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Basic Controls of Camera to control Exposure

The three basic functions of any digital still camera to control exposure are Shutter Speed, Aperture, ISO.


Shutter Speed:-

Shutter speed is nothing but amount of time sensor is exposed to the scene or light from the scene. Or amount of time shutter is open to allow light to reach sensor

There are two types of shutter 1. Mechanical shutter

2. Electronic shutter


Mechanical shutter: Speed of mechanical shutter ranges from 30secs to 1/4000secs in entry level DSLR/Mirrorless, 30secs to 1/8000secs in professional and semi-professional DSLR and Mirrorless.

Electronic shutter: Mirrorless cameras are equipped with both mechanical shutter and electronic shutter. In latest Flagship mirrorless cameras the electronic shutter speed ranges from 30sec to 1/64000 secs.

All mobile phone cameras are equipped with electronic shutter. To my knowledge mechanical shutter is not available in any mobile camera.

One more setting/mode based on shutter speed is “Bulb Exposure”. Will discuss this in detail in Shutter speed topic (next week)


How shutter speed affects exposure?

If the amount of time sensor get exposed increases the exposure will increase. It means high shutter speed sensor will receive less light, Low shutter speed sensor will receive more light. Example: For a scene if 1/2secs is the required shutter speed for proper exposure then if we increase the shutter speed to 1/4secs we are cutting the amount light by half. This called as a “stop” of light in photography.

Before getting in to further explanation, Let see about how light is calculated in photography. In photography light is calculated in “Stops”

A stop refers to the doubling or halving of the amount of light that makes up an exposure.

Let us consider, for a scene required shutter speed for proper exposure is 1/250 seconds. If we increase the shutter speed to 1/500 seconds then we are reducing the light by half which is nothing but a stop. If we increase the shutter speed to 1/1000 seconds then we are reducing the light by 2 stops from initial exposure. Similar way if reduce the shutter speed from 1/250secs to 1/125secs we are doubling the light which is a stop. Further if we reduce the shutter speed to 1/60 again we are doubling the light.

Below image shows the shutter speed in seconds at full stop difference.


Most DSLR and mirrorless can be set to 1/3 stops of increment in shutter speed to have more precise control in shutter speed. Aperture:

This is a mechanism which present in the lens to control the amount of light entering the camera. Below image shows the aperture mechanism of Canon EF-M 32 F1.4 STM lens



The centre heptagonal hole is called aperture. No. of blades is not standard will differ lens to lens.


In any DSLR or Mirrorless you will have option to control the size of the aperture or opening

Most mobile phones have fixed aperture. But they are providing multiple cameras with different fixed aperture respectively. Please search mobile phones with variable aperture for more details. The f-stop, which is also known as the f-number, is the ratio of the lens focal length to the diameter of the entrance pupil. If you did not understand that, don’t worry, because there is a much easier explanation of it for beginners. In very simple language, f-stop is the number that your camera shows you when you change the size of the lens aperture.

If you change the aperture settings the f-number will change.


Below image shows the change in f-number in full stop difference.

There are lens available with f/1.2 aperture. In the past there were lens with f/1.0 aperture

And there are lens with narrow aperture f/32



Most DSLR and mirrorless can be set to 1/3 stops of increment in aperture to have more precise control in f-number


ISO:

The change to above two mechanisms 1. Shutter 2. Aperture will directly affect the amount of light reaching the sensor. But ISO is not such mechanism which control amount of light to control the exposure.

To understand easily, ISO value will give the sensitivity of the sensor. If the ISO increases the exposure increases, if the ISO decreases exposure decreases. ISO of a sensor ranges from 100 to 102400 in Canon. Each Manufacturer will define the maximum and minimum value of ISO based on the capacity of sensor and other processing capacity of the camera.


Below image shows the ISO changes in full stop increments.



Canon 100 to 102400, Nikon 64 to 25600. Extended modes are available in professional bodies.


Most DSLR and mirrorless can be set to 1/3 stops of increment in ISO to have more precise control in ISO value. In all above three functions all OEMs are pushing the boundaries in either ends with their latest inventions. Follow the review websites to get latest tech updates on these technologies. Exposure Triangle:

Above image shows all three variables/functions which we need to adjust to get the proper exposure.

For any given exposure setting of shutter speed, Aperture, ISO if we change any one setting at least one of the other two setting need to be changed to get the same exposure. Or both can be changed depends on the final output


Example:

In below table each row will give the same exposure


There is no standard or default value for shutter speed, Aperture & ISO with respect to exposure.

All three will change depends on final output. As a photographer it is our own choice to decide the values of each variable depends on required final output, considering the light and limitation of your equipment.

Shutter speed and Aperture we will discuss in detail in coming topics.

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