Sunday 3 June 2018

terminology - What is the definition of a "prime lens"?


There are many discussions of differences between prime, zoom and macro lenses. I have not heard about prime lenses until recently.


Could someone explain what exactly a prime lens is?


Is it just that the focal length is fixed?


And if so what are the advantages of having the focal length fixed?


Also why the name 'prime'?



Answer




In practice, you're correct and it means that it's a fixed focal length lens.


Historically, the term "prime" derives from cine work, where it had a more literal meaning of the primary lens of a multi-lens system.


The concrete advantages are typically that they are much more compact, and have a much higher quality/cost ratio, as they're easier to engineer to a high degree of correction. There is no such thing as an f/1.4 zoom lens, for instance, but f/1.4 primes exist in several focal lengths.


Zoom lenses are catching up on the quality front, a particular example being the Nikkor 14-24, which is reputedly as high-quality as the primes of similar focal lengths (and the Nikkor 24mm is considered a classic design).


The more subjective pros/cons are – obviously – a lot more subtle, and vary from person to person. For example, some people find that primes let them focus more immediately on the composition of the image and/or their surroundings (i.e., it's one less camera setting to think about), while others prefer the ability of a zoom to quickly change the field of view, producing extremely different compositions in quick succession. The same person might like both in different situations. I think the only fair answer to this aspect of the different approaches is to try using a prime regularly and see how you get on with it.


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