Elementary question for some

[rickp1]

I have a question that I just can't seem to understand the answer to, even after reading and researching.
As obvious from this question I'm new to photography and I have a question regarding the term f stop or just stop. I'm looking for the actual adjustment setting meaning.
When people use the term 1 f stop or 2 f stop, do they mean i click on the wheel, for example from 4.5 to 5 or is it a larger setting?? I hope my question is clear.

Also the term 1 stop or 2 stop when referring to exposure, same thing, does the term mean 1 click or 1 bar in the setting or the full range from 0 to + or -1??

Thanks again.
R

[dcclark]

f/stops have become a sort of fundamental measure of how you can change an exposure. First, numbers: f/stops come in multiples of the square root of 2 (which is because they're related to the size of a circle... mathematical details available if you really want!)

So starting at f/1, FULL stops go:

f/1
f/1.4
f/2
f/2.8
f/4
f/5.6
f/8
f/11 (approx., it's actually 11.3, but basically all cameras use f/11)
f/16
and so on. Each of these is (square root of 2) times the previous one, where (square root of 2) is about 1.4142.

When referring to exposure in general, the truly correct term is "exposure value," (abbreviated EV) which is basically exactly the same idea. If you go from f/2 to f/2.8, your exposure has changed by one f/stop, which is exactly one EV (you have one EV less light coming in). However, technically "f/stop" referrs only to aperture. So, if you go from a shutter speed of 1/100 second to a shutter speed of 1/200 second, you've changed by one EV (but the change in how much light gets in is exactly the same as if you'd changed by one f/stop, as in the above example).

Many cameras measure EV compensation and shutter speeds in 1/3 or 1/2 of an EV (equivalently 1/3 or 1/2 of an f/stop). For example, my Nikon D40 goes from f/2.8 to f/3.5, which is 1/2 of an f/stop (1/2 of an EV). When it comes to exposure compensation, it goes in 1/3 of an EV. Typically, you will see a bar in your viewfinder which looks something like this:

|..|..0..|..|

The dots (.) are 1/3 of an EV, and the lines (|) are 1 full stop.

Hope this is clear and helps!

[Preacherman]

Hi Rick. I trust you found dcclark's answer above helpful. Don't forget that this is the Digital Photography "SCHOOL". Just click on 'About DPS' at the top of the screen, then on 'Photography Tips & Tutorials', then on 'For beginners'. Then go down to the topic in question and hey presto, it's all there. Enjoy your read and just come back if you need to. Keep on clicking and posting. God bless for now. PAUL

[rickp1]

Hey guys, thank you for taking the time.

So for exposure each bar is 1 full stop, and for Aperture each number is a 1 stop.

For some reason, I could not get that from reading and reading. This really will help my understanding of settings and recipes out there.

Again thank you both.

R.

[OsmosisStudios]

You can also use shutterspeed and iso to affect exposure. In this case it's a bit simpler: every time you DOUBLE or HALVE your number, youre moving a stop.

so,
from 100iso to 200iso is 1 stop.
from 100iso to 400iso is 2 stops (100 -> 200, 200 -> 400).

The same goes for shutterspeed.
1/60s to 1/125s is 1 stop
1/250s to 1/60s is 2 stops (1/250s -> 1/125s, 1/125s -> 1/60s)

[inkista]

Originally Posted by rickp1

...f stop or just stop. I'm looking for the actual adjustment setting meaning.

Two different terms. Two different meanings.

A stop is a doubling of the light in the exposure. You can add/delete a stop of light by doubling/halving the iso or shutter speed, or moving one number of the f-stop for the aperture.

The aperture is how large the opening in the lens that lets in the light is. f-stops is a way of switching the aperture setting by stops, so you can equate it to the other settings, and uses f-numbers to describe the setting.

The f-number itself a ratio of the lens's focal length to the diameter of the aperture opening: focal_length/diameter.

So, for example, if a 50mm lens is set to f/2, that means the diameter of the aperture opening is 25mm across. If a 100mm lens is set to f/2, that means the diameter of the aperture opening is 50mm across.

The f-number means the same amount of light from the aperture across lenses, irregardless of focal length, which is why it's more convenient to describe the diameter as an f-number ratio than the actual diameter measurement; you don't have to do math to account for focal lengths. And if you solve the ratio above for diameter, it's focal_length/f-number, which is why apertures are written as f/f-number: f stands for focal length. And this is also why smaller f-numbers mean larger openings. Just as 1/8 is smaller than 1/4, f/8 is smaller than f/4.

[Benji]

Originally Posted by rickp1

Hey guys, thank you for taking the time.

So for exposure each bar is 1 full stop, and for Aperture each number is a 1 stop.

For some reason, I could not get that from reading and reading. This really will help my understanding of settings and recipes out there.

Again thank you both.

R.

I'm not sure what a "bar" is but with most DSLRs a "click" of the shutter speed dial and/or a click of the aperture is 1/3rd of one stop. So three clicks equal one stop, on either one.

Benji

[amberskies]

great thread! thanks for the explanations.