How much of an effect of a blue filter and can anyone post examples

Discussion in 'B&W: Film, Paper, Chemistry' started by ymc226, Oct 11, 2011.

  1. ymc226

    ymc226 Member

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    I was on the beach in Nantucket a day this summer when quite suddenly, a thick fog rolled in perpendicularly to the shore. It was quite dramatic and I regret that I did not have my camera with me, only my fishing rod.

    I've read that using a blue filter for B&W film, an effect of fog and haze in the distance will be achieved. Is this true and how dramatic is this effect?

    If anyone has examples of the magnitude of this effect, I'd would appreciate it if examples can be posted.
     
  2. segedi

    segedi Member

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    I would think it would intensify any existing haze, just as orange - red drastically cut through it. But I don't think it will create anything that isn't already present.
     
  3. keithwms

    keithwms Member

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    Yeah well the filter only helps if you have a camera :tongue:

    There are two different scattering mechanisms that come into play: Rayleigh and Mie. The strength of the former goes as 1/wavelength^4, so indeed the shorter blue wavelengths scatter most strongly. Thus Rayleigh scattering is often cited when we talk about the anti-haze effect of infrared film. And you will tend to see more haze in blue-sensitive or blue-filtered film than with red or infrared.

    But the scattering mechanism you really care about for ground fog is Mie, and the strength of that is related to the match between droplet sizes and wavelengths; you get a white cloud because the spectrum of colours is scattered more or less equally by a distribution of droplet sizes in the cloud.

    If you think about it, narrowing down the wavelength range is usually not going to help you see more Mie scattering. What you're doing with a blue filter is admitting only that portion of the light scattered by a subset of the particles.... and what you really want is to see as much scattering as possible.

    So... you may see some minor enhancement of fog by using a blue filter, but a more effective way to build up fog is simply to do a longer exposure. Or consult the local dew point and temperature forecast and plan accordingly!