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Colour Correction Filters
With the number of light sources available to video and film makers increasing almost daily,
matching one to another is getting more and more difficult.
It’s not made any easier by the fact that High Definition is much more sensitive to these differences
and that colour meters don’t always accurately reflect what the camera actually sees and records.
But then, it’s challenges like this which make cinematography so rewarding, isn’t it?
Correction filters are different from conversion filters
in that conversion filters convert one light source to another,
whereas correction filters sort out any unwanted colour casts.
A lot of non-incandescent sources, in other words fluorescents and LEDs,
tend to produce a green colour cast.
This can result in unhealthy skin tones and drab and dreary colours.
What we need to do is remove some of the green from the source
and the filter we use is conveniently called minus green.
It comes in different strengths from full right the way down to one eighth.
If you’re using a colour meter, it will give you a reading in CC magenta telling you what filtration you need.
This is a measure used by camera filters but it translates easily to lighting gels
as 247 or full minus green is equivalent to magenta CC30
and that means, half minus green is CC15 and so on.
Just mix and match the various strengths to get what you need.
It’s relatively easy correcting one tube,
but if you have got an office full, it can take all day and use a lot of filter.
So LEE offer these fluorescent sleeves which just fit over the tube.
If you’re working on location with lots of fluorescents and a limited budget,
it’s often easier to correct your film or video lights to the ambient light
and then white balance everything together.
For such instances there is a range of green filters, imaginatively called plus green.
They also come in full, half, quarter and eighth strengths.
Like the magentas the greens also relate to the correction indicated by a colour meter.
With LED sources, it becomes a lot more complicated as getting an accurate colour reading from an LED
with a cinematographer’s colour meter is almost impossible,
especially with some of the cheaper units which have hundreds of LEDs, often with wildly different spectrums.
Now this isn’t a cheap LED by any means, but it also has issues delivering a clean white.
Helpfully, LEE have a range of Cosmetic filters which combine diffusion with colour.
They are starting to be used a lot with LED fittings
as they warm up the light, reduce the green and add some diffusion all in one.
A lot of videographers are starting to use cheap LED sources,
and they're finding that they just don’t do skin tones justice at all.
These cheaper lights have a tendency to lack the amber and red end of the spectrum,
and they have quite a lot of green.
There are some awful lights out there
and in some cases it may even be necessary to use a cocktail of filters to get an accurate white light
which reproduces acceptable skin tones on film or video.
You’ll certainly need a magenta of some sort
and a 248 minus green is a good place to start, adding more layers if necessary.
This has only been a brief introduction to colour correcting your lights,
but hopefully it will save you time and money in post-production.