ECOR 1100 Lecture 2: Understanding depth of field


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Since last lecture, you have known an important element in Photography: the Exposure Triangle. You learn that the aperture value controls depth of field. In fact, there are
2 more critical factors affecting depth of field.


FACTOR 1: THE FOCUS DISTANCEinstant-university_yellow-border


Focus distance is a calculation from the subject to lens. By changing the focus distance, you will get different depth of field of an image. If you are closer to the subject you are focusing on, you will have an image with shallower depth of field, and vice versa.


FACTOR 2: THE FOCAL LENGTHinstant-university_yellow-border


Focal length (usually measured in mm) is a calculation of an optical distance from the convergence point in the lens to the sensor or film inside the camera, but IS NOT the actual length of a lens. Basically, the longer the focal length, the narrower the angle of view and the more magnifying effect in your picture with shallower the depth of field, and vice versa.

**Shallower lens (e.g. 200mm) → longer focal length→ shallower view captured + shallower depth of field → telephoto effect
**Wider lens (e.g. 28mm) → shorter focal length → wider view captured + deeper depth of field

ECOR 1100 Lecture 1: Understanding exposure (aperture, shutter speed & ISO)




If you have no idea about the Exposure Triangle, you are in the right place!

In this lecture, you will learn the relationship among shutter speed, aperture, ISO as well as the most important element – lighting. They are interrelated and by adjusting one of them, another component must be adjusted at the same time to compensate.

If you are unsure about the concept and this can cause a lot of problems to your photography: shaky pictures, or not getting everything in focus. If you learn this simple concept, you will know exactly how everything works and you will be able to fix those problems!


THE EXPOSURE TRIANGLEinstant-university_yellow-border


Shutter speed, aperture and ISO are combined to form the Exposure Triangle. The trick is to balance the triangle by getting all three elements to work together. The more you can identify their role in exposure, the easier you know how to determine the exposure setting to achieve the effect that you want to.



• To control how much light to enter the camera
• To affect the depth of field (DoF) – how sharp or blurry the area behind your subject is

Aperture range


Adjusting the aperture changes the depth of field, that is, how much of the shot is clear or blurry. The larger aperture, say f/2.8, the more light enters the camera, bringing a brighter picture and shallower depth of field, and vice versa.



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f/5.6 (left) & f/22 (right)


Shutter speed

• To control the duration of time the light is allowed to enter the camera
• To freeze the moment using faster shutter speed, or to capture long exposure using slower shutter speed.

As you adjust the shutter speed, the amount of light enters the camera changes, thus  exposure time and brightness of the picture change. The faster the shutter speed, say 1/1000s , the lesser light goes into the camera, bringing a darker but less blurry image, and vice versa. When you determine a longer exposure time, you need to hold the camera steadier or use tripod in order to obtain a clear image.



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1/15s (left) & 1/2000s (right)



• The higher the ISO is, the more sensitive it is to light, and vice versa
To manipulate the shutter speed by adjusting ISO

By adjusting the ISO, the amount of light needed is affected. The larger the number, the higher the ISO, say ISO1600, requires less light then lower ISO 100. For example, when ISO is 1600, shutter speed is only 1/125s. While ISO is 100, shutter speed will become slower significantly to a few seconds.



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ISO400 (left, more noise) & ISO100 (right, less noise than ISO400)