DISCLAIMER - This post originally appeared on another blog of mine. In the process of closing that one down I found this post deserved a spot here.

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A few days ago I was asked by a friend, and keen photographer, just what a 'Normal' lens is. Which got me thinking, how you define what a normal lens is?

I know there is the old assertion that the Normal lens is one with a focal length equivalent to the diagonal of the sensing medium, be that film or digital, 35mm or Medium Format etc etc. Whilst that may be a wonderfully mathematical definition, I am left feeling a little cold by this explanation and not really any wiser as to what a Normal lens actually is, or what it does.

Taking the diagonal of a 35mm sensor I believe you arrive at a focal length of around 47-48mm. Great, but what exactly does this mean? How does it relate to the image I want to create? How does the lens allow me to relate to my subject? What if I don't use a Normal lens? Simply stating to my friend that a Normal lens has a focal length of around 50mm didn't really seem to fully explain the concept at best and bordered on inaccurate at worst.

I have heard it said that a Normal lens is one that most closely approximates the field of view of human vision. Put a 50mm lens (the closest focal length in production) up to your eye and immediately you'll see a problem with this definition. Perhaps it would be more accurate to say a Normal lens is one that closely approximates the 'perspective' of human vision in that the perspective between objects within the frame is as close to 'natural' as possible; as close to our normal vision as it's possible to recreate. Again what does this actually mean? If the perspective is as close to normal vision as possible with a 50mm lens, the field of view is certainly narrower; so how would this effect the image I am trying to create?

Trying to give a straight definition of what a normal lens is, given the different definitions available, proved to be a little tricky; but trying to explain what this actually means in terms of the image making process was tough. To me, the whole concept of a Normal lens is built on the myth that it in some way relates to how we 'see'. Take for instance a wide-angle lens, which certainly doesn't 'see' in the same way we do in that we do not see sharply in our peripheral vision. Wide-angle lenses, primes at least, are or course traditionally very sharp right across the frame. None of this affect’s the way I see an image, just how I choose to represent my vision within a photograph. The same can be said of this so called Normal lens, which is as different from the way I see as that wide-angle lens is.

Perhaps we have to stop thinking of lenses in terms of focal length and what is normal or not and instead think of them in terms of relating to our subjects. Perhaps we should think about the relationship between different elements within the frame, think about scale, about perspective, about positioning or about how the background relates to the foreground.

I know I often find myself thinking how I want to relate my subjects to the environment in which I find them, do I want them to appear similar in size to the background? Then I reach for a longer lens. Do I want them to recede into the background? I might then reach for the wide-angle lens. In this vein, perhaps we could begin to think of our  'sorter' lenses as 'intimate' lenses or 'personal' lenses or some such definition in that they cause us to be closer to our subject, to interact with them or generally to be nearer to them.  Maybe our longer lenses, with their narrow field of view and telephoto effect which can increase the distance between us and our subjects, could be thought of as 'anonymous' lenses or 'distance' lenses or some similar terminology;  lenses that forgo the need for contact with our subjects.

Again, none of this actually affects how I see but it does inform my decision as to how I want to represent my vision within an image. When I reach for a lens I am not thinking about its focal length but rather my primary concern is how I am going to represent my subjects within the final two dimensional plane of a photograph.  Secondly, I am usually thinking about my position, about scale and about the relationship between the subject and the environment. That is what powers my decision, not the knowledge that a lens is somehow Normal or otherwise.

Unfortunately for my friend, such an explanation was perhaps a little too involved to be of use at their stage of photographic development. Then again, perhaps not. Too bad there is no easy way to relate the measurement and description of lenses to the concept of 'seeing'. Until there is, I'm afraid we will be stuck with this, somewhat dissatisfying, 'diagonal of the sensing medium' contrivance.