GS-DC: Testing It Out and Buying/Using Lenses

Review:

1. When things go wrong...
2. Evaluating MegaPixels
3. Digital SLR's
4. RAW vs. JPEG

Physical Review:

1. How much power is left?
2. Turning the rear screen off/on
3. Changing AutoFocus Priority
4. Locking Focus (half button push)
5. Auto Exposure (over/under expose)
6. Locking Exposure (half button push)
7. Flash Settings - Always/When Necessary/Always Off
8. File format - RAW or JPEG
9. White Balance (JPEG only)

Remember to Format Your Memory:

• When you first buy a memory card or use it in a different camera you should format it. Every camera that accepts these cards has a Format command listed somewhere in it's menus. Formatting prepares the card for use in a camera and reformatting it when you change cameras just ensures the card will be accurately written to and read in that specific camera. You may also find that formatting a card that has developed problems will also fix it. Just be aware that the Format command will erase all of the images from the card.

Meta Data:

• Information about the image can be displayed on many cameras. This information, called EXIF information or 'meta data', is stored in the image file but not the image itself. It may include the date and time the picture was taken, shutter speed and aperture used, and a small thumbnail image. Many cameras will also display a histogram and highlight (overexposure) warning. Some cameras let you select how much information is displayed so you can display it all when reviewing images and turn it all off when giving a slide show. 
• See if you can find how to display a photo's meta data on your camera

Lenses:

• The focal length of the lens or the zoom range is always shown in mm. On fixed lens cameras the zoom range is often given as a multiplier. For example, 6.0-72.0mm is 12x (72 divided by 6).
• The maximum aperture determines how wide the lens will open. It's listed on the lens as a ratio such as 1:2.4 or 1:2.8-3.7. On most zoom lenses, two maximum apertures are given because the aperture changes as you zoom the lens in and out. However, some lenses don't change the aperture as you zoom them. A larger maximum aperture is better because it lets you use shallower depth of field, a faster shutter speed to freeze action, and increases the range of your flash. A lens with a maximum aperture of f/1.4 is three stops faster than a lens with a maximum aperture of f/5.6. This means that instead of using a shutter speed of 1/15 you can use one of 1/125. The problem with lenses having large maximum apertures is that they are expensive, large, and heavy. 

• The size of filters or other accessories that can be screwed into the threads is shown as a diameter, often preceded with the symbol f as in f85mm.

Choosing Focal Length:

• The focal length of a lens has a huge impact on your images and is one of the most important tools in your creative tool box. On fixed lens cameras you change the focal length by zooming the lens. On SLRs you can do the same or change lenses. The various focal lengths you can use are referred to by synonyms that can be confusing at first.

• Wide-angle, short focal length, short lens and zoom out refer to the same thing lenses that capture a wide expanse of a scene.
• Telephoto, long focal length, long lens and zoom in refer to the same thing lenses that bring distant subjects closer.

• The focal length you choose is a creative choice because it has two effects on your images:

• Angle of view refers to how much of a scene the lens covers. Fisheye lenses, the widest available, can capture up to 180-degrees. As you zoom in or change lenses to increase the focal length, the field of view narrows and you can isolate small portions of the scene without moving closer to the subject.
• Magnification is related to the lens' angle of view. Since using a short focal length lens or zooming out includes a wide sweep of the scene, all of the objects in the scene are reduced to fit into the image.

• The impact of sensor size on focal length isn't limited to fixed lens cameras. Digital SLRs are often adapted from 35mm film cameras and use lenses designed to project an image circle large enough to cover a frame of 35mm film. When these lenses are used on a digital camera, the angle of view captured in the image depends on the size of the sensor placed within this image circle.

If your camera has a zoom ring on the lens, you can turn it during a slow exposure to streak lights.

Zoom Lenses:

• Most fixed lens cameras have a built-in zoom lens and zooms are also very popular with SLR users. These lenses are popular because they let you choose any focal length within the range the lens is designed for. Zoom comes in three varieties; optical, digital and cropping:

• An optical zoom actually changes the amount of the scene falling on the image sensor. Every pixel in the image contains unique data so the final photo is sharp and clear.
• A digital zoom, found on many fixed lens cameras, uses sleight of hand by taking a part of the image falling on the sensor and enlarging it to fill the sensor. It does this by adding new pixels to the image using interpolation. The interpolated image doesn't have as many unique pixels as one taken with an optical zoom so is inferior. In fact, you don't even need this zoom feature because you can get exactly the same effect just by cropping a normal image in a photo-editing program and then enlarging it.

Normal Lenses:

• A "normal lens" for a 35mm camera usually refers to a fixed focal length lens of 50mm or a zoom lens zoomed in a little from its widest angle. When using a lens of this focal length, the scene looks about the same as it does to the unaided eye. With a longer focal length, everything appears closer than it actually is. With a shorter focal length, everything looks farther away.

• A normal-focal-length (50mm) lens isn't necessarily the one photographers normally use. Many photographers prefer the wider angle of view and greater depth of field provided by a slightly shorter focal length.

Short Focal Lengths:

• Using a short focal length lens or zooming out gives you a wide-angle of view that lets you capture a wide expanse of a scene. This view is ideal for use in tight spaces, such as when photographing landscapes and in small rooms where you can't position the camera a great distance from the subject. A short lens also has great depth of field so it's good for street or action photographs. When responding to quickly unfolding scenes this depth of field lets you respond quickly without worrying about focus.

• Short lenses also let you focus very close to your subject, and the effect this can have on the perspective in your images can be dramatic. Objects very close to the camera loom much larger than those farther in the background. This distortion in the apparent size of objects can deliberately give emphasis and when carried to an extreme, give an unrealistic appearance to a scene.

Long Focal Lengths:

• A long focal length lens acts somewhat like a telescope in that it magnifies the image of your subject. This is especially useful when you can't get close to your subject— or don't want to. Long lenses are ideal for wildlife, portrait, and candid photography, whenever getting close to a subject might disturb it. The long focal length lets you keep your distance and still fill the viewfinder frame with the subject. Keeping at a distance eliminates the exaggerated perspective caused by working very close to a subject with a shorter focal length lens. It also helps relax your subjects if they get uneasy, as many people do, when a camera comes close. As the focal length of a lens increases, the depth of field gets shallower so you must focus more carefully. Also, a long lens visually compresses space, making objects in the scene appear closer together than they actually are. The primary drawback of a long lens is that most (but not all) such lenses have a smaller maximum aperture. This may force you to use a slower shutter speed. Also, since a long lens magnifies movement, just as it magnifies the subject, you may also have to use a tripod instead of hand-holding the camera. (They may also be heavier.)