Well, there's basically two types of diffusion/softening, the different filters on the market do one or both to a greater or lesser degree.
There's diffusion, where the filter has small particles that scatter light. This is usually what makes highlights bloom, or in other words, has a halation effect. An old type of filter in this category is the Wilson Supa Soft. However, these were made of plastic and scratched very easily, so Tiffen came up with the Pro Mist that are made of glass. Schneider also has a filter in this category, they call it White Frost.
One of the effects these filters have is that they raise the light level in the shadows. To keep them dark there's also diffusion filters that has black specks in them. Examples are Tiffen Black Pro Mist and the Scheider Black Frost. The black diffusion filters are often considered to have a somewhat less obvious effect than the white diffusion filters.
There's more filters of the diffusion type, such as Tiffen Glimmerglass and Pearlescent, that some may prefer. These pretty much do the same thing as the filters above, but they do it somewhat differently.
Diffusion filters that really scatter the light a long way from the source cause a general drop in contrast, and there's filters made to do exactly that. On old example is the Tiffen Soft Contrast, used a lot by Stanley Kubrick in Barry Lyndon. More modern contrast-lowering filters are the Tiffen Ultra Contrast and Schneider DigiCon.
There's also optical resolution filters, these basically have small lenslets in them. The lenslets make an out-of-focus image, that is superimposed on the in-focus image made by the light that doesn't hit the lenslets. Filters of this type are Tiffen Soft FX and Schneider Classic Soft. Schneider also make a HD Classic Soft that has more but smaller lenslets than the regular Classic Soft, which reduces the risk of the lenslets coming into focus under certain circumstances. When using strong optical resolution filters, you can sometimes see the edge of the out-of focus image. This can be undesirable or it can be an artistic choice.
Some optical resolution filters have a very subtle effect, only doing a slight softening without any visible artifacts. This can for example be used to soften skin in some clips in an otherwise unfiltered movie, where a more stylized filter effect would have drawn attention to itself. Examples of these filters are the Tiffen Black Diffusion and Digital Diffusion.
For many of the filters above, there's also "warm" versions, for the Tiffen filters this is the same effect as combining it with their 812 filter. This lowers the color temperature by about 200K.
There's also filters that combine a diffusion effect with an optical resolution effect. The number one in this category is the Schneider Hollywood Black Magic, abbreviated HBM. This combines an 1/8 Black Frost with a HD Classic Soft, the strength of the HD Classic Soft is what's different for the different strengths of HBM.
Tiffen has made some very good comparison films where you can see the effects for yourself and compare. Only you know exactly what you're after, so here's the link:
https://tiffen.com/diffusion/
Posted: Thu Jan 11, 2018 11:59 pm
