I sometimes read articles or watch videos where photographers wax lyrical about the beauty of natural light, claiming that there’s something special about natural light that you just can’t get with flash. Since photons are photons, this has puzzled me — Physics is a fairly simple and predictable discipline, so in theory at least you should be able to re-create a flash-lit scene and make it look identical to a scene lit by natural light.
One of the main ways in which natural light photographs differ from flash photographs is to do with the size of the light source. Windows tend to be quite big whereas most light modifiers are comparatively small. I recently made a large scrim (about the size of a single bed), so I thought this was a good opportunity to test out the theory.
I have a large window in my sitting room, so I placed the scrim in front of it and drew all of the other curtains in the room. I placed a chair by the window, like this:
Then I took this photograph (1/30s, f2, ISO 100). It’s lit by natural light only.
I then went outside and set up three Speedlites on a stand.
I then came back into the room and adjusted the camera settings so that there was no ambient light contributing to the exposure. At these settings (1/200s, f8, ISO 100) the image was totally black.
I then turned on the Speedlites and took this photograph. This is lit by Speedlites only.
The only post-processing I’ve done on the two images is a white balance correction.
Now there is an obvious difference in depth of field between the two shots. (I couldn’t shoot the flash-lit image at f2 because too much ambient light leaked into the image. I did try taking the shot using high speed sync, but it was underexposed by about a stop, even at full power). So when you’re comparing the images, you need to disentangle the quality of the light from the depth of field.
To make this easier, I’ve cropped the images to just show a strip from one ear to the other. You can see these below.
Natural light crop:
Flash light crop:
When I look at these images, I do see a small difference in the light. It looks to me that, in the natural light image, the light falls off more gradually than in the flash-lit image. In other words, the flash-lit image is a bit more contrasty.
But it’s a very subtle difference.
If I put an ND filter in front of the lens, I could then shoot the flash lit image at f2 and I don’t think anyone would be able to tell the difference.
I suspect that when people say they like the look of natural light shots, what they are really saying is that they like images taken with a shallow depth of field.