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Lens filters are flat pieces of clear glass or resin that are placed in front of the lens to change or improve the image. They are often round and can be screwed directly onto the lens. Some are square/ rectangular and can fit in a Matte Box.
Lens filters are flat pieces of clear glass or resin that are placed in front of the lens to change or improve the image. They are often round and can be screwed directly onto the lens. Some are square/ rectangular and can fit in a Matte Box.
At Bath Spa we have the round versions which are more common in stills photography and easier to use. Square filters are more expensive and require a matte box.
At Bath Spa we have the round versions which are more common in stills photography and easier to use. Square filters are more expensive and require a matte box.
When using filters it is best to keep as much stray light from out of your field of view away from the lens, as this can cause unwanted flare and reflections between the filter and the lens. A Matt box or Lens hood will be of help. (Here is a link to why you should use a matte box, particularly when using filters)
When using filters it is best to keep as much stray light from out of your field of view away from the lens, as this can cause unwanted flare and reflections between the filter and the lens. A Matt box or Lens hood will be of help. (Here is a link to why you should use a matte box, particularly when using filters)
This page covers:
ND Filters
Variable Filters
Black Pro Mist Filters
Polarising Filters
Skylight or UV Filters
Close Up Filters
ND Filters
ND Filters
ND or neutral density filters are grey, colorless filters that reduce the amount of light coming in through the lens, like a pair of sunglasses. More ‘production’ type video cameras have these built into the camera body behind the lens (Sony X70, Z90 and Canon C100) but for the Sony A7 111 and Panasonic GH4 you may want to use NDs. The NDs are normally rated in stops, point nine being 3 stops in reduction.
So why would you want to use an ND filter?
If you want to reduce your depth of field- or focus you may want to film with your lens at a wide F stop.(here is a short film explaining depth of field) This means you are letting a lot of light into the camera. This may be fine when inside where there is not so much light, but outside, particularly when sunny there can be too much light.
If taking a still, it's no problem, you just reduce your shutter speed to something like 1/100- to 1/4000 of a second, but in video, if you do this it can make the movement of fast moving objects look a bit odd. For most dramatic films, the shutter speed is set up at 1/50th or 1/48th of a second, which promotes the ‘Film look’ that we are so used to seeing, which lets in a lot of light.
Image from Robert Emperley on Flickr
The asset store has a bookable item called ‘Filter kit’ which includes a 77mm diameter which can screw onto the Canon 24-105mm zoom lenses and most of the Samyang primes. This is an ideal lens for the Sony A7 111, when used with a Metabones adaptor (booked separately)
Our four Sony A7 111 cameras all come with screw in ND filters to fit the supplied Zoom lenses as does the Panasonic GH4.
If using the Samyang Primes on the Sony A7 111, the 77mm ND will fit most of the lenses. Remember, if filming with a C100, you can use the internal NDs.
Variable Filters
Variable Filters
These filters cut the light back like normal NDs filters, but you can simply vary the amount by twisting the filter. The two layers of glass are polarising filters and by rotating them against each other, they let less light through.
For still photography, NDs and Variable NDs are often used to allow the longer shutter speed to create blurred movement, like this water here. For live action, they are normally used to enable a wide aperture, whilst filming at the standard 1/50th of a second.
Variable NDs are particularly useful as they are very quick to use and provide exactly the amount of light reduction you want without having to unscrew and change them. They have some drawbacks though.
As you are looking through two pieces of glass instead of one, your final image can be a bit softer. Also, if you use one on a wide angle lens, and cut the light back a lot, they can produce this weird soft cross effect.
We have a variable 77mm ND which will fit the Canon 24-105mm lens on some of the C100 kits and most of the Samyang Primes.
Sony A7 111 kits 1 and 2 have 58mm Variable NDs to fit the zoom lens included.
There are Variable NDs also available to fit the Canon 700D cameras for stills.
Black Pro Mist Filters
Black Pro Mist Filters
These filters serve to soften the image before it hits the sensor. You can always soften or defuse an image in post production, but using a filter gives a more organic, natural feel. So why would you want to do this?
Photo from the Tiffin Website
Video cameras are often criticized for having a harsher image than film cameras, either due to higher contrast levels, or the amount of detail that the camera uses when processing the image. (When filming with the Sony X70 and and Z90 I always reduce the detail in the Picture Profile settings)
A softer image harks back to older film cameras and lenses.
The beauty of the Black Pro mist filter is that it softens the highlights but has little effect on the overall contrast as the filtration comes from thousands of microscopic black dots scattered through the filter. Here is an excellent example of how the filters work and the best conditions for them.
We have 1/8th and ¼ black Promists in 77mm and 82mm diameter, which fill fit the Canon Zooms that come with the C100 kits and fit most of the Samyang Primes except the 14mm and the 85mm. The ¼ is the most commonly used with the 1/8th being more subtle.
Polarising Filters
Polarising Filters
These filters cut back the shine reflected from surfaces.
They work really well when filming through car windows, and looking into water. They also cut through atmospheric haze and can increase the contrast in skys, bringing out the blue to its strongest level and creating separation from any clouds.
Before Photoshop and digital grading, the Polariser ruled, and is still essential when filming cars and landscapes. It does however make people look dead as it can rob them of their shine. Makeup is a better approach to this problem.
Photo from B&H
Photo from Mark Vargo.
Photo from Mark Vargo.
The filter is screwed onto the front of the camera, but the forward section can still rotate. This rotation sets the level of Polarization. Here is a video made by cameraman Mark Vargo showing how this works, with some theory thrown in.
Skylight or UV Filters
Skylight or UV Filters
These are the most common filters found on stills cameras. Their effect is subtle as they cut back UV (Ultraviolet light) pollution) which can be seen when photographing landscapes in sunny conditions. Often these filters will stay on a lens to provide protection from scratches and thumb prints.
Occasionally you will find one of the lenses of the 700D stills kits at BSU. We don't have them for the video cameras.
Image from Allan Weitz of B&H
Close Up Filters
Close Up Filters
Close filters reduce the minimum focus of a lens, bringing it closer to the camera, at the same time bringing the far focus closer as well, which means you can only use it for close up situations.
A Macro lens is different as it is able to shoot very close, but still focus on infinity.
We have a 77mm +2 Dioptre lens in the store which will fit most of the Samyang Primes and the Canon 24-105mm zooms that come with the C100 mk2 kits (nos 6-10).
Written by FR
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