Originally Posted by maestro
Another interesting experience:
My S&B scope has a standard M58 photo thread at the front lens. Once I tried to apply a Circular Polariser filter, and it caused the scope to ranging lower with many metres! It wasn't the lightness reduction because I tried it with some Neutral Density filters without any difference but the polariser filter affected rangefinding obviously. I don't know whether it was the effect of the polariser part of the filter or the quarter-wave plate but it was interesting to see how the picture goes in and out of focus when I put the filter on and off...
Did you use a high quality one, or a cheap one Andras? Because it's a known effect of cheap filters on camera lenses that they can affect image quality by some margin. Not necessarily focus point, but flare etc can be made worse.
Interesting the ND filters made no difference, that seems to rule out the light dark stuff as affecting the scope, and probably affecting the shooter.