Thursday, June 16, 2011

Flash Series - Part 6: Use Flash in Daylight? Really?

I hear this exclamation a lot whenever I advise someone to use his flash as a fill light in strongly backlit situations, or when someone sees me using it in broad daylight. Despite being initially counter intuitive, this is perhaps the only practical use (image quality wise) of your built-in camera flash. Hit the jump for more explanation.

It's summer time again, and more people will be shooting at pools, one of the usual problems that you face is the harsh sun light and the strong shadows it creates. Mic has already discussed the same subject in this post, so consider this one as a refresher. You see, the sun is considered a hard light source because it's too far and relatively small, this causes the shadows to be defined and strong, this is not a flattering light for portraits. How to solve this?

One solution that several websites recommend is shooting in a shaded open space, i.e. not covered by direct sun light, but rather diffused light, another one is to use a piece of silk or some diffusing material directly above your subject to prevent direct sunlight from hitting him, but both of these techniques are not an option with your subjects swimming in the middle of the water under direct sun light, my favorite solution is to use the flash light to lift these shadows to some degeree and reveal more details in your subject's eyes.

If you look carefully at the introductory picture you will notice from the shadow on the subject's shoulder that the sun light was coming from above and behind him, if I had not used fill flash his face would've fallen into the shadows. Using the built-in flash is usually a no-no in low light conditions because the flash light is quite close to the lens and results in a flat looking picture, but this condition is different, the flash will not be the main light source but rather a fill light to lift some of the shadows caused by the high contrast sun light, thus it won't cause the usual flat look that accompanies most built-in flash lit pictures (read: facebook party pictures).

One other thing to consider when using a DSLR is the sync speed, this is a very famous mistake that people face when they use their flash in strong sun light, most DSLRs have a maximum shutter speed of 1/250 sec when the flash is used, so if your normal shutter speed without flash under sun light was around 1/2000 sec, then when you switch on your flash and the camera will limit your shutter speed to 1/250 sec resulting in a seriously overexposed image, there are two solutions to this problem (point and shoots usually don't have this problem, and some DSLRs too):
  • The first solution is to make sure that your shutter speed doesn't go above the sync speed, you can try closing your aperture down, reducing the ISO or even using ND filters.
  • The easier solution requires an external flash with high speed sync abilities, high speed sync enables you to shoot at any shutter speed but at the cost of reducing the maximum power you can get from your flash.

All the pictures in this post are shot using an external flash mounted to the camera's hotshoe and operating in high speed sync mode, I was using an 85mm lens and shooting subjects from quite a far distance and my aperture was f/8, so to make sure my flash had enough power to illuminate my subjects I increased the ISO to 400 and used the 580EX (not the II version) because it makes a recharging sound like studio flashes, and that way I can easily know if it was firing at full power so I need to increase the ISO or open my aperture a bit.

One good thing is that the flash's white balance is similar to daylight, so you can use it with your camera set to daylight white balance, my flash was on TTL and zoomed all the way in (105 mm) since my equivalent focal length was 135mm. In the example below I used the exact same settings in both pictures, but one without flash and the other with flash on, look for differences at the blue tiles on the pool edges and the subject's face. I admit that the second picture isn't as good as the other examples but this is the only example I had that shows the flash effect, I have better examples below.

f/8, 1/1600 sec, ISO 400 - No Flash

f/8, 1/1600 sec, ISO 400 - Flash On

Here are two more examples, the first one is taken on the same day as the rest of the pictures, and the seocnd one is taken a while back with my G11 and a 430EX, the G11 didn't have any limitations on the sync speed.

Flash successfully lifted most of the shadows and resulted in a good exposure

Sun coming from above and to the right of the subject, the flash eliminated shadows


Fill Flash: Summer Pool Party! (Basic)
Flash Series - Part 1: Canon Speedlites Chat (580EX II vs 580EX vs 430EX)
Flash Series - Part 2: Home Made (DIY) Gels & Gel Holder
Flash Series - Part 3: Rogue Grid Review
Flash Series - Part 4: Triggering Your Hotshoe Flashes + eBay RF Trigger
Flash Series - Part 5: Remote Adjustment Radio Triggers