The exposure triangle diagram
Here we have the exposure triangle,
this is an integral part of learning how to master manual mode in photography. The basics of it are pretty simple, the lower the aperture, the more light is let into the camera sensor. A longer shutter speed will also allow more light to hit the camera sensor, and a higher ISO will make the sensor more sensitive to light. You can look at the diagram to help you achieve a correct exposure whilst maintaining creative control.
Let's say you want a shallow depth of field, but that is making your photo too bright. From looking at the diagram we can see that a longer shutter speed and higher ISO will make the photo bright too. Assuming our exposure is set at an aperture of f1.4, ISO of 800 and shutter speed of 1/250th, we could achieve a darker photo with better image quality by lowering the ISO. Instead, we could adjust the shutter to make it faster (1/2000th instead of 1/250th). This would give us the same exposure, with the faster shutter speed freezing more motion.
Reversing the situation to get more light to the camera sensor by slowing the shutter speed will increase the risk of motion blur however. Keep this in mind when choosing which pillar of the exposure triangle to adjust.
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