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My journey into Photography, Horology, and Audiophilia

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My take on Exposure, part 1

As a hobbyist, the first challenge I had to deal with was to take photographs that are properly exposed. And in order to achieve that, I need to learn what are the factors that involve exposure.

In order for an image to appear on the photographic film or sensor, we have to let light in. The amount of light allowed during the process of taking a photograph is called Exposure.

Shutter speed

So how does a cameral let light in? It is through the use of a shutter. The speed at which the shutter cycles, which starts with the opening, closing, and resetting is called the Shutter Speed and is expressed as a period of time. Fast shutter speed is expressed as a fraction, such as 1/60 or 0.0166666666 of a second. A very fast shutter speed example would be 1/2000 (0.0005) or even 1/4000 (0.00025) and is normally used to freeze motion. A slow shutter speed is expressed in seconds, i.e. 1s, 6s, or 30s or even infinity, which is sometimes referred to in your camera as Bulb.

To achieve proper exposure, we need the right shutter speed, and in some situations, the "right" shutter speed is determined by the effect the photographer wanted.

When a photograph loses highlight details, which is exhibited as all white in the bright parts of an image, it is referred to as overexposed. The opposite of overexposure is underexposure, in which the shadow details, i.e., the dark areas, become indistinguishable from black.


Aside from the shutter, the amount of light entering the film or sensor, is dictated by the Aperture. The aperture is basically an opening where light travels, and that is through the lens. So a lens set with a bigger opening, let more light in compared to a lens set with a smaller opening.

In most lenses, there is a diapraghm placed in the light path to limit the light entering the film or sensor, and these are called Stops. The Aperture Stop determines the brightness at an image point. Having said that, the Aperture is expressed as a measurement of the diameter of the Aperture Stop.

Now this is where it gets complicated- the Aperture is usually specified as f-number, which is focal lenght:aperture diameter ratio. Luckily for us, most lenses have a marker to indicate the f-number. We rotate a ring, called the Aperture Ring to set the aperture. As digital cameras become popular, the setting of the aperture has become electronic, and many new Nikkor lenses (designated "G") no longer has aperture rings and you set the aperture via the dials on the camera body.

A lower f-number, such as f/4 allows more light due to a bigger opening than one at a smaller opening such as f/22. As my other hobby is also audio, I tend to relate this to a term called decibel (dB). My Harman Kardon receiver normally shows a large positive value such as 60 and you will barely hear anything. As you turn the volume control, the number approaches 0 and the sound becomes louder. Every 6dB increase in volume makes it twice as loud. So going back to Aperture, every change in f-number at a factor of √2 is called an f-stop.

In conjunction with the Shutter Speed, the Aperture size will regulate the amount of light entering the film or sensor.


Finally, we have ISO. ISO sensitivity is basically the film's sensitivity to light. ISO is actually an acronym for International Standards Organization, a governing body for international standards. The actual standard that determines the speed of a film is ISO 5800. However, we loosely refer to this as plain ISO. There are two scales in the ISO standard, and we normally use the ASA scale, which is an arithmetic scale.

Film are rated according to this scale, i.e., Kodachrome 64 is ASA 64, and Kodacolor Gold is ASA 100. Probably the film most sensitive to light is Konica 3200 at ASA 3200.

Because digital cameras don't use film, we can freely set the ISO setting via menu options and that flexibility is unbeatable compared to film, where you physically need to change film rolls for a different ISO setting.

So there, knowing the Aperture, Shutter, and ISO settings of your camera will let you take photos that are properly exposed.