[houseofstyles]

I've puzzled for years about the two commonly nominated lens apertures F3.5 and F4.5. These seem to be used for the half stops between F2.8 - F4 and F4 - F5.6 respectively. However these numbers are more like 1/3 stop numbers, ie F3.5 is 1/3 of a stop faster than F4, and F4.5 is 1/3 of a stop slower. The true numbers should be ~F3.36 and ~F4.76 respectively, or say F3.4 and F4.8.


Does anyone have any comments or an explanation of this?

[Digitalis]

The true numbers should be ~F3.36 and ~F4.76 respectively, or say F3.4 and F4.8.

Actually, the f/stops between f/4.0 and f/5.6 is f/4.0,f/4.3, f/4.5, f/4.8 f/5.0, f/5.6, But why stop there? To be realistic 1/3rd stop increments are deliver an acceptable amount of precision for exposure control especially when you take into account the Dynamic range of current digital sensors. The only situation where really high precision lens transmission and aperture control was needed was in cinematography, where older film stocks didn't have much DR (4 stops or so) and a 1/8th of a stop variation in exposure could ruin an entire shoot.

[houseofstyles]

Actually, the f/stops between f/4.0 and f/5.6 is f/4.0,f/4.3, f/4.5, f/4.8 f/5.0, f/5.6, But why stop there? To be realistic 1/3rd stop increments are deliver an acceptable amount of precision for exposure control especially when you take into account the Dynamic range of current digital sensors. The only situation where really high precision lens transmission and aperture control was needed was in cinematography, where older film stocks didn't have much DR (4 stops or so) and a 1/8th of a stop variation in exposure could ruin an entire shoot.

-----------------------------------------
But what I was getting at was I think the lens (and camera) manufacturers use 3.5 and 4.5 when they mean half stops, not 1/3. I have my camera set to move in 1/2 stops, yet as I adjust the aperture it goes 2.8, 3.5, 4, 4.5, 5.6. Why doesn't it go 2.8, 3.4, 4, 4.8, 5.6? The next half stop after 5.6 shows correctly as 6.7

[Adam]

But what I was getting at was I think the lens (and camera) manufacturers use 3.5 and 4.5 when they mean half stops, not 1/3. I have my camera set to move in 1/2 stops, yet as I adjust the aperture it goes 2.8, 3.5, 4, 4.5, 5.6. Why doesn't it go 2.8, 3.4, 4, 4.8, 5.6? The next half stop after 5.6 shows correctly as 6.7

The exposure settings (both shutter speed and aperture) are stepless on modern cameras. I think the camera just rounds the displayed number to be user-friendly. Also, most lenses have their F numbers and focal lengths rounded slightly as well.

Adam
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[dms]

You asked:

"But what I was getting at was I think the lens (and camera) manufacturers use 3.5 and 4.5 when they mean half stops, not 1/3. I have my camera set to move in 1/2 stops, yet as I adjust the aperture it goes 2.8, 3.5, 4, 4.5, 5.6. Why doesn't it go 2.8, 3.4, 4, 4.8, 5.6? The next half stop after 5.6 shows correctly as 6.7"

fstops are not linear--just as f/2 to f/2.8 (is a difference of 0.8) and f/2.8 to f/4 (is a difference of 1.2)--the same holds true between f/stops. The scale is logarithmic (and the series is termed a geometric one). As the f/stops get larger the differences between them gets larger--and so too for 1/2 stops [or 1/3 stops] between fstops.

[Lowell Goudge]

You asked:

"But what I was getting at was I think the lens (and camera) manufacturers use 3.5 and 4.5 when they mean half stops, not 1/3. I have my camera set to move in 1/2 stops, yet as I adjust the aperture it goes 2.8, 3.5, 4, 4.5, 5.6. Why doesn't it go 2.8, 3.4, 4, 4.8, 5.6? The next half stop after 5.6 shows correctly as 6.7"

fstops are not linear--just as f/2 to f/2.8 (is a difference of 0.8) and f/2.8 to f/4 (is a difference of 1.2)--the same holds true between f/stops. The scale is logarithmic (and the series is termed a geometric one). As the f/stops get larger the differences between them gets larger--and so too for 1/2 stops [or 1/3 stops] between fstops.

I wouldn't sweat it

The difference is 1/6 of a stop, or as viewed in a photo editor histogram about7 greyscale around the middle of the histogram.

[Stone G.]

However these numbers are more like 1/3 stop numbers, ie F3.5 is 1/3 of a stop faster than F4, and F4.5 is 1/3 of a stop slower.

Not quite so:The f-numbers are a relative measure of lens aperture diameter so, for each time we multiply the f-number with the square-root of 2, we deminish the light capturing area by a factor of two and THIS is what we used to call one full stop down.

Hence, we get the traditional sequence of full- and half-stops (in rounded numbers):

f/1.4 = sqrt(2)
f/1.7 = sqrt(3)
f/2.0 = sqrt(4)
f/2.5 = sqrt(6)
f/2.8 = sqrt(8)
f/3.5 = sqrt(12)
f/4.0 = sqrt(16)
f/5.0 = sqrt(24)
f/5.6 = sqrt(32)
....and so on

You will note that f/5.0 rather than f/4.5 is the half-stop between f/4.0 and f/5.6

[maxfield_photo]

On most modern digital cameras, the user can pick whether they want to subdivide aperture stops into half or third stop increments. I normally use half stops because most of my old manual lenses had half stops between the whole stops.

In the studio however, I have my light meter set to full stops plus tenth stop increments. So I might measure a light to be 5.6.6, which is read "five six, six", and I'll know I need to pull the light back just a bit to get to "five six, five" i.e. half way between f/5.6 and f/8, but what I would set on my camera is f/6.7 (assuming only one light in the setup).

[Parallax]

[stevebrot]

Down the rat hole we go...

I recommend the Wikipedia article on F-number

F-number - Wikipedia, the free encyclopedia

There are several tables and a number of formulas that explain all.


Steve

(...what the heck is "Aperture Value" and why does reading the term bother me so much...)

[johnyates]

OK, now we're on this topic, I have a related question . . . .
On my SuperTakumar 35mm f3.5, there is an unmarked click setting between wide open (3.5) and 5.6. What is it? is it f4, 4.5, 5? Anyone know?

[Parallax]

It's most likely f4. Meter something at f5.6, turn to the unmarked click and see how much it changes the shutter speed.

[EssJayEff]

I know it's not the same thing, but this thread reminds me of the "ring around" exposure and development test from sheet film days to determine the effective ASA for a batch of film. Is there a digital equivalent of that, maybe using f stop increments along with EV +/- adjustments?