The aperture in your camera's lens is one of three fluid elements of the Exposure Triangle. An awful lot like your eyes, it dilates and constricts to control the size of the lens opening.
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It collaborates with shutter speed and ISO to regulate how much light reaches your sensor.
Multiple combinations can generate the exposure your meter says you need... but coming up with the perfect combination is essential for the look and feel you want for your image.
So, back away from AUTO and take control of your photography... your aperture is a good place to start.
In the true sense of the word, it means an opening. .. but in your camera's lens it's also the system of blades that change the size of the opening.
It works in sync with your shutter speed to regulate the amount of light that reaches the sensor (or film).
I compared this system with your eyes a minute ago. The hole in the centre is like the pupil in your eye. The blades are like the iris.
Look at this particular lens. It gives you 8 different sized openings for your exposure.
The jump from the largest aperture f 1.4 to the next size f 2 is called 1 stop. That's a measurement of 1 stop of light.
As an aperture increases by 1 stop, the amount of light doubles. If you decrease by one stop, the amount of light is halved.
It's a bit difficult to understand why an aperture of f 1.4 is gigantic compared to f 16.
Same as shutter speed, it's just understood that you have to make the numbers a fraction. So f 1.4 is really 1/1.4 which is a really big number compared to f 1/16.
Here's an image to help you visualize the concept.
If 2.0 becomes a fraction, it becomes 1/2. So that's 1/2 of a blue pie. .. I agree, blue pies aren't very appetizing!
And 4.0 as a fraction is 1/4 and that's actually smaller than 1/2. If they weren't fractions, 4 would be twice as large as 2, right?
Then, f 8.0 is really half as small as f 4.0 and 4 times as small as f 2.0 - see where we're going with this? Smallsville... all the way small to f 16. Check that itty bitty hole in the middle. Wow, how small do you think f 22 is? Or f 32.... yes, there is an f 32, as minuscule as that is.
So, what you have to remember is:
This may help you understand what f stop you need for the picture you want to create...
Suppose there's a fire in your kitchen and if you don't act fast, the kitchen won't be the only thing burning!
There are two components here.
Switch from water to light coming through your camera lens.
The smaller window needs the shutter to stay open longer for the same amount of light to get to the sensor.
If your plan is that your subject will be in focus and your background blurred, use a large aperture, maybe f 2 or f 4 which has a shallow depth of field.
For shooting a grand landscape, like mountains and a stream, use f 8, f 11, maybe f 22 which has a very deep area of focus.
A portrait of a peony plant in a ceramic pot.
I’m close to the plant and my DOF is smaller than if I stood 12 feet away... so I can’t use f 2.0
The same peony plant.
My camera was on a tripod.
If your intention is to have everything sharp, then this does the job. My personal preference is have a blurred background and only the plant in focus.
Will you help me adjust my exposure settings?
I'm about to take a photo of some red roses on a rose bush.
I had everything figured out :
But, darn it... I don't have my tripod with me and I can't hold my camera steady at 1/30th, plus... there's a breeze and the roses are blowing around a little!
I want to freeze all motion in the leaves and petals. What would you do?
I need 1/250th of a second for my shutter speed. That's 3 stops away from the exposure I have now and I need to figure out how to get 3 stops of light back. Your thoughts?
I don't have much leeway in my f-stops because I'm close to the roses and my DOF decreases the closer my camera is to the subject.
Maybe f11 - 1 stop - would be alright but no more than 1 or I'll lose my DOF.
ISO is the only other change to make. I know my camera doesn't produce much noise on ISO 800 so there's my best bet. That gives me 2 stops more light.
There's my 3 stops and I can still keep a reasonable depth of field.
I think that's easy enough to follow on this chart. The 'red' numbers are what I started with and the 'blue' numbers are the changes to get the 3 stops of light I lost when I increased my shutter speed to 1/250th.
Just to let you know.... it's not always this easy. There are times you won't be able to get the f-stop or the shutter speed you want. You will have to compromise sometimes.
But things will be more forgiving if you have a tripod and you don't have to rely on hand holding your camera. With a tripod you're more flexible with your shutter speed.
Since your selection of apertures depends on your lens....
Changing your lens means you may change your range of apertures.... and your 'sweet spot' (your sharpest aperture).
When you shoot landscapes, use what’s called hyperfocal distance. That basically means - “What’s the closest point to me that I should focus on to make sure my foreground, middle ground and background are all in the sharpest focus possible?
You can get as technical as you want with this. Go online and search for a good article. There's lots I don't care to dive deeply into and this is one subject! Instead....
Here's a quick and effective cheat -
… focus about a third of the way into your landscape and that should about do it. ... at least for landscapes. This will get your entire scene in focus from foreground to background.