Posted on May 9, 2012 in Other stuff, Tech & internet
So I just got a new DSLR camera, and I’m unclear on what all these settings are for. These f-stop things seem pretty important from what I can tel… so what are they?
The world of photography is filled with numbers. ISO, shutter speed, focal lengths, resolution, guide numbers, and of course, f-stops. When I decided to go to school for photography, I stopped taking math classes in 11th grade since I was going to get an art degree. Thankfully, I had already made it to calculus by then, because photography is almost as much science as it is art — at least if you want to get the most out of it.
One of the most misunderstood — or at least one of the more confusing numbers in photography are f-stops, also known as f-numbers or aperture. Let’s take a further look at this camera control that seems so daunting to the novice photographer.
The f-stop is defined as the measurement of the ratio between the focal length and the diameter of the entrance pupil, where light enters the lens.
I’m sorry, I’ll wait a minute while your head stops spinning and you choke that one down.
While that definition would thrill my sophomore year Materials and Processes of Photography professor (whose name escapes me at the moment, but it was over 13 years ago now), it probably doesn’t help you much at all. There’s plenty of sites out there that go on and on about the mathematics of the f-stop and detailed explanations of where the numbers come from and all that hocus pocus that was crammed into my brain in a windowless room of a large brick building all those years ago.
This will not be one of those sites. Let’s keep this simple and accessible.
A photograph is simply capturing light reflecting off of objects. On that note, the f-stop (or aperture) is the number representing the size of the opening in the lens — thus controlling, in part, how much light makes it to the image sensor of your camera (or film, if you’re old school). The shutter speed, or how long the shutter remains open is the other variable controlling the amount of light, but we’ll leave that for another answer.
So. Bigger opening = more light. Smaller opening = less light. Seems rather straightforward, right?
Here’s the catch: The smaller the f-stop number, the larger the lens opening is. So f/2.8 lets in more light than f/4 does.
Why? Who cares. It doesn’t matter. Seriously. I could go on to write an entire essay on the relationship between these numbers and bore you to tears, but it’s not important at a basic “I want to make good photographs” level. Just remember — small number = big opening, and big number = small opening.
So no problem. Now you know which way to turn the dial when you need more light coming in the lens. There’s a tradeoff here, however. You see, how big that lens opening is also dictates how much of your photograph is in sharp focus. This is called depth of field, which I’ve discussed previously in my answer about bokeh.
The relationship here can be expressed simply as well. Larger opening (smaller number) = shallower depth of field. Smaller opening (larger number) = deeper depth of field.
So… what the heck does that mean?
Well. If you want to take a portrait of a person, you really only want their face in focus — if you can see the details on the tree/house/mountain/porta-potty in the background, that’s distracting. You want the face sharp but the background blurry. So you use a larger aperture (smaller f-stop number!) to keep just the small area between the nose and the ears in focus, causing the foreground and background to be blurry. If you want to take a picture of a landscape and want everything from the bushes at your feet to the mountain 30 miles off in the distance to be in focus, you would use a smaller aperture (larger f-stop number!) to ensure everything is nice and sharp.
You must keep in mind that you cannot adjust aperture without also correspondingly adjusting shutter speed (or ISO, but let’s keep this simple for a moment). Letting less light in? You have to leave the shutter open longer to compensate. Letting more light in? You have to speed up the shutter to compensate. Again, we’ll leave a detailed discussion of shutter speed for later, but do remember that they are always connected.
The good news is, modern cameras will let you play with one or the other, while automatically taking care of the one you aren’t playing with. If you’re interested in playing with the aperture to see what it does, set your camera to “aperture priority” mode. You can pick whatever f-stop you choose, and the camera will choose the correct shutter speed for you. If you own a Canon that’s “Av” on the big dial, or “A” if you have a Nikon. Of course, RTFM if you’re still not sure, or if you happen to own a brand of DSLR I haven’t touched in more than 5 years.
I can explain all this until I am blue in the face — or fingertips, I guess, since I’m typing — but nothing is going to teach you better than experience. I remember one of my old professors’ first assignment was to go and shoot a minimum of ten rolls of film between class on Thursday and Monday. That was an expensive assignment in the film days.
You don’t have to pay for film and processing anymore. Digital images don’t cost anything — you already paid for all that when you bought the camera and memory card. Get out there and experiment. Play with stuff. See what works, see what doesn’t work. You don’t even need to keep a notebook handy to compare your settings from shot to shot anymore — the camera embeds that information in the image file!
So go forth, shoot lots, and don’t be afraid to play with those settings. Mistakes don’t cost anything and the knowledge is priceless.
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