Have you ever looked at portraits, or pictures where the subject is reasonably close and the background behind is blurry? Well, the key to this effect is all to do with the camera aperture.
This is part of the exposure triangle on the camera, along with shutter speed and ISO that all relate to one another. Whereas shutter speed deals with the amount of time light is allowed through to the sensor, and ISO is the sensitivity to light, the aperture deals with the amount of light allowed through.
In other words, it is the size of the opening after the lens and is fully adjustable. To obtain a properly exposed photo, if you change the size of the camera aperture, then you will need to change the shutter speed or ISO to compensate.
For example, if you wish to take a photo of a flower, you would want a large hole (or camera aperture) to allow as much light in as possible.
Once you have set the ISO (likely to be 100 or 200 for an exterior shot of a flower), then you would need to increase the shutter speed otherwise your image would be over exposed.
In contrast, for a landscape shot, you would need to decrease the camera aperture size because you have so much light in the scene. This would mean a slower shutter speed to obtain the correct exposure for the shot.
Use of a tripod is recommended in these situations.
Camera aperture is measured in stops, known as f stops. Adjusting the f stop one way or the other means that the size of the hole is either halved or doubled in opening size.
The smaller the f stop number, the larger the hole. Now, if you drop down an f stop, to allow the same amount of light onto the sensor, then you would need to change the shutter speed by one speed slower.
But if changing the camera aperture size only means having to change the shutter speed or ISO, then what’s the point? This is a very important question, because the camera aperture relates to something very important.
This is something known as the depth of field. The depth of field relates to how much of the image is actually in focus. So, in the example in the introduction where the subject is crisp and clear, but the background is out of focus, then this has a shallow depth of field.
The camera aperture has a large hole, and the f stop setting would be something in the range of F 5.6 or less.
If you go the opposite way and have a high f stop number (meaning you will have a small camera aperture hole), then your depth of field is very large. In other words, the whole image appears crisp and in focus.
And this is why you would have a small camera aperture hole for a landscape shot, because you would want the entire image to be in sharp focus.
So in simple terms, if you have a subject close up and want this to be the focal point of the image, then set a low f stop number (large camera aperture hole), and you will have a shallow depth of field.
The subject will be prominent with the background blurry and pushing the subject to the forefront. And conversely, a small camera aperture for far away objects so that you have a large depth of field, bringing everything into focus.
The camera aperture is an extremely important element of the trinity of the exposure triangle.