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I've got a very difficult shot coming up. I'm photographing moonlight on a country meadow. I do not want to do post work. I need to do everything real time (for reasons too long to get into, there is more going on in the shot that will just complicate the question.)

My only option is to use filters during my shot, to capture the way we perceive moonlight. The camera picks up moonlight as white light. Our eyes, however, perceive it as very desaturated with a slight hint of blue. I've got a blue filter, but the shot just comes out far too blue. I need to desaturate the light coming in to the camera (almost black and white.) Is there any possible way to use lens filters to desaturate light?

I can't shoot in b&w as I'm not only exposing the moonlight, but also a girl with a glowing balloon in the scene. It's all got to be done in one exposure.

Is there any way I can desaturate the light with use of a filter or series of filters?

Thanks a heap guys.

More info: thanks so much everybody, you all are right, but here's why and what I need. I'm having the girl and the balloons to be illuminated with lights and the balloons are going to be different colors and glowing. So she is going to be in full glory color, but she's going to be sitting in dim moonlight. To get the moonlight look, I can desaturate in camera settings and use a filter. But when its time to take the cap off the lens (shutter still open after capturing moonlight) and exposing the girl and balloons, the camera is going to capture her and the balloons in those same desaturated settings. My camera will not change settings in mid exposure, and although I think it can combine two exposures, this is a messier way of getting where I'm trying to go. And post is just about impossible. To capture full color in the image, and then darken and blue and desaturate the rest of the scenery is extremely imperfect.

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  • \$\begingroup\$ You seem surprised that your blue filter, on a scene with blue light, makes everything more blue. Bear in mind that a blue filter doesn't filter out blue light, it filters out everything except blue light. \$\endgroup\$
    – Steve Ives
    Jun 30, 2015 at 9:49

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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".

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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.

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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 (to emphasise it) and by playing with the exposure and/or saturation controls.

Alternatively - what about a double exposure - one desaturated for the scene without the girl and another with filters etc with the girl?

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  • \$\begingroup\$ Surely a "double exposure" would require post work though? \$\endgroup\$
    – Digital Lightcraft
    Jun 30, 2015 at 10:15
  • \$\begingroup\$ Normally, although some cameras can do it in-camera. \$\endgroup\$
    – Steve Ives
    Jun 30, 2015 at 10:21

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