hopefully this will not make matters worse for you. keep in mind that the light from the flash is going ot have more effect on near obects than far objecs, so if filling shadows behind the subject is the goal, your flash will make the condition worse.
the general idea for "balanced fill flash" is to use it to illuminate foreground objects to the same level your background is illuminated. the classic example is someone sitting in a window while it is bright outside. you want the rose bush outside the window to be your backdrop for this image, this is where the "balance" part figures in.
its daylight but not high noon, and you have 100 speed film. so we'll say your sunlit rose bush needs 1/125 at f11. keeping in mind your flash syync speed on your camera is limited on the top end, you need to figure out what distance from the subject ot the flash will render a correclty exposed person at that same aperture. if you set the flash to manual i think you have a guide number of about 90 on that flash. so to shoot at f11, you have to be 90/11 or about 8 feet from your subject to get enough light on them to get your f11 exposure on your subject. now the flash lit subject has the same exposure value as the naturally lit backdrop outside your window and it will look like they are essentially in the same light. this is daylight balanced fill flash.
in some conditions if your subject is in shade or indoors, it can take a very powerful burst of flash to match the ambient light on your background. if you happen to want a large aperture for a shallow depth of field, life gets bad becasue if you happen to have fast film in the camera, you are going to have to have a very fast shutter speed for the ambient light, and it may well be beyond the flash sync speed. this is why the people photographers cuss focal plane shutters that have sync speeds under a 250th, and why fully synched leaf shutters have such favor amongst portrait pros.
if you want to fill the shadows behind your subject, that is an entirely different problem for the flash, becasue it is nto going ot have a significant influence on the background compared to your subject that is much nearer. for cases like that, you have to get the flash off the camera to get the light where it needs to be, or add an additional flash to illuminate the background separately from your subject lit by the on-camera flash. indoor portraiture often involves using a flash with a lot of controlability to dial it way down and allow you to "drag the shutter." you use the flash to illuminate the subject a little bit, but still use a long exposure so the ambient light in the room will bring the background exposure within one stop or two of the subject's exposure value. an example of that is a bride posed in front of a candle holder. if you use the flash auto setting and have the shutter set to the highest sync speed, you will get the bride, but you will only see the flames of the candles behind her and maybe a few hot spots from the shiny brass holders. if you meter based on the room light and it tells you to use 30th of a second at f4 with 400 speed film, you will need a flash with an auto range that will let you shoot with an f4 aperture. put the camera on a tripod and basically shoot as if there is no flash, and the matching flash exposure ADDS TO the room light making the bride lighter than the rest of the frame. this is a contrast range that will usually hold in the print and the lab can get you a print with the smiling bride, and you can actually see the candles behind her and not just the flames.
sometimes its tricky to get the numbers to work right, but conceptually fill flash is just about matching the flash exposure on the point of interest to the ambient light exposure of the background features of interest. it can work in reverse conceptually, but it takes an off-camera flash to reverse the roles of subject and background.
2cents@large.
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