Fred Parker explains how to use your brain to compute exposure. One step up in complexity from my little rant on the subject, with the added bonus of actually being useful.

Also, another better article about what to do with your camera set to ‘manual:’ Hyperfocal and zone-focusing techniques. After reading this, and using one of the many online depth-of-field calculators, I learned that with the widest zoom at f/8 and focused at 3.4 ft, my camera has an acceptable depth of field from around 1.4 feet to infinity. I’ll need a tripod, though.

Alice mentions not knowing much about the intricacies of photography, but still being able to make good photos. And she’s right. It’s good to have a little device you can point at an object and automatically steal its soul.

But I was thinking about it, and it seems to me that the basic concepts of photography aren’t that difficult to understand, and knowledge of these concepts can really help you take better pictures.

So with that in mind, I thought I’d present a discourse on the most basic basics of photographic theory, as I understand them.

The Lens

Here’s what a lens does: It takes light coming in and focuses it on the film plane (or CCD, in the case of digital photography). Light entering a lens is flipped upside down and backwards, in terms of the image you see. The point at which this flipping occurs is called the focal center of the lens. This is usually somewhere in the middle of the lens barrel.

Light that happens to hit the front of the camera lens falls through the lens and gets bounced around a little bit, reaching a point where all the light crosses paths (the focal center), and then continues its same trajectory until falling on the film.

Lenses are like funnels for light, and the narrow end of the funnel is the focal center.

This focal center is important, for a bunch of reasons. The most important is that the distance from the focal center to the film is called the focal length of the lens. So if your camera has something like ‘f = 40mm’ written on the lens, then it’s 40mm from the focal center (in the center of the lens) to the film plane (on the back of the inside of the camera).

Now, that’s the focal center and focal length. Next is the aperture.

The aperture is a little round opening through which the focal center passes. It’s like a choke on a car; you can open it up and let more gas through, or you can close it down for leanness. Opening the aperture lets more light through, obviously. Closing it does what? Yes, that’s right, it lets less light through.

Back in the good old days when ‘instamatic’ meant ‘portable tripod made of wood,’ photographers would use a sheet of wood or metal with a hole in it for the aperture. They’d have a number of these sheets, called ‘stops,’ with different diameter holes, each for different situations. Going back to the last section, we know that ‘f = 40mm’ means the focal length is 40mm, so it stands to reason that ‘f’ refers to the focal length. If we put a stop in the focal length, we then have… an f-stop.

The term f-stop is still used, even though the stop itself has ceased to be a chunk of wood and is now a finely-machined sphincter valve for light, which would amaze you if you were to ever see it outside a lens. But the term remains.

When you see an aperture reading on a camera lens, or written beneath some photo you admire where the photographer is telling you what the settings were, it’s expressed as a fraction: f/some number, like f/2.6. That’s because the only real way to express aperture is in terms of the focal length of the aperture; different focal lengths with the same aperture can yield different results.

So we now know that the aperture changes the amount of light which reaches the film, but there’s another effect it has on the light in the lens: Changing the aperture changes the depth of field of the lens. As you close the aperture, the depth of field increases. This means that more stuff will be in focus, regardless of how close or far away it is. Within reason, of course. A wide aperture limits the depth of field to whatever specific thing the camera is focused on. So if you’re taking a picture of someone standing on the rim of the Grand Canyon, you want a smaller aperture so both your friend and the other side of the canyon are in focus. This is why your point-and-shoot camera has a ‘mountains’ setting.

Naturally, if you want a big depth of field, and you’ve closed the camera’s aperture, then you’ve also reduced the amount of light coming into the camera. This means you have to have film that’s super-sensitive to light, or you have to increase the amount of light reflecting off the subject. Or you could increase the length of time the film is exposed to the light. By changing…

Shutter speed.

The shutter controls when the film will be exposed to light. It opens and closes for a set period of time. If you tell it to stay open for 1/4-second, then 1/4-seconds’-worth of light comes in and exposes the film.

Now, the film is like a rechargable battery (an analogy that will fall apart under careful scrutiny, but work with me, folks). It stores energy that comes to it. If you don’t send it enough energy, it won’t store it, depending on how efficient the battery is. If you send it too much energy, it ‘blows out.’ Right? Right.

So light is energy, and you’re sending the light energy to the film. If the shutter is open for too short a time, then the capacity of the film to store energy is wasted, and the exposure is dark. If the shutter is open for too long, then the white parts of the exposure are really, really, white, and the dark parts are also really, really white.

This is why you want to make sure that the shutter speed is not too fast, and not too slow. Moderation in all things, including shutter speed.

Now, the very thing you’re trying to avoid by buying an easy-to-use camera is learning what I’m about to tell you: You can only take a technically-competent picture if you can balance the demands of lens focus, aperture (and thus depth of field), and shutter speed. You want to point and shoot and not have to deal with this, but here’s the good part: If your camera has any manual settings at all, you can change only one of these things and let your camera compensate for it by adjusting the others.

For instance, if you have a camera like mine, you can put it into aperture priority mode. This means you’re free to change the aperture, and the camera will do whatever it needs to do in order to take a decent picture. In the example of the friend on the rim of the Grand Canyon, you might experiment with narrowing your depth of field and focusing only on your friend. You’d have to change the aperture to do this. So you switch to aperture priority, crank open the aperture, and let the camera figure out exposure. Or, if the sun has set, and there’s not much light, you could open the aperture and let more light in that way, and thus maybe avoid the need for a flash.

If you read this far. Congratulations. Here’s your reward: A link to a picture I really like, that couldn’t have been taken with a point-and-shoot camera.

I don’t know if you know this already, but the essentially gnarly Rudy Rucker is the current guest ‘blog on BoingBoing.net.

Imagine if science were a drug. An hallucinogen. Rucker is there to put the tiny tab of LSD (Like, SCIENCE, Dude!) on your tongue.

Washington Trails Association volunteer opportunities.

Click for a larger verson.

This is the Snoqualmie (rhymes with ‘no-qualm-y’) River valley, near Duvall, WA, at around 2am.

A car went over the bridge at just the right moment, leaving a streak of light.

You might not believe how hard it is to find a place to park your car on E. Snoqualmie Rd. at 2am, and set up a tripod to take a picture. The picture I wanted to take would have had me pulling into a farmer’s driveway and setting up in front of his barn.

Also, the more I try to take consistently good pictures, the more I realize how lucky I’ve been.

Next day: The thing about this kind of photography is that you can’t really be sure what will be revealed. For instance, you can see the mountains behind the hills, which were completely invisible to me while shooting. If I’d known they were going to show up in the picture, I’d have composed it differently. I also thought I was framing the fence out of the picture, too. Note also the brown haze… That’s smoke from a forest fire to the south, reflecting the light of the full moon into my camera.

Next time I do this kind of thing, I’ll have to keep the 16″ exposure, stop down by half, and take more exposures. If you zoom in on the star trails, they’re very exaggerated blobs in a line, rather than a more smooth transition, but if they were stopped down, they might not blow out the CCD quite so much. I also need better software for combining the images; being a nerdy geek, I might just write it.

NASA’s Visible Earth web site.

Of interest to certain parents of mine: Deltas and Sedimentation.

And… Welcome to my watershed (picture taken from the International Space Station). See the checkerboard pattern? That’s a series of forest clearcuts. And look for the I-90 floating bridge.

I mentioned ‘For All Mankind’ a few entries back, and one of the things that struck me about that movie is how technology enabled the filmmaker to do things and say things that wouldn’t otherwise be possible. The original footage was digitally enhanced so it wouldn’t look like crap on a theater-sized screen, and, if I recall correctly, much of the audio was mastered to digital.

What this enabled was to make it artistically worthwhile to include a lot of footage that had been ignored as irrelevant in previous documentaries about the Apollo mission. We see the astronauts going up the gantry in an elevator, experiencing both how high up and how devoid of fanfare it really was. Another example is the camera located in a jettisoned stage, which tumbles toward earth.

Another technological development: Not long ago, NASA released a significant chunk of the Apollo images as high-resolution digital files. Previous to now, files so large wouldn’t have been useful to anyone, since they’d occupy a whole hard drive, so I’m glad someone‘s on the ball, and sees the opportunity.

And that’s a good thing, because now, someone has used these images to create a series of full-screen panoramic images shot on the surface of the moon. The Apollo 17 one is my favorite.

What’s a party without Polaroids?

(Which reminds me of a joke I saw once on Benny Hill: If people from Poland get Polaroids, what do people from Hemmel-Hempstead get?)