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No, don't raw convert them first. But white balancing should be one of the first operations you do after stacking - while the data are still linear.
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Those histograms do not look like the histograms of linear data. White balancing cannot be performed on non-linear data. It raises the question about what kind of workflow you are following. For instance, are you raw-converting your images before stacking or do you put your raw files directly into DSS?
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Very nicely done!
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Read noise, light pollution and a DSLR (Canon60d)
sharkmelley replied to MalcolmP's topic in Discussions - Cameras
If you choose ISO 1600 then shorter exposures will be sufficient to achieve your chosen 5*read_noise criterion. -
Read noise, light pollution and a DSLR (Canon60d)
sharkmelley replied to MalcolmP's topic in Discussions - Cameras
Your Canon 60D read noise at ISO 800 is approx 3e: https://www.photonstophotos.net/Charts/RN_e.htm#Canon%20EOS%2060D_14 If you want the light pollution noise to be 5x higher then you want it to be 15e. That means you need to collect 225 (i.e. 15^2) electrons. http://tools.sharpcap.co.uk/ will allow you to approximate your sky background rate (e/sec) which will depend on the f-ratio of your lens/scope. You can then work out how long your exposures need to be to achieve 225e. -
It looks as if it could be done...
sharkmelley replied to ollypenrice's topic in Imaging - Discussion
That's a stunning result that puts those popular Winter targets in their context. -
Total integration vs individual subs.
sharkmelley replied to nickp87's topic in Imaging - Discussion
You will capture the same amount of light with both approaches. But the stack of 1000 subs will have 1000 contributions of read noise whereas the stack of 80 subs will have only 80 contributions of read noise. Almost certainly the stack of 1000 subs will be noisier therefore making it a bit more difficult to detect fainter objects. -
Why would light leaking through the viewfinder be purple?
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What happens if you take a long-exposure dark frame - first with the lens on and secondly with the lens removed.
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Star halos
sharkmelley replied to WilliamAstro's topic in Imaging - Image Processing, Help and Techniques
To help diagnosis, you need to calculate the additional length to the light path caused by the reflected rays. The CCDWare dust donut calculator will do this for you: http://76.12.87.114/resources/dust.cfm -
What's the best ISO setting for a Nikon D5300?
sharkmelley replied to Trippelforge's topic in Discussions - Cameras
The Nikon D5300 is a special case. It's best to keep ISO really low e.g. ISO 100 or 200 in order to keep the peak of the back-of-camera histogram well over to the left and avoid those annoying coloured concentric rings in the background, caused by Nikon's badly implemented lossy compression. Mark -
It looks like the scope is VERY out-of-focus.
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Simon Pepper started following sharkmelley
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The factor of 4.34 is the wrong factor to use because it is calculated from the ratio of noise. Generally speaking accumulated dark current in an exposure will double for each 5C-7C increase in temperature, so the thermal noise increases by the square root of this. The factor used for dark scaling is usually calculated using max entropy or calculated from the relative brightnesses of the "warmer" pixels. Alternatively use "trial and error" to determine the factor that minimises the noise in the final image.