(1/3) APERTURE

1. What is the diaphragm in a lens?

It's the adjustable opening that controls how much light enters the camera (the aperture).

2. Why are apertures expressed as f/1.4, f/2, f/2.8, etc?

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These numbers (called f-numbers or f-stops) are part of a standard scale used in photography to describe the size of the aperture: the opening in the lens that lets light in.

The scale goes like this:
f/1.0, f/1.4, f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, etc: depends on the lens.

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Each full stop change on this scale either halves or doubles the amount of light entering the camera.

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3. Explain this 'stop' in more detail: 

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Each full stop change on this scale either halves or doubles the amount of light entering the camera.

This concept is called a 'stop' or more specifically a 'full stop' in photography. A stop is a unit of measurement used to describe doubling or halving the amount of light in exposure. It's used with aperture, shutter speed, and ISO.

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Here's how: 

• Going from f/2 to f/2.8: the aperture gets smaller → lets in half as much light.

• Going from f/4 to f/2.8: the aperture gets larger → doubles the amount of light.

So, even though the numbers seem irregular, they follow a mathematical pattern based on square roots of 2 (~1.41). This ensures each step is a doubling or halving of light — which matches how exposure is calculated in photography.

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4. What is this mathematical pattern based on square roots of 2?

Each next f-number is approximately equal to the previous f-number times the squared root of 2. 

f/1 → f/1.4 → f/2 → f/2.8 → f/4 → f/16 → ... 

These are rounded for practical use but mathematically grounded in this sqrt(2) pattern.

5. Why do we multiply the previous f-stop by the square root of 2 in photography?

In photography, we multiply the previous f-stop by sqrt(2) (about 1.414) because the amount of light entering the lens depends on the area of the aperture opening, which is proportional to the square of the diameter.

Here's why:

The f-stop number is a ratio:​

f-number = (focal length)/(aperture diameter)

--> To halve or double the light, we need to halve or double the aperture area (not just the diameter).

- Since the area of a circle is pi * (diameter/2)^2 , the area changes with the square of the diameter.

- Therefore, to double or halve the light, the aperture diameter changes by a factor of sqrt(2) (because (sqrt(2))^2=2).

- So, when you multiply an f-stop by sqrt(2), you're moving to the next standard aperture size that lets in half (or twice) as much light, keeping exposure changes consistent.​​​​​

3. Where do aperture numbers come from? 

They're derived from the focal length divided by the diameter of the opening.

Let's say you have a 50mm lens (that's the focal length), and the opening inside the lens (the aperture) is 25mm wide.

Then the f-number is:

f-number = 50mm / 25mm = f/2

So that setting is called f/2.

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4. What does the letter "f" represent in f-stop/f-number?

The “f” in f-stop or f-number stands for “focal length.” The f-number is the ratio of the lens’s focal length divided by the diameter of the aperture opening. So, it’s called an f-number because it describes how big the aperture is relative to the focal length of the lens.

4. What is an f-stop/f-number

An f-stop (or f-number) is a number that describes the size of a camera lens’s aperture, controlling how much light enters the camera. A smaller f-stop (like f/1.8) means a larger aperture, more light, and less of the image in focus (shallow depth of field), while a larger f-stop (like f/16) means a smaller aperture, less light, and more of the image in focus (deep depth of field).

5. What is the smallest and largest f-stop?

It depends on the lens. Some go as wide as f/1.2 and as small as f/22 or more. 

6. How does aperture affect depth of field?

Wider apertures (lower f-numbers) create a shallower depth of field, less is in focus. 

7. What is a 'stop of light'? 

Doubling or halving the light in your exposure

8. What is 'bokeh' ? 

Bokeh refers to the quality of the blurred background in a photo, making the subject stand out. It's created by using a wide aperture (small f-number), which produces a shallow depth of field. Longer focal length lenses and being close to your subject also increase background blur. Having a distant background from the subject makes the blur more pronounced. The shape and smoothness of bokeh depend on the lens design and aperture blades. 

9. What is the difference between f/1.8 and f/2.8?

f/1.8 allows more light in, ideal for low light or shallow depth of field.

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(2/3) SHUTTER SPEED

1. What is shutter speed?

It's the time the sensor (or film) is exposed to light.

2. What's a fast shutter speed?

Usually 1/500s or faster, freezes the motion.

3. What's a slow shutter speed?

1/60s or slower, can create motion blur or light trails. 

4. How do I choose the right shutter speed?

Depends on motion: 1/100s for hand movement, 1/1000s for racing cars.

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(3/3) ISO

1. What is ISO?

ISO controls the sensor's sensitivity to light.

2. What does ISO do in low light?

Higher ISO brightens the image but adds noise.

3. Why prefer low ISO in good light?

To reduce digital noise and preserve image quality.

4. What is diffraction?

Image softness at very small apertures (like f/22).

5. What is lens flare?

Light artifacts caused by direct light hitting the lens.