We continue our look at external camera filters, focusing on what makes the most sense for outside shooting. Like the last blog, we feel strongly that today’s cameras and post abilities are so versatile, it only makes sense to use filters when time or money keep you from achieving the desired look.
UV Filters and Common Thread Size
Like frequent oil changes in your car, a UV filter on every lens that can accept one is a great investment. For under $20/lens you are adding one more layer of protection. Scratches, abrasions, dirt and “bumps” all take it out on the UV filter first before permanently damaging your expensive lenses. Buy a decent quality UV filter, one with decent threads and then forget it is even there. If your lenses have several filter sizes try step-up or step down rings (If you aren’t losing field of view) to make a common filter size for all your shooting lenses. If all the lenses end up the same size, then they can share ALL of your screw on filters. If you can’t do that, consider a Mattebox. The goal is to be able to use all the filters on all the lenses.
If your camera does not have internal ND filters or you often find yourself in lighting situations where it is just too bright for what you want to do, then ND filters are a must. 0.3 ND equals 1 Stop of latitude, so a 0.6ND would be 2 stops, 0.9ND would be 3 stops and so on. Fixed ND Lenses work well, but consider getting a screw-on variable ND Filter. This will allow you to “dial-in” the exact amount of ND you require. If you have had the joy of working with a de-clicked cine lens, then you know the benefit of working between the hard stops.
Graduated ND Filters
As the name implies, these filters are graduated from full ND to No ND over half of the filter, then clear on the other half). Move the filter, No ND side first, into the frame until you lower the light level sufficiently for the desired look. You can move from top to bottom, bottom of frame to top, or side to side. In a multi-tray Mattebox, graduated ND’s can be used from multiple directions. Obviously, camera (Tilts and Pans) moves at right angles to the line of ND will not work, but if you shoot 4k then you know what to do….
Graduated Colored Filters
These filters are designed to give in-camera, dramatic effects. Our take: if you don’t have to, don’t. So much can be done in post, if you have even a small amount of time the flexibility of what can be done in post far outweighs committing to a colored filter effect in the field.
Polarizer (Linear and Circular)
Linear and Circular Polarizers do the same thing. They reduce reflections on glass surfaces, increase color saturation in foliage and darken a blue sky. All polarizers have a linear polarizing element. Circular Polarizers contain a Linear Polarizer component that does the main work of polarization, as well as a second layer inside the filter called a Quarter Wave Plate, which “spins” the light after it goes through the linear layer and before it enters the camera lens. This prevents "cross polarization" with any reflective surfaces in the system.
The main problem is that a linear polarizer can cause cross polarization on other reflective surfaces in your system such as mirrors and beam splitters.
Reflective surfaces polarize light, which is why a polarizer can reduce or eliminate those reflections. If you have a mirror or other reflective surface inside your camera, a linear polarizer can cross polarize the reflected image and possibly black out the image.
If you ever shot 16mm or 35mm film with a video tap while using a linear polarizer you know the video feed would often go dark because the partially silvered mirror in the video tap would get cross-polarized. This same type of cross polarization is used to create the Variable Neutral Density Filters.
With a circular polarizer, the quarter wave plate on the rear of the polarizer spins the light before it enters the camera lens so that it doesn't get cross-polarized on any reflective surfaces in the system, such as the partial mirror in a video tap or a DSLR mirror. If there are mirrors in your optical system, the circular polarizer solves any problems or potential problems.
Day for Night
Although it was a classic movie by FrançoisTruffau, there is not much to recommend it as a filter. Today’s cameras have such a great latitude and low light capabilities that shooting at night or low light is infinitely preferable.
Use these outdoors only if it makes sense for what you are shooting, specifically faces and beauty product shots. Remember this is committing to an effect that can not be removed in post, so shooter beware!