What is Focal Length?
Long story short, focal Length is how zoomed in the image will appear and is always measured in mm. The lower the mm number, the wider the angle of view is and the more of the scene will be in your photograph.
The actual meaning is the distance between your lens and the camera’s image sensor when your subject is in focus. While zoom lenses do tend to be longer, the length of the actual lens doesn’t mean anything.
What use will my focal length be?
10-28mm = Ultra-Wide Angle Lenses
These lenses are mostly used by landscape photographers to get as much of the scene in front of them into the shot. They can also be used by interior photographers to get as much of the room in the picture as possible.
28-85mm = Normal Lenses
These are generally found on most cameras from phones to DSLRs. As you get towards the end of this focal length, around 85mm, these lenses get used more by portrait photographers
85-300mm = Telephoto Lenses
These are usually used by wildlife and sports photographers. It makes the most sense for these to be used by people who need to stay far away from their subjects so they don’t get run over or mauled.
300mm+ = Super Telephoto Lenses
Use mostly by wildlife photographers.
What is crop factor?
Manufacturers make a number of different type of sensors, there are full frame, medium format and crop sensors. Full frame sensors are the same size as 35mm film and crop sensors are a smaller size. When a crop sensor is using a lens made for a full frame sensor it will magnify the image. There are many types of crop sensors and depending on how much it magnifies the image, is the sensor’s crop factor. A sensor could have a crop factor of 1.6, so when a 14mm, which was intended for a full frame is attached, you end up with a 22.4mm (14 x 1.6).
