Paul C. Buff, Inc. Technical Forum

First, while I've had access to these for ten years, one was personal and one belonged to my previous company. Neither was used with umbrellas in "reflective" mode, where the light travels over the flash unit, before. I just received the second unit (no longer needed by the company) and started experimenting with umbrellas in reflective mode this weekend.

I've thought of a quick way to test this out: I'll use flash at the angle that gives the yellow blob with an umbrella in reflective mode, then take a second shot with the flash at exactly the same angle but shooting through the umbrella (so the light doesn't go over the flash unit body).

OK, I took the shots, using two different umbrellas in reflective mode (one Wescott, just bought yesterday, and one unknown brand at least 5 years old), and the Wescott in shoot-through mode. Here are the shots:

Wescott, reflective


Old umbrella, reflective


Wescott, shoot-through


So, there is a clear yellow pattern in the two reflective shots, which differs between the two umbrellas. And suprisingly, there is a slight, yellow, blob in shoot-through mode. Note that the room is fairly small, so there's a lot of bounce from using the flash in shoot-through mode (due to some reflection and spill), which could be lighting up the flash unit enough to create the lighter yellow blob.

Any other ideas?

Based on your studio setting, it does appear that the light is bouncing off of the white shoot through umbrella, back to the white wall (assuming) and lighting up the body of the AB800.

No way! If so it would be on both glasses. I think the glasses themselves have some sort of prismatic effect. As I suggested before, try wrapping the Bee loosely in black paper, and also try some different glasses.

Also, notice small yellow dot catchlights apparently coming from another light source.

Well, still confused. I tried another pair of glasses. Same result, BUT, these were my old glasses and may have the same coating. Next, I did what was suggested - I wrapped the yellow flash head in the black cover removed from my second umbrella. With all of the yellow covered, the yellow blob was still there!

So, I am begining to accept that my initial thought, about the color of the flash unit body being the problem, is wrong. But I'm no closer to a solution, except to play with the height/angle of the flash to try and avoid it.

A polarizing filter is likely to help.

Hello Jeff, have you tried covering the yellow body of the flash unit with either a black bag or something alike? It seems to me it will be a good experiment to rule out the reflection off the body of the flash.

regards,
Jim

Jim,

I guess you missed part of my last post - I tried covering the yellow body with the black fabric from the outside of a reflective umbrella and it didn't help. So, that essentially rules out my original thought that I was seeing light reflected from the yellow body.

Thanks for posting your images. From what it looks like,(each lens has a different color reflection of the PLM) you may have found your answer. But only an optics expert would really know. Hope you find a solution(polarize?)

RMS

This is not a problem with the housing color. First, as you have tested, with the housing covered, the problem persists. Second, the sides of th housing are parallel with the direction of light travel. It will not leach color off of the housing, and any reflection of the housing would be minute. Also, it cannot bounce off the housing and then into the umbrella, then onto the subject. If the housing was a source of color cast, the umbrella would still be silver. Additionally, in shootthrough, the light never passes the housing, and therefore would not be affected by the housing color. As well, If the ubrella itself was that color, the entire image would have a yellowish cast, not just a specular highlight.

My guess is these glasses are UV coated, and possibly transition lenses (the kind that darken in light).

The glasses (both pairs) have transition lenses. I accept that my original conclusion was wrong - as verified by my additional research into the cause. I guess I'll just have to live with the problem and take care of it in post-processing. One thing I have learned is that by changing the angle of the light, I can change where the "blob" appears on the lenses, and move it to an area where the post-processing correction will be easier.