Which difusion filter for which focal length?

Markus Fraunholz · August 9, 2007

Hi, I am a german Cinematographer prepping a TV Mini Series with an older actress (60)

performing the main part. I own a set of Schneideroptics "Classic-Soft-Filters", which I intend to use for the two films. In the past I used these filters more "unconscious" in this way: for wide shots the smaller numbers, an eighth or quarter, for close ups, the one or even the two.

Interestingly enough, there are a lot of colleagues, who are doing the opposite: Using the bigger numbers on wide shots and the smaller on close-ups.

What makes more sense and WHY?

Every explanation will apreciated! Thanks

e gustavo petersen · August 9, 2007

Generally, for closer shots you would use a heavier diffusion and on wider shots use a lighter diffusion. The reason is that the wider the shot, the finer the detail in the image and so a lighter diffusion. Remember audiences look to the eyes of actor. How dense the diffusion needs to be with close ups can be determined by either experience, testing or you could look at the subject's eyes judge the image sharpness. (If you're shooting with a optical viewing system, remember that the ground-glass image will look softer than the projected image. Since you're shooting for TV, it's less of a consideration.)

Edited August 9, 2007 by Eric Gustavo Petersen

Michael Nash · August 9, 2007

Eric's right. When people use heavier diffusion on wider lenses it's usually with the argument that longer focal lengths magnify the softening effect of the filter (which is true), so a heavier diffusion is needed on wider lenses to maintain the same degree of softening. What this argument doesn't take into account is that the smaller a subject is in frame, the less detail it has by virtue of resolution. Blowing up a wide shot of a subject to match the size of a medium shot of the same subject proves this.

Looking at it this way you might even conclude that the magnification of lens diffusion cancels out the extra detail gained with larger image size (which is also true, up to a point). This is what allows to people to use the same filter, or no filter at all, on a zoom lens with acceptably consistent results.

But the reality is that not all lens sets match resolution through all focal lengths, and the distance to the subject (creating image size) isn't always the same. So you end up selecting your filter grade shot by shot, usually guided by focal length first (longer lens gets heavier filter) but also by the distance (shot size) and the subject itself. The best thing is to shoot some tests, and see what filter grades you need to match with focal lengths and shot sizes, to make your actress look good and consistent from shot to shot.