Your flash has a ZOOM function. This allows the light to be sent “where the lens looks”. If you use a telephoto lens, why send light to the sides, where the lens cannot see? This would waste energy.
Normally, the zoom factor is set automatically, depending on the lens. Look at the back of your flash and zoom your lens just after touching the shutter button: the flash will alter its zoom as you move the zoom lens through its range. No work for you. So the light goes only where the lens looks.
But you can override this. Set flash zoom to “M” (manual). Like here: Wide lens, but I zoomed the flash in as much as I could:
See? A small oval of light.
Why would I want to do this?
- Sometimes, I do this for effect.
- Sometimes I do it to get more power: A concentrated small beam is brighter than a wide area, of course.
- And sometimes, I do it for correction.
My garage during the recent garage art sale.
Without flash, it looked like this:
The back was dark, so I needed flash. But I did not want that flash to light up the close areas, which were already very bright. Solution: zoom the flash in manually. The lens was 16mm; I zoomed the flash to about 50mm if I recall correctly. That sent light only there where it was needed.
Problem solved. More even, without overexposure of the foreground.
Opportunity Knocks: Learn everything I know. See http://learning.photography for all my photography learning books. And decorate your home or office with wall art: the garage sale is permanent. Contact me if you want to see my prints.