In this post I am going to share a fundamental technique that enables you to create dramatic sunset images in your camera with little or no Photoshop enhancement. To get started you must know the manual guide number of your flash unit and how to use it creatively to achieve predictable results. I have found that nearly all guide number ratings are exaggerated by the manufacturers and suggest that you determine an accurate guide number for your particular flash unit and commit it to memory. A good flash meter is helpful in determining the guide number of your flash, but it is not essential. A few test shots in a darkened room will serve the same purpose.

Start by placing both your camera and flash unit in the manual mode. The guide number of your flash unit, at any given ISO value, is determined by multiplying the flash-to-subject distance by the aperture value required to make the correct exposure. As a simple algebraic equation: Guide Number = f stop X Distance. At ISO 400 my flash unit, a Nikon SB900, delivers a proper exposure of f22 at a distance of 10 feet. The guide number of my flash therefore is 220. It is important for you to understand that in a darkened room, with no ambient light affecting your exposure, your exposure will be f22 at 10 feet regardless of your shutter speed. When I teach Guide Number to my students I demonstrate this by making a series of exposures, in a totally dark room, from 1/8 second to 1/250 second at f22 with my flash 10 feet from the subject. In that darkened room all of the exposures are identical. In manual mode your flash output will be the same on every single shot, and, in the absence of any ambient light, all of your exposures will be identical, regardless of the manual shutter speed chosen.

Now the fun starts. Take your camera and flash out of that darkened room and point them at your subjects who are standing against the sky at sunset. In this image I have my assistant positioned 20 feet from my subjects. My Guide Number tells me that a proper exposure will require an aperture value of f11. Remember, Guide Number = f stop X distance or, in this case, 220 = f11 X 20 feet. (11 X 20 = 220…Simple). In this image I set my camera in aperture priority mode and the camera determined that a proper exposure, based upon the ambient light, would be 1/60 second at f11. The camera returned this image in which the background is properly exposed and accurately rendered. My subjects are properly exposed by my off camera flash unit positioned 20 feet away from them.

Knowing that my subjects will be properly exposed by my flash unit, regardless of the shutter speed, I am free to alter the ambient light in this scene to my liking. I put my Nikon D3 camera in manual exposure mode and select a shutter speed of 1/250 second. The shorter shutter speed underexposes the background by two full f stops while my flash unit still properly exposes my subjects with it’s predictable, constant manual output. This time my camera returns this dramatic image with a deep saturated (underexposed) sky!

I have employed this fundamental technique for more than 30 years. It worked with film and it still works in today’s digital environment. The digital technology we enjoy today has opened up new creative possibilities that we only dreamed of in the past, but they can only be fully exploited by those photographers that have a thorough understanding of the fundamentals. I encourage you to take your cameras and flash units out of the automatic exposure modes and practice some of the basics that will enable you to predictably create stunning imagery on a consistent basis. Guide Number is a great place to start…I’ll be sharing some more “secrets” in future posts.