What is the correct way to express aperture and focal length?

[Frank Petronio]

Perhaps Dan will oblige. Or Oren. Or someone German, they can pretend to sound authoritative even if they aren't... what is the best way, in English, to "formally" describe a len's aperture and focal length?

For years I've been doing what most people do and writing "90/8" or "210/5.6". If I feel fancy I might use "210mm f/5.6". And I know that gets the information across. But please indulge me here. Should there be a slash before the aperture as though it is a fraction? Is "f/aperture" correct?

Also is it "len's aperture" or "lens's aperture" for a single lens?

[Vaughn]

210/5.6 is good enough for me when talking to fellow photographers.

The Rodenstock enlarging lens on my desk says: 1:4,5 f=135mm -- same for a couple Rodenstock view camera lenses.
But I have another newer Rodenstock that 1:5.6 f=150 -- using a point instead of the comma (but 150mm f/5.6 on the box!)
The Schneider says: 1:5,5/240 and another is 1:8/90
Graflex says: f/4.7, then the serial number, then 135mm
Wollensak says: 15 inch f/5.6
Nikkor says:150mm 1:5.6 (also the same on the enlarger lenses.
The Turner Reich triple convertible is just confused

So I don't think one will find a standard way of denoting focal length and aperture!




And it is the lens' aperture

[Preston]

Frank,

I will usually write something like this: 210mm/f-5.6 @ 1/30s, when I write anything at all.

I have no idea if my way is 'technically' correct, but it gets the point across.

--P

[Leigh]

Hi Frank,

The presumably "correct" way is to give the name of the lens and its aperture, followed by the focal length, as in
Planar f/2.8 80mm. All the lenses I've seen for all formats show the aperture first, followed by the focal length.

The reason is that Planar f/2.8 identifies the design. Designs can be scaled to different focal lengths.

I normally do it the other way around, because anybody will understand 210/5.6. That's f/5.6 since f = 210mm.

- Leigh

[polyglot]

You can do what you like with the numbers, but it's "lens' aperture".

[Sal Santamaura]

...what is the best way, in English, to "formally" describe a len's aperture and focal length?...

The best way is the way that is understood by your target audience.

...I might use "210mm f/5.6"...

That's the correct way.

...Should there be a slash before the aperture as though it is a fraction? Is "f/aperture" correct?...

It is a fraction. When fully open, the aperture's diameter (in the case of your example) is 37.5mm, which is 210mm divided by 5.6.

..Also is it "len's aperture" or "lens's aperture" for a single lens?

I've sworn off correcting grammar when intent is clear, but, since you asked, Vaughn and polyglot got it right: "lens' aperture."

[Oren Grad]

"Lens" is singular.

As Vaughn pointed out, various notations are used in practice to indicate the aperture. One advantage of the "f/" notation is that it's a nice reminder of where the number comes from. For a compound lens, at infinity focus, the entrance pupil diameter e, the equivalent focal length f and the relative aperture N are related by the formula N = f/e. If you turn it around, you have e = f/N. If you look at an aperture specified as, say, f/4, you're reminded that the entrance pupil diameter is equal to the equivalent focal length divided by the aperture number, in this case 4.

[Leigh]

The colon is frequently used to indicate ratio, as f:5.6
It means the same thing as f/5.6

- Leigh

[Tim Meisburger]

Oren is correct. Lens is singular, and no possessive is either needed or wanted.

[Vaughn]

Oren is correct. Lens is singular, and no possessive is either needed or wanted.

I think it depends...if one is meaning, "The aperture of the lens", then it would be the lens' aperture. If lens is used as a description of the type of aperture, then it would be a lens aperture.

If one is describing the type of hair, then it is cat hair (cat used as an adjective, I suppose). But if you are wondering whose hair it is, then it is the cat's hair.

And the grammatical rule is that if a word ends in 's', the possessive is s' - not s's. Hope the grammar police do not raid my home tonight!

Good night!

Vaughn