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View Full Version : Is there a way to use a ND gel on an AB with an umbrella?


TMR Design
14th of June 2007 (Thu), 13:05
I'm wondering whether, without modifying or making anything, if I can use my B800 with an umbrella and have an ND filter on the strobe as well. I thought about just getting a B400 but since it's only one stop less it doesn't really help me much. I'm experimenting with doing some portrait work at larger apertures than normal and if I have my main light giving me f/4 or f/5.6 and I want to have my fill giviing me 1 1/2 to 2 stops less I can't do it. When I'm at the bottom of the power slider I'm still getting too much on the fill side. I can't use barn doors in this application to regulate quantity of light because the doors, although limitiing quantity, are also decreasing the apparent size of the light source. I also can't move my fill light further back.

So the only thing I can think of is to use a 2 or 3 stop ND gel but I can't think of a simple or clever way to use the gel while an umbrella is mounted. Is the answer to just not use an umbrella and use another form of large diffuser that doesn't need to use the umbrella mount?

tsaraleksi
14th of June 2007 (Thu), 13:07
Probably not the best choice but could you just punch a hole in the gel for the umbrella to go through and then attach it over the light like you'd expect? If you're desperate, anyway :D.

TMR Design
14th of June 2007 (Thu), 13:14
I thought about that but then that gel can only be used with that setup. Also it would still require the use of either the LiteMod frame or something like the Impact universal filter holder I use now. The only other thing that comes to mind is to have the B800 on top of an umbrella bracket and just point the strobe in to the center of the umbrella. This would allow the umbrella in any position and the gel on the strobe but I don't like the idea of having a pivoting umbrealla bracket with the B800 mounted on top with it's own pivoting head.

TMR Design
30th of June 2007 (Sat), 16:27
Hi tsaraleksi,

I ended up just getting Rosco 21" x 24" .6 ND gels and doing just what you suggested. It proved to be the easiest and best way to do this with no fuss. I made a small whole in the exact spot it needed to be to allow the umbrella rod to go though and it's nice and snug so spill or leakage isn't an issue. My meter confirmed that. One gel sheet gave me gels for my 4 B800's and now I can operate my whole lighting setup with the power levels no lower than 1/4. The main is up near full power and now the fill in the umbrella can go up to 1/4 or 1/2 power.

Life is good 2 stops down :D

SkipD
30th of June 2007 (Sat), 16:44
Once the light bounces off an umbrella, any polarization done at the light source is again scrambled.

You'd have to use a large polarizer sheet that goes across the whole umbrella or softbox to have it polarized as it reaches the subject.

To the best of my knowledge, once you reflect the polarized light with something that acts like a diffuser (unlike a mirror), the light rays get essentially un-polarized. I believe that even a curved reflective surface would play games with the polarization.

TMR Design
30th of June 2007 (Sat), 16:46
Hi Skip,

I'm usually quick to catch on but I'm not really sure what it is you're saying..lolol
Is there something wrong with the idea of using an ND and then bouncing into an umbrella? I haven't noticed a difference in the quality of light and it is doing what it should in terms of cutting the metered light by 2 stops.

wilvoeka
30th of June 2007 (Sat), 17:37
Skip he is not trying to polerize the light, hes trying to reduce the output without using the low end of the flash setting.

Robert what your doing is fine, and is used by alot of people that have really powerfull lights when they need to get the Depth of field down lower than the flash output will allow.

TMR Design
30th of June 2007 (Sat), 18:04
Thanks Jim,

I thought I was missing something. :D

PacAce
30th of June 2007 (Sat), 18:09
Any reason you can't use an ND filter on the lens itself?

TMR Design
30th of June 2007 (Sat), 18:11
HI Leo,

There's no real reason except that the large sheets of ND gel sell for $6 and I can control each light as I choose for any situation with any combination of lights.

PacAce
30th of June 2007 (Sat), 18:24
HI Leo,

There's no real reason except that the large sheets of ND gel sell for $6 and I can control each light as I choose for any situation with any combination of lights.

I thought that maybe you already had an ND filter or a filter holder that can take the cheaper ND sheets (cut to size) for your lens. If not, then you're right, the ND sheets over the strobe would be much more economical.

SkipD
30th of June 2007 (Sat), 18:53
Don't know why I thought it was a polarizing sheet that Robert wanted to use....

Guess I'd been working too hard out in the woods... :rolleyes: