For those of you who have made or bought a bunch of these, I am hoping you can share what you know here. I'm also hoping this will generate fresh ideas and experiments about what works and what is easy to make. To seed the thread, I'll open with the following questions organized into four categories:
Design questions:
101) Which works better to wrap light evenly around a small subject--a curved surface, or the easier-to-make broad flat surface?
102) Is a design which spreads light left-to-right around the subject sufficient, or is top-light also important?
103) What's the best way to avoid center hot-spots in the diffuser? To what extent can light distribution be improved with internal reflective patterns?
104) Which is easier to design from--a flash mounted on the camera's flash shoe, or the flash suspended over the subject on a flash bracket?
105) How much does distance from subject, size of diffuser, and size of subject affect the design?
106) Is it easier to design a diffuser attached to the front of the lens? How much does this depend on subject size and lens used? Can a single lens-based diffuser work for multiple lenses?
107) Has anyone designed diffusers capable of using colored filters (eg: gels)?
108) Has anyone designed diffusers which can be quickly modified with blackout zones, allowing greater control over the light output across the diffuser?
109) How much does flash output affect both designs and results? Can one obtain decent results with a middle-of-the-road flash at high magnifications?
110) Has anyone tried a bent translucent strip, a dome, other shape for the front face?
Materials questions:
201) A number of folks have shared easy-to-make diffuser designs from bottles. What works or doesn't work from this source material?
202) Reflection materials: How easy is it to use foil to bounce light inside a diffuser to the places you want it? Do curved or semiparabolic patterns help, or are they too hard to manufacture in a way that spreads light evenly? Should the foil be crinkled and smoothed, or kept pristine? Has anyone tried using mirrors to bounce the light internally? How about angled translucent interior baffles, or a semicircular reflective dome inside to spread light around? Reflective-coated fabric (like light discs are made of)? Other reflective materials?
203) Where do you find the best source material for the outward diffuser face?
204) What material is best suited to structural components (eg: cardboard, plastic, wood) and where did you find it? Is it hard to find structural elements that are sufficiently stiff and also malleable?
205) Do more expensive materials permit better designs and less light loss, or do you see diminishing returns from costly materials?
206) Does clear translucent material for the face of the diffuser transmit more light than white material does? Does some white material create a color cast, and if so is it hard to correct for?
Design evaluation questions:
301) Are there any software tools which would help with the design of a diffuser? [Something that would show the resulting distribution of light across the face of the diffuser?]
302) What tools are available to measure the light coming from different angles at the subject's position?
303) Is it possible to create a good macro test subject which can easily be recreated or found by others, something with enough dimension and texture that the lighting effects are obvious?
Will you use it questions:
401) How ungainly are diffusers to use in the field? Do they interfere with your ability to get sufficiently close to subjects, or add excessive weight or bulk?
402) How compact is a diffuser in your camera bag?
403) How long does it take to prepare a diffuser for use, or take it down?
404) How durable is the diffuser?
If someone wishes to come up with a similar list to start a multi-flash diffuser design thread, please do so! I'm hungry after writing all of this, so I am going to eat lunch instead.
Please throw in your own evaluations of commercially available diffusers, too, particularly with respect to the issues raised in the thread. Please don't be bothered if someone evaluates your favorite product differently--remember, we're all at different experience levels trying to control light to capture different subjects and evoke different emotions so naturally folks will find some tools less practical than others will.
Similarly, please feel free to add in additional questions or to suggest changes/subsections to these as we go. Please post annotated photos of your attempts (both successful and not!), as well as good test subjects (see 303). I hope this can be a long-lived thread, a resource for those in the community and something which spawns new ideas and perhaps new products too.
-Scott