Lesson 5: Optical Zoom

Optical ZoomTo define optical zoom, first I’ll have to briefly explain you what is focal length (or focal distance). If you look on the lenses of any decent camera you’ll see written there something like this: 5.8 – 34.8mm (or any other pair of values like that). This is the focal length specification and it is a characteristic of the lenses. I will not enter into physical theory of lenses and stuff like that, the main thing you have to understand about focal length is that if you are at the same distance from the subject, with the same camera (it is important, because the sensor is part of equation), the smaller the focal length is the further the subject will appear in the final picture.
Here is an example:

– focal length 18mm:

– same distance from the object, but focal length 55mm:

As you can see, the bigger the focal length is, the larger the object will appear in the picture, but the angle of visibility will be smaller.

Now that you have an idea about focal length, lets talk about optical zoom. This specification of cameras will always be seen just on point and shoot digital cameras, but it’s also applicable on DSLRs lenses. You will find it as a value like 3X, 5X, 10X or something like that. These numbers are obtained by dividing the biggest focal length of the lenses to the smallest. For example, if you have a lens with focal length 18 – 55mm, the optical zoom will be 55 / 18 which is approximately equal with 3, so 3X. In other words the optical zoom is the number of times the subject will be magnified compared to the subject dimension at the minimum focal length of the lenses. So in the example above the object has been magnified 3 times.

In the next lesson we will talk about the difference between optical and digital zoom.









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