Relationship between Diffusion, Softening and Distance

I came across this interesting article by Ed Moore and Stephen Murphy, where they tested a lot of different lighting diffusion materials. I recommend checking it out: Here is the stills version and thevideo version.

Some selects from that post:

Half soft frost diffusion

Half soft frost diffusion

Half soft frost, one of my favorite diffusions because it’s most efficient, getting you the most softening for the least loss of output available. Not surprisingly,  that’s what I use as the front face in Airbox Inflatable Softboxes.

Half Grid

half grid cloth diffusion, aka “light grid”

Light grid cloth is another favorite of mine when I’ve got brighter sources to work with.

Diffusion and Distance from Subject

It’s an interesting study but what I didn’t see them mention is the distance from the diffusion material to the subject.  That is hugely important to the effect.  A leko right next to a tennis ball will wrap more than a 10K through and 8x diffusion frame at a great distance.  You want the source soft?  Then sit that diffusion frame just on the very edge of frame, as close to the subject as you can get it. You want it a touch harder?  Back the frame up a bit towards the light. The apparent softness is largely about the size of the source relative to the subject.

Here’s a quickie test I did in my office on the topic using some of my daughter’s dolls, a Litepanels Astra EP (generously on loan from Litepanels), and an Airbox Model 1×1 softbox. The photos go from nearer to farther.

diffdist 1

Airbox Model 1×1 w/ 250 in front sleeve at 11″

diffdist 2

Airbox Model 1×1 w/ 250 in front sleeve at 32″

diffdist 3

Airbox Model 1×1 w/ 250 in front sleeve at 52″

diffdist 4

Airbox Model 1×1 w/ 250 in front sleeve at 75″

Notice the drop shadows.When the 16″x16″ source is just out of frame, there is no visible drop shadow on the girl doll’s face from her left hand, and barely any visible on the male baby’s face from the girl doll’s right hand.

Here’s a sketchup to illustrate the concept:source distance comp

This is why you never can get as soft by putting diffusion directly on the face of your light as you can when using a softbox or frame that’s a distance in front of the unit.
Tom Guiney