In the Buyer’s Guide section of BP, there is a column that mentions ‘maximum magnification (ratio)’. What is this magnification ratio and how does one calculate it? When a zoom lens is reversed, does the ratio change depending on changes in focal length?
Sandeep V Khambait, Nashik
This article was originally published in September 2011.
A magnification ratio is the comparison between real-life subjects and how they are captured on the sensor or on film. For instance, the ratio 1:1 means that an object which is 1 sq cm long in real life, will measure the same on the sensor. On the other hand, a 2:1 or 3:1 ratio means that the subject captured will appear to be twice or thrice its size respectively. Therefore, while moving from life-size captures to smaller and smaller captures, the numerical sequence would be expressed as 1:1, 1:2, 1:3, 1:4 and so on. When a zoom lens is reversed, then the magnification ratio is at its maximum at the wide end. However, this also means that the minimum focusing distance is reduced and the subject needs to be placed extremely close to the lens. On the other hand, at the telephoto end, the ratio is relatively lower. Also, you will be able to position yourself so that the subject has enough space around it and can be well-lit.