Measuring Light – Flash Photography Simplified

Although digital technology has made cameras more user friendly than ever before, technical aspects of photography can be puzzling. One of the most misunderstood aspects of photography is the flash.
To make understanding your flash more simple, consider this fact: your flash is a simple light source, and it’s available on demand, whenever you need it. The flash is easy to control; expanding your knowledge regarding technical aspects of the flash will make it even easier, and as a result, your photos will come out better than ever.

In order to understand more about the way your camera’s flash feature works, you’ve got to expand your vocabulary. We will continue some of our details on off camera lighting and how to get creative lighting but today I wanted to do a review of how light is measured. Since photography is really all about light understanding how light is measured and exposure is key to great images. There are three aspects that are absolutely indispensible to making the most of flash photography. Those three aspects are: Shutter Speed, Aperture, and ISO.

Shutter Speed Simplified
Every camera has a shutter, which opens to capture the image you’re photographing and closes once the image has been caught. Fast shutter speeds are best for action shots. Slower shutter speeds soften action. Very slow shutter speeds, 1/3 – 1 second, are great for capturing flowing water, for instance. If you’ve ever wondered how to get soft waterfall effects, the answer is to slow down the shutter speed!
If you took a photo of a race horse running at 1/30 (one thirtieth of a second), you could see his legs suspended in mid-air, and great clods of turf flying from his hooves. If you took the same photo at 1/3, you’d only get a blur of colors.

When using flash (on camera or off camera) your flash will freeze the action, so no matter what shutter speed you are shooting at your subject will be frozen by the flash. What your shutter speed will mainly control when using flash is the amount of ambient light (light surrounding your subject). So for example if you are indoors in a dark room and take a photo with your flash on at 1/125 second shutter speed the background will be fairly dark. But if you change your shutter speed down to 1/30 of a second your subject will still be exposed the same by the flash and will be frozen by the quick pulse of the flash but your background will now be illuminated much more with light from the background.

Understanding Aperture

Very simply put, aperture is an expandable hole that controls light. Your eye’s pupil is a great example of an aperture – when you need less light because of bright conditions, the pupil shrinks. Your pupils dilate to help you see clearly in dim light. A camera’s aperture works in much the same way. Most cameras are equipped with automatic aperture, which you never need to think about. In that way, it’s very much like your eyes – you don’t have to remind yourself that you must see, you just do it.
If your camera permits manual aperture control, there are some additional considerations:

  • f-numbers – An “f/stop” refers to a certain common setting for aperture control. High f/stops allow distant objects to remain in focus when photographed. Low f/stops are the best to create a soft background and work best for most portraits.
  • the shutter speed with flash photography controls the exposure of your subject in relation to the power of the flash. If your flash is too bright or too close to your subject you can either turn it down or change the aperture to close it down more. Moving from f/ 4 to f/5.6 will cut down the amount of light that will hit your sensor, so if your flash is too bright you can dial down your aperture to darken the subject.

    • ISO Made Easy

    Back in the days before digital photography was the standard, high ISO shots were often grainy, due to the nature of film. Now, you can control ISO and with some of the most recent dSLR cameras shoot at high ISO’s (1600 and up) and still have clear shots. ISO is like the sensitivity of your sensor. At a low ISO 200 for example you need a good amount of light to get a correct expsoure. At high ISO’s like 3200 you don’t need much light at all to get a correct exposure and can shoot with candlelight if you wanted.

  • Low Light – Set your ISO to a high number, like 800 or 1600. High ISO lets in the most light. If you use high ISO and your photos are coming out too bright, you’ve got too much flash. Lower the exposure of your flash. Use extreme high ISO to capture shots in dim areas, like concert halls, where flash is not allowed (ISO 3200 and above). Just make sure to get your exposure perfect. At high ISO’s there will be digital noise in the photo and if you underexpose and have a dark photo and brighten in photoshop or lightroom the noise will appear even more and take on a muddy and grainy look.
  • Bright Light Conditions – Setting your ISO to the lowest number possible when in bright light conditions to have the cleanest, sharpest file to work with. Even if you want to go for a grainy artistic photo as your final product you can always do that in Photoshop later, but it’s better to start with as clean of a file as possible and work from there.

    • For some more advanced lighting tutorials check back later or view our lighting category. We have tons of great tutorials on off camera lighting and using flash photography.