Are Cheap ND Filters Worthless and How To Correct Their Color Cast?

Recently I’ve bought a Sony a6300 to replace my Sony A7s. Unfortunately for me, I sold my at the same time, which now I regret as it is an essential piece of equipment to shoot with the S-log2 and S-log3 picture profiles.

Having an outdoor shoot coming up and not enough time to put my hand on a new ND Throttle I had to find a solution. That is when I remembered that I had an “untouched since acquired in 2013” 4 x 4 in my goody bag.

SWEET MOTHER OF GOD! As soon as I put this in front of my lens, the ugliness entailed.
ND filter Color cast example

So, let’s talk about how good (or bad) are those China made eBay ND filters and how you can correct the color cast.

First, I did the test with the Sony a6300 in 4K to have as much detail as possible. During the test, all the settings were the same, except for the aperture as I was trying to keep the same exposure between the 2 shots.

The focus was on the 1000x and SD Card image on the box. As you can see the cheap creates a little bit of ghosting compared to the naked lens, not surprising as it’s made of cheap resin AKA plastic, but in my opinion, for 99% of the applications where there are motion, and when we are not pixel peeping, this $5-$10 is adequate.
ND Filter comparison

Now for the color cast. This creates a heavy magenta / purple color cast, and, how do you get rid of it? Pretty simple, but a lot of people overlook this “easy” fix. I’m talking about custom white balance, here you can see that an in-camera custom white balance correct 99% of the color cast and the remaining 1% can be corrected with color correction in post production by introducing some green/yellow in the image.
ND Filter 400%

If your footage already has the cast baked in, you are in for a ride!! We could make a full tutorial on this but in a nutshell, what you would need to do is introduce the opposite color back in the image. If you look at the color wheel below, Green and Purple are opposites, so if you have a purple tint, introduce green, and vice-versa.
color wheel

All and all, I think I will keep this in my goody bag as a back-up. For $5… I can’t complain!

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