Understanding focal length

Well, the canonical usage is to call those lenses whose focal length cannot be altered "prime" lenses. And this is the Canon Digital Photography Forum.

Jon wrote in post #2253166
Well, the canonical usage is to call those lenses whose focal length cannot be altered "prime" lenses. And this is the Canon Digital Photography Forum.

I would like to learn the usage by Canon. I just tried Canonusa.com and find not a single use of 'prime' on their web site. Can you direct me?

. . . or of "fixed focal length" either.

I think photographer's use the term "prime" in the same way as we say "glass". It's the photography lingo.

CyberPet wrote in post #2253228
I think photographer's use the term "prime" in the same way as we say "glass". It's the photography lingo.

Exactly. And anyone who get into photography enough (or even asks once and remembers!) will from then on know that glass=lens. That is no way makes it a poor choice of words, or promotes miscommunication. It's simply lingo, nothing more and nothing less. It doesn't even matter where or when the word came about.

Sorry I brought up the subject.

ScottE wrote in post #2253560
Sorry I brought up the subject.

You should be. You made my fingers hurt.

Wilt wrote in post #2252860
Rick, In the vernacular of those in camera manufacturing and optical design and in the vernacular of those who write professionally in publications about the topic, I have not seen 'prime' in any glossary or discussion of 'fixed focal length' vs. 'zoom'. That was what I was pointing out.

'fixed focus' and 'fixed focal length' deal with different concepts (how did 'fixed focus' enter this thread?)

Fixed focus entered the thread because I put it there. But I have used that term with other advanced photographers to mean the same thing as "prime" and they always know what I mean. After all, they are reasonably sure I'm not talking about an Instamatic. And in fact, fixed-focus theoretically means the same thing, given that the focus of a lens is indeed its focal length.

As I said, I didn't learn photography from books. I learned it from other photographers--the kind who got paid. And I taught photography, too.

Maybe the fellows who write books were out of touch with common usage. That wouldn't be the first time that had happened!

But nobody before the 60's or so ever talked about prime or fixed focal length, because
zoom lenses were so rare that nobody felt they needed a special word for a non-zoom. There were lenses, and then there were zoom lenses. The rise of the popularity of the word "prime" seems to have tracked the rise in the use of zooms as daily lenses rather than special-use lenses. This started to occur when zooms came out in wide-to-short-tele focal lengths, and that didn't happen until the late 70's.

If you want to complain about usage, complain that the word "telephoto" doesn't just mean a lens that is longer than normal. A telephoto is a design where the optical center is in front of the physical center of the lens, just as a retrofocus wide angle has the optical center behind the physical center of the lens. But all those people are out there calling their Sonnars telephoto lenses, when Sonnars are, in fact, centered normal lenses of long focal length. Do you think we'll persuade anybody to change their usage?

Rick "wondering why Ansel Adams would have needed the word 'prime', since he didn't own a zoom" Denney

'Fixed focal length' does not imply 'fixed focus'. If a lens barrel has no provision for moving the optics so that it can focus closer than infinity, for example, it is indeed fixed focus. Large format lenses are fixed focus and must be mounted to lens boards and put onto moving standards in order to focus. But try to find a lens for 35mm body which is 'fixed focus', and it would be quite difficult since they virtually all have mechanisms in the lens barrel to suitably move the optics relative to the film plane, in order to focus. Focal length and focus point are quite different concepts given the lens barrel is designed to move closer and farther from the film plane...variable focus, yet fixed focal length. They may be related topics, but they are hardly synonymous.

Just to further add fuel to the fire, my interpretation of a 'prime' lens is a fixed focal length lens which has a focal length approximately equal to the diagonal of the format.

That is: 50mm for 135, 75mm for 645, 150mm for 4x5" etc.

In my mind 'prime' equates to 'standard'.

rdenney wrote in post #2254702
Rick "wondering why Ansel Adams would have needed the word 'prime', since he didn't own a zoom" Denney

His zoom lens was mounted on the bottom end of his legs.

ScottE wrote in post #2256604
His zoom lens was mounted on the bottom end of his legs.

Actually, that's not quite so. I saw a film of him giving a photo class in the field at Yosemite, and he looked for camera position first, using a 4x5 viewing mask. Then, he established the correct spot, marked it with a rock, and then said "Now, all we need is the right lens".

He clearly did his zooming with his hands, not his feet. When he needed a longer lens, he took the lens off the camera and mounted a different one.

For most of his career, he certainly had no need of lingo to describe zooms, primes, or the distinction between them.

Rick "who thinks Adams's skill was knowing when he was already standing in the right spot" Denney

Wilt wrote in post #2254775
'Fixed focal length' does not imply 'fixed focus'. If a lens barrel has no provision for moving the optics so that it can focus closer than infinity, for example, it is indeed fixed focus.

Sez you. The problem with being so dogmatic about what words mean is that you may end up communicating only to yourself.

Rick "who has NEVER applied 'fixed focus' to view camera lenses merely because they lacked a focusing mount" Denney