Using ambient light

I was asked at a photography forum how to choose and use ambient light for photography - how to make good images with the light that exists on location. ¬†One thing to keep in mind is that “ambient light” and “light control” are not incompatible. As a photographer you can be reactive and use the light as you find it, which is easy, or be proactive and use ambient as the raw material, but not the finished light for your photographs. On the images above I use some light as I found it, and I also controlled it, see below.

  • Natural light can be colored, just like flash light when it’s reflected by a non-white surface - so that’s the first thing to worry about. If the enviroronment is reflecting colored light, getting the white balance right is going to be critical. I always use a gray card as a reference.
  • Northern light has a very beautiful quality - so pay attention to the orientation of the window you’re using, and pick northern light if you can.
  • It’s important to understand the relationship between the value of the background and that of your main subject. By value I mean the brightness. If you place a diffusor between the subject and the source of illumination, you’ll have a subject with a lower value than the background, which means that when you adjust the exposure to be correct on the subject, the background will be lighter. This is great for high key portraits, but not so good if you’re looking for a low key mood. The opposite is true is you use a reflector to raise the value of the subject but not the background.
  • Flat natural light can be a problem - while diffused light will be better than high noon, it can also produce blueish, dead skin tone. There is also the issue of not having hair highlights with flat lighting. There are two solutions to these problems. First, get the white balance right by using a gray card. Second, you can pump some light onto the hair using a mirror. You can even diffuse mirror light usng a diffusor like a light panel. And of course sometimes it’s best to mix ambient and flash. For example if you cannot reflect sunlight on the hair, you can use a portable flash.
  • You have to be aware of a sensor’s ability to capture a range of values, or its dynamic range. Ambient light make look good to your eyes, but the dynamic range of most cameras will not be more than 6 f-stops, which means that you’ll get blown out highlights or really dark areas, depending on how you expose, if the dynamic range is greater than a few f-stops. The solution is to use a long lens if you can to reduce the amount of ambient in the background, or supplement ambient with flash.
  • Most of what I know about controlling light I have learned thru Dean Collins’s teachings. There are some really good DVDs out there if you’re really interested.
  • Ultimately light control is the same whether the light is ambient or created. The tools can be the same, and the ideas are the same. There is no reason why you can’t use butterfly lighting, short lighting, or Rembrandt lighting with natural light. You need to train yourself to see the right as the digital sensor sees it. So a good approach is to use ambient light, but control it as you would studio light. Sometimes you get light and you don’t need to control it.

Edit: I forgot, sometimes I use a 1/4 or 1/2 CTO gel on a portable flash used for fill outdoors. This allows me to compensate for blue color casts under trees, and produces a warm, healthy skin tone. I posted an example of that here.

Edit 2: The three first images would have benefited from using a small, portable plastic mirrr bouncing window light back on her hair. I had someone there that could have held the mirror in place for me. Oh well, I will remember it next time. I keep a log of all my mistakes, and I am very proud of them :-)

One more thing about using ambient light combined with flash - it’s important to decide which is the key light, and which is fill. Then set the exposure for the key light, and set the intensity of fill to be less than the key. Here are a couple of examples.

Case 1 - Sun is key light, flash is fill. This is the most common case in bright days - rely on the camera/flash built-in fill flash capabilities, or do it manually. The advantage of using an advanced flash system like Nikon’s CLS is that you can increase the shutter speed to control depth of field with an open aperture. If you want to do this manually, measure ambient light to decide how bright you want the background, and then measure again with the fill flash set to manual, and set the exposure accordingly. For example.

Ambient light measures at f/16 and 1/125, typical of a sunny day.
Set the flash to 1/2 power for example, and place it close to the subject - let’s assume you get f/16, combined exposure of flash and ambient.
If you want the background to be less dominant, change the shutter speed to 1/250 to darken it, and keep the aperture at f/16.

It’s a good idea to place a warming gel on the flash to achieve more natural skin tones, especially if the day is cloudy or you’r shooting under trees. Note also that if you’re shooting manually, you can’t go over the maximum sync speed provided by your camera/flash, normally 1/250, so apertures are going to be small and you can’t really control the depth of field unless you use neutral density filters.

Case 2-Flash is key, ambient is fill. This case is a bit different, as the flash will produce most of the illumination on the subject, and ambient will illuminate the background. The aperture controls the amount of light falling on the subject, and the shutter speed controls the exposure on the background. Again, you can rely on automatic camera/flash controls, or you can do it manually. For manual operation, measure the ambient first to get an idea of what shutter speed you need, for a certain aperture. Then set the flash to give you that same aperture. For example:

Ambient measures f/5.6 and 1/30 - say a restaurant.
Set the flash to 1/2 power and measure exposure, let’s say it’s f/8. You want shallow DoF, so lower the flash power to 1/4 to get an exposure of f/5.6, then set the shutter speed to 1/30 to capture ambient light.

Case 3 - overpowering the sun. This is the technique where your flash is main, and the sun is fill, but the sun is very bright, brighter than the light produced by a small flash. For example f/16 and 1/125 sunlight, and you want to underexpose by two f-stops, for a dramatic dark blue sky. This means that you need to shoot at f/32 1/125 or f/22 1/250. Let’ say you want three f-stop underexposure on the sun, so you’ll need to shoot at f/32 and 1/250. Now you’ll have to illuminate your main subject with enough flash power to produce f/32 light. This is a lot of light, and you probably need 1000 watt-sec or more, depending on how close the flash is, what light modifiers you use, etc. While you may want to rely on Nikon CLS to do this, remember that the intensity of the flash at 1/2000 is really not that much, but you may be able to do it if the flash is very close to the subject and the aperture quite open.

That’s is, no more technical stuff for a while!

Category: Technical

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