The Sto-Fen Omni-Bounce diffuser in straight-on flash shooting

The Sto-Fen Omni-Bounce diffuser is a translucent plastic "dome" that fits on the head of a shoe-mounted flash unit. Models are available for a wide range of flash makes and models.

The principal use of the device is intended to be in "bounce" flash work (hence the name). It substantially enlarges the beamwidth of the flash unit, result in an enlargement of the ceiling area that is illuminated. Accordingly, the source of the reflected "downlight" is broadened, generally resulting in a desirable illumination situation for much general-purpose work.

We sometimes find the Omni-Bounce diffuser used in "head on" flash work. I often ask, "what might that do", and the answer is generally, "well, it diffuses the light, resulting in a softening of shadow effects."

I have trouble understanding how that might be. Based on fundamental theoretical concepts (the last resort of we non-photographers), we might expect three potential beneficial effects of such an accessory (in the context of "straight on" flash illumination work):

• If the emitting area of the source is very small (for example, a small flash tube with no effective optical system in front of it) the addition of the diffuser will enlarge the dimensions of the source to those of the diffuser. However, for the typical flash unit on which the diffuser is used, the emitting area is already about that size (as a result of Fresnel lenses and the like in the flash head.)

• If the luminance of the flash head face varies substantially over its area (perhaps as a result of an ineffectual lens system), the benefits of the substantial area are somewhat diluted. Then the addition of the diffuser can produce a more consistent illuminance, restoring the potential value of having an emitter of that area. However, I suspect that for the typical flash unit on which the diffuser is used, the luminance is already fairly uniform across the emitting area. (I plan to makes some tests of that presently.)

• The addition of the diffuser substantially enlarges the beamwidth of the flash unit emission. Unless the beamwidth is too small to embrace the subject, there would seem to be no advantage to this. The emission of light off to the side of the subject should have no effect on the "shadow" issues (how creases in the face are rendered, etc.), unless of course there are reflecting surfaces off to the side (pieces of Foamcore board held by one's assistants, etc.).

So I don't get it.

Could the real photographers here fill me in on how and why this works. Or does it really?

Now, although the practices of hobbyist snapshooters like myself may be of no interest to the real photographers here, let me nevertheless mention that we are able to get a substantial enlargement of the emitting area in straight-on flash shooting with the help of a Sto-Fen Omni-Bounce diffuser.

We cut away and discard the dome portion, leaving only the attaching ring portion, which fits snugly on our shoe-mounted flash unit head. We use that as a "speed ring" to mount a small soft box on the flash unit such that it can easily be mounted and demounted during the shoot.

The Sto-Fens do work to soften flash light...to a degree. The most concise analogy that comes to mind is the difference between a frosted light bulb and one with clear glass. The light sources are, as you've suggested, the same size and therefore would seem to have identical point-source properties. But the diffusion scatters more of the light to bounce from peripheral surfaces (walls, ceilings) and thus -can- add just a bit of fill to lift harsh shadows.

You don't really have to buy one to give the idea a try. Creating a diffusion bubble with wax paper (or baking parchment) and a rubber band works almost as nicely, sometimes more so depending on the size of the bubble you build. Ok, so you'll look like a goof...who cares.

Hi, Ken,

Ken Tanaka said:

The Sto-Fens do work to soften flash light...to a degree. The most concise analogy that comes to mind is the difference between a frosted light bulb and one with clear glass. The light sources are, as you've suggested, the same size and therefore would seem to have identical point-source properties. But the diffusion scatters more of the light to bounce from peripheral surfaces (walls, ceilings) and thus -can- add just a bit of fill to lift harsh shadows.

Click to expand...

Yes, I can see that that could be a useful phenomenon.

Thanks.

Best regards,

Doug

I also use a cut off of the neck and part of a plastic milk carton. So it can fit over the Canon flash unit. The top can be open and it wraps around the flash giving a larger light source than the Omni Bounce and also allow some light to flash of the ceiling from the top wide opening. Looks more geeky but engineered on a higher level and well respected by event guests as some technique of smart photographers.

A great way of getting to talk to folks as usually someone asks about it!

Asher