One of the tricks for making the most of your lights is to use gels. The typical way to use gels on smaller shoots is to just clip them to the barn doors. This works fine for color gels, but not for diffusion gels. Diffusion gels soften light, scattering the rays so that it seems to wrap around objects. However, to really get this effect, you need to not only scatter the rays by punching the light through diffusion, but also enlarge the apparent size of the light source. To do this right, you really need a gel frame.
Gel frames are pretty simple—they’re aluminum rectangles in various sizes that you can mount a sheet of gel to. Each has a 5/8″ spud so a grip head can hold it. Affix a sheet of gel to a 4′ X 4′ gel frame and all of a sudden, your 1/2 inch-diameter hard light source is a 4′ X 4′ soft light source. In contrast, mounting the gel sheet directly to the light gives you about a 6″ X 6″ sized light source—1/64th the size—which is why people are often frustrated with the effects of diffusion gels mounted this way.
Using Gel Frames
There are a couple of ways to use gel frames—big shoot style and small shoot style.
On a big shoot, you’ll likely have a large selection of 4′ X 4′ gel frames. When you use a type of diffusion, you’ll affix it to the frame using snot tape—and leave them for the duration of the show. For consistency, you’ll likely use only a few types of diffusion, so you may have several frames built with different strengths of your diffusion standing by on a taco cart just of set for whatever the scene calls for. You can do this because you’ll have a truck full of 4-by-4 gel frames and some lighting department guys with some downtime to pre-dress them for you on the first few days of the shoot.
On a small shoot, things may be different. You may only have 18″ or 21″ X 24″ gel frames because they’re a lot easier for a small crew to manage and schlep around in a van. Also, you’ll probably have fewer of them than you would on a big shoot, so it’s common to make them do double-duty. That means you’ll probably be using the same gels frames for a number of different gels. So you’ll probably attach the gels with C47s (wooden clothespins) so that they come off again easily rather than using snot tape to semi-permanently dress them. Fortunately, these fit pre-cut get sheets perfectly, so they’re pretty slick to use.
A couple of tips when using gel frames… First, if you’ll be using them outdoors, stretch the gel tight and use snot tape to attach them. Loose gels tend to rattle in the wind and create sound problems for your shoot. Second, watch where the shadows from your gel frames fall. Unless you’re using very strong diffusion, the frames will make discernable shadows that tend to appear at the worst times and places (like when you’re watching the footage after the shoot!). So make a point of consciously noting where the frame lines are falling. If you see them, you may need to march your gel frame closer to your light. Ideally the diameter of your light will be the same as the inside of your gel frame. That way there won’t be any hard frameline shadow to worry about.
Douglas Horn is a feature film writer-director and a creator of independent series. Douglas and Dan Southworth founded the web media company Popular Uprising. The company’s action/sci-fi series DIVERGENCE will release its first season in 2012. More information at: DouglasHorn.comandWhatIsDivergence.com