Strobist: Apparent Light Size

So this week's assignment is about apparent light size. The last two assignments were about putting the light somewhere, now we're dealing with how big the light looks to the subject. For this exercise, I bounced the flash off of the wall. The first image, the flash head is zoomed all the way out to 24mm:

The second image, the flash head was zoomed all the way in to 105mm, causing the light to be a much tighter beam pattern:

The difference between the two images? Notice how "quickly" the shadows come in with the smaller light source. I'll over-generalize and say that big light source = softer shadows.

I also had a bit of a mini-epiphany about aperture and strobist photography. I'll often see people writing about adjusting aperture to brighten up an image when using flash. I always shoot in manual (I know, I'm a photography caveman, etc etc), so this concept was odd to me. I kept thinking "you could adjust aperture or shutter, shouldn't matter." Until today when I realized that a strobe only fires for 1/1000th of a second or so. The shutter speed doesn't matter at that point. The choices you have when adjusting brightness of the exposure using strobes are:

1. Adjust the aperture to allow more or less of the 1/1000th second flash of light to hit the recording medium (digital sensor or film emulsion). This, of course, affects depth of field too.


2. Adjust the power of the strobe up or down. This is limited by the highest and lowest power available on the strobe, distance between subject and flash, and other factors.


3. Adjusting the shutter speed will only affect the ambient light visible in the image. Faster shutter speed means less ambient, and slower shutter means more ambient light. If you're shooting anything that moves, blur becomes a factor with slower shutter speeds, intentional or not.


4. Change the ISO.