What is focal length..?
If you google focal length you will find thousands of explanations as to what it really means, most are very technical and go into superficial detail, that i feel confuse the issue and leave you with no better understanding.
My explanation below is for the general photography enthusiast who would like a brief overview, but a clear picture in their head. Some will argue my explanation does not cover all the technical issues and mathematics…. you are right… it doesn’t.. !! but in my opinion you don’t need to know this, my overview will give you the basics you need.
Right then here we go…..
When you decide to buy a new lens for your camera, you are not short of choice. You will probably already have a good idea of what lens you want, maybe a zoom for wildlife photography or a wide angle to capture landscapes. The two main factors (although there are many, including price..!!!), will probably be the focal length and the lens speed.
In this blog we shall discuss the focal length.
So lets say you have decided you need a 28mm wide angle lens…. what does the 28mm really mean…? and what do they mean by wide angle.?
The 28mm is a measurement; it is the distance from your camera sensor (in the body of your camera) to the point of focus in the lens.
This distance will establish the angle of view (or field of view) from the lens. What does that mean…?
The field of view is the extent, far left to far right of what you can see in the horizontal plane. Your eyes, when looking straight ahead have an approximate field of view around 55 degrees.
When you fit your 28mm lens the horizontal plane, field of view, will be 65 degrees, therefore a wider angle fitting more content in your picture from far left to far right.
If we now change the lens to one with 100mm focal length, this would change the field of view to 20 degree, meaning a much narrow angle and less content from far left to far right.
So really all you need to know is that the focal length value of a camera lens, say 28mm, is a measurement which determines the field of view (angle), meaning the extent (far left to far right) of the content in your image.