I see many forum threads extolling the virtues of the latest and greatest camera flash diffuser, wiz-bang light modifier or best ever bounce attachment.... the "must have gadget that makes your on camera flash produce studio lighting".... etc etc
Well the fact is.... physics has not changed! Light still travels in straight lines, is diffused and bounced just like it always has been, sees it's intensity drop to 1/4 as the distance doubles and can only be made "soft" in ONE way..... by making it BIGGER in relation to the size of the subject lit.
This is the principal behind both bouncing and diffusing our flash units. Bounce the flash off a ceiling or umbrella and the light source becomes much bigger. Diffuse our light source through a much larger attachment like a light box and it becomes much bigger.
Of course size is relative to distance... ie: a 100cm soft box will give lovely soft light when 50cm from your subject, but put it a 5m and it starts to become "relatively" small to the subject and the resulting light will be much harder.
What about on-camera diffusers that are not much bigger, how well do they work?
Basically these "diffusers" would be better off called "bounce" attachments, as the relatively small increase in physical size does little to provide a softer light. Instead, they spread the light in all directions, so that it can bounce back off walls and ceilings etc.
Naturally a percentage of this diffused light makes direct contact with the subject and it is the combination of this direct light (which is strongest because it took the shortest route) and the weaker bounced (or "fill") light that makes for a more pleasing light with no harsh shadows.
How do these diffusers work outside, or in large open rooms with nothing to bounce off of?
The short answer is.... not very well. As I stated earlier, the relatively small increase in physical size does little to provide a softer light and if there is nothing to bounce off there will be no secondary "fill". So in effect these diffusers make things worse in these situations, as they waste light that could otherwise be used to light the subject.
I have seen demonstrations where one flash attachment is used to fill a whole ball room of people!
Yes I have seen those too, but don't be fooled by what information is conveniently left out. In the demonstrations that I have seen, the photographer avoids mention that a much wider aperture or higher ISO has been used. When this is done the pre-existing ambient lighting becomes a very large player in the exposure. So the result is NOT as much about how good the attachment is, but equally (if not more) about the different photographic technique used. In the case of a wider aperture, the result comes at the loss of DOF (depth of field) and this is not desirable when trying to keep large number of people in focus.
So what is the best flash diffuser that covers all applications?
None! All the diffusers work given the right situation (normally enclosed spaces), but no "one" is the best at everything. It is my advise to have a number of techniques in your bag of skills and apply the best one for any given situation.
Here are a few guides to remember when you search for your new flash diffuser....
1: Diffusers are LARGE (ie soft boxes and umbrellas) and need to be set close to your subject to maintain relative size.
The following image is to give you some idea of the results from various techniques..
Full Size Image
AustralianLight - Landscape Photography
UPDATE: As mentioned previously mentioned... Without an object to bounce off, any and all small on-camera flash diffusers are useless. So in this outdoor situation, the flash was fired through a 36 inch translucent umbrella. (See more information in the comments below)
Tags: diy flash diffuser home made stofen bounce flash light modifier photography photographic camera speedlight