There are any number of opinions and thoughts about what constitutes photography. You do not need another one, so instead, I will talk a bit about equipment. The basics of what does what and such.
Disclaimer: I am using basic terminology and concept. For more complete understanding, follow the hyperlinks or ask my friends, Bing and Google.
First, the sensor. To understand the differences in sizes, here is a comparative chart. The bottom row represents the majority of pocket cameras. Most camera phone sensors are considerable smaller than this.
Sensor, Part 1 – Gathering light
The larger the physical size of the sensor, the more light gathered. The more light gathered, the greater the tonal range. Meaning more dark greys before descending into darkness and more light greys before disappearing into white. More information to use. And less noise, AKA grain. Less colour weirdness. Why is this important? No information captured, no chance of using that part of the image. Noise, contrast, distortions and aberrations can be added, but removing these? Not nearly as easy, not always possible.
Sensor, Part 2 – Depth of field
The smaller the sensor, the less control of depth of field. Depth of field is the area in front and behind of the focus point that is also in focus. Smaller sensors result in a greater depth of field for the same aperture. To the point that achieving blur is difficult. More on this later.
Sensor, Part 3 – Megapixels.
Pixels count is confusing. More is not inherently better. It is a relationship between sensor size and design. Larger sensors typically have the advantage here. The more pixels for a given sensor, the smaller the pixels will be and the less accurately the information gathered.
Controls
The more control, the more one can affect the image. Simples.
Controls – Aperture
The aperture is a diagram which controls the amount of light passing through the lens. It also affects depth of field. The larger the opening, the more light of course. But also the less depth of field. The smaller the aperture, or f stop, the larger the number. f 22 represents a smaller opening than f2. It is a mathematical ratio, not a fixed number.
Controls – Shutter speed.
This is measured in seconds. The larger the number, the longer the shutter is open. The more quickly the shutter opens and closes, the less blur, but also less light.
Controls-ISO
ISO is a measurement of sensitivity. Essentially, the higher the ISO, the more sensitive to light the sensor is.
Controls – Aperture and shutter speed combinations.
For sport, one generally wishes a fast shutter speed to “freeze” the action. This requires using a larger aperture. This also results in a blurred background, so the same combination is often used for portraits. Or anytime one wishes to separate the foreground, mid-ground and/or background. In landscapes where one wishes more to be in focus, a smaller aperture is used and therefore a slower shutter speed. Here is a page showing a bit of this concept.
Lenses
Everything in small format cameras, DSLRs, pocket cameras, and smaller, references 35mm equivalent. This is because 35mm was the most prevalent film format used prior to the advent of digital photography and, with sensors varying so much, a common frame of reference is needed.
Lenses – Focal Length
The focal length is the distance between the front of the lens and the point of focus. Small number = wider angle, larger number = greater magnification. Wide angle lenses allow for more area side-to-side to be covered, but also make objects appear smaller, farther away fro the camera and farther away from each other. The wider the lens, the greater the depth of field possible. The larger, (more telephoto) the lens, the closer things appear to the camera, the closer to each other. More compressed. The greater the telephoto, the less depth of field.
Lenses – Zoom
The zoom range of a lens is the change in focal length. Zoom lenses allow for greater variation in how a photograph is taken without changing lenses or moving. The trade is quality. The greater the zoom range, the lower the quality of image. In order to gain back some of the quality lost, much engineering is needed and better material used, therefore greater cost.
There is more, of course, but I will end for now. One piece of editorial comment before I finish.
The photographer/artist is the most important part of the equation. This is true. Learn to use what you have to the best effect. However, the kit can matter very much. It is dependent on your intent and requirements. One can create a great image with almost anything capable of capturing information. But no one can create any image with any piece of gear.
To put it simply, anything one can make with an iPhone can be made with a DSLR. The reverse is not true.
mad monkey Ramblings 
