What you said doesn't match what we see in the video clips. When you used the DJI ND16 filter, main camera was using f4.0. When you used the Freewell Split ND32 filter, the main camera was set to f3.2. That makes a lot more sense than your stated f4 because a stronger ND filter would need a larger fstop opening to make up for the greater light filtering of ND32 compared to ND16. You were filming the same subject but it looks like the sun was lighting up the white barn more when you used the Split ND filter compared to the DJI filter when your lighting condition looked like the sun was behind clouds. This could explain why you needed an ND32/ND4 split filter.
Thank for great video. I just buy spit ND. I also have freewell wide angle adapter. I’m OK with their vignette because after correct fish eye distortion the vignette is gone.
