UNDERSTANDING CAMERA LENSES
Types of Camera Lenses
In photography, there are generally 3 types of lenses - normal lens, wide angle lens and telephoto lens. There are other specialized lenses like fisheye lenses and macro lenses but I won't talk about them in this lesson.
A Normal lens got its name because it has the same field of view as what our own eyes would normally see. In full frame digital sensors, a normal lens has a focal length of 50mm. In a normal lens, all the elements in the scene would appear the same way our eyes see it. The distance of the elements will be the same distance that we see with our own eyes. The size of each element would appear similar to the size of the elements we will see with our own eyes. So just think of a normal lens as taking a photo of the same view that our eyes are seeing. See example image below.
For digital SLR cameras with cropped sensors, the focal length to achieve the normal field of view will be different. Multiply the crop factor of the sensor to the lens' focal length to get the actual field of view. For example, on a Nikon D40 which has a crop factor of 1.5, a 35mm lens would be around the 50mm field of view on a full frame sensor.That is, 35mm x 1.5 equal 52.5mm. Refer back to Focal Length on Full Frame and Cropped Digital Sensors.
Wide Angle Lenses
Lenses that have a wider field of view than a normal lens are considered Wide-angle Lenses. For full frame DSLR camera sensors, lenses that have focal length less than 50mm are considered wide-angle lenses. So, a 35mm lens is a wide angle lens for full frame sensors but as noted above, a 35mm lens can be considered a normal lens for a cropped sensor cameras like the Nikon D40.
As shown in the example photo below, a wide angle lens does not show an image that is equivalent to what we normally see with our own eyes. First of all, the angle of view is much wider than our eyes' field of view. Secondly, the distance and the size of the elements in a wide angle photo is an exageration of what our eyes normally see. In other words, objects that are closer to the wide angle lens appear even closer in the photo while objects that are farther away appear even farther away that what our eyes would normally see. Similarly, objects that are near appear bigger than what we would normally see with our eyes while objects that are far appear smaller. Wide angle lenses are also notorious for distorting near objects making them appear out of the ordinary or abnormal.
On the other side of the spectrum, lenses that have a narrower angle of view compared to the normal lens are generally considered Telephoto Lenses. Just like a telescope, a telephoto lens makes object appear closer than they really are. On a full frame digital SLR cameras, a typical example of the telephoto lens are lenses with focal lengths of 70mm, 100mm, 200mm and up.
Prime Lenses and Zoom Lenses
Prime Lenses are lenses that have a fixed focal length. Zoom Lenses are lenses that have variable focal lengths. Zoom lenses are now widely used because it normally comes with the camera when you purchase a new digital SLR camera. Some zoom lenses cover all focal length ranges from wide angle to telephoto like a 18-105mm zoom lens. Some zoom lenses are just wide angle like a 10-24mm lens and some are just telephoto lens like the 70-200mm lens.
Obviously, the advantage of zoom lenses comes from its versatility. A multi-range lens like an 18-105mm would be perfect as a walk around lens. It covers pretty much most of the angles you need on a daily basis so it would be very convenient to have.
Prime lenses generally produces better quality photos, a wider maximum aperture (f/1.4 or f/2.8) and can be cheaper also. Prime lenses are also much lighter than its equivalent zoom lens (e.g. a 50mm prime lens is lighter than a 50-200mm telephoto lens).