How Neutral Are Your ND Filters? Check out This True ND Filter Color Shift Test
Neutral density filters are an essential addition to your toolkit, particularly when shooting outside in the bright light of the sun, attempting to get proper exposure or shallow depth of field. Certain brands of filters, like any piece of filmmaking equipment, are going to have their pros, cons, devotees, and naysayers. In this ND test by Matthew Allard, we are shown how different ND filters, Redrock Micro, Tiffen, and True ND affect the color temperature of your image, how drastically (or not) different filters can add unwanted color shifts, and the great neutrality of True ND. Check out the video after the jump:
Neutral density filters are only supposed to affect the amount of light that enters the lens, but some filters add color shifts. Why is this an issue? Well, given that you're probably not going to be using the same ND filter all day long, switching between them may affect the color temperature of your images, resulting in inconsistency.
"Oh, I'll just white balance before each shot," you say? Well, yes. That'd be ideal, but we all know that when we're running out of time on a shoot, certain details tend to fall by the wayside or forgotten completely. Having a piece of glass that doesn't change your image's color temperature (or just ever so slightly) will make your shoot a lot less troublesome.
I think it goes without saying, even though Allard mentions this in the video's description, that this isn't a very comprehensive ND filter test, since he only tests 3 different brands: Redrock Micro, Tiffen, and True ND. Tiffen tends to be an indie favorite, since they're inexpensive and get the job done. However, Allard claims that True ND, though significantly more spendy, offers the most neutrality out of the other filters he tested. Take a look for yourself:
Given that True ND is a high-end ND filter, it's to be expected (or should be) that they'd perform better than the Tiffen and Redrock Micro. Allard mentions that True ND filters are manufactured differently: that instead of adding the ND inside the glass, they're putting a film on the glass (which makes it susceptible to smudges, so watch out.) The True ND filters performed well, even at high levels of ND.
However, if True ND filters are outside of your budget (around $600 each,) I wouldn't worry. Just being aware that not all neutral density filters are created equal will help you manage your shoot more capably, giving you the chance to counteract any change in color temperature by white balancing -- or simply not being surprised when your subject's face all of a sudden looks like a tomato.
What filters do you use and recommend to others? What tips would you offer someone if their filters add color shifts? Let us know in the comments.