sniper scope dark?

What would the correct gpu / incorrect setting be to fix a dark scope whilst aiming?

Look directly with ahead 7x or 8x, fine and clear image, enemies running around, windows / ledges viewable etc.  The same as without aiming.

However, aim, and change the angle very slightly and look left / right at another building, or refocus a bit further / closer, and the scope view goes really dark and I cannot make out any details.  Depth of field is off, should I have it on maybe?  Release aim and re-aim, makes no difference, the scope view remains dark and unusable.

Sometimes, moving and aiming the scope back towards its original view helps and the image clears up again and looks normal.

Sometimes, not changing the angle at all, aim, un-aim, aim, un-aim, aim gives a random dark / normal scope view.  Precinct 7 is the map this happens on most frequently.

Please advise which gpu / option setting I have set incorrectly.  Thanks.