UV light might cause haziness in the sensor. A UV filter tries to cut out ultraviolet (UV) light, while passing everything else.
There are strong UV filters that cut out haze, but with side effects. Most of the time, though, UV filters are harmless filters usually left on the lens forever.
Why would anyone want to do that? UV filters, because they don’t negatively impact the image, are usually left on the lens permanently to protect it from the elements, or from being scratched due to incorrect cleaning practices or the occasional bump or drop. A scratched filter is cheaper to replace than a scratched lens. Some lenses also need a UV filter to complete its weather protection system.
Are there any negatives?
Some argue that having an additional optical element unnecessarily degrades the image, especially if it is a cheap UV filter. If you use a good filter, this point is a non-issue in my experience.
One important negative is that people tend to forget they have a UV filter on a lens, until its time to remove it. A filter can get stuck to the lens thread if not regularly removed and cleaned. As long as you don’t forget this important step you’re gold.
There are two kinds of polarizing filters – Linear and Circular. Both of them do these things:
- Darken the sky
- Remove reflections from water, mirrors, shiny surfaces, etc
- Take the gloss off shiny surfaces
- Increase color saturation
I’ll keep it simple – stick to circular polarizers (CPL). They do everything linear polarizers do, and they are not hard on your camera’s exposure meter.
Neutral Density Filters
These work like sunglasses. They cut light. For outdoor video they are almost a necessity.
ND filters are measured in stops of light:
|ND Number||Optical Density||Stops of Light Cut|
Finding it hard to remember? Use my method of 1-2-3:
One stop of light = Two Power ND = 0.3 Optical Density.
If you want to cut four stops, then:
4 stops of light = 24 (16) ND number = 0.3 x 4 (1.2) Optical Density.
Not that hard anymore, eh?
There are three broad classes of ND filters:
- Fixed value ND filters
- Variable ND filters
- Split or Graduated ND filters
Fixed value ND filters offer the greatest precision, with the downside that you’ll need many filters to cover all scenarios. What happens if light is changing constantly?
Variable ND filters often cover a limited range. If you’re going for this kind of filter, get the best. You change the density by rotating the filter. Sometimes its affect is almost imperceptible on small viewfinders or LCD screens.
Split or Graduated filters are ND filters with the ND over a limited area only, like if you want to stop down only the sky, for example:
Obviously, if you have moving elements in your frame, or if you’re moving the camera, a graduated ND filter might not work the way you want it to.
These filters soften the image, which can be a good thing when dealing with skin, etc. Like ND filters, diffusers have different ‘powers’, depending on the intensity of the effect you are after. E.g., The Tiffen 77mm Glimmer Glass Filter has numbers 1, 2, 3, etc – where 1 is the subtlest effect and it goes up from there. Test thoroughly before you use.
Filters form an integral part of any cinematographer’s arsenal of tools. It’s so much easier and cheaper (and not to mention more artistically satisfying!) to get certain effects on camera rather than in a color grading suite.
Considerations for professional use:
- Quality of materials and construction
- Uncompromising optical quality
- Constant performance, no vignetting
- Negligible difference between different samples of the same glass
- Easily available and replaceable
- Scratch, water and dirt resistant if possible
Choose your filters wisely. It is the height of stupidity to spend a lot of money on a camera and lenses and then ruin it all with cheap filters. At the end of this chapter I will give you my recommendations.
Circular Threaded Filters
Filters can be divided into two broad groups:
- those that screw directly on to the lenses, and
- those that are used on matte boxes.
This is an important consideration. Which type you choose will depend on whether you need a matte box or not (if you don’t know what a matte box is, don’t worry. I’ll get to it soon).
A circular filter is screwed on to the front of the lens. Sometimes, circular filters themselves have threads so that you can screw another filter on it, forming a filter stack.
What are some of the disadvantages of circular filters?
One problem with screw-filters are that you might have to buy different filters for each lens filter thread. E.g., the Canon EF 24-70mm f/2.8L USM has an 82mm filter size while the Canon EF 70-200mm f/2.8L IS II USM has a 77mm filter size.
You can overcome this problem by using adapters called ‘Step up rings’ or ‘Step down rings’ to match the filter with the thread of your lens. Talk about the tail wagging the dog.
Secondly, circular filters are difficult to stack. Let’s say you you’ve stacked three filters and have now decided to remove the closest one to the lens. How many filters will you have to unscrew to get the job done?
Traditionally, circular filters have been a good fit for photography. They are light, and along with lens hoods, are easy to carry around.
What if we can combine them? Are there any advantages to such a system?