DIGITAL PHOTOGRAPHY #101: APERTURE Part 1 of 2
by 
VSPHO
May 12, 2012
VSPHO
May 12, 2012 Life is a series of moments that leaves us with memories, both splintered and whole.
If you are just joining us, the PRELUDE & SYLLABUS section is the logical starting point for the series.
Welcome to Digital Photography #101,
by Virtual Studio Photography (VSPHO)
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Understanding the concept of the Aperture is key to understanding the manipulation of light.
The aperture on a camera is a function of the lens.
When utilizing the features of a more advanced DSLR (Digital Single Lens Reflex) camera, understanding the aperture settings is paramount.
The aperture itself is the adjustable opening towards the back of the lens and functions as the Iris does in the human eye.
The opening and closing of the aperture regulates the quantity of light (photons) that are allowed to project onto the digital camera's sensor chip (or film on a 35mm film camera).
This is metaphorically the equivalent of regulating the amount of water pressure allowed to flow when regulated by opening or closing the kitchen faucet.
With the aperture, the bigger the hole, the more light (photons) that are allowed into the camera.
The measurement of this orifice/aperture is called the "f-stop".
I will make this easy below, so hang on.
The f-stop is a ratio between the focal length of the lens divided by the diameter of the orifice/aperture; hence the f-stop.
OK, let's make this easy to comprehend.
Just relate RATIO to Alice in Wonderland, "everything SMALL is BIG, and everything BIG is SMALL." Say that phrase ten times and you will have memorized the concept, really.
Because it is a ratio of division, it's always the same: a SMALL number = a BIG orifice. A BIG number = a SMALL orifice.
We'll get to some practical examples to illustrate in a minute.
To keep this simple, we will only be using the standard fixed focal length, 50mm lens as our example.
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We are using 50mm as our focal length as 50mm is the visual/spatial perception that compares most closely to the human eye.
Other focal lengths and spatial perception will be discussed in the section on lenses.
NOTE: The actual diameter of the front element (the first/front lens) has a role in lens performance, but is not involved directly with the aperture calculation.
Theoretically, a 50mm focal length with a 50mm aperture would equal a 1:1 ratio. The usefulness of this ratio would not be beneficial to the absorbent costs to manufacture such a lens.
The largest lens ratio commonly manufactured is a 1:1.4. These lenses are very expensive and are also the most light efficient.
Let's look at the practical f-stops now.
The standard f-stops are 1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22, 32. Pretty much the "smallest" f-stop I've seen is a 32. To be clear, a f-stop of 32 is not much bigger than a "pin-hole." ( 50 mm lens divided by f-stop 32 = 1.56 mm diameter of the aperture)
Understanding the ratios is an intermediate level comprehension, so follow along if you're interested.
Because this is a ratio, the actual area will be in proportion to the focal length, but the area of the front lens correlates to the lowest f-stop available. To clarify, you can only get to an aperture of 1.4 on any focal length if the FRONT lens diameter is large enough, a more expensive lens.
This is why we are not comparing actual lens sizes, (bigger lens cost way more money) just how much light they allow to pass to keep the comparison of light transmission apples to apples.
If our lens starts with the largest aperture (smallest number) at 1.4, then the next f-stop of 2.0 will let in HALF the light. f-stop 2.8 lets in HALF the light of 2.0. f-stop 4.0 lets in HALF the light of 2.8...
Let me explain, we are working with the area, not diameter of an opening/orifice.
So if you do the math, in a nut shell, approximately a 40% reduction in diameter will decrease the area by half. If you do the math, you will find the actual f-stops are rounded to the nearest tenth anyway.
Conversely, when you INCREASE the DIAMETER of the orifice/aperture by approximately 40% (rounded to the nearest tenth), you DOUBLE the area.
Another analogy that works well with f-stops are the notes on a piano. From middle C, the next C note up is exactly double the frequency. Every C note down is exactly half the frequency of the previous C note.
So, two f-stops bigger (smaller number) equals four times as much light allowed to pass through the aperture. Say from f-stop 8, we go three f-stops bigger (smaller number) to 2.8 (from 8 to 5.6, 4.0, 2.8) we are letting in eight times more light (2x2x2=8 or 800% more light).
This is a good stopping point for APERTURE part 1.
Hold the CNTL key and hit + or - to control the image size.
Click HERE for larger PICTURE. Then hit the "back arrow" at top left of page to return.
In APERTURE part 2, we will look at the implications of changing the aperture, both technically and artistically.
Virtual Studio Photography (VSPHO)
Tags: PHOTOGRAPHY , DIGITAL PHOTOGRAPHY
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.
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