This is the third installment of the “You Asked For It” series and we will discuss Shutter Speed today. Shutter speed is one method which controls the amount of light that reaches the film or digital sensor.
Oh no, their’s more than one method ?
Yup ! Last week we discussed aperture or lens opening which is the other way we control the amount of light reaching the film or digital sensor.
OK, now you’re full of it Joe, you wrote a whole damn article on depth of field and you had me believing that ?
Aperture does control depth of field, but it also is another way to control the amount light that reaches the film or digital sensor.
Remember last week when I told you I didn’t want you to worry about how aperture is related to shutter speed and formulas ?
Guess what, I lied 🙂
We have to understand the relationship between aperture and shutter speed to be able to control light in manual mode.
The above chart will show in graphic form how aperture and shutter speed are linked. You will see as the aperture is increased (lower number) shutter speed must increase. Think of this graphic as a child’s SeeSaw with the pivot point in the middle indicating the perfect exposure and it will become clear how aperture and shutter speed are linked.
Why is this ?
When we increase the aperture or open the lens (lower number) we are letting more light into the camera. By doing this we have to also increase the shutter speed so the shutter stays open for a shorter time or else we would overexpose the image. If we were to use the opposite example by closing the aperture (higher number) we are letting less light into the camera so the shutter speed must be decreased so the shutter speed would stay open for a longer period of time to compensate for the lower light.
To prove the above chart is accurate i would like you to take your camera and put it into Aperture Priority mode (remember when we are in aperture priority mode we are controlling the aperture and the camera is selecting the shutter speed). Point the camera towards a brightly illuminated window or go outside if you prefer and change the aperture from its lowest number to the highest number. I want you to take notice to how the shutter speed is reacting as you change the aperture. Open the aperture and the shutter speed gets higher, close the aperture the shutter speed gets lower.
OK Joe but I thought this lesson was about shutter speed, and I’m still playing around with the aperture ?
Good point, now lets put the camera into Shutter Priority mode.
Can anyone tell me what happens when we put the camera into this mode ? A show of hands please !
Yes you in the back with your hand raised really high Pauline, you are absolutely correct we are choosing the shutter speed and the camera is automatically selecting the corresponding aperture to achieve the correct exposure.
Why on earth do I need to know this ?
Lets say you wanted to take a photo of a fast moving object such as a train or an automobile. You really would not be too concerned with depth of field you would be more concerned with how to capture this object so it is clear. To do this you would have to freeze motion.
How do we freeze motion and am I going to be cold during this lesson ?
I am talking about freezing motion by using a higher shutter speed not by temperature 🙂 By choosing a higher shutter speed (higher number) we are keeping the shutter open for a shorter period of time.
If you notice shutter speeds are expressed in fraction form 1/8000, 1/4000, 1/2000,1/1000, 1/500, 1/250, 1/125 and so on.
Do you notice a pattern with these numbers ?
Very good Elina, they all look like they are exactly half of each other. For example 1/1000th of a second is half of 1/500th of a second. We can also state this as 1/1000th of a second will let exactly half the amount of light into the camera as 1/500th of a second, or expressed in photography terms 1 stop faster. If we reversed this 1/500th of a second will let exactly twice the amount of light into the camera as 1/1000th of a second or 1 stop slower.
You might have noticed in the previous lesson on Depth Of Field the lens opening or aperture is expressed in numbers also. Lets show that chart again.
Do you notice any similarities with the numbers on this chart ? f/4 looks like it’s letting half the light into the camera as f/2.8, and f/5.6 looks like its letting half the light into the camera as f/4. These are called f stops and f/4 is one stop slower than f/2.8 or we could also say that f/4 is letting exactly half the light into the camera as f/2.8. As we look at the chart we will see that as we close the aperture or increase the number (higher) each f stop or f number lets in exactly half the light as the previous f stop.
OK so now that we know the camera aperture and shutter speeds are calibrated in stops we could make sense of why aperture and shutter speed are linked.
Lets say we point the camera at an any object and the meter on the camera is reading 1/125th of a second at f/8 for proper exposure. Now lets say that object is a person and we want to isolate this person from the background by using shallow depth of field. Well the camera is reading f/8 so I am not going to be able to isolate the background with that aperture so I want to open the aperture to f/2.8 to get the pleasing background. I cannot just change the aperture and expect not to compensate with the shutter speed and still achieve proper exposure so lets count backwards. As I change from f/8 to f/5.6 (one stop increase) I am letting twice the amount of light into the camera so I would have to increase the shutter speed by one stop from 1/125th of a second to 1/250th of a second (one stop decrease).
Why are you saying decrease when the shutter speed is getting higher ?
Because as we increase the shutter speed from 1/125 to 1/250 we are letting half the light into the camera to compensate for the increase of twice the light by opening up the aperture from f/8 to f/5.6. Starting to make sense ?
Lets continue to count backwards because I want to open the aperture to f/2.8 to photograph this person. Now lets open the lens to f/4 or 1 more stop so once again we are letting twice the amount of light in so we have to increase the shutter speed to 1/500th to compensate or 1 stop less. Lets continue and change the aperture to f/2.8 or 1 stop more and once again we are letting twice the amount of light into the camera so we compensate by increasing the shutter speed to 1/1000th one stop less. We now have the aperture where we want to have a pleasing background and we are still getting correct exposure. In other words 1/125th @ f/8 is the same exposure as 1/1000th @ f/2.8 all we did was adjust the camera from its suggested exposure to properly fit the situation of taking a photo of someone where we wanted to have a pleasing out of focus background. I showed you an example of a camera in manual mode, if your camera was in aperture priority mode the shutter speed would change automatically as you changed the aperture.
First I am going to show you the difference between a photo taken with a slow shutter speed and then I will show you one taken at a faster speed. The photo on the top was taken with a shutter speed of 1/13th of a second. This was done intentionally to convey speed or motion. This technique is known as motion blur and even though the bicyclists and car are really not moving that fast using a slow shutter speed exaggerates their motion.
This performer was in the Quincy Market Square in Boston and was using a giant Pogo stick. He was about 5 to 6 feet in mid-air as the interested crowd looks on. Notice how using a shutter speed of only 1/200th of a second almost totally froze him in mid-air. If I would have had the light to increase the shutter speed to lets say 1/500th of a second this photo would have been totally sharp. This is known as freezing motion.
As you become more familiar with aperture and shutter speed and practice using different settings you will begin to understand why some of you photos are turning out great and why some not so great. When you understand these concepts you will be able to identify settings or mistakes you might of relied on the camera to take care of before and correct them on the spot so you don’t miss the shot. I know this lesson was a little more difficult than the previous ones but as we progress the lessons will get more complex. I am trying to make these lessons as easy to understand as I can but if you do not understand something please email me through the contact me page.
Next Friday – Metering and Exposure