A diffuser is a useful piece of equipment which can help you control harsh light. You place the opaque material between your subject and the light source (usually the sun) and it cuts down the light . It is similar to moving a person from outside into the open shade in a doorway or beneath a tree, except you’re moving the shade to them.
As with reflectors, most portable diffusers for photographers are circular and collapse in on themselves for storage. Lastolite make a range of triangular trigrip reflectors and diffusers which have an integrated grip and are easier to maneuver.
Lastolite TriGrip Diffuser
The medium size trigrip is a good size for putting a person or couple into shade when shooting in the harsh Okinawan sun. It is also a useful way to reduce the strength of the light when shooting into the sun backlighting the hair. In the shot below I used it to control the light on the model and her white dress. It also stopped her from squinting. The size of the diffuser will determine the area of soft light, for example with a medium trigrip I wouldn’t have been able to put both the model and horse into shadow. (Lying on the beach is a large reflector rather than a diffuser.)
Using a Lastolite TriGrip Diffuser on the beach
There is one problem that can occur with the collapsible diffusers and reflectors and it has a lot to do with the design of samurai swords…
Samurai swords are made of both low carbon flexible steel and high carbon hard steel. Use only low carbon steel and the blade doesn’t have a decent edge. Use only high carbon steel and the blade will shatter. Collapsible reflectors / diffusers whether circular or triangular work by having a steel band running inside them. For it to be able to twist and spring back into shape without breaking it must, I presume, use low carbon steel. One side effect of this is that things made of low carbon steel easily rust. If you are using your equipment on the beach, a little bit of salt water is going to make your diffuser do this…
Rusty Diffuser
On a previous shoot (model on a surfboard) one corner of the diffuser must have been dipped into the ocean. I dried it out before storage but the steel band is sown into the edge and I guess a little dampness was enough to unleash the rust. The diffuser still works fine, but looks a little worse for wear.
The solution for people who are working in wet or salty environments is to use a frame based diffuser made from aluminum such as Lastolite’s Skylite
The Lastolite TriGrip Diffuser
TRAVEL 67 : Chris Willson Photography 
Very useful information about the corrosion. I’ve been doubting between a Skylite and the TriGrip diffuser and just got the TriGrip as well, simply because it’s much cheaper, easier to handle and lighter to bring along. I’ll be careful near water!
I agree that it’s probaby low carbon in the frame, but I think its also probably a plain carbon steel to cut costs (the lack of chromium in the alloy makes it more likely to rust). Even after you dried it I’m guessing there was some salt left in the fabric which accelerated the oxidation process with the humidity on Okinawa. Ships (and rebar in concrete buildings) solve the problem by attaching bars of zinc to the steel to act as sacrificial anodes, and piping systems often add a slight electric charge to fight it off. Probably not practical for you though.
I’m thinking that the best way to fix this in the future is to wash it down with freshwater and then dry it off really well. That should get rid of your salt problem and after the freshwater dries it should be able to handle the humidity again no problems.
Sorry to nerd out on you…this is what I went to school for and I really like steel 😀
Thanks for the information. Really interesting to hear what could be done. Rust is a huge problem in Okinawa of everything from cars to bicycles to homes. Zinc as a sacrificial anode sounds like a great idea.