Off Camera Flash – Blog post 1 of 3

Alienbees 1600 Manual Flash

You are ready to take that next step in photography—getting your flash off the camera.  Today there are basically two directions to choose: 1) Manual Flash or 2) TTL Flash.

When I made this jump there was only the one choice of “Manual Flash.”  If I were starting over and having to make that decision it would be very difficult one to make.

Nikon SB900 TTL Flash

This first blog post will give you an understanding how each system works.  In the blogs following this I will go into the advantages each system has over the other.

Manual Flash

There are 3 settings on a camera that impact the photo when you push the shutter with flashes.

  1. ISO – This is the light sensitivity setting.  The lower the number the more light is needed to make a good exposure and conversely the high the number the less light is needed.  As a general rule the lower the number the less noise in a digital image, so the idea is to always pick the lowest number you can.
  2. Shutter Speed – this is what controls how long the shutter stays open.  The longer the more light that will reach the sensor and the shorter time will decrease the amount of light on the sensor.  The longer the shutter stays open the more existing light will be factored into the exposure.
  3. Aperture – This is what controls how much light is passing through the lens to the sensor.  This is an algorithm that is expressed as a fraction.  The number you see is actually the bottom number of the fraction.  The larger the number the smaller the opening.  Think of it like getting a piece of a pie.  If you get 1/8 of the pie you have a lot less than the person getting ½ of the pie.

If you had the camera set to take a perfectly exposed and in focus photograph and then added a flash, the flash will most likely over expose the photograph.  You must take into account the flash output to get a well exposed photo.

The easiest way to know what the settings on your camera will be with a flash is to use a flash meter. 

To keep everything simple, we will first use a room that is totally dark.  If you stand where the subject is and fire the flash you can use the meter to tell you what to set your camera.  You need to tell the meter two pieces of information:

1) What is your sync speed?  What is the fastest shutter speed your can take a picture with a manual flash?  This will be in your owner’s manual.  Many cameras use 1/125 or 1/250 sync speed. 

2) You need to tell the meter what ISO you will be using.

flash meter
Flash Meter

Once those settings are put into the flash meter you just need to put the incident dome facing the flash and where the subject will be sitting or standing for a portrait.  You can plug the sync cable into the meter to trigger the flash or a different mode letting you just first the flash and it will sense the flash.

After you fire the flash the meter will tell you what f/stop or aperture to set the camera.

TTL Flash

To figure all the above you just put the camera flash on TTL mode and take the picture.  You will pick the aperture on the camera and the camera will tell you if the photo is under or over exposed.  For all the same reasons your camera may over or underexpose photos without a flash will be pretty much the same reason it does it with a flash.

Check back for more posts on flashes.