I was asked today about mixing flash with natural ambient light. It is something I probably do all of the time. Even during blazing summer afternoons I will use off camera flash. Sometimes this will just be to fill shadows or to try and reduce the harsh contrast of bright sunshine, sometimes it is because I want to completely change the feel of an image - notably to darken the background and add drama or pull details out of bright skies.
Where to start?
If you are not being slap-dash about the whole affair the first place to start is knowing what your 'normal' exposure is. This is the camera settings you need to get a reasonably well exposed shot without flash. The way we do this is to simply take a test shot. Now I have to confess I do not tend to keep many baseline shots and really struggled to find some examples for this blog but did manage to find a quick behind the scenes shot, and some images from the final edits, that show what I mean.
Our baseline settings
If we look at the EXIF data for the image above we can see that it was shot at 1/125 at f4. No flash was used, I was literally grabbing a behind the scenes shot whilst my friend Gino was actually shooting with the lovely Kamie. It is not a great shot but you can see that the exposure is basically right for Kamie herself (and for that matter, one of my long suffering makeup artists, Kailey).
What we also see though is the sky and water is basically overexposed and practically white.
Ideally we would want to dial down the exposure, to get some detail back into the sky and water, but doing that would mean Kamie would be underexposed. I have kind of simulated this below by reducing the exposure and highlights in Lightroom.
Enter the flash ...
We can see from our baseline shot that the background is overexposed. We will set our camera up to deliberately underexpose the shot so that the background can retain some detail. We will use the flash to light Kamie and get a 'correct' exposure for her. Ideally we should use a flash meter and look at setting the flash power so that I get a meter reading around the same f-stop as whatever I have set the lens aperture f-stop to. You could of course tie your horse to a nearby post and take a few test shots, varying the power, until you get something that looks correct.
For the final shots we changed the angle slightly to get a bit more interest into the background.
Our modified settings
The shot above was taken about 10 minutes after the baseline shot but the ones below were taken no more than 4 or 5 minutes after the baseline shot. In short the ambient light had not really changed at all in such a short timespan.
What the EXIF data shows though is we have gone from f4 to f9, no other settings have changed, and this has obviously reduced the overexposure in the sky behind Kamie. I believe, in this particular instance, my horse was munching on some oats and I did not meter the flash but took a few test shots, increasing (or decreasing) the flash output until I liked the exposure on Kamie.
The most natural looking flash is going to be when it matches the ambient light reading, so in this case we would meter the flash for f9, but by varying the levels you can obviously change the effect.
For even more natural looking shots we should consider colour temperatures as the colour of evening sunlight is not the same as the colour a 5600K daylight balanced flash outputs but that is really a bit beyond the scope of this blog.
It would be rude not to share a few more ...
When you need to condense the day ...
We have talked about trying to get a natural looking amount of flash and also how you can vary the settings to create drama. We can also take the settings to extremes and simulate night even during the middle of the day. This is one reason I love to use flash outdoors. This very old shoot shows how in the space of 10 minutes I managed to go from a daytime shoot to a nighttime one - all around midday!
You can click own the images to enlarge them. The first shot demonstrates matching the flash with the ambient light giving a fairly natural look. In the second and third images I have deliberately underexposed the background to make it look like night at 1:30 in the afternoon.
E-TTL
Throughout this blog I have assumed we are using manual flash settings and, in my particular case, off camera flash. With both off camera flash and speed lights on camera, you can sometimes have evaluative through-the-lens (E-TTL) metering. With E-TTL the camera and flash talk to each other to correctly expose the subject of a shot. It effectively takes away the need to meter the flash or take test shots whilst your horse is being stabled. You can still use the aperture and shutter speed settings to expose the background.
Most speed lights will also have the ability to set a plus or minus compensation to deliberately over or under expose the flash should you need to.
I quite often use E-TTL for small outdoor group shots with on camera flash. I will set the camera to shutter priority and set the shutter speed to the flash sync speed (see below in a minute). I may then use exposure compensation on the camera to deliberately under-expose the background. I sometimes use the flash exposure compensation to over expose the subjects a little but that depends on how dark or how much shadow they may have on them. It's a kind of dilute to taste thing!
Last leg, shutter sync speeds and HSS
I just mentioned setting my camera to the shutter sync speed. What is that you may ask? Well it is the maximum shutter speed you can use with flash. It is usually around 1/200 or 1/250th of a second. Your manual will tell you what it is for your camera or it may even have a mark on the shutter speed dial. If your flash system supports something called 'high speed sync' (HSS) you can turn on that option and basically ignore this bit as HSS allows you to shoot with flash at shutter speeds higher than your sync speed.
Without using HSS you must not go past your sync speed as you will start to see shading down one side of the image. I'm not going to get into the mechanics of sync speeds but, in short, if you go past the sync speed not all of the sensor will be exposed to the flash whilst the shutter is open resulting in the shading.
The maximum sync speed can be a problem if you are shooting in bright light and want to open the aperture to get shallow depth of fields. It may not be possible to have a wide aperture like f2.8 or f4 and keep the shutter speed down to 1/200th or 1/250th (or whatever your camera's sync speed is). In these situations you will either have use the aforementioned HSS if you have it, or look into using neutral density (ND) filters to reduce the ambient light levels to start with (or invest in cameras with leaf shutters but that is another story).
I hope that gives a little insight into mixing flash with outdoor ambient light. it has served as a handy refresher for me as I am doing an outdoor shoot tomorrow for the first time in what seems like ages and I now stand a chance of knowing what I have to do!
