Aperture & shutter speed explained

Affordable DSLRs are spawning everyday, amateur photographers everywhere. More and more people are asking how to take a better photograph now that they’re equipped with more serious equipment then the ubiquitous pocket digital camera.

I get asked questions such as “how many megapixel camera should I get?”, “what is the perfect shutter speed?”, “should I buy Canon or Nikon?”, “what is the best lens?” There are no right answers for any of those questions. My best response is usually, “It all depends.”

I’m not professional-level photographer by any means. However, having gone through three semesters of photo and darkroom studio courses during the course of my design studies and having fiddled with SLR cameras since 1983 puts me in a slightly better position to answer these questions with ample amount of credibility. So, here goes my humble yet believed to be solid attempt at Photography 101.

First of all, why would anyone want to shoot with an SLR when any decent modern pocket camera is capable of capturing great photos? Simply put, it’s like driving an automatic transmission vs. manual transmission, Chef Boyardee vs. making your own ravioli, pre-arranged marriage vs. freedom to pick your own spouse. The automatic version gets the job done. But it’s the manual version of things that produce something far more interesting.

Here are couple of basic camera terminology in plain English:

Aperture refers to an opening of a diaphragm in the camera lens that controls the amount of light taken in by the lens. This is indicated by an f-number or f-stops written as f/1.8, f/2.0, f/2.8, f/3.5 or simply 1.8, 2.0, 2.8, etc…. The lower the number, the larger the opening. Larger opening lets in more light into the camera. Higher the number, the opposite.

Shutter is a curtain between the lens and the sensor. Shutter speed refers to how long the shutter stays open. Therefore, the shutter speed controls the ‘duration’ of the light hitting the sensor. This is indicated in seconds. 1/1000 (1 thousandths of a second), 1/500, 1/250, 1/125, etc… or simply 1000, 500, 250, 125, etc…

ISO refers to the sensor’s sensitivity to light. In the film days, the film itself was given the ASA/ISO number (100, 200, 400, etc…) which indicated the film’s sensitivity to light. The digital camera lets you dial in these numbers right in the camera which mimics the film ASA/ISO. The higher the number, the sensor becomes more sensitive to light. Higher light sensitivity means it needs less light to achieve a given exposure.

How does aperture and shutter speed work in combination? How do they affect each other?
I like to use the analogy of running water and a bucket. Let’s picture a faucet and below it, a bucket.
The amount of water flowing out from the faucet determines how fast the bucket gets filled and ultimately affects the duration needed to fill the bucket. In this analogy:
WATER is the light LIGHT
BUCKET is the camera SENSOR

More water means it will take less time to fill the bucket – in camera, the larger the aperture (larger the opening), less time is needs to achieve a given exposure.

Less water flowing out from the faucet means it will take more time to fill the bucket
– in camera, the smaller the aperture (smaller the opening), more time is needed to achieve a given exposure.


That pretty much explains the relationship between aperture and shutter speed.
Basically, the more light the lens takes in, the less time the shutter needs to stay open for a given exposure.

Given this relationship, it’s possible to use LARGE APERTURE at FAST SHUTTER SPEED or use SMALL APERTURE at SLOW SHUTTER SPEED to achieve the same exposure.

Following combinations would yield to same exposure:
a.) 1/500s + f/5.6
b.) 1/250s + f/8
c.) 1/125s + f/11

Combination a.) has faster shutter speed and a large aperture.
Combination c.) has slower shutter speed but a smaller aperture

However, even though the above combinations result in same exposure, the effects on the resulting image can be very different depending on the subject, lighting condition, and motion. This is where the text-book definitions end and fun and imaginations begin. Faster shutter speeds freezes action. The aperture of a lens affects the depth of field (the range of distance the subject is in focus). ISO also affects how much light is needed for a given exposure.

Shooting in manual mode allows you to explore endless possibilities. Mastering the exposure triangle (aperture, shutter speed, ISO) breaks you free from what has been pre-set in the camera. There are thousands of articles out there written about creative picture taking techniques. Understanding the basics of the relationship between aperture, shutter speed, and ISO will help you learn those techniques faster.
Shoot away!

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