Lately I saw an amazing video by photographer Glyn Dewis on how to get a completely black background while taking a portrait, anywhere. This means you can be outdoors, even in the middle of the day, as you'll see in Glyn's video, and still get a completely black background for your image. This, I thought would come in pretty handy, so I decided to give it a shot. Check out Glyn's video here:
As it turns out, it's a pretty simple technique, and the results are very powerful. Take a look at this image I took of my brother's dog; Maia. Would you believe I took this in the middle of my living room?
The trick, as he mentions, is to make your ambient go completely black by using a very slow ISO (I used 100 ISO for this image) and increasing your shutter speed to the maximum sync speed for your camera/flash combo (I had mine at 1/200 of a second). Since you're using such a slow ISO, you'll want to have your flash at full power. Then, just adjust your exposure through your aperture settings and you're good to go.
For more details, I highly recommend checking out Glyn Dewis' blog post for the full walk through.
Additionally, photographer Nick Fancher wrote an awesome post, for Digital Photography School, on this same subject, and took it a step further by painting their subject black for one of the images. Talk about a challenge!