Does anyone have information or an opinion on how critical focus is when shooting flats - in my case dusk flats. At New Mexico skies I have no control over when the roof rolls off of Pod1. As a result the optical train is going to be warmer than it was at dawn. Therefore when dusk flats are being taken the focusser will be as it was at shutdown or at its center point and so likely will be out of focus to some extent. Intuitively this does not seem a problem, but intuition can be very misleading.