Okay crowd, now it's time to step it up to the DSLR level. Some of this will still be relevant to the p&s crowd, since many of your cameras have a "manual" function where you can control things like aperture and shutter speed.*
Aperture: What is it, and why do we care?
These are aperture disks for my lensbaby lens. You can see the sizes labeled. The smaller the number, the larger the aperture (which just means "hole.") This post will be very basic, because many of these things require algebra in order to give you hard numbers regarding focal lengths.
Aperture controls two things for your image: #1 - how much light it takes to record the image. If you have a very small aperture (like f22) it lets only a tiny amount of light in to be recorded. Imagine placing that f22 disc over a light source, and trying to find your way around a room. Lesser amounts of light means the shutter (the flap over the hole that starts and stops your image recording) has stay open longer to record enough light.
If you have a big aperture, you are letting more light into the camera, and it can record your image faster.
#2 - the second thing aperture controls is the distance in your image that things will be in focus. In the diagram above left, you have a very wide triangle that lets in lots of light, but that very wide angle flattens out the area that you can have in focus. In the diagram on the left, you have less light coming in at a time, but the focal triangle is elongated. So even thought it takes more time to record the image, you also get more distance where the detail is preserved.
This perfectly in-focus area is called your depth of focus/field, or DOF.
These are important distinctions when you are deciding what kind of image you want to make. Smaller aperture (bigger f-number) will show off more detail, where the larger aperture (smaller f-number) will give you a softer, artistic feel.
The Poppets are going to help with a demonstration.f1.4, 1/80th of a second shutter speed
You can see in this image, that the front poppet is mostly in focus (I focused on her little eyeglasses.) Things in front of and behind her are blurry because my aperture is very wide, so my DOF is only a couple of millimeters deep. It took 1/80th of a second for enough light to enter the camera and capture the properly exposed image.f4.0, 1/15th second shutter
In this image, the aperture is smaller, and the shutter needed 1/15th of a second to get enough light. You can also begin to see how the DOF is affected by the focal triangle starting to become elongated. Now we have two poppets in focus.f8.0, 1/4th second shutter
f8 is a very commonly used aperture to preserve detail yet make the focal object stand out a bit from the background. It makes a very useful DOF. In my lighting for these images, I would no longer have had any chance of hand holding the camera, as my time to record the image is a full 1/4 of a second. Back to the tripod!f16, 1 second shutter,
4 poppets are in focus.f22, 2 second shutter
f22 is as small an aperture as my camera allows. You can see that all of the poppets are pretty much in focus. You should also note that it took 2 whole seconds for the camera to get enough light to properly expose the image.
Some of the really fancypants digitals now go as tiny as f32. And pinhole cameras, like the shoebox version some of you made in High School, usually has an aperture that is around f72 or smaller. You can see here that there is a large area behind my focusing point that is still clear. This is great to know for shooting landscapes where you want things in the foreground to be in focus, as well as things in the background.
Let's see now what all of this does for our teaware.f22,
you can see here that all the detail of this bowl has been captured in this image. The front lip, foot and back lip are all in focus. It's not "artsy," but it is detailed and accurate. This type of image works if you want to show the entire piece, such as if you were posting an item for sale. The downside (for me) is that you can now see specific items in the background that are irrelevant: my curio hutch, my xmas tree base, outside my windows... f8.0,
at f8.0, you can still see a fair amount of detail in the teabowl, the back lip is a little fuzzy, but still okay. Bonus, you now can't see inside my curio hutch, and the object stands out from the background just a little.f1.4,
oooh, ahhhh, ummmm... While a super wide aperture can make some great "special effects," you can see that this might be taking it a little too far. I've lost detail in nearly all of the teabowl, since the DOF is only a few mm, the foot is very blurry, and only a small half-dollar size spot on the front is truly in focus. Let's back it off just a touch.f2.8,
this is an aperture (f#) that I use a lot for tea photography, since it gives me that artsy shallow DOF that I like so much, but still lets me keep enough of the front and center detail so that people don't say "was it really meant to look like that?" (well, they might say it anyways, but that's okay.
Thus endeth the aperture lesson. If you have any questions, please throw them at me, and I'll try to lob them back.
*Photos in this post have been color corrected. For color correction, before starting, I took one image with a white neutral color card in the frame.
Then I used the tool in the photo processing software to tell it to adjust the color. It's a little bit more sophisticated way of using white balance, which we discussed on page 1 of this thread.
This is the uncorrected version: