Well, you piqued my curiosity so I ran downstairs and gave it a try. It actually worked very well. The PLM front diffusion cover has a drawstring type of setup on its elastic band so it's possible to tighten it up some for the smaller diameter Westcott collapsible. It looks a little like a baggy suit on someone who's lost 10 or 15 pounds but, so what?
I tested briefly by mounting the 43" Westcott collapsible with silver interior on a PCB Einstein. For a reflector I used the AB USK "spill kill" which is a very shallow, 7-1/2 inch saucer-shaped affair. The Westcott umbrella is quite shallow so most strobes would probably have to be backed down the umbrella shaft a bit to allow full interior coverage. The Einstein with the USK reflector offers a tremendously wide dispersion pattern so it was possible to position the light pretty far up the shaft and still retain full interior coverage.
Meter readings taken a few inches from the diffusion material and around its face fell within a spread of .3 or .4 f/stops. This was a *very* quick test so I'd like to have an opportunity to verify those readings. With the Einstein powered down to 60Ws to simulate a 580EX or SB-900 class flash unit, I was metering a little over f/8 at about 3' and ISO 200.
I'd say the small Westcott with the PLM diffuser seems to be a pretty good combination bearing in mind the need to position the strobe properly to insure good illumination of the umbrella interior. I think there's enough potential here to warrant retesting the setup with one of my Elinchroms.
And Leo, while I do have a sizable collection of lighting tchotchkes, most of the modifiers are of the bargain basement variety. I own two Rotaluxes and a gaggle of no-names. In any case, doesn't everyone own at least one collapsible Westcott umbrella?
Dave F.
Thanks. I'm sensing that there may be the purchase of a couple of 51" diffusion fabrics in my near future. 



