Digital Photography the Magic Revealed

Digital Photography the Magic Revealed

The large field of view of a wide-angle lens makes it useful for photographing installed work in a gallery.

by Steve Meltzer

Courtesy of The Crafts Report
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Arthur C. Clarke, author of 2001: A Space Odyssey , once wrote, "Any sufficiently advanced technology is indistinguishable from magic." and wow was he ever right.

This was driven home at a weeklong digital photography workshop I recently taught. Participants came with a wide variety of digital cameras--everything from big digital reflexes to small pocket compacts. And to my surprise, no one had an idea how they worked. They just turned them on with the big dial to AUTO, snapped the shutter, and abracadabra, the cameras took pictures. While this camera magic worked for ordinary folks, when it came to photographing crafts, my students realized they had to learn how the magic worked.

That's why I spent the first day of the workshop explaining to my students the magic spells--the techniques and terms--that would make them better magi-cians/photographers. It was out of this experience that this column and the next one grew. So put on your favorite magic cap, grab a magic wand, sit back, and read on.

The Lens Captures the Light

We see things because our eyes sense the light reflected off of them. Lenses like our eyes capture this light, modify it, and send it to a light-sensitive device, the sensor. So the starting place is to understand the camera lens, which is perhaps the most important part of any camera. Basic lens terms are: focus, focal length, and aperture.
1. Focus. To get the sharpest image on the sensor, the lens elements must bend and organize light. They do this with tiny micro-motors inside that move one or more of the glass elements. The motors are controlled by the camera's autofocus system, which tells the motors how to move and when to stop.

2. Focal length. This term relates to the distance between the lens' back element and the sensor. It's important because it tells us how much of a scene the lens sees--its angle of view. Measured in millimeters (mm), lenses range from super-wide-angle 8mm fisheyes to the extreme telescopic view of a 1200mm telephoto. Cameras usually come with multi-focal length (or "zoom") lens, which can be very handy for general photography.

Focal length lens markings can be very confusing. For example, a "50mm lens" on a "full-frame" DSLR has an angle of view of 46°, but when used on a smaller "4/3" sensor camera its view is 25°, or about half that. Confusing? Yes. To reduce the confusion, lens focal lengths are given in terms of their 35mm equivalent. This means the 18-55mm zoom lens sold with many cameras is described as 28mm-90mm 35mm equivalent. I told my students the magic focal length for crafts photography is 90mm (or 100mm 35mm equivalent). With a lens like a 18-55mm zoom, 55mm will give them the best shots of most objects.
Focus Lever Cameral Lens

A lever like this one tells the lens motors to change their focal length and thus their angle of view. * Amazingly, there are 16 million pixels on this sensor.


3. Aperture. The aperture is an adjustable diaphragm in the lens that regulates how much of the light reaches the sensor. Apertures have measured intervals called F/Stops: F/2, F/2.8, F/4, F/5.6, F/8, F/11, and F/16. As the aperture number gets larger, the aperture opening gets smaller. Most lenses optically work best at around F/8 and F/11. Aperture settings control the picture's depth of field, or how much of the area around an object is in focus. There is some magic thinking here because the smaller the aperture opening, the bigger the field of sharpness. And in crafts photography, the magic number is an F/8 or smaller opening. Aperature Ring on Camera

On this lens, the aperture can be set by moving an aperture ring to the F/Stop you want to use.


The "Shutter" Lingers On

Using a 200mm Telephoto lens

A long telephoto 200mm lens lets me focus on a small section of a large work.

Exiting the lens, light enters the camera and heads toward the sensor. In a digital reflex camera (DSLR), it is blocked by a mirror that bounces it up into a penta-prism/viewfinder for viewing and framing. When the picture is taken, the mirror flips out of the way and the light reaches the sensor.

In film cameras, light was blocked from the film by a shutter--a clockwork device of fabric curtains or metal blades. When the "shutter button" is pressed, the shutter opens for a preset length of time called the "shutter speed," which is denoted in fractions of a second (like 1/4 second or 1/125 second).

The term exposure refers to the combination of the aperture controlling how much light reaches the sensor while the shutter controls for how long. Correct exposure is the amount of light that produces a photograph with texture in its highlights while retaining detail in the shadows.

Although we still talk about shutter mechanisms, most cameras no longer have them--exposure time is controlled by an electronic signal from the camera's exposure metering system. In mirrorless cameras without anything blocking it, light constantly reaches the sensor and an image is always available on the LCD screen or viewfinder. This is called "live view."

Sensors Again

When it comes to digital photography, there is nothing more hotly debated than sensors and their physical size, construction, and pixel count. There are big sensor advocates and small sensor champions and manufacturers locked into a competition to jam more and more pixels onto their sensors. Over time, this debate has lost its relevance, as most modern digital cameras can produce great pictures.

Sensors have millions of incredibly tiny photocells called pixels (PIX ELements) on them. These pixels turn light into electric signals that are sent to the camera's Central Processing Unit (CPU). There are sensors the size of film negatives and sensors smaller than a dime. Another confusion is despite their size difference, both can be packed with 12 or 16 million pixels (16 MP).

The pixels on small sensors are more tightly packed together than on large ones. They are shaped like thin, round cones while on large sensors, they look more like flat mountain buttes. Flatter pixels gather light better than pointy ones, so they work better in very low light at high ISO. ISO is the universal standard for light sensitivity and the bigger the ISO number, the greater the sensitivity of the sensor or film. This gives large sensor cameras an advantage when it comes to shooting a high school football game at night, but is not any particular advantage in a well-lit crafts studio.
Using a Wider Aperture Causes a Narrow Field and the Backgroud Goes Out of Focus

Using the lens at its widest open aperture, the depth of field is very narrow and the necklace chain goes out of focus.


The CPU

The information from pixels is an analog electric signal--the stronger the light falling on one, the stronger the signal. But when this signal gets to the CPU, it is converted into digital information by magic spells called algorithms that make everything in the universe a string of 1s and 0s. The CPU saves this digital infor-mation as either a RAW or a JPEG image file. A RAW file is just that, the raw unpolished data from the sensor. The RAW file is large and has to be edited in special software before it can be used for the Web or printing. A JPEG is different. In creating the JPEG, the CPU incorporates the photographer's choice of color type and white balance and compresses it into a small file. JPEGs are universally standard and readable by all sorts of devices. Photographers are divided about RAW and JPEG because in the early days of digital photography, RAW files were far better. Back then, JPEGs' algorithms often produced files that exhibited problems like color shifts and splotchy contrast. But that's an old story and today's JPEGs are, for most uses, equal to RAW files.

The Proof Is in the Photos

To demonstrate that concerns about sensor size and megapixel counts are overrated, toward the end of the workshop I brought the class six 11" x 14" prints. Each photo had been taken with a different camera, ranging from a very old 8 MP camera to a current 16 MP model. I challenged them to determine which camera took which photo. After a few minutes, they gave up, surprised at how hard it was to tell the images apart. That was a magic teaching moment to say the least!


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