>This may be a silly question, but since I'm not very familiar with these types of filters, I wonder what the difference between them is? ProMist, White mist, Black mist, fog filters... what do they exactly do?
>Well, describing the image affects of various diffusion filters is a little like describing wine -- it's simpler if you just looked through some of these filters, maybe shot some tests.
>Most of these filters contain light-scattering particles that spread light, causing :
(1) halation (glowing around lights)
(2) loss of contrast, and
(3) loss of definition.
>You can sort of break them down by how much of those three qualities or artefacts they display. Some are designed to reduce definition without loss of contrast or halation (like Diffusion-FX). Some are mainly designed for halation effects. Some of the older designs tend to throw the image slightly out-of-focus, which is different than what diffusion is supposed to do, which is basically layer an unsharp image over a sharp image.
>Some have a colour cast to the halation while others are neutral -- for example, the halation around a light caused by some older fog filters is bluer than that caused by a ProMist filter.
>The black specks, particles, pattern of dots, etc. in some filters like Black ProMist (Tiffen) or Black Frost (Schneider) -- not to mention Black Diffusion-FX, Black Dot Texture Screens, Black SupraFrost, etc. -- are meant to restore some of the loss of contrast caused by the spreading of light into dark areas due to the "mist" particles.
>Also, these filters can change in characteristics within their range of strengths. Hence why testing is necessary.
>"Image Control" by Gerald Hirschfeld is a good book on using these sorts of filters. There are also some websites with examples of these filters.
>David Mullen, ASC
>Thank you very much for the nice explanation. I visited Tiffen's website and had a look what the effects are like. Your explanation though, gave me some insight.
class="style11">>"Well, describing the image affects of various diffusion filters is a little >like describing wine..."
>As usual, David provides excellent insight into these filters. Not much to add except that one of the differences among the Pro-Mists and Fogs is that highlight flare is spread differently- in the Pro-Mists it is slightly more concentrated nearer the light source. This is a subtle difference that testing alone can demonstrate. Alterations to contrast and resolution are otherwise handled in a technically similar manner.
>Older "Diffusion" filters (such as those phased out at Tiffen some 15 years ago or more) had surfaces that were completely wavy, causing a "soft-focus" effect, where the image isn't actually sharp. As David points out, it is better to retain focus while reducing fine unwanted detail, which is accomplished by the more current filters like Pro-Mists and Diffusion/FX's by combining light-altering elements separated, however finely, by clear spaces that allow light to pass through unaffected.
>Ultimately, the best filter selection guide is your eye, but it always helps to understand what you're looking at (the filter, in this case, and how it does what it does), enough to know how to manipulate it to your desires.
>Thanks to everybody for the posts. I Feel a lot smarter now.