Thursday, July 15, 2010

Natural Light and Filling a Background with Flash

The topic of today's post is a bit odd in that it just isn't the way most people use flash for their outdoor photography. Not that it is unusual to light a background, at least in the studio, but when the background is a shady spot outdoors, the usual line of thought is to put the subject in the shade and use the flash on the subject. In this case I thought, what if I put the subject in the sun, but light the shady background? Can it be done? Not that this is anything all that useful in terms of normal shooting, but if nothing else, it is something to throw in the bag of tricks for that one odd time it is needed. (more after the jump)

Sometimes it pays to play, and that is what this is all about. David Ziser has been known to promote the concept of asking yourself, I wonder what would happen if. I'm grateful for that nugget of advice and try to remember to do so once in awhile (though not often enough).

As some of you may know, I do not do a whole lot of outdoor shooting. So in preparing for an outdoor shoot awhile back, I was pondering how to work with direct sunlight should the need arise. I know to put the sun behind and/or to the side if I'm going to use flash for fill. A scrim can be used to create shade where there is none.

Using a silver reflector for lighting in bright sun is generally frowned upon because the light directed into the face will cause the subject to squint and possibly say bad things about the person responsible for their discomfort. This is why flash can be so useful in direct sunlight. Best is to use a flash with high speed sync, which allows the camera to use fast shutter speeds at wide apertures, which is useful for obtaining background blur. Conventional wisdom says that if you don't have a flash with high speed sync, then get a flash that can output at around f/16 and set the camera's shutter as high as your max sync speed allows, which is usually 1/200 – 1/250.

The Sunny-16 rule says that for a clear sunny day at noon, using an exposure equivalent to f/16 1/100-sec at ISO 100 will yield a perfect exposure. So, using ISO 100 at 1/200-sec means the direct sunlight will meter at f/11. Putting the flash at f/16 makes it 1-stop higher so that it acts like a key light. I might add that one can use smaller camera apertures by placing a neutral density filter on the lens. However, the flash must still be powered to overcome the sun, so there is no affect on the flash settings.

Okay, that's where my head was at, but then I started pondering the background. The shoot would be in a park and I knew that there were some nice treed backgrounds. However, if the subject is in daylight and the trees are creating shade, then the background will be significantly underexposed. What to do about this?

The Experiment
This is one of those, what would happen if, type experiments where the what if was, what if I use flash to fill in the background? Can it be done? Will the coverage look natural? How much power will it take? Well, if the Sunny-16 rule puts daylight at f/11 at 1/200 ISO 100, then I probably need to put the background somewhere between f/5.6 and f/8. That sounds doable, so let's see how it turned out.

The Progression
Here is a shot with only sunlight. The exposure is good at f/11, 1/200, ISO 100 just as the Sunny-16 rule predicted. You will notice two things about this shot, the contrast is excessive and the background is very dark, as expected.

There were some clouds in the sky and a breeze was moving them over the sun periodically so that it was difficult to predict the proper exposure. I found it best to just wait for the cloud cover to blow over and then use bright, direct sun. This took a bit of patience, but for the most part I played the game this way.

This shot has a reflector added subject right. I tolerate it because of my nifty sun-shifting shades. Better would be a flash for fill, but since the experiment involves lighting the background and I didn't feel like setting up another flash, I went with the reflector. It is a 32” soft silver at head height. The background is of course still quite dark. The aperture is at f/10 for this and all subsequent shots, so I assume that there was a thin layer of cloud obscuring the sun causing a 1/3-stop drop in light. Pretty insignificant, but noted.

This time I have added a light to the background. I am using my 300 WS monolight running on a battery pack. The light is at about 2:00 (my left elbow points toward it) and you can see the shadow on the fence post just to the side of my right elbow. This is an improvement and the photo is starting to gain some dimensionality, but the background isn't quite bright enough yet and the shadow cast from the fencepost is too obvious, it just doesn't look natural.

Here I have moved the light forward quite a bit and cranked the power all the way up. Yep, that's 300 WS of light. Looks real natural now and the shadow on the fence post is about right for the position of the sun. For the record, that's my Polaris light meter in my right hand.

In this final image I've turn the flash down just a bit. It still looks quite believable, but the subject now stands out better without loosing the dimensionality brought by the lit background. Hopefully I will have a more pleasant looking model for some of the future postings, but this at least gets the idea across, and if you use your imagination, you can see how this kind of lighting setup might be used for, shall we say, a more attractive person.

Coming Next
That's enough on this subject, hope you found something useful to chew on. Still plenty of subjects to cover, so stay keep coming back.

Until then...


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