Monday, April 2, 2012

Using flash to alter your background


BTS of one of my recent flower shots
Up until this point I have been discussing exposure dealing with natural, available light. However, there are times when nature needs a little assistance. This is where light modifiers come into play. There are many types of light modifiers available to a photographer. Commercial and home made reflectors, diffusers, lighting setups and who knows what else. But one of the most common type is the speedlight.

The speedlight (or off-camera flash) is that piece of equipment most photographers go out and purchase early in their gear collecting. More so than springing for a better lens. After all, we are told that if we don't have enough light we will need to use flash. But introducing a secondary light source changes our exposure triangle from the familiar triangle to a new shape, the square.

To give a little insight into how off-camera flash can be used to control light I will show a step-by-step example based on the recent daffodil meet up at Hubbard Park.


In camera metered for goo exposure on flowers
The first image is of a group of flowers I found in a roadside bed near the entrance of the park. I loved their composition and their color. I decided to shoot them from and angle equal to them in order to see the yellow centers better. I took a meter reading, keeping in mind that the bright sky would affect the reading, and shot of an exposure.

As you can see from this image the flowers are nicely exposed but the sky is blown out. Actually the white of the petals at the top of the flowers have also lost some of their texture.

Because of the bright sky the tops of the flowers are now lost. There is not enough contrast to separate the subject from the background. In order to make the white petals stand out the obvious decision is to darken the background.

Slight under exposed to darken the sky
Here's the catch; I know I will be introducing an external light source to lighten up the flowers in the foreground. That means I have to make sure I stay within my sync speed for my flash. That means I have to keep my shutter speed somewhere between 1/60 to 1/250th of a second. That means I can't go faster than 1/250th of a second on my shutter speed.

The photo above was taken at 1/160th of a second at f/11. I increased my shutter speed to 1/250th of a second (the fastest I can safely take the camera to and still capture the flash) and closed up my aperture to f/25. This cuts down on the light entering the camera effectively darkening the sky. You will also notice I gained some sharpness to my background.

You can see that the new exposure has darkened the flowers in the foreground. That's okay because, as I mentioned earlier, we will be lighting the flowers with a flash.

Flash used to bring our attention to the flowers
Up to this point it has been rather simple. Expose for the flowers we discover they get lost in the sky. Expose for the sky and the flowers get lost in the shadows. Keep the sky and light the flowers and we're good to go. But how much light do we need?

This is where experience and understanding how light works comes into play. A few trial and error settings and soon you'll have a shot like this one. In this case I started with the flash on 1/4 power and took a test shot. The result was too hot (too much light) and it washed out all the white petals.

I then powered down the flash to 1/16th power and it barely did anything. The third shot was at 1/8th power and that gave me the results you see here. A little backwards I know but I thought the 1/4 power was so much that 1/8th would have been too bright too. So you see, it's all about correcting for the problems.

Final image with post processing done  in LR3.
So now I take that last image, open it up in Lightroom, tweak a few settings and, viola, the end results. I am of the opinion that even if a photo looks good straight out of the camera it still needs to be developed. How much is done is up to the photographer and what the final results are imagined for the image.

In this case I was looking for more drama. The first thing I did was crop to an 8x10 format and added my vignette to see how the flowers stood out. I then burned in some shadows on the background flowers (bottom left and bottom right) so they weren't as prominent. Once the focus was on the flowers I boosted the luminance and vibrancy of the colors, deepened the shadows and did some spot removal.

Overall the whole processing time was less than ten minutes. The results, however, are awesome. Hope this inspires you to play around with light balances on your next session.

P.S. The result of the flower shot taken from my prone position shown above can be view on my 500px.com page.

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