New answers tagged filters
You can't do this - the brightness of light and it's colour cannot be separated, so you cannot filter out colour whilst leaving the intensity. You say you cannot shoot B&W because of the girl & the glowing balloon - I assume you are trying to keep the colour of the balloon? You might have some success with a filter the same colour as the balloon ...
There is no way to desaturate an image optically (short of a deep infrared filter that only allows frequencies that the sensor colour filter array is invisible to). Assuming you are shooting digitally, why don't you just turn down the saturation setting on the camera? That doesn't require any post work and counts as doing things "in camera".
So, if I'm correct you want to make the moonlight slightly blue, the only way I can think to achieve this is by playing with White Balance. There is no way to "desaturate" with a filter and have the result not heavily colour cast.
The most common size for under-the-lens filter holders is 3x3" and those designed for use in the head or bellows run the gamut. Other than sets that are built for specific enlargers, generic filters are usually sold in 3x3", 6x6" and sometimes 12x12". If the filters you have are regular gel filters, they're usually cut down to fit your drawer and then stay ...
I did a OFX plugin that does the color correction job. Please find the source code here: https://github.com/edubois/kaliscope I will post a binary release very soon (OFX plugin that you can use inside DaVinci resolve for example). You only have to put the RGB values of the filter. Eloi.
You can get sheets of polarizing gel filters designed to be used on studio and theatrical lighting and trim a piece to fit the rear gel holder. They're not cheap, though. The main problem would be the sheets are linear polarizers and so the auto focus system on you camera would likely be disabled. The other significant issue would be that since polarizing ...
I reckon my Lee ones are 99mm give or take less than half a mm.
80 filter corrects tungsten light sources to daylight balanced film 85 filter corrects daylight sources to tungsten-balanced film There are variations - see http://en.wikipedia.org/wiki/Wratten_number
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