Happy Labor Day! I hope you are enjoying your day off and if you didn't get the day off, I hope you find some time to relax.
I wrote a post a while back all about how to get that sweet, blurry background in photos (check out that post for more information on blurriness/bokeh/aperture). That blurriness is called bokeh. It's a pretty easy trick. Just keep your aperture or f/stop number really low.
I took a few quick pictures this morning to demonstrate how that works. I have a 50mm/f1.8 lens (I highly recommend it if you are on a budget but still want a quality lens). What this means is that the lens has a fixed focal point of 50mm and that the aperture can open all the way to f/1.8 If you are lucky enough to have a 50mm/1.2, then your aperture opens all the way up to 1.2, which is awesome!
You can see in the first two pictures that the background is nicely blurred. You eye isn't drawn to the background, but rather to the subject. I was able to keep my ISO relatively low (400 is pretty low for inside the house). The second number-the fraction-represents the shutter speed I used. The first picture is 1/30th of a second, which is fast enough, although ideally I'd like to keep it above 100.
If you are really wanting your subject to be the star of the photograph, then f/22 is too high of an aperture number to use.
Also notice that the higher aperture number used, the higher I had to set the ISO. I was barely able to take a picture with an aperture of f/22 because even with the ISO set to 6400, the shutter speed was only 1/6th of a second, which is really too slow to use without a tripod.
In the picture below, I used a low aperture number, which kept the flower in focus but blurred the background and got rid of all distractions. This makes for a much more visually pleasing image than if I had kept the entire picture in focus.
Will I ever need to use a high aperture number?
Yep! There are plenty of times when you will want a high aperture number.
In this landscape picture, I wanted the entire scene to be in focus. I did not want an ounce of blurriness.
I set the aperture to f/22, which also helped create that sun flare.
What happens if you mess up?
In the picture below, I had the aperture still set to a low number. I believe it was set to 2.2. I focused on the moon in this shot. See how the top of the picture is in focus, but the ferry is slightly blurry? That wouldn't have happened if I would have set the aperture to a higher number.
When shooting in manual mode, you get to control whether the entire picture is in focus or if just one part of the picture is in focus.
Just remember this:
Low number = blurry background (bokeh)
High number = clear, crisp picture