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you will need to accumulate at-least 2 hours minimum
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With wich camera ?
Canon, for example, don't like too much time of exposition. The stars will be RGB saturated, showing all stars with only white color.
Actually, I think that too much time can be not good for any color camera. This situation is very different if you work with mono-camera and LRGB filters.
ISO 1600: It is not true that high ISO will enhance your capture. It depends from light pollution, sky glow, temperature, model of camera and others.
For my set and site of my observatory I have ISO 400 and 800 as the better ISO to use. I use ISO 1600, also, but only in special condition and with few targets.
Today, I am having much more noise in red channel than normally. With or without sense, I am thinking about the atmosphere condition at Atlantic near South America. It seems that I am having more intensity of iR or NIR radiations that are causing some influence in the result of my captures.
My last try with ISO 1600 - Horse Head published here, also - was terrible with this issue ! And only in red channel.
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How are you focusing you're camera??
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Many people ask about this. I use FWHM of BackyardEos and short capture to analyse the shape of star (round or not) and the single line in spikes. After this I always check the quality of the first frame of a session.
What happens here is refraction. As I am near of the beach I have much umidity and therefore much refraction. I use 10 frames for FWHM in BackyarEos, and I haven't a stable reading of FWHM. Maybe I must use more frames. I will try with 20 or 30 frames.
I tried mask, but it is the same for FWHM. You haven't a stable image to tell: ok, good focus !
Did you saw how Jupiter dances when we want to shot him ? Ok, the stars, with my set of equipment of 0,7 arcsec/px and my normal refraction, dance alike... or more !
An example:
http://astronomia-e-astrofotos.10697..._193335.00.gif
So my stars are more chubby and seems to be out of focus:
http://astronomia-e-astrofotos.10697...lcent_rgtx.jpg
Some times, I see a good image ... a lucky frame. I think it is a good focus, but it is only a lucky frame !
I always try to publish the full resolution of my set. I crop the image to publish it. Therefore you can perceive any problem with the photo. If I reduce the photo, perhaps you will never will perceive the problems.