Canon 5D mkII 24-105 f4L IS Lens iso 200 firstname.lastname@example.org
Shooting a subject with flash against a sunset background using all manual settings on the camera is something that I struggled with learning for the longest time. At first it kinda went like this:
When I first started shooting sunset portraits, I would usually put the camera in Program mode and set the on camera flash to ETTL mode. Most of the time it would do a pretty good job, but there would always be the odd frame where the exposure went wacky and was either too dark or too bright. Usually it would be THAT frame where everything else was right - the model's pose, hair, expression, whatever. It would have been the Perfect Shot.... if only the exposure didn't suck.
The main problem with shooting sunset portraits in Program mode with an on camera flash is that every time the camera angle or the distance to the subject changes, the camera and flash have to recalculate everything. Camera manufacturers love to say that the chips in the cameras are so powerful that they can instantly compare your image to hundreds of thousands of images in their databases in order to give you the correct exposure. When you shoot a whole bunch of shots in a row however, you'll occasionally get a bad exposure because the camera isn't smart enough to know what exactly it is that you're shooting. No matter how powerful the computer inside your camera is, it will never be able to compete with the supercomputer that is between your ears.
Shooting on all manual settings can be daunting at first, but I've found that it actually makes it easier to get more consistent images and wastes less time in the long run.
When using flash as the main light on the subject at sunset, the aperture controls the exposure level of the subject and shutter speed controls the exposure level of the background. This was the hardest concept for me to wrap my brain around when I first started learning how to use manual flash at sunset. What made things easier for me was learning to control or eliminate the variables that affect exposure (flash to subject distance, iso, aperture, shutter speed) in steps.
disclaimer - I am NOT an expert at this. The following is just to show what I learned over the years so that I don't break out into a cold sweat whenever I am asked to do a sunset portrait.
Step 1 - Get the flash off of the camera, set it up on a lightstand and trigger it with a set of Pocket Wizards. This gives me the freedom to move around while keeping the distance from the flash to the subject constant. By keeping this distance constant, it eliminates one variable of the exposure I need to worry about. I'll usually set it up about 10 feet away from my subject at about a 45 degree angle off to one side. I'll then use a 70-200 lens to zoom in and frame the lightstand out of the shot. If I need a wide angle shot, I'll include the lightstand in the frame, but try to keep it on a "Photoshoppable" area of the frame (like against a clear sky) where it will be easier to take out in post production. Having the flash on a lightstand away from the camera position also eliminates the problem of "red-eye".
Step 2 - Keep the iso constant - usually for sunsets I'll keep it at iso 400. This eliminates another exposure variable.
Step 3 - Wait for sunset light level to go down to where a shot of just the sunset sky looks good at camera settings of 1/125 @ f8.
Step 4 - Set the flash power settings to manual mode and set the power level to get a good exposure on the subject at f8. Don't really need a super powerful flash to do this. At iso 400 I can easily get this with a small Nikon SB-26 set to 1/2 power at about 10 ft away. Keeping this constant takes away another variable I have to worry about.
Step 5 - Start shooting at 1/125 @ f8. If I want to make the sky darker, I change the shutter speed to 1/160 or 1/200, which is about the flash sync speed limit for my 5D mkII. If I want to make the sky lighter, I'll slow the shutter speed down to 1/100 or slower. As long as I keep the iso/aperture/flash power/distance from flash to subject the same, the exposure on the subject will remain the same and I only need to think about changing one thing - the shutter speed. Having only one thing to worry about makes things hella easier for me and my Homer Simpson level brain.
Step 6 - Eventually it'll get dark enough where I can drop the flash power down to where I can get a good exposure on the subject at f4, then repeat Step 5 at this wider aperture setting.
The great thing about learning how to do it manually is that once you get used to it, you can have fun with it and experiment. With the newer cameras that can handle much higher iso speeds and IS lenses that let you handhold at really slow shutter speeds, I've been able to do handheld shots like the one below at 1/4 of a second.
Canon 5D mkII 24-105 f4L IS Lens iso 400 handheld at email@example.com
Light is from an AB800 on lowest power setting with a 5ft Octodome to camera left. This was long after the sun had set that day and I literally could not even see Skyler's face at this point (couldn't use the modeling light on the AB800 since I was running it off of battery power) and I had to guesstimate the focus distance.
Even at 1/4 of a second shutter speed, I don't have to worry too much about the subject being blurred since the flash freezes her movement.
Hope you found this post useful and that it will keep you from making the same mistakes I made when I first started learning this stuff.