August 11, 2013

How Neutral Are Your ND Filters? Check out This True ND Filter Color Shift Test

True ND FiltersNeutral 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.

Link: Testing Out True ND Filters -- Filmmaker IQ

Your Comment

5 Comments

Pretty awesome test! I agree with everything he said with the addition that knowing the color shift of the ND's could also be used to achieve the look in camera the director may want to take it in post which could mean a little less grade work to push it in that direction (depending on the budget or level of production the project has).

August 11, 2013

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I did a simple test: On 3200 preset and using a tungsten fresnel, I shot a properly exposed gray card using each Tiffen ND filter I own (N6, N9, N1.2). I used a different shutter speeds to compensate for light loss of each ND. The N6 and N9 looked fine, no real noticeable shift. On the gray card, the N1.2 showed a noticeable magenta shift. But when used in the field, the shift with the N1.2 is barely noticeable. I never make any manual white balance adjustment for exteriors, so I just leave it alone. However, if an ND is slightly green-biased, then an adjustment is needed in-camera.

August 11, 2013

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James

This test is useless. "Bad" ND filters WILL NOT affect colour equally through the spectrum. Different wavelengths will be attenuated with a variable shift. White balance can't solve this kind of problems.

A more relevant test:
- Try shooting a Macbeth card with and without a cheap filter, then try to white balance to match. Check your results, by comparing in Photoshop. Surprise. You can spend 10 hours white balancing and it will not be even close. Some patches will match, some not.
It will not be possible because every colour patch has a different attenuation.

What can you do if you know that your ND filter is not quite up to the task, but you have to use it:
- shoot a macbeth card everytime light changes in a significant way and create a colour profile for your filter look (DCP file), then apply it. It is the most accurate way to solve this.

August 11, 2013

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Kuky

I was extremely surprised by the Redrock Micro ND filter with the indoor portraiture test near the end and how much the image warmed up.

Do you know if this tester also tried out the Polaroid ND filters? I was recommended those a little over a year ago for their price, though I've noticed things move towards a cooler color temp.

August 11, 2013

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Wouldn't it have been a better comparison going against the IRND Tiffens and similar as opposed to just regular ND filters against an IRND True ND?

August 12, 2013

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