Using flash outdoors on a bright day can greatly improve your photos. The sun is a harsh light source and creates photos which have high contrast. Also, you have deep shadows in addition to the vivid colors. with all these contrasts, exposure can become difficult – exposing the highlights will make you lose the shadow detail while exposing for the shadow detail will blow out your highlights. In the photo of the two ladies on the right, you can see them clearly because the day is bright but without flash, the background is a little washed out.
To balance the light levels you should use your fill flash (also known as fill-in flash). It brightens your photo since it is lit from behind (remember how to make outdoor portraits?)
In the photo of the man and woman on the left, you see more of the background because the flash was turned on and the light coming from the sun was neutralized. Moreover, the glare actually created a more artistic effect on the photograph.
The best way to avoid the problems of direct flash is through the use of bounce flash. Here, you will have to angle your flash units so you can create a soft, diffused light which is perfect for portraits. This will also help you prevent red eye and eliminate reflections.
Unfortunately, bounce flash is not as easy as it sounds. Before you use this method of flash photography, you will need to visualize the angle of the light. If you point the light to the ceiling, where will the light fall? At what angle will it hit your subject? You need to make sure that the light does not drop down too far in front or behind your subject.
Also, you need to keep in mind that if you make the light bounce off the ceiling, then you will lose some of the illumination. If you are using a dedicated flash with TTL (through the lens) metering, then you don’t have to worry about correcting your image. However, if you are using a manual flash, you will need to adjust your aperture in order to correct for the light loss.