pattern is crucially dependent on the wavelength of the light because it is caused by constructive interference. The (almost) monochromatic light passing through a narrowband filter produces a very clear pattern. This pattern becomes smaller as the wavelength shortens. A broad spectrum filter ( e.g. R,G or B ) will produce the continuous superposition of the different sized patterns produced by each wavelength that passes through the filter - in other words it will be an indistinct smeared artefact. So the only effect you will see in a broad spectrum image are weird variations in colour in a halo around the star. There's quite a good example here: https://www.cloudynights.com/topic/565014-new-to-narrowband-imaging-question-about-strange-pattern-in-bright-star-halo/?p=7706969 Mark

Don't bother changing spacing of filter etc. because it won't make any difference. It's a diffraction pattern generated by the microlenses and a reflection off the sensor coverslip so the position of your filter and field flattener won't make any difference. The pattern is most obvious with narrowband filters, especially H-alpha. Mark

It's nice to know there are multiple solutions. But a proper menu option would be far easier! Take the Sony A7RII for instance - the "star eater" spatial filtering can be worked around by putting the camera in continuous mode. But try it on the A7RIII and you still get the star eater! Go figure. Mark

Having looked at this in more detail, it's certainly true that the D7500 is using less aggressive spatial filtering than the D5300. However this does not explain the observed difference in thermal fixed pattern noise (FPN). The D7500 really does appear to have a higher FPN than the D5300. The practical consequence of this is that you are more likely to need dark frame calibration with the D7500 than with the D5300. Mark

Thanks for reviving this thread. I've been playing with a Nikon D5300 recently and noticed that the spatial filtering (a.k.a. hot pixel suppression or HPS)was causing all kinds of problems with star colours - mainly turning them green, just like the latest variant of the Sony star eater algorithm. It's all being discussed over on Cloudy Nights: https://www.cloudynights.com/topic/635441-aa-filter-spatial-filter-and-star-colours/ It's early days and it's not yet fully understood. However, it appears that the Nikon D810A (the one built for astrophotography) doesn't have the same issue because the spatial filtering is much less aggressive. So it's just possible that the D7500 is also using less aggressive spatial filtering than the D5300 and that's why it appears noisier. I'll take a new look at Mike's D7500 darks and see what I can determine. It'll definitely provide another interesting data point for my analysis. Mark