Wednesday, January 13, 2010

Balancing fill flash with ambient light

When it comes to balancing your flashes with the ambient light, there are some simple ideas and a few basic rules that will make the job MUCH easier.  One thing that has always helped me, is to remember that the amount of light from your flash is controlled mostly by the aperture.  This in turn, means that the amount of ambient light can be controlled by your shutter-speed and ISO settings.

For example, in the shot above I put my powerful AlienBee B1600's at a setting of about 1/2 power, and bounced them off the ceiling.  This provides quite a bit of light.  For architectural shots, I know that I will be using an aperture of around f/8 or smaller to provide a better depth of field (More of the image will be in focus).  I also keep my ISO relatively low at ISO 200 to help reduce noise.  Because of the somewhat closed aperture and bouncing the flash off the high ceiling, I will definitely be needing it to be on a powerful setting.  Using the spot-meter setting on my camera, I placed my focus point through the open wall, and set it to match the surrounding peaks. In this case, the perfect setting for my shutter speed was 1/80 of a second.   The idea with this shot is to showcase the beautiful scenery, and create a well-lit interior.  

I will first take a test exposure with no flash.  This allows me to verify that my camera is set correctly.  Once I have made sure it looks correct outside, I will turn on one flash.  I take my first shot, and maybe see that the image is too bright and my histogram shows some blown-out highlights.  I can either turn my aperture to f/9 or f/10, and lower my shutter, or lower my flash power.  For this image, I chose to lower power.  The best way to get a shot like this, is by using a flash meter like the Sekonic (L-308s) that I use.  Without a meter, you will definitely have to take a couple shots, unless you can magically nail it the first time (Everyone gets lucky sometimes!).  If you find yourself at full flash power with an under-exposed image, you will need to open up your aperture to let more of that light in.  Remember: Flash output is controlled by aperture.  If you keep this in mind, you can create a perfect exposure in any situation!  From there, I will build up the image by adding additional flashes.  It's never a great idea to fire all of your flashes in the first exposure because they might all be way off.  Building up one at a time allows for more control over each unit.

There are certain situations where using a flash at full power, won't allow you to create the shot you want.  To create an image where the sun is starred in the picture, you will need to use the sunny f/16 rule.  Because the aperture is so small, it create blades around the sun.  Different lenses will have a different blade count, and more blades generally look better. This usually creates more pleasing results than shooting into the sun at a wide-open aperture thus creating a big yellow blob in the sky.  In this scenario you are going to need a LOT of power.  WAY MORE than most standard flash-heads will provide.  These are the times for bringing out the studio strobes.  And if you are on a tight budget, there are several affordable options.  I use the Alienbees B1600 with a vagabond battery pack, but there are many great options out there.  Total price: Roughly $560.  For the shot above I had an Alienbee ringlight and a B1600 both set at full power.  At f/16 they were still not powerful enough to light this whole room, especially with the B1600 bounced off the ceiling.  I lowered my aperture just a bit to f/14 which still allowed a fairly starred looking sun.  I also could have added one more B1600, and kept my f/16 aperture.

This should be enough information to give you a head start.  Whatever you do though, do not forget:  flash is controlled by aperture!  Please comment below if you have any questions.


deciblast said...

I understand how to start with a basic exposure sans flash and then build it in. But I'm having a hard time understanding how aperture affects the flash and shutter speed affects the ambient. Any suggestions on how I can make that more clear? Why wouldn't aperture and shutter speed affect the ambient exposure?

Connor Walberg said...

Hi Deciblast,

Aperture will have some control over the ambient exposure, not as much as the shutter speed though. However, because flash has such a short duration, it is almost 100% exclusively controlled by the Aperture. Therefore, aperture controls flash, and shutter controls ambient. Please let me know if this helps, if not, write in again and I will find another article for you.

Thank You,

Olin Redmon said...

Have you tried putting the single AB1600 in different locations and layering in the results in Photoshop?

Post a Comment