When I set out to do this comparison, I thought I knew what to expect. I thought putting the Tiffen Variable ND next to the SLR Magic Variable ND would produce similar results with minor differences. I typically use these during the day to cut a substantial amount of light. So in this test, I have the Panasonic GH4 shooting 4K with the Natural profile, set with an ISO of 200. Without ND the 25mm’s aperture is at a T/8 and I’m cutting 5 stops with each ND to bring the aperture to a T/1.4.
Have a look, and then we’ll talk.
So the the obvious difference is the Tiffen appears to be affected heavily by infrared light. This is often referred to as IR Pollution. The symptoms vary, but here it’s producing a muddy, brownish quality that’s altering the image drastically from how it would appear without any filtration. The SLR Magic on the other hand, is adding a tiny bit of warmth to the image (probably just a much lesser degree of IR pollution). It’s minimal enough that it could be corrected out.
This video also exposes one of the signature complaints against variable ND filters and their affect on skintones. In the first setup, if you look at the tree leaves in the top left corner, you’ll see the light reflected off them is diminished when a variable ND is added. The reason for this is a polarizing effect that occurs, and the same thing happens to light that bounces off skin. This can create an unnatural look, but can be avoided by using dedicated individual ND filters in singular strengths. When it comes to ND, the polarizing effect is specific to the variable variety due to how they’re made.