@Derrel: looking at your example, I’m wondering if the“focal length” of the umbrella has something to do with the pattern you areshowing. The Lastolite umbrella shows aneven pattern that one would expect if the flash was at the focal point of the umbrella’scurvature. The “Other” one either has a stronger curvethan the Lastolite umbrella, or the flash head is further away from theumbrella’s focal point (actually, closer to the umbrella on the axis), orboth. If my guess is correct, then the positioningof the flash or light at the correct location/position relative to the umbrellaaxis and curvature becomes very important.
You mayalso have solved a WB problem for me in that I never really considered thequality of “white” that I get from the bounced light from the umbrella. I was getting a slightly magenta cast in someshots but not others, using the same equipment. Now that you mention it, I am thinking that the magenta cast may havebeen happening when I used a specific umbrella. I’m going to test this theory, maybe even as early as tonight.
The thing I've picked up from other people off the web is that the COLOR TEMPERATURE of a LOT of the Chinese, low-cost, no-name products is inconsistent with 1) different lots of the same product and 2) sometimes inconsistent/incompatible with other "name-brand" reflectors and modifiers. Meaning that mix-and-match between say, Photoflex and Brand XX may yield weird and impossible-to-correct WB problems.
As far as the "focal legnth" of the umbrella, or the curvature: the cheapie is set up with the flash head set along the umbrella shaft at the same distance as the Lastolite. On both, the front panel fabrics are "tight", and the flash head could not be pulled farther away, because the fabric was drum-tight...also, the curve of the two umbrellas is different...the Lastolite is a bit deeper, but it also has a VERY different backing...as I think is obvious, the cheapie umbrella on the left is not containing "all" of the light...a good deal of the light is going right through the back of the umbrella's semi-transparent fabric, and is being lost at the edges of the front diffusion panel. This is not an exhaustive test, but it does show some differences with the same watt-seconds and the same flash head models.
The Lastolite, on the other hand, has a 100 percent, light-containing black, coated fabric...light is NOT lost, but is scrambled/diffused well, and then it goes through a "thicker", "coated" type of diffusing material that is very different from the cheap, rip-stop nylon used in the $19 umbrella box face...the degree of specularity is also different. I'm not suggesting that the low-cost softbox ChristopeherCoy is a terrible modifier, compared against the $250 Lastolite JoeMcNally softbox, but I was just using a test shot I happen to have on hand that shows how
there **can be** differences in the way apparently very similar products perform.
For me, the "name-brand" umbrellas and softboxes have been very good investments. But I will also admit that the lure of $25 and $38 and $59 e-Bay items is very strong, and I have bought three low-cost items, 2 softboxes and 1 beauty dish, and they have been good...when used ALONE. But the color temp of the soft boxes does not match my Photoflexes or my Lastolite stuff, so, they do not play well together. For me, at least. The way I see it, there is no way to pair a "warm" main light with "cool" fill light or hair light, and have it look right.