Question by MK: Why is it that when you make the aperture on a camera lower, the people’s movements are frozen?
I thought that when you make the aperture lower the lens opens less wide, restricting the amount of light. I am confused as to why the movements are also ‘frozen’.
Best answer:
Answer by mywaphel
Aperture doesn’t directly affect movement. Shutter speed does. If you stop down (higher aperture number, ex. 32) then you have to use a slower shutter speed. If you open up (lower aperture number, ex. 2.8) then you can use a faster shutter speed.
The faster the shutter, the less motion blur.
Give your answer to this question below!
The aperture scale on a lens is an inverse relationship – the smaller the number (f1.4, f2) the larger the opening of the diaphgram in the lens. The larger the number (f8, f11, f16) the smaller the opening.
Correct exposure is a triangle composed of f-stop, shutter speed and ISO.
ISO is a measurement of the sensitivity to light of a light sensitive surface, whether fiilm or digital sensor. A low ISO (50, 100) is very insensitive and requires either more light or a slower shutter speed. A high ISO (400, 800) is more sensitive and requires either less light or a faster shutter speed.
The size of the f-stop determines how much light is admitted by the lens. At f1.4 all available light is admitted; at f16 very little light is admitted.
The shutter determines how long the light admitted by our lens is allowed to expose our film or sensor to make a correct exposure for a given ISO. Our shutter speed also determines whether motion will be frozen or blurred. A fast shutter speed (1/500, 1/1000) will literally freeze motion. a slow shutter speed (1/15, 1/30, 1/60) will cause motion to be blurred.
The following chart is based on the old “Sunny 16 Rule” which states: “On a sunny day, set your f-stop to f16 and your shutter speed to 1/ISO.” (Note: This was invented when shutters were mechanical so we used the shutter speed setting closest to the ISO we were using.)
ISO 100
f16 @ 1/125 sec.
f11 @ 1/250 sec.
f8 @ 1/500 sec.
f5.6 @ 1/1000 sec.
f4 @ 1/2000 sec.
As you can easily see by reading down the chart from f16 to f4, our shutter speed increases every time we “open up” our lens. Why? Because f11 admits twice as much light as f16, our shutter speed doubles. Use the shutter speed at f16 for f4 and our picture will be overexposed and ruined. Reading up the chart from f4 to f16 you see our shutter speed decreasing. If the shutter speed at f4 was used at f16 our picture would be underexposed and ruined.*
The book “Understanding Exposure: How To Take Great Photos With A Film or Digital Camera” by Bryan Peterson would be a good addition to your personal library.
* If you’re having difficulty believing this, take your camera outside on a sunny day and set it in Aperture Preferred Mode (you select an f-stop, the camera selects a shutter speed). Set your ISO to 100 and your f-stop to f16. Note the shutter speed the camera selects. Now open up to f11 and note the shutter speed. Since your camera has an electronically controlled shutter which is essentially “stepless” you may see f16 @ 1/100 sec., f11 @ 1/400 sec., etc.
Now place your camera in Manual Mode at ISO 100 and set the aperture to f16 and your shutter speed to 1/125 and take a picture. Now open up to f11 BUT leave the shutter speed at 1/125. Repeat for f8, f5.6 and f4.
Now do the reverse. With the camera still in Manual Mode at ISO100, set your aperture to f4 and your shutter speed to 1/2000. Stop down to f5.6 BUT leave the shutter at 1/2000. Repeat for f6, f11 and f16.
From looking at the resultant pictures you’ll see the ISO/shutter speed/f-stop relationship.
Think of it this way… I like to use painting as a quick teaching tool.
Stopping motion is relative to painting fast. A lot of paint (wide aperture) and a fast painter (Shutter speed) are necessary to accomplish that.
As with all things in photography, in order to get one thing, you need to sacrifice something in exchange. In this case, it’s depth of field or quality of clarity throughout the ‘painting’ if you will.
Because a massive amount of paint was used (open aperture) in a very short period of time (shutter speed), the fine details get lost in other parts of the image… backgrounds are blurry… the subject may show partial clarity but loose some of the other details that may have escaped the limits of the shot/painting.
Actually “when you make the aperture lower the lens opens less wide, restricting the amount of light” is NOT true… in fact, what you are doing is opening up the gates so light can expose your film faster. The lower number represents a wider aperture (i.e. f/22 is a pin hole when compared to f/1.4 which is wide open).
Here is some reading from a site I located on the web that can help you with this: http://www.cameratown.com/guides/aperture.cfm
If you are lowering the aperture number, you are making the opening in the lens that lets the light in larger. The lower the number, the larger the opening.
Since you don’t mention that your images are over or under exposed, I assume you are shooting in Aperture Priority (AP) mode. What the camera will do to keep the exposure ‘correct’ is increase the shutter speed. By letting in more light with the larger aperture, the shutter speed has to be adjusted to a faster speed in order to let light in for a lesser time. That’s what is freezing your movements.
Vance