Tiffen Black Pro-Mist 1/4 Circular Polarising Filter - 58mm

Yes, but you may need a specialized hood that allows you to reach through and rotate the CPL ring without removing it.

Generally, no. As long as the filter is clean, modern autofocus systems function normally through the glass.

Yes, all circular polarizers reduce light. You should expect a light loss of approximately 1.5 to 2 stops depending on the rotation.

It is not recommended to stack a CPL with a variable ND, as this often creates an 'X' pattern or color shift across the image.

Look through your viewfinder or at your screen while rotating the outer ring; you will see reflections on non-metallic surfaces diminish to their minimum point.

No, the diffusion effect is fixed at 1/4 strength. Only the polarization effect is adjustable via the rotating ring.

The CPL element naturally reduces light transmission. Increase your ISO or open your aperture by 1-2 stops to compensate.

Ensure no other filters are stacked on top of this unit. If using a wide-angle lens, consider removing the lens hood or checking for physical obstruction.

Do not force it. Use a rubber filter wrench to provide a better grip without applying uneven pressure to the glass.