Cinematographer James Tocher says:

Central recommends against using softening filters of any kind when shooting standard definition (SD) video, whether PAL or NTSC. SD is a significantly lower resolution format compared to the film and HD, therefore SD footage will naturally “soften up” when it's blown up to the big screen.

If you're shooting HD however, softening filters may be okay. For HD, I like to use the "rule of halves" here. Whatever I think looks good on a small monitor I usually back off from that by half – in other words by using half as much softening; if I like a Soft FX-1 on the monitor, I’ll go with a Soft FX-1/2 instead because I know the blow up to film (or the digital projection) will do the rest.

Color filters for effect or color correction (Sunset Grads, ND’s, 85’s, etc.) or Polarizers are okay for either SD or HD because they don’t usually have any softening qualities.
Please contact one of our Digital Film Specialists for more information on how to set up a consultation session on these and many other topics.

Happy Shooting!