# Exposing for background



## curly (Apr 8, 2015)

Sorry if this is a stupid/basic question, but I would like to learn and improve on my photography.

When taking a portrait using off-camera flash, what are the correct steps to take? I have heard to expose for the background, then add in flash to illuminate the person in the foreground.

So does this mean locking the exposure without the individual in the frame, then have them walk into frame? Or do you usually do this all with the person in the frame and tell the camera to set the exposure based on a specific area of the frame using spot metering?


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## tirediron (Apr 8, 2015)

It depends totally on what style of portrait you want to produce.  It sounds to me like you're trying to create a balanced ambient/strobe shot.  In that case, the process I follow is to meter the background, and with the camera in manual, set that exposure.  Then place  your lights and adjust output until you get the appropriate exposure.  I generally like my flash about 1/3 stop over highlights which does two things:  Darken the background, and ensure that the face is the brightest part of the scene.  I don't want the client waiting for me, so with very few exceptions, I ensure everything is ready before they come on set.  It shouldn't take more than 2-3 minutes to set up and dial in anyway.


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## Derrel (Apr 8, 2015)

Well, this is a tricky question to answer, somewhat akin to asking the question, "So, what's the correct way to make dinner for a family?" There really is not one answer, or even two, or even three answers. I have been shooting flash pictures since the mid-1980's, and most of the time I use manually-set flash power adjustment, meaning on speedlights, setting like Full, Half, Quarter, and one-eighth power, in M-flash mode AKA "manual power" mode, sometimes called "fractional power mode", which means that **I** manually set a flash power level, and make the adjustments myself, and see how the various flash power settings work out in relation to 1) how close or far the flashes are and 2) the f/stop in use and 3) the ISO level the camera is set to and 4) If there are areas that the flash does not reach, like the background, I evaluate the ISO and shutter speed and f/stop for the degree of background brightness the exposure triangle is creating.

If you want say, *a dimly-lighted background using natural light*, then a low ISO setting, a fast shutter speed, and a small aperture would be a good start, like say ISO 100, shutter at 1/250 second, and lens set to f/13. Then, the main light needs to be set at high enough power, and close enough, so that the subject gets a good, generous flash exposure at the f/13 exposure that is in use, at that ISO 100 setting.

If you have an adjustable power flash, you can crank the power high enough, or place the light close enough so that f/13 is the right exposure. If you wanted that same,dimly-lighted background to be lit by a flash, the background flash might be set to 1/8 power, while the main light might very well be at full power.

Scenario Two: You want a pure-white background using GRAY SEAMLESS paper. Aim two flashes at the paper from both sides of the seamless, aimed in toward the center from about 40 degree angles, set those flashes on FULL power. Set the main flash on the subject at about 1/4 power. Pick an f/stop of f/7.1. Presto...the gray seamless will be "key-shifted" from gray, to pure white, and because the main light flash on the subject is much lower in power, when you expose for the main light, the person will look normally-lighted, but the backdrop paper will go to pure white. This is a way a person can get a pure white background using three, low-power flash units, by using LESS light on the subject, and MORE light on a dark background to make that dark into "light". With my studio lights, I would light the gray background with two lights, with 65-degree reflectors, each light firing at 800 Watt-seconds, and then fire 200 Watt-seconds onto the subject, which is_* the same power output ratio as*_ two speedlights, each at Full and Full power, and then one speedlight flash at 1/4 power.


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## TCampbell (Apr 15, 2015)

curly said:


> Sorry if this is a stupid/basic question, but I would like to learn and improve on my photography.
> 
> When taking a portrait using off-camera flash, what are the correct steps to take? I have heard to expose for the background, then add in flash to illuminate the person in the foreground.
> 
> So does this mean locking the exposure without the individual in the frame, then have them walk into frame? Or do you usually do this all with the person in the frame and tell the camera to set the exposure based on a specific area of the frame using spot metering?



Exposing for the background is used for mixed lighting problems where the intensity of background light is significantly different than the intensity of light on your foreground -- and in those situations, yes you do add some light to bring up the foreground subject so that the exposure isn't too far from the background exposure.

If you don't have these mixed lighting problems then you can just expose for your subject. 

But since you asked about mixed lighting portraits... here's an example:






While the human eye sees something like this when you look at the scene, the camera does not.  You really "see" with your brain... the eye collects information and the brain assembles the image.  That means your brain can do a bit of "high dynamic range" mental tricks to make the image look a bit more balanced.

We know the background is in full "sun" and it is roughly mid-afternoon.  That makes that background a "Sunny 16" exposure meaning that if we used f/16 then the shutter speed simply needs to be the inverse of the ISO setting (e.g. 1/100th at ISO 100, 1/200th at ISO 200, etc. they all work).

The "foreground" is actually just about 3 stops darker.  Without a flash, this subject would have been plunged into darkness.  This actually is a flash exposure (my speedlite is in the hot-shoe, so this is "on camera" flash).   I don't actually want the flash to try to over-power the sun... I want this to look somewhat natural.  If using an E-TTL (Canon) or i-TTL (Nikon) then you might want to dial back the "Flash Exposure Compensation" power to roughly -1 (which means use about half as much power as it normally would.)

This shot is a bit different than a typical mixed shot because I actually put a 3 stop ND filter on the camera to bring the background down... then used flash to bring the foreground up.   This just allows me to drop the f-stop down without having too much light -- but I could have taken this shot without the ND filter -- I'd just need to use a higher f-stop to avoid over-exposing the background.    Note that since I'm using flash, I have to either (a) keep the shutter speed at or below the camera's max "flash sync" speed (for this particular camera that's 1/200th) -or- I could also have enabled the flash's "high speed sync" (HSS) feature to shoot at faster shutter speeds (assuming the flash supports HSS.)

While this doesn't "look" like I used a flash... inspect the tree very carefully just adjacent to his hat and you'll see the shadow of his hat on the tree.  It's the only place in the photo where there is a visible shadow from the flash.  Had he not been resting against the tree, you wouldn't have even seen that shadow (most people don't notice it if I don't point it out.)  But this shot wasn't posed... I just happened along while he was resting and asked him if he wouldn't mind my grabbing this shot.


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## Vtec44 (Apr 15, 2015)

The basic concept is that you take the light reading of the background (either using the cameras internal meter or a light meter) then light your subject using the same reading.


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