Our Two Allies: Focal Length and Depth of Field

Focal Length and Depth of Field

Our Two Allies

When defining the tools that we are going to use in a photographic session, lenses come into play. In fact, we will have to handle the terms: focal length and depth of field at one point.

Focal Length​

   According to the definition that we obtain in Nikonusa.com; the focal length is the calculation of an optical distance from the point where the light rays converge to form a sharp image of an object to the digital sensor. It is the basic description of a photographic lens .

   To understand it even more simply, the focal length is the number in millimeters (mm) that appears on our lenses. In fact, the lower the number the larger the photographic space that the lens covers; and the more objects will enter our frame.

   We have several examples of focal lengths in the following images:


   Remember that with zoom lenses, the focal length can be variable. However, many specialists resort to the idea that these lenses offer less sharp photos than a fixed lens.


   In my personal opinion; I have three fixed lenses and two zoom lenses, you can see the equipment I use on my blog “What’s in my backpack? And I can say that indeed, the fixed lenses give us somewhat sharper photographs. We can use less artificial light of the ISO because they can maintain their maximum aperture all the time.

   On the other hand, zoom lenses have great comfort due to their various focal lengths. However, some of them have a variable aperture depending on the focal length we use. For example; the new NikKor Z 14-24mm F / 2.8 maintains its aperture f / 2.8 in its entirety from 14mm to 24mm, on the other hand, the Nikkor Z 24-50mm f / 4-6.3 changes its aperture from f / 4 up to f / 6.3 depending on the focal lengths (mm) you have. I refer more to the aperture of photographic lenses in my article “What tha F!“.

Depth of Field


   Depth of field is understood to be the area that comprises from the closest and furthest point of our field that is acceptable in terms of sharpness.

   Depth of field is not the same as focal length, there is a keyword in its definition which is “sharpness”. The sharpness, the focus and therefore the depth of field can change depending on the lens we are using. For example; in the following image, we have a totally out of focus background; that is, the depth of field is out of focus while the plant is totally in focus and sharp.

  This blur is called “Bokeh”. And the more wide angle we find, the less bokeh we get. This means that if we have a telephoto lens of 85mm or more; the bokeh will look even more blurry giving focus to a certain object or subject that is close to the lens.

  Without a doubt; managing the focal length and depth of field of the lens will definitely improve the result that we will obtain in our photography. Clearly, they are our best friends who will enhance our skills as a photographer.


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