The prefix "Photo" means "light" and "graphy" means "to paint, or to draw." Therefore, Photography literally means "painting with light."
(picture displaying the DSLR)
1. The light enters the lens and passes the aperture and lens elements. What is important here is the
aperture, which controls the amount of light that enters the lens. As the aperture size increases (big hole), more light enters, and as the aperture decreases (small hole), less light enters the lens.
2. After passing through aperture and the lens elements, the light reflects off the flip-up mirror (also called the shutter curtain), and it reflects off of the viewing system (also called penta-prism) and we are able to see the image after multiple reflections.
At this point, look at the diagram of the DSLR once again. The yellow lines are pathway for light, and we can see how it hits the 45 degree shutter curtain and reflects off the penta prism and enters our eyes.
3. When we press the button to take a picture, the flip-up mirror rotates as the
shutter opens and the light is recorded. The reason why the view finder turns black for a second is because the flip-up mirror changes its position. If you capture this light a highly light-absorbent material called film, then the camera is called film SLR, and if you capture the light with a computer chip, it's called a Digital SLR.
Now for a question. If a shutter is open for a long time, would the film (or the chip, usually called either CCD or CMOS) capture more light or less light? Obviously, it would capture more light, making the film brighter. We can see that the amount of time the film (or sensor) is
"exposed" to the light would have a profound effect on the brightness of the picture.
Back in the day, they called pictures "exposures" because that is basically how pictures are made - exposing highly light sensitive material to light for a certain amount of time. But for our purposes, exposure basically refers to the brightness of the picture.
There are 3 ways to control exposure:
1. Shutter Speed
2. Aperture
3. ISO
Shutter speed should be obvious because the shutter protects film (sensor) from light and opens up for a short period of time to "expose" the film to the light. If the shutter is open for a long time, more light would come in and make the film brighter and vice versa. Aperture should also be somewhat obvious because if the hole is big, than more light will enter; if the hole is small, less light will enter.
Then what is ISO? ISO is an acroynm for International Standards Organization, and it measures sensitivity of the film. Some films absorb lighty quickly while others are slow. If it's dark, you would probably want to use a film that absorbs light quickly, while using slow absorbing light for bright situations. With DSLRs, there is no need to change film to change the ISO levels. We still call it ISO but the sensor could change its sensitivity whenever you want.
Now, let's go into detail:
1. Shutter Speed:
Shutter Speed is measured in seconds, or fraction of seconds.
30s... 2s, 1s, 1/2s, 1/4s, 1/8s, 1/15s, 1/30s, 1/60s... 1/4000s
"s" here means seconds, obviously.
With all else being equal, if you open the shutter for a long period of time, say 30 seconds, your picture will turn out brigher than slower shutter speed, say 1/30 seconds.
Using less drastic example, if you chose your shutter speed to be 1/60 seconds but the picture turned out to be too dark. Then what should you do? How about using a slower shutter speed? Say 1/30 seconds? as your shutter speed decreases (slower) your pictures will become brighter.
The pictures below started with a shutter speed of one second, and gradually increased. What should happen as your shutter speed increases? It should become darker right? That's exactly what happens here.
Shutter speed: 1 second (200mm f/5.6 ISO 400). Don't worry about numbers in parenthesis, you'll learn them soon. The point here is that the exposure (brightness) will change if we make the shutter speed faster with all else being equal.
Shutter Speed: 1/2 seconds (200mm f/5.6 ISO 400) It's still too bright. In photography, we call this "overexposure."
Shutter Speed: 1/4seconds (200mm f/5.6 ISO 400)
Shutter Speed: 1/8초 (200mm f/5.6 ISO 400)
Shutter Speed: 1/15seconds (200mm f/5.6 ISO 400)
Shutter Speed: 1/30seconds (200mm f/5.6 ISO 400)
Shutter Speed: 1/60seconds (200mm f/5.6 ISO 400)
Shutter Speed: 1/125seconds (200mm f/5.6 ISO 400)
Now let's compared the last and the first picture. First picture is far too bright, which we call "overexposure," and the second picture is far too dark, which we call "underexposure."
Let's review what we learned through a graph:
30s... 2s, 1s, 1/2s, 1/4s, 1/8s, 1/15s, 1/30s, 1/60s... 1/4000s
◀----------------Brighter Darker -------------------▶
Here's one more essential vocabulary:
stops. In photography, a change of 1-stop means that the amount of light is either doubled or halved. For example, change of shutter speed form 1 second to 2 seconds would be a change of 1-stop, because the shutter is open twice as long, allowing twice the light to expose the film. The difference between 1/4 seconds and 1 second would be two stops, because it's letting in four times the light.
If your shutter speed is 1/4 seconds and I tell you to make it one stop faster, you should change it to 1/8. If I tell you to slow it down 2 stops, you should change it to 1 second.
As you can see, the above chart is written in increments of 1-stops. (2s, 1s, 1/2s, 1/4s, 1/8s...) but be careful - from time to time it's not exactly doubled or halved. For instance, after 1/8, 1-stop increase is 1/15, not 1/16 (look at the chart above). And though not on the charts, after 1/60, it's 1/125, not 1/120.
Should you memorize the numbers? No. Your camera will tell you the figures. Just know that 1-stop means that the lighting will either be halved or doubled, 2-stop x 4 or x 1/4.
2. Aperture
Aperture is measured in f-number, or f stops.
...f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 ...
Many people have trouble understanding f-stops because the numbers look funky and it's in fractions. Here's an easy way to understand it. Change the "f" into a "1." Now, f/4 becomes 1/4 and f/16 becomes 1/16. What's bigger? 1/4 or 1/16? Which hole allows more light to enter the lens? The bigger one, which is 1/4, or f/4 in this case.
Now the numbers above should make more sense. f/2 or 1/2 is actually a quite large fraction, while f/16, or 1/16, is quite small. We can see here that the aperture, or the hole, is gradually getting smaller.
Here is a picture of what f/2 looks like:
Here is a picture of what f/16 looks like:
(we can see that aperture is not exactly a "hole" but a collection of blades resembling a polygon. But for our purposes, calling it a hole is good enough)
Now, if I took a picture in f/5.6 and gradually made the aperture smaller, say f/16, what would happen to the picture? If you said it would turn darker, you are absolutely right. As the hole gets smaller, less light will enter the lens.
aperture: f/5.6 (200mm, ISO 400,
1/4seconds) Now you should understand 2 numbers here. f/5.6 refers to aperture, while 1/4 seconds refer to shutter speed. Now, we will keep everything the same and change the aperture gradually.
aperture: f/8 (200mm, ISO 400, 1/4seconds)
aperture: f/11 (200mm, ISO 400, 1/4seconds)
Our pictures are becoming darker, or "underexposed." This should be obvious since we are closing up the aperture.
aperture: f/16 (200mm, ISO 400, 1/4seconds)
aperture: f/22 (200mm, ISO 400, 1/4seconds)
Let's review with a chart:
... f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16...
◀---------Brighter Darker --------▶
Again the above chart is written in 1-stop increments. f/2.8 to f/4 halves the amount of light entering the lens. Therefore the difference between f/2.8 and f/4 is one stop. The difference between f/2.8 and f/5.6 would be two stops, etc.
ISO: (International Standard Organization)
The value of ISO usually starts off with a 100 (not always) and doubles each time.
100, 200, 400, 800, 1600, 3200...
As ISO increases, the film (sensor) becomes more sensitive to light and the picture becomes brighter. If you take a picture with an ISO 800 and find that it's too bright, you could lower the ISO to 400 and your next picture will become brighter.
ISO: 100 (200mm, f/5.6, 15seconds).
By now, you should be able to understand most of the numbers. ISO 100 means... that ISO is 100, or the sensitivity of film or sensor. f/5.6 refers to the aperture value, 15 seconds refer to the shutter speed.
200mm refers to the focal length. I will explain it in later posts but for now, think of it as "zoom." On most point and shoot compacts, 200mm equals a zoom of x11 or x10.
Going back to ISO. ISO of 100 was too low for the above picture. Let's gradually increase the number and see what happens.
ISO: 200 (200mm, f/5.6, 15seconds).
ISO: 400 (200mm, f/5.6, 15seconds).
ISO: 800 (200mm, f/5.6, 15seconds).
ISO: 1600 (200mm, f/5.6, 15seconds).
ISO: 3200 (200mm, f/5.6, 15seconds).
Compare the last and first picture. First picture is too dark (underexposure) and last picture is too bright (overexposure)
Let's review with a chart one more time:
100, 200, 400, 800, 1600, 3200...
◀-----Darker Brighter -----▶
Why does ISO double every time? Because film with ISO of 200 absorbs twice the amount of light than a film with ISO of 100. Again, the ISO chart above is written in 1-stop increments. ISO 100 and 200 differs by 1-stop, and ISO of 200 and 1600 differs by 3 stops, etc.
Now, it's time for a quiz to see if you understood everything:
Hypothetically, my camera setting was ISO 400, f/11, 1/8 seconds when I took a picture.
1. What do those numbers mean?
2. What do I do if I want to make the picture brighter by 1-stop?
3. What do I do if I want to make the picture darker by 1-stop?
I will rewrite the chart for your convenience:
Shutter speed:
30s... 2s, 1s, 1/2s, 1/4s, 1/8s, 1/15s, 1/30s, 1/60s... 1/4000s
◀----------------Brighter Darker -------------------▶
F stop:
... f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 ...
◀---------Brighter Darker ----------▶
ISO:
100, 200, 400, 800, 1600, 3200
◀-----Darker Brighter -----▶
Answer
1. First answer is quite easy. 400 is the ISO, f/11 is the aperture, and 1/8s is the shutter speed.
2. To increase the exposure by 1stop There are 3 ways.
a. Change the shutter speed from 1/8s to 1/4s (slower shutter, brighter picture)
b. Change the aperture from f/11 to f/8 (bigger hole, brighter picture)
c. Change ISO from 400 to 800 (higher ISO, brighter picture)
You could choose any of the three methods, and your picture will be exactly 1 stop overexposed (brighter) than the first picture.
3. There can be multiple answers, but it's similar to question number two.
a. Change shutter speed from 1/8 to 1/30.
b. Change aperture from f/11 to f/22.
c. Change ISO from 400 to 100.
d. OR you can change shutter speed from 1/8 to 1/15 (1stop darker), AND change aperture from f/11
to f/16 ( another 1stop, so it's 2stops darker)
e. Change Shutter speed from 1/8 to 1/15 and change ISO from 400 to 200.
f. Change Aperture from f/11 to f/16 and change ISO from 400 to 200...
Then your picture will be exactly two stops darker. All 6 pictures all will have exactly the same exposure.
Now on to the second question:
My camera setting was ISO 400, f/11, 1/8second. If I wanted to change my aperture to f/8 but keep the same exposure, what should I do?
Answer: Change from f/11 to f/8 means that the the picture will be 1stop brighter. If you want to keep the same exposure, there are two ways:
a. Change shutter speed from 1/8 to 1/15.
b. Change ISO from 400 to 200.
Why? My picture became 1-stop brighter because of the aperture, so in order to keep the same exposure, I need to adjust either the shutter speed or the ISO by 1-stop to make it darker.
But now you should have a question that's something like this:
If a picture taken with: ISO 400, f/11, 1/8s,
and a picture with ISO 400, f/8, 1/15s has the same exposure, will it look the same too?
The answer is NO. Though the above two pictures will have the same brightness, it will not look the same.
I will write about the differences in the second post...
