Quote Originally Posted by Doremus Scudder View Post

Sorry, I beg to differ.

Water vapor and most particulates and pollutants absorb or scatter the longer wavelengths and pass the shorter (blue end of the spectrum) (this is what makes the sky blue, not red...).

Anyone who has been more than a few meters underwater (snorkeling or scuba diving) knows that everything turns blue; the longer wavelengths (red, yellow, green) get filtered out because they are absorbed; the blue passes through. The same thing happens with water vapor in the air. Cloudy days are markedly more blue than sunlit days for precisely this reason; the longer wavelengths are filtered out by the clouds.

UV or yellow filters are sometimes called "haze filters." They "eliminate" the haze by darkening it, i.e., by blocking the predominantly blue (and near UV) shorter wavelengths making the haze darker and less noticeable in the print. Using a blue filter passes those shorter wavelengths and makes the haze lighter, thereby "emphasizing" it.

A clear UV or haze filter is what is generally used in color photography to "eliminate" or "reduce" haze, which it does by blocking the near UV and a bit of the darkest blue. These are the wavelengths that are predominant in haze.



Have you ever used filters?!

It's not a matter of transmitting or absorbing. It is a matter of scattering the light. The sky is blue simple because whatever is in the sky scatters blue rays more.

Go up on an elevated area such as a really tall building or a mountain and then take a landscape picture with some fine grain film with a deep red filter (3 stops of compensation). Then take the same picture without the filter. You will be able to see a lot more detail with the red filter. Once you filter out the scattered blue light you will get the more direct red light. Now take the picture with the blue filter. Details will be obscured.

I read about red filters cutting through haze but I didn't realize how dramatic the effect was until I tried it for myself. I took the pictures on a clear bright day and you could still see a difference. Try it with a red filter AND a polarizer. It's even more dramatic. Bring a tripod and cable release.

The benefits of a red filter particularly a strong red filter cannot be duplicated with a digital camera or photoshop. It really is one of the unique tools of analog photography.