When I first switched my camera from Auto to Manual mode, I spent about twenty minutes completely confused before switching back. Aperture, shutter speed, ISO — three numbers that all affect brightness, but in completely different ways with completely different side effects. It took me longer than I would like to admit before it finally clicked.
What Exposure Actually Means
Exposure is simply how much light reaches your camera sensor. Too little light and your photo is dark and muddy. Too much and everything washes out to white. Getting the right amount of light is what exposure control is about.
The tricky part is that you have three separate tools to control this, and each one affects the image in ways beyond just brightness. That is the exposure triangle: aperture, shutter speed, and ISO. Change one and you usually need to adjust another to compensate.
Aperture: The Opening in Your Lens
Aperture is the opening inside your lens that lets light through. A wider opening lets in more light. The confusing part for beginners is that aperture is measured in f-stops, and the numbers work backwards from what you might expect: f/1.8 is a wide opening (lots of light), while f/16 is a narrow opening (very little light).
Beyond brightness, aperture controls depth of field — how much of your image is in sharp focus. Wide apertures like f/1.8 create that blurry background effect (called bokeh) that makes portraits look professional. Narrow apertures like f/11 keep everything sharp from foreground to background, which is what you want for landscapes.
When I photograph Prague's architecture, I typically use f/8 to f/11. This keeps both the foreground details and the distant buildings sharp. For portraits at the Wallenstein Garden, I drop to f/2.8 or wider to separate the subject from the background.
Shutter Speed: How Long the Sensor is Exposed
Shutter speed controls how long your camera's sensor is exposed to light. Fast shutter speeds (1/500s, 1/1000s) freeze motion. Slow shutter speeds (1/30s, 1s, 30s) blur anything that moves during the exposure.
The practical rule for handheld shooting is to keep your shutter speed at least as fast as 1/focal length. If you are shooting at 50mm, keep your shutter at 1/50s or faster. Go slower and camera shake starts to blur the image.
For night photography in Prague — the Charles Bridge, the castle reflection in the Vltava — you need a tripod and long exposures of several seconds. The moving water becomes silky smooth, and the city lights create trails. This is one of the most rewarding types of photography to try in Czech Republic.
ISO: The Sensor's Sensitivity to Light
ISO controls how sensitive your camera sensor is to light. Low ISO (100, 200) means the sensor needs more light to create a proper exposure. High ISO (3200, 6400) means the sensor can work in very low light.
The catch is that high ISO introduces noise — a grainy, speckled look that degrades image quality. Modern cameras handle high ISO much better than older ones, but there is always a trade-off. I try to keep ISO as low as possible and only raise it when I cannot get the exposure I need by adjusting aperture or shutter speed.
In practice, I start at ISO 100 outdoors in good light, move to ISO 400-800 on overcast days or indoors, and accept ISO 1600-3200 for low-light situations where I need a fast shutter speed or cannot use a tripod.
How the Three Work Together
The exposure triangle means these three settings are always in balance. If you want to use a narrow aperture (f/11) for a landscape but the light is low, you have two options: slow down your shutter speed (which might blur moving elements like leaves or water) or raise your ISO (which introduces noise).
There is no single correct answer. The right combination depends on what you are photographing and what trade-offs you are willing to make. A fast-moving subject needs a fast shutter speed, so you accept a wider aperture or higher ISO. A static landscape at night can use a slow shutter speed on a tripod, so you keep ISO low and aperture narrow.
A Simple Starting Point
When I am learning a new shooting situation, I start with Aperture Priority mode (A or Av on most cameras). I set the aperture I want for the depth of field effect I am after, set ISO to Auto with a maximum of 1600, and let the camera choose the shutter speed. This gives me control over the most visually important setting while the camera handles the technical balancing.
Once I understand what shutter speed the camera is choosing, I can switch to Manual and fine-tune from there. This approach helped me move from Auto to Manual much more smoothly than trying to understand all three settings simultaneously.