Q&A: Bleeding Power from Big Lights with Big Mods
Could you share how you use the ND gel sheets on your big lights? I'm wondering how I could maybe use them on my monolights with big modifiers like a giant octa or softbox.
The good news is that's actually pretty easy, Diego. And you might not even need to buy any ND gel, either.
First off, Diego brings up a good point. Too much light output can be a problem with big lights even at the bottom of the range. That was one thing I had to solve with my Profoto Acutes. Lately, monobloc makers are getting savvy about this. Einsteins, for example, drop down to about 3 watt-seconds.
But even if your mono will go as low as you want, you might not want to hang out at the lowest power setting. For one thing, if a color shift is gonna happen, it tends to happen at the extreme end of the power range.
Another reason is that you lose flexibility. You cannot dial out more power from the bottom of the range if your light turns out to be too hot, or you need less depth of field.
Looking at some of Diego's recent work, I am gonna guess he is looking to combine big, soft light sources with wide open apertures. (A nice look.) With most big soft boxes and octas, doing that is easier than you think.
To avoid the problems above, consider setting your flash a couple of stops above the minimum power level. You'll still have a very fast recycle, but you will be in the middle of your power range for better color temperature. And/or you'll have the ability to dial the power up or down easily.
With ND (neutral density) gels, you can knock out some of that power very easily. And it's not as if you need to cover up every square inch of the front surface, as you might if you were gelling for exact color. If you can knock the light down before it gets to the front diffusor, you do not need to be so exact.
I like to use the internal baffle panel as a good platform from which to kill light. Just paper clip a piece of black construction paper to it, making it partially opaque. You get some spill around the edges, so it is not an exact science. But the general rule of thumb is to cover half of the panel to knock out one stop, 3/4 of it to knock out two stops, and so on.
If keeping the exact quality of the light is important, cover the panel in an even way -- in center, stripes, whatever. But you may find it easier to just work from one side, and you might end up creating a more interesting final light source in the process.
Diffuse the panel from one side and you'll get a light that is a little hotter on one side (or top or bottom) than the other. Rotate your light and see if this effect works for you in the final image. If not, blog the internal baffle more symmetrically.
While we are on the subject, you should experiment with your boxes and octas to see what kind of light quality you get without the baffle, or front panel, or both. It will be more specular, and can even act more like a giant, shiny beauty dish. Definitely worth your time to check it out.
But as for dropping the power, that's cheap and easy. It's getting all of that power in the first place that is expensive.