How does a camera works?

I know it sounds very “basic”, but I wanted to write some basics of how cameras works and how this can be used in photography.

Sounds nice, doesn’t it?

So let’s start. As said before, I’m not an expert in the topic, but I’ll try to bring some information.

Three parameters define how much light is “stored” in the detector. The aperture of the lens, the shutter speed and the sensibility of the detector, also called ISO.

In film we basically could only play with aperture and shutter speed, since changing the film was “a bit too much” (there were options like, underexpose and then get it developed with longer exposure, and so on).

Each one has consequences, or a price.

ISO: the higher the ISO, the higher the sensitivity, therefore more of the incoming light is effectively registered by the detector. The trade off is the noise. The higher the ISO, the larger the noise.

The usual very low noise ISO value (also very used in film) is ISO 100, but the newest detectors in “normal” dSRL’s, can get up to ISO 12800 and the noise from ISO 1600 is perfectly dealt by software like Adobe Photoshop. Sometimes the creative needs of your photo require a high ISO, for example, because you need a fast shutter speed and a small aperture, or because it’s dark, like indoor without a flash.

I don’t remember the exact quote, but Jay Maisel has commented in Scott Kelby’s “A day with Jay Maisel” that, if you increase the ISO you might get noise, if you DO NOT increase the ISO you DO NOT get a picture. Better a noisy picture than no picture.

Than you have shutter speed and aperture left to be set and they have very important creative and technical impact in your photo. I’ll make further posts on the topic, but I’ll comment things “in a nutshell” now.

Aperture: it has impact on the depth of field, i.e., how much of your image will be in focus. But first getting back to the aperture itself. You can control the amount of light you allow into your detector, by closing or opening the lenses’ pupil. This amount of aperture is given in focal ratio (f-stop or f-number) and expressed in f/N. The larger the N, the smaller the aperture, so that a “2” aperture, allows more light than a “4”.

Pupil aperture expressed in F-Stops. The larger the number, the smaller the aperture.

A common expression is “one stop“. To “add” one stop means twice as much light. This can be achieved by increasing the aperture, or the shutter speed, or the ISO.

The f-stop is not a linear scale, but a power of square root of two. This way, f-stop 2 is not twice as much light as f-stop 4, but actually 4 times as much light.

This way we have square root of two, to the zeroth power, and this is “1”. The next stop will be square root of two, to the 1st power, and this is square root of two (~1.4, f-stops are rounded up to a “reasonable” number). The next stop will be square root of two, to the square, and this is “2”, and so on.

So we have f/1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 …

Of course, if your lenses allow it, you can set apertures that are not “full stops” from “1”.

Shutter speed: the other counter part is the exposure time, i.e., how long will you allow light to get to your detector.

Shutter speed is given in fraction of a second, so that the larger the number, the smaller the time light goes into your camera. The number you see is actually 1/the number, unless specifically indicated with a (seconds) after the number.

There are several creative reasons to choose one or other shutter speed. You can “freeze” action, or “allow” the action to be seen. It also has to be adequate for your situation. If you handholding your camera, you want your exposure short enough to prevent you natural hand and body shacking from blurring your shot, or to prevent your subject from moving and getting blurred …

Shutter speed, as ISO, is a linear scale. 1/125 of a second allows twice as much light (one stop more) as 1/250 of a second and four times more light than 1/500 … ISO is the same: ISO 100 collects half the light (one stop less) of ISO 200 that, in turn, collects half the light of ISO 400 …

Those are the three points you control in your camera, apart from focus, and to where do you point it 🙂

In the next post I’ll comment and exemplify on the effects of ISO, aperture and shutter speed in the photography.

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About Cris Da Rocha

Astrophysicist, DB manager, cyclist, musician and, why not, "photographer to be". Back to enjoy photography after many years ... it's cool. Might share something nice and get something new.
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3 Responses to How does a camera works?

  1. Emad says:

    Very Helpful Post !

  2. Pingback: Photography for beginners – Exposure | Photo and Coffee

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