Basic Camera Exposure

So first off we know that a photograph is essentially made up of light hitting a sensor or a piece of film and then the sensor/film reacting/interpreting to said information and turning into a photograph.

You’ve probably seen lots of photos with traffic streaks like this. In case you didn’t know, this effect is essentially obtained by using a long shutter speed i.e. long exposure

The term exposure kind of refers to the light that actually hits the sensor and this is affected by three different things:

  • Shutter Speed: this is how long we expose the sensor to light. I find for most people, anything less that 1/60 is susceptible to camera shaking. I personally risk going down to 1/30 and maybe even slower but either I’ll hold my breath (just for a split second) or use some other fanciness to keep my photo nice and sharp

  • Aperture: So this is the size of the opening in the lens. It is measured in f-stops. The relationship between aperture and f-stop is kind of like what happens with distance and meters. You can say something is a long distance away but you need a number of some unit to quantify that distance. As such, you can say a large aperture or a small aperture but you need a number to quantify what that aperture actually is. A low f-stop number means a high aperture while a high f-stop number means a small aperture. On the camera you will see the f-stop number. The lower this number, the wider the opening and the more the light can come through.

  • ISO: This is the sensitivity to the light and can be anywhere from ISO 50-409,600 depending on the camera of course. Crop sensor cameras, which are most of the cheaper cameras in the market, have ranges typically between 100-12800. I wouldn’t advise shooting higher than ISO3200 cos otherwise the photo will probably be just too grainy. A higher ISO means the camera is more sensitive to light so needs less light to get the right exposure than if you used a lower ISO. However the tradeoff is that using a higher ISO means you get a grainier image so the general rule is shoot in the lowest ISO you can get away with for your situation.

The combination of all these things will come together to create the exposure. The exposure is essentially the sum of light that has come through the camera. If we want to use a faster shutter speed, to keep the same exposure we would need to increase the ISO or use a higher aperture. Alternately if we want to use a lower ISO, we would need to use a slower shutter speed or a higher aperture or a combination of both. We could also fire the flash as this would increase the amount of light the camera could capture. Although this would bring in additional considerations. In the next post I’ll try to explain some information about camera modes and what modes are useful where.


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