Too cold outside to leave the house but bored so I thought I would compare some binos. Casually compared the Swaro 7x30 to Steiner 8x44 and the Leica 10x42 by looking through the window. Expected results, then compared two spotting scopes, again through the double pane window and could not get either one to really focus clearly. Went to the garage and opened the overhead door and compared the two spotting scopes and thankfully crystal clear clarity was back. Why would the binos not be affected by looking through the window but the spotters would at 23x magnification. When I compare binos in the store I often look through the window, actually a local bird shop has the spotters set-up next to the window for comparision.
Short answer is power.
You should not compare any optics through plate or float glass; it is optically very inferior to optical glass. Look at reflections in glass windows for bows and distortions to get some idea how inferior. Each piece of glass will have its own refraction, which is not optically flat.
Consider a glass in front of an objective lens like Swaro and some others use. These are very good optical glass made with surfaces flat and parallel to a fraction of a wavelength or fringe and mounted perpendicular to the optical axis.
Plate or float glass can have many dozens of waves error in a short distance and bows in the glass or sag from it own weight. At 1x,not noticeable. When magnified and the aperture is expanded to the FOV at the glass distance and probably viewed off axis giving an oblique plane, the errors can be very obvious.
Best
Ron
PS: Statestat, to get some idea just how bad this can be, look at the reflection of the glass or a mirror at steep angle, say over 45 degree from perpendicular
Thanks, I have seen the ripples in window glass, and have noticed that when looking at the bird feeder it is best to be square or perpendicular to the window. At the bird store they might have better windows and maybe single pane of glass, actually now that I think of it their scopes are very close to the window, so maybe that helps. Thanks again