Virtually perfect consistency of brightness at all focal lengths except very wide.notice noticed X at around ND32 and above at 16mm focal length. At 24mm X appears closer to 64, by 28mm X still faint but apparent at ND64, at 35mm all ND values are completely X free (subjectively - i did peep, but i didn't use any analytical tools to objectively verify ZERO variance in brightness caused by the filter, however, with close examination I failed to see any inconsistencies below ND32 at any focal length, and all focal lengths above 35mm are completely "X" free. All focal lengths 16mm + are usable at ND32 or lesser.All and all its an outstanding variable ND. Its clear and crisp and highly functional. This filter does not degrade contrast or resolution as some variable NDs are prone to do - this is highly functional and a great value. My only advice would be to test out all your lenses on your largest sensor body to find out when and if any artefacts appear so you know what, if any, your limitations are.I found that the X was quickly noticeable - at say ND32 it may be a question as to whether its there or not, but by say ND36 it would be clearly apparent. This is a great filter, but especially with wide angle lenses you should test the water so you know before a bunch of images turn up with artefacts too subtle to see on the display in full sun, but treacherouslu obvious on a display or a print...