Capturing Passion and Magic

January 06, 2010

Single Speedlight Challenge 1 - A Big Soft Light

One of the things I've been exploring a lot over the last year has been using small strobes, aka, "speedlights", off camera to improve my photos.

It's easy to get carried away with this - I now own 5 speedlights! The more speedlights you own, the more complex the lighting set ups you can do, and the easier it is for you to override the existing light.

Still, there's a lot you can do with just a single speedlight. This, for example:


This is lit with a single speedlight firing through a 46" Phototek Softlighter II. The light is about two feet or so away from the face.

Since the light source is so huge relative to the face, and diffused to boot, you get this amazing soft light that only gradually falls off. Simple, but oh-so-effective.

Also note the black background. In real life, there's a wall of book cases back there. That happens when your studio is your library.

However, three things conspire to remove the bookcases from the photo.

1) The Softliter pushes it's light out the front, with very little spilling out the sides and almost none out the back. This cuts the amount of light hitting the bookcases dramatically.

2) Light falls off over distance. For flashes, it generally follows the inverse square law of light, i.e., light intensity decreases by the square of the distance increase from the light source. In English: if Object A is 1 foot from the flash, and Object B is 4 feet away from the flash, then Object B receives 1/16th the amount of light as Object A. In photographic terms, if the correct exposure for Object A is f/11, the exposure for Object B is f/2.8 .

So, the little light that's spilling over onto the bookcases or bouncing back onto them off the walls and such, is way dimmer than the light hitting my face in this photo. Face to flash distance is about 18 inches, light to bookcases distance is about 120 inches.

3) Cameras cannot record as wide a range of brightness values as our eyes can. A good Digital SLR can record 8-11 stop range. So, if the exposure here is f/8, then anything registering a 1.4 or below is going to go black.

Add all of these together, and the bookcases don't get enough light to register on the camera sensor.

A really good, long, detailed set of illustrations of this can be found here.

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