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.
Hey, just wanted to say thanks for sharing….I’ve often wondered, and never understood, guide number. Thanks for explaining it.
I enjoyed your explanation but have a couple of questions if you don’t mind?
It was my understanding that the aperture controlled the power or output of the flash to the subject, and the shutter speed controlled the ambient light. So if I wanted a darker background I just raised the shutter speed from f/250 to f/500 ect…
am I mistaking with my statement?
Thanks
Allen
Hi, thanks for sharing, I am always too lazy to carry flash & stands around and just fake the same ligiting in Photoshop. Althought I tried this technique a few weeks before and it worked… It looks loke you used an STO gel as well to make skintones warmer??
Thank you for your comments. To Allen…The combination of aperture and shutter speed controls your exposure. In the image shown I would have gotten the identical exposure at 1/125 sec. at f16, but then my subjects would have been underexposed by 1 stop. To compensate I could move my flash closer to my subjects…in this case from 20 feet to about 14 feet (Remember the formula: Guide Number = f stop X distance – or, in this case 220=f 16 X approx. 14 ft). To Elena…my off camera light is managed by my assistant…light stands are too static for creating spontaneous images but could be used in a pinch. I would have to disagree with you in saying that you could “fake” this lighting in Photoshop. Impossible, for sure…besides Photoshop is an enhancement tool for fine photography, not a band-aid for inadequate capture. My off camera light did not carry any gels. The warmth of the image is my personal taste based upon the white balance setting of my camera and perhaps some adjustment in RAW image processing. By the way, this image received Accolades of Excellence in the 2008 WPPI 16 X 20 Print Competition.
-Michael
Thanks Michael for sharing your experience with us. For once, I’ve found some worthwhile reading about little bits and tips that actually help me become better.
Keep it up
Joel
Thanks, Michael…great article, I’m familiar with many of the principals but hadn’t used your guide number calculation technique. I’m assuming that the guide number is with the flash at full power in manual mode?
Dan
Yes, Dan…your assumption is correct. Once you master your full power guide number feel free to experiment with the options your flash unit gives you. For example: by cutting your power to 1/2, 1/4 or lower you can determine a smaller guide number which can be useful when working with higher ISO ratings in darker ambient light conditions. Most high end flash units, like my Nikon SB900, also allow you to adjust the beam to compensate for the angle of view of the lens you are using. By adjusting the beam pattern of my flash to, say, 135mm while using a wide angle lens I can keep my remote light out of the picture and create a spot light effect on my subjects. The creative possibilities are endless once you know the fundamentals. Enjoy!
[...] gel (Why? Because that’s what happened to be on when I got this shot). Inspired by this post, I used shutter speed to control the ambient. I used a fast shutter speed to darken the ambient [...]
Congratulations on the award for the image Michael! You totally deserve it! Your work is great!
thanks, a real insight…
I loved reading it. I require to read more on this issue…I am admiring the time and effort you put in your blog, because it is plainly one great place where I can find lot of useful info..
Like the info, thanks. I have a question though, do the new flash metering modes that measure the distance and fire a flash from the measured distance give equal results. I assum you will be more accurate using it manualy. Hope I am making sense.
Just subscribed to the blog last month, keep the great updates coming.
Hey gratitudefor sharing this tutorial. Worked for me.
Your site is nice. I m gonna bookmark, thanks. Continue working on blog.
I always enjoy reading spot on articles by an individual who is obviously up to snuff on their chosen subject. I’ll be following this thread with much interest. Keep up the good work, see you next time
good share, great article, very usefull for us…thanks!
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