Dear Customer, Thank you for your question. Please check the following steps to setting the focus: (Do not look at too close objects) Step 1. Cover the right objective lens with your hand or close your right eye, rotate the central independent focusing wheel until the image in the left eyepiece is sharp and clear. Step 2. Now cover the left objective lens or close your left eye, rotate the right eyepiece focusing wheel to adjust the diopter of the right eye until the captured image is sharp. 

There is a Far-Near logo on the focusing wheel. Depending on the viewing distance, rotate the focusing wheel in the corresponding direction. If the viewing distance is far, please rotate the lens to the left. If you are close, rotate the lens to the right. The optimum focus can be adjusted repeatedly according to the actual viewing distance. 

From 1-5 stops, there will be a slight X cross for lens under 24mm. An X cross will appear at the highest stop and can be removed by rotating the filter ring, which is a normal situation instead of a quality issue. 

I don't see why not, remember that the filter goes on the lens, not on the camera. 

You change the ND level by rotating the filter, but, per my earlier review (q.v.), I found it hard to know how much ND I was applying.