I talked about how you can control the exposure of the ambient light and the strobe independently of each other. Shutter speed affects only the ambient, so you can set the brightness of the background or parts of the photo not lit by the strobe exactly how you want it.
Adjusting aperture affects both the ambient light and the strobe light. I don't think I explained why this was however. An aperture is a diaphragm that gets bigger or smaller depending on what f-stop you want. f2 is larger than f16, and therefor it lets in more light. The aperture is not selective as to what light is lets to the sensor. All light must go through it to the sensor. So when you stop down (close the aperture down to a smaller size, but higher number), you restrict both the light from the strobe and the ambient. This can be used to darken the whole image, or to control the strobe output if you compensate with the shutter speed.
Here's an example of how you can play with balancing the exposure with your camera of your scene of strobe used in conjunction with ambient light, without touching the power levels on the strobe.
These two photos were taken under the same lighting, but with vastly different results.
Aside from the obviously change of a normal lens to a fisheye, what else do you notice?
You're right! The second photo is different in that background is blurred, but the foreground is not! How is that possible you ask? Strobes and shutter dragging.
The first photo was taken with a high shutter speed. This froze everything, background and subject. The strobes further stopped the motion, as they have essential a shutter speed of at least 1/250 of a second.
In the second photo, I slower the shutter speed to around 1/2 of a second. But this overexposed the crap out of everything. So I had to stop down the aperture to compensate. Say maybe from f2 to f8? Don't remember exactly. Not the point here though. Continuing, after I got my exposer for the ambient light right, I was left with a very blurry image. Why? Because my strobe had a power output set for my wide open aperture, not my stopped down, light restricting one. To solve this, I did two things. I put on a wide angle and moved everything, lights and camera, closer to the subject. This way, the lights would be brighter without adjusting anything else. But not bright enough. So I raised the power setting up as must as I had stopped down my aperture, and then took it back down just a hair because I had moved closer. This yielded the correct exposer and motion freezing of my subject, but let the background blur because the strobes weren't lighting that area.
To recap, I wanted to have a blurred background, so I lowered the shutter. To compensate, I stopped down. To compensate for that, I turned up the strobes.
It's all a balancing act, everything you adjust had an effect on the image, and there's usually a readjustment of some other setting to compensate for the original adjustment. The key to photography is to slow down and think. You have a very powerful tool to capture the world exactly how you see it. Don't squander that opportunity by being sloppy.
Spelling doesn't count^
See you tomorrow.
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