Explained- Focal Length Part I of II
Today I am here to explain the Focal Lengths of a lens. Most of us are in a dilemma about the lens to buy and what focal length to consider for purchase. But before I get into which focal length to go for I want to explain about the focal length of a lens. This is Part I of the Two part series in which I will cover the basics of focal length in detail.
Most of the beginners, graduate from a zoom lens camera to a DSLR and most of the times they ask. ” What is the zoom in this Camera” or “how much zoom x is in the lens of the camera, 21x/51x etc?”.
Okay..for those who are aware of this please get the smug out of your face (of, you know it all). So for the beginners, the answer would be: The DSLR have interchangeable lenses so you can change the lens if you want that mysterious x as zoom.
To put it simple if you want a 3x zoom then the equivalent focal length would be around 18-55 mm (the standard kit lens for any budget DSLR camera).
The very next question or explanation I get after this answer is: “Oh, I have a 21x/51x zoom in my camera why should I buy the camera with 3x”.
Well my answer to them is .. “dont buy it :)”. Well, wait… please consider the following before making your decision.
1. That is a marketing gimmick by the camera selling companies and 2. Have you ever shot with a 21x on your camera, if yes then you would have definitely seen the huge shake through your view finder. You cannot take a decent picture with that shake. The point is:
You don’t need the so called 21x or a 51x zoom
Being said that, there are different lenses which provide manageable zooms on a DSLR. So buy a DSLR instead of that expensive Zoom.
Coming back to the focal length.
Focal length is usually measured in millimeter or mm. It is not the length of the lens but the optical distance from the image sensor where the light rays converge to form a sharp image.
If you did not understand the above statement, don’t bother…
Theoretical definitions are often useless for practical purposes.
Coming to the practical explanation of focal length.
- Focal length tells us the angle of view i.e how much scene would be covered; and
- The magnification i.e. how much large the subject would be after the image is taken.
Take your Kit Lens the 18-55 lens you have got. Set it to 18mm on the camera. Look through your viewfinder. You can see the large area (though small subjects) of the scene through the view finder…Now set the focal length to 55mm you ll see some larger subjects but the whole scene is now narrowed and you can cover less angle.
To explain it further in one simple line: With 18mm you will have wide angle of view and at 55mm you have narrow angle of view.
If you have a 18-135mm lens then at 135mm you’ll see that the angle of view is even narrower.
I hope you got the basics of Focal length in this part. In the next part i.e. Part II of the Focal Length, I’ll explain in detail about the lenses you can buy by considering the focal length you need.
For the next part watch out this space.