Day 7: Unravelling the "mm" mystery in lenses

It was Karva Chauth a few days ago - a day when married women in parts of India fast all day long for the well-being of the chaps they married. The beneficiary of this non-eating generally rewards his better half with some sort of ornament or item of clothing.

I gave Anupama (that's the wife, my life, my friend, my...well, well...you get the idea) a 50mm camera lens for her Canon EOS 1000D DSLR camera. There was shock and scandal in the traditional circles - jewellery and clothing are supposed to be the giveables on these occasions, not camera lenses. But fortunately for me, Anu loves her photography and has been clicking away happily with the lens ever since.

However, in technological circles, I have been asked why I picked the 50mm lenses. And in slightly less technical ones, what the devil is this chakkar (mystery) about mm when it comes to lenses - we keep seeing these 18-55mm, 50-200mm figures on lenses.

Well, the answer to the first question is: because I know Anupama wanted a 50mm lens. The answer to the second one is...ah...a tad more complex.

As I understood it, the "mm" in the lens refers to the focal length of the lens. Which of course, begs the question as to what the devil is this focal length. Well, it is the distance between the lens itself and the sensor of the camera on which the image is formed (it used to be the film in the good old days). Now, without getting TOO complicated and talk of focusing on infinity and whatnot - here's a simple rule of thumb to be followed by DSLR beginners - the higher the focal length number, the greater the magnification of the lens. Simply said - you can zoom in more with a lens that has a bigger "mm" number parked on it. On the other hand, the lower the figure, the wider a perspective you can get.

So, keeping things simple - if you want to shoot a wide landscape, go for a lens with a relatively smaller mm figure on it, while if what you want to shoot is some distance away, go for the higher mm figure ones.

A very rough break-up of focal lengths would be in this manner:

• 10-35 mm: generally called wide, ultrawide and fisheye lenses. Great for architecture and landscapes
• 35-70mm: Generally considered normal. All right for general, impulse snaps without too much fuss.
• 50mm: This is widely accepted as being close to what the human eye sees. Great for portraits. 
• 75-135 mm: We are getting into telephoto lens territory here. The zoom-in element starts coming.
• 135-300mm and greater: Very telephoto territory. The stand from a distance and deliver zone.

 So there ye have it - the mm mystery in lenses as per Yours Truly. A trifle oversimplified and not entirely technically correct, I suspect, but kind of handy, if you are a DSLR beginner. Like I am. Will reveal more as the days pass, as the stripper said to the oily Sheikh, but as of now this is what I think I know of the mm chakkar.

Now, excuse me, I have to try and convince Anu to let me use that lens on MY EOS 600D.