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Before I read all of the responses, this was going to be my answer. Take it outside, don't shoot or observe through a window. Despite how clean it may be, a window is not an optically corrected piece of glass. There are varying thicknesses throughout and each small area can act as a kind of prism, refracting light in all directions. It may not be discernible to the naked eye and the glass may well be clean but there's a lot going on inside its structure to distort a magnified image viewed through it.
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