The 3 Factors of Exposure – Part 2 – Shutter Speed

<- Back to Part 1 – ISO

Introduction

On the previous page, I described how ISO impacts the exposure of a photograph. ISO is what I call “Sensitivity” in my 3 factors of exposure:

  • Sensitivity
  • Duration
  • Amount

We will now look at Shutter Speed, or, in my 3 factors, “Duration”.

What is a Shutter?

To understand Shutter Speed, we need to look at the mechanics of photography a little more than we have done so far. With ISO, I described this was the measure of sensitivity of the media you’re capturing the image on. In modern cameras this is often a sensor chip that turns analogue light, into digital data.

But before light enters the camera and hits the sensor (or film if you’re shooting with film), the camera can “manipulate” the light, to control the exposure in other ways too. For the purposes of this guide, I’ll stick to talking about digital SLR cameras, but the principles are the same across all forms of photography, even if you don’t have a physical shutter mechanism on the camera!

Shutter Speed is all about how long your media will be exposed to the incoming light. Before you take the photograph, the shutter is already “shut”, and no light is exposed to the sensor. As you take the photograph, the shutter “opens” and light hits the sensor to be recorded. The final stage to the photograph is for the shutter to “shut” again and stop the flow of light to the sensor.

This all happens very quickly.

How Does the Shutter Speed Change the Photograph?

The basic principle is this: The longer you let light in, the brighter the image.

But as with all of the 3 factors, there’s a side effect to using Shutter Speed to control the exposure. The longer you let light hit the sensor, the more Motion Blur you will get.

What is Motion Blur?

Motion Blur is simply when something (or everything!) in the image has moved while the camera was exposing the image. The most common form can be seen in image stability. If you’re using a slow shutter speed, and you don’t hold the camera still enough, you’ll get a blurry image as everything moved while the shutter was open.

Another form of Motion Blur is when a moving object is travelling too fast for the shutter speed. It will leave a trail of light across the image as it moves. This isn’t always a bad thing, you might want to do this to demonstrate movement. But often it isn’t desired at all.

So let’s start to look at some examples to really demonstrate the impact of shutter speed.

Let’s go back to our original photographs of the herb jar from the ISO examples. I set the ISO to 500, the aperture to f/3.5 and the shutter speed to 80 and this is what we got:

iso1

Shutter speeds are measured in fractions of a second, so a Shutter Speed of 80 is 1/80 of a second, and if you know your maths, you’ll work out that that’s about 12.5 milliseconds.

A shutter speed of 80 is relatively slow already. If I don’t hold the camera reasonably still while taking this photograph, I’m going to end up with some blur, but with the ISO and Aperture I’ve set, to get enough exposure, this is the shutter speed I need to work with.

Let’s speed up the shutter, I’m going to go for 250 now:

shutter1

I can’t see anything! The shutter speed is so fast, that with the ISO and Aperture I’ve set, there’s not enough light getting to the sensor to expose a good image. Only the brightest of areas are getting through.

Let’s go the other way and slow it right down. It’s actually become a lot darker in my kitchen while writing this so I’m going to slow it right down to 6, which doing the math, is about 166 milliseconds; so slow that I can hear the shutter (and the camera mirror) click open and then separately click shut.

shutter2

Now I have a much brighter image, but with a lot of movement blur! Take a closer look at what’s happened:

shutter2b

Not good at all. This demonstrates that at this shutter speed, I can’t keep my hand steady enough to avoid blur. Of course I could have used a tripod with a timer or remote shutter release to avoid this, then the only blur I would have got is if something in the scene moved rather than the camera.

…which moves us nicely onto Motion Blur from moving objects. One of the easiest ways for me to demonstrate this is by photographing water dribbling from a tap.

It has become even darker in the kitchen now and I’ve had to turn the light on. As a result, I’m going to have to use some very high ISO values to get some good images if I don’t want to use a flash.

Let’s start with some basic settings. The kind that would be perfectly OK if I didn’t want to photograph something moving. Im using an Aperture of f/3.5, ISO of 2500 and a Shutter Speed of 1/320. These settings are already way over the top for a shot in this lighting, I could probably get away with a much lower ISO and Shutter Speed, but I want to capture at least some of the water so I’ve gone quite high. Here’s what I get:

water1

Not bad, you can see the water, and the image is well exposed, however I can see Motion Blur. If I wanted to demonstrate water moving using the motion blur, I’d want more, and if I wanted to capture the water, frozen perfectly in time, I’d want no Motion Blur at all.

Let’s try slowing the shutter even more to get even more Motion Blur. I’ll also lower the ISO a bit to account for the extra amount of light being let in. The following photograph is taken with f/3.5, ISO 1000 and a Shutter Speed of 1/125:

water3

 

 

That’s a pretty good effect! It conveys the movement of the dripping water perfectly without it being too blurred to tell what it is.

Now let’s go the other way, and get a nice sharp image of the water drops, without blur. I’m going to use f/3.5 again, with ISO 6400 and a Shutter Speed of 1/800:

water2

 

 

And there it is, there’s still a touch of motion blur if I’m being picky, but any higher on the ISO and the noise will be too much for me to bear. The only way I would have been able to increase the Shutter Speed now without raising the ISO, is to change the Aperture setting, which leads you nicely onto the next part

 

Next, Part 3 – Aperture ->

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