I have a pair of Sunpak 555s that I use with PocketWizards... just wondering if anyone here has had experience using these with a softbox, and if so, what type/size softbox you used... also, did you attach it with a universal speed ring or something made for the 555? 

Does the 555 have enough power?  Its got a guide number of 150, and I'm powering it with Quantum Turbo packs.

You might want check photoflex.com . I have some of their large equipment but they have softboxes for potato mashers and other smaller heads in their catalog. Call them if you want... they're very friendly and helpful.

A few years ago I called Photoflex and talked to one of their techies.  At the time I was using the largest Canon flash (GN 185, I think) and they told me it wasn't enough power for a SB.  Umbrellas will work okay though.

Paul

I frequently use a Sunpak 544 (the non-TTL version of the 555) on location in a 3x4 softbox. It works fairly well up to around 8-10 feet, where I get f/4 or so, though I try to get it closer for most situations The softbox is mounted on the lightstand itself , and use a hollywood head/grip head with a short arm to mount the flash itself. use my normal speedring (speedotron) and some mini-bungie cords to keep it in place. Chimera, Plume, and others make speedrings for this flash, but it didn't seem worth the effort when 30 seconds of elastic works just as well.

If you need a smaller aperture than f/5.6 for ISO 100, though...

I use a one by one half foot softbox for most of my work and I like to get the softbox really close to my subjects. I have two softboxes. One is a 30 year old Chimera whose white rip stop nylon has gone cream yellow so it gives a very warm light. The inside is white (not silver) so I like to use it in my studio with more powerful studio lights. For the field I use a more light efficient Plume that is silver on the inside. When I remove the inner baffle I gain one stop. For these softboxes I use (I have posted this many times but I may be the only holdout using good old American technology) three Norman 200Bs. One unit is 30 years old and the others are perhaps 20. All three now use the third generation nicad so I get 75 full power (200 watt seconds) flashes from each charge. One of the Normans I have had adapted to produce 400 watt seconds. The Norman system for putting a soft box and then the rig on a light stand is efficient and sturdy. There are two Norman flash tubes available. One (my preference) is a UV coated one for a warmer light. Best of all my technician modified my Profoto ringflash so that I can plug it in to the Norman. This means I have an extremely powerful ring flash that I can take anywhere. When I have to photograph more than one subject with my Norman and I have to pull back the softbox in the field I switch to 200 ISO so I can always shoot at f-11 which is the optimum apperture of my Mamiya RB- 67. The picture you see here I took with that softbox and Norman combination. The picture itself is a scan of the Polaroid 669. Polaroid is still available in Canada. It is manufactured in Mexico.