Lens Trivia: Figuring Half-Stops

[Mark Sawyer]

Just a little lens trivia some may not know...

Most all of us have the standard f/stops memorized: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64, 90...

And most of us know that the value doubles every other stop...

But do you know how to figure what the half-stop is in-between the standard stops?

Say you have an f/6.3 Tessar, an f/6.5 Cooke Series III, an f/6.7 Fujinon W, and an f/6.8 Dagor. Which is exactly mid-point between f/5.6 and f/8?

Anybody know how to figure it? It's pretty simple!

[Kevin Crisp]

When the pointer is right between two numbers?

[Mark Sawyer]

When the pointer is right between two numbers?

Nope! We're talking an actual numerical value!

[TXFZ1]

I was going to give the same flippant answer, but it's logarithmic and thought I heard of an easy remembrance to help out. f/5.6...f6.3.^.f7.1...f/8.

David

[R.K]

https://en.wikipedia.org/wiki/F-number

It all explained there.

[photog_ed]

A quick way to figure it is to multiply the next lower F/# by 2^(1/4) = 1.189.

Ed

[Mark Sawyer]

I was going to give the same flippant answer, but it's logarithmic and thought I heard of an easy remembrance to help out. f/5.6...f6.3.^.f7.1...f/8.

David

Nope, those are third-stops, and I don't want to memorize the whole scale...

https://en.wikipedia.org/wiki/F-number

It all explained there.

They don't explain how to figure half stops, (and some of what they do explain is wrong...)

A quick way to figure it is to multiply the next lower F/# by 2^(1/4) = 1.189.

Ed

There's a quicker way...

To find a half-stop, just add the two stops that are lower than the stops on either side. So for the stop half-way between f/5.6 and f/8, just add 2.8 and 4. So f/6.8 is half-way between! Half-way between f/16 and f/22 would be 8 +11 = f/19. Etc...

[TXFZ1]

You missed the "^". So, now tell why I should care if it is 6.8 or 6.6596.

David

[Jac@stafford.net]

We can calculate fractional F-stops to the end of math, but neither our lenses nor shutter speeds are accurate enough to matter.
.

[Mark Sawyer]

...So, now tell why I should care if it is 6.8 or 6.6596.

David

We can calculate fractional F-stops to the end of math, but neither our lenses nor shutter speeds are accurate enough to matter.
.

That's why it's lens TRIVIA!