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Mike, to use the chart, simply draw a straight line from your right to left. i.e start with your pixel size (right) and draw a line through to the left for DSO arc/sec pixel (left). As the line intersects the middle virtual line - you will know the focal length in mm to achieve this desired combination. You can of course calculate from left to right - what ever way, the result is the same.
I should point out that this is only a reference. There isn't any hard and fast rules. For example, the Tak FSQ I use has a arcsec/pixel of 3.501 when coupled to the SBIG STL11k 9ux9u pixel size and makes an excellent all weather wide field instrument that is not troubled by seeing. Nyquist Theorem indicates you should sample at twice the frequency you want to resolve.
Arcsec/pixel = pixel size in microns / (0.00485 x telescope focal length in mm).If your pixels aren't perfectly square you can simply square root the two - sqrt(W x H)= X microns). The most accurate way to determine the arcsec/pixel combination is to plate solve.
The downside of a DSLR is the lack of support for binning. Binning provides greater flexibility when trying to reach the optimal arcsec/pixel combination.
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