Quote:
Originally Posted by tilbrook@rbe.ne
Thanks David!
You raise a question though.
While my 8" f/4 is doing a good job, it hasn't the resolution of a larger scope or something with 20th wave optics. So how far do you go before hours of imaging become redundent because of resolution?
Or is that a how long is a piece of string question?
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Well, I think that the seeing conditions would limit the resolution more than the accuracy of the optics - I used to get quite good resolution from my home made 200mm which had a cheap chinese mirror. I believe that the rule is that the SNR (signal-to-noise) increases as the square root of the number of exposures; so 25 stacked sub frames would have 25% better SNR than 16 sub frames (5:4 ratio). The optimal length of the sub-exposure is another issue (I think that CCDWare have a calculator on their website for this). With DSLR cameras, I believe that using a higher ISO rating increases the noise as well; also DSLR cameras are OSC (one shot colour) which means that each pixel is dedicated to a single colour (RGB - layed out in a Bayer Matrix), and so the "missing colours" for each pixel need to be interpolated from neighbouring pixels which thus affects the colour resolution (as well as the sensitivity per pixel). Others would have more experience with DSLRs than I so can probably offer better advice.