I bought the WonderPana Filter system to use with my Nikkor 14-24mm for video. The system consists of 145mm round filters and 168mm rectangular/square filters. There are two slots for mounting two 4mm rectangular filters at a time. You can also mount one round and one rectangular filter at a time. As you know at 24fps the shutter speed is always 1/50 of a second. In order to shoot with a narrow depth of field I need low ISO and ND filters in bright daylight. Here’s the question, as I can’t stack the ultra slim 145mm ND filters(no front threads), should I buy separate two, three, four, and five stop 145mm filters to deal precisely with varying light levels, or would it be better to use square .3, .6., .9 and 1.2 ND that can be stacked? I already have one 4 stop 145mm ND. Thanks in advance.