ND Filters with Flash

by Mickey Rountree

In my last article, I described using high speed flash to shoot in bright light at shallow depth of field. But what if your speedlite doesn’t have High speed synch? Or maybe you don’t have a speedlite and you’re using a studio strobe outdoors, again with no high speed synch. Here the trick is use an ND filter to bring the exposure down to allow a wider aperture at the camera’s synch speed.

For example, let’s say the exposure that gives the background look is 1/200 at f/16. But we want a much shallower depth of field than f/16 provides. If we use a 3 stop ND filter, we can use 1/200 at f/5.6. With a 6 stop ND filter the exposure becomes 1/200 at f/2.0.

Sounds pretty easy so far, so there have to be some problems, and there are. Most cameras will have no problem focusing with a 3 stop ND filter, but it may not focus well with a 6 stop (or more) filter. In that case, focus carefully without the ND filter and then carefully hold the ND filter in front of the lens without disturbing the focus. Also with a backlit subject and a ND Filter it may be very hard to see facial expressions or even if the eyes are open. It helps to have a model who can give a good expression on command, and sometimes it helps to count down to the shot. Lots of chimping (looking at the LED after the shot) and overshooting help make sure you have the expression.

Also many ND filters create a slight color cast. And from a past article, you might remember that the easiest way to fix that is once you have your exposure figured out, shoot a shot with a gray card and use that shot to color correct all of the other shots using that ND filter. If you use two or more different ND filters during a shoot, remember to shoot a gray card with each, since each density of ND filter will have a different color cast.

Just like with high speed synch, this works much better manually setting the shutter speed, aperture and flash power.

Here’s a sequence showing the technique in use. The first shot is the test shot to set the background exposure. Exposure is 1/200 at f/16 with no flash. This is also about what you see through the viewfinder, so you see more of a silhouette and will have a hard time seeing expressions.