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Showing results for tags 'dark frames'.
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The screen print below is of two images containing identical lights, flats and bias frames. The right hand one has a fresh set of Darks added. The 240 second darks were shot at the same iso, exposure and temperature on a stock Canon 5D4 I've process the two images with exactly the same PixInsight settings (just background neutralisation, colour calibration and stf applied to see them) DBE wasn't applied because that would affect the output for this test. I'm getting these strange slightly curved bands, ringed in the right hand image when I add the darks during the calibration routine Is it possible to shoot bad dark frames? Previous sets of darks on the same setup have worked correctly so I'm struggling to see why this dark set would be 'faulty'? The same effect is seen on other data sets as well using this set of darks. For reference this is what I get with a basic edit from the lights/flats/bias image regards Kev
Below is a comparison between single dark frames taken with the Nikon D7500 and D5300 with exposure durations varying from 1 sec to 240 sec ( my usual main light frame exposure ) all at ISO400. Firstly a graph of the standard deviation of the noise in the dark frames versus exposure time: The standard deviation of the noise is a fairly constant 2 ADU less for the D7500 compared to the D5300 ( pretty much the difference in the read noise between the two ) However, the difference is not just in absolute terms but also in the quality of the noise ... Below are the dark frames - ranging from 240 sec exposures at the top to 1 sec at the bottom: D7500 D5300 The D5300 dark frames clearly show the pattern in the read noise ( banding down the bottom ) and also have far more chrominance noise compared to the D7500. At 240 seconds ( the main exposure I have been using ) the difference is starkly different; the D7500 produces images with much lower noise that is significantly more even and random and hence more likely to be reduced during integration.