What's a f stop and how it can improve your photography

You probably have heard photographers referring to stops or f stop (f relates to aperture stops. More on that later). What are stops and why are they important to improve your photography? What we are talking about a relationship between aperture, shutter speed and ISO and how they relate to the overall exposure of the image.

Check these 2 images. They look identical but they both have different camera settings.

compare

How can these images look the same when the camera settings are different?

Its all to do with stops. All three settings control exposure which some call the exposure triangle. They also control other stuff like depth of field, freezing (or not) movement and your cameras’ sensors sensitivity to light.

If you set your camera on auto and point it at a flatly lit scene (overcast day, no sunlight), half depress the shutter button (depending on your camera you might not need to do this) and you will see what settings the camera has chosen to shoot the image with what it determines the correct exposure. Take a picture and make a note of the settings. Set the camera to manual and use the settings you copied. Take a picture. Its the same right! Lets make an adjustment. Cut your shutter speed by half (i.e.  200 to 100) and half your ISO speed. Take a picture. Its the same as before right!

ISO, Shutter and Aperture

Lets explain. The shutter controls how quickly or slowly light hits the image sensor. The aperture controls the amount of light that is let through the lens and the ISO controls the sensitivity of the image sensor to light. All these controls are related by….stops!

What measure is a stop. Easiest explanation is that its a measure of brightness. And a 1 stop difference is the same wether the stop is adjusted by the shutter, aperture or the ISO. Here is a chart showing full stops of all the exposure controls ( there 1/2 and 1/3 stops as well but lets keep this aa simple as possible). The higher the number with ISO speeds let more light in, the lower the number on shutter and aperture let more light in. The amount of light between stops remains the same. So any 1/2/2 stop change in one control will reflect the same as the same change in another. Check the chart

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So if the perfect exposure for a scene was ISO 800, shutter 125 at f5.6 then you could render the same exposure at ISO 800, shutter  60 at f8 (slower shutter letting more light in and closing the aperture to f8 to let less light in). Get it?.

To go 1 stop darker we could use ISO 800 1/125 and f8. same as above for perfect but 1 stop smaller aperture. Go a stop lighter then use f4. Get it now?

What does it look like. This is 1 stop lighter

exp+1

This 2 stops darker
exp-2

This is 1 stop darker

exp-1

Check the exposure slider in Lr. You see I have moved the slider in 1 stops. If you change the stops in the camera it will have the same brightness affect on the images you shoot. If you can gauge the brightness of the scene you want shoot it will help you to adjust exposure and how to set up your camera. You learn how to read light and relate it to how your camera will record it. The better you can interpret light the better photographer you will be.

5 Comments

  1. […] So if your exposure is out when you take the shot you can correct it in Lr (and if you read the f stop blog you can also gauge how much you should correct it […]

  2. […] What's a f stop and how it can improve your photography […]

  3. […] So if your exposure is out when you take the shot you can correct it in Lr (and if you read the f stop blog you can also gauge how much you should correct it […]

  4. […] What's a f stop and how it can improve your photography […]

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