Hi and welcome back. This week we going to talk about the shutter of the camera, this opening is the part that allows light through, and working with the sensitivity and aperture selected becomes the third port of the exposure triangle. We are not talking about flash here, this is all about how thing work in natural or ambient light. Flash is a little different.
If you missed or would like to review the earlier blogs, just visit the articles page and select the story of interest. So to recap really quickly, there are three sides to the exposure triangle. These three parts work together as a balancing act to achieve a correctly exposed image, and to determine the key parts which are the primary points of interest and focus.
Before we get too far into the shutter and speed, let’s consider what shutter really is. Here we’ll talk about a camera which has a mechanical shutter. Mobile phones operate using electronic shutters of a fashion as they have no moving parts, they capture an image from a frame of continuous image capture, like a video rather than opening a shutter to capture a single frame as a still image. If you’ve ever taken the lens off an old SLR or modern DSLR camera and looked inside you may have seen that in older cameras there may have been a fabric screen and in more modern cameras a rectangle of metal leaves which cover the hole between the lens that leads to the rear of the camera where the film or in digital cameras the sensor is found. This screen or curtain is actually the shutter inside your camera, it’s made up of a first shutter or curtain and the second shutter or curtain. In between taking each image the shutter resets after the curtains pass. When pressing the shutter release, the first curtain travels down until the frame is entirely open and then the second shutter follows the first and blocks out the light. Depending on the shutter speed, the opening may be fully open before the second curtain starts, or with fast shutter speeds, the curtains are close together, and the opening is never fully open, it’s like shining torch light and moving it from one spot to the other, only when the light hits, is that part of the sensor between the two curtains actually exposed to light.
Look at this image, you can see that the shutter starts off in a closed state. When the shutter is released by pressing the button the first screen begins to move, depending on the shutter speed you’ve selected, this will determine how quickly or slowly the second curtain will follow the first. Looking at the first row we can see that the first curtain moves all the way open and full light comes through and the image is seen. And the second row you can see that the second curtain starts chasing the image away and comes to a completely closed state which then resets for the next shutter release. This is a very slow speed and the shutter is fully open, if higher speeds, the entire sensor is not exposed as a while, but just a part as the curtains are very closely following each other.
So now we have the basic understanding of what the shutter is, but why is it the third part of exposure triangle? Let’s think about this, it all has to do with how fast the two curtains move and how long the light is allowed to come through. When taking a photograph you’ll hear a lot of terms like 1/60, 1/128, 1/800, 1/1000, 1/2500, 1/8000 and alike. You might also hear the terms ‘half a second’ or ‘a full second’. You may also sometimes hear these called things like a 60th of a second or 128th or something similar, well these all basically talking about fractions of a second. The higher the number the less time the shutter is open and the lower the number the longer to let more light through.
Using shutter speed, balanced with the ISO or sensitivity and the aperture we can adjust the amounts of light coming through the lens to be exposed onto the film or sensor of the camera. Balancing between the sensitivity in the first part, determining how much we want to be in focus from a depth of field perspective will then assist us in determining how fast or slow we need shutter speed to be. The other side of the equation is if we want to capture a really fast moving objects and freeze the action and we will need a higher shutter speed which then may mean we need to open up the lens with a lower aperture number. In a dark situation we may need to look at increasing the sensitivity to let more light in, maybe also opening the aperture more to let in more light and then also slowing the shutter to let in more light.
So it’s a balancing act of those three main parts, but is that all there is to? We just mentioned that you might want to freeze the action, what is it mean to us? Well if you have someone running and you want to stop the beam in motion you need to have a very quick exposure of that image, whereas if use a slower shutter speed it may be a blur because they’re still moving while the shutter is open or their feet and arms may be more blurred than other parts of the image for that same reason. So keeping the shutter open for a longer time allows more movement to be captured and for a lesser time allows you to stop movement, whether you want slow or fast shutter speeds is your creative decision.
The use of shutter speed is one of those things that may be a prime thing you need to consider when you take a photograph because you may want to stop the action or in fact create motion blur. The choice is yours, but to achieve that you need to understand what the shutter does at the different settings and then balance that with the amount of light coming through by adjusting the aperture and the sensitivity to suit. But then again you may have to adjust your shutter speed as you may have decided on a your depth of field for you point of interest and the only option then left is speed and adjusting the sensitivity to get a correctly exposed photograph. Likewise in a dark situation you’re then stuck with not having enough light coming through and may have to look at adding more light through the use of using a flash or an open window if there is light outside or something else. These are things to talk about it later time.
Hopefully this will give you a little bit information on how the shutter works and the need to adjust the speed of the shutter, this is something that you can experiment with. The classic long exposure for people starting out might be light trails on a busy road. Adjust for a long shutter speed to capture motion, the adjust your ISO to say 800 and aperture to maybe F15 to start and supporting your camera take a picture of the cars driving away from you. You’ll have the classic trial of tail lights moving up the road. You may need to adjust your part of the exposure triangle like sensitivity if it is too dark or maybe stop down your lens for less or open up your lens with a lower aperture to balance the light. Alternatively you may want longer lines and need to decrease and slow your shutter speed. Or if the lines are too long, decrease your shutter speed and maybe freeze the lights in the image. The choice is yours and something to experiment with.
We have now looked at all three main elements of the Exposure Triangle in this series. Adjusting any one of these three elements will impact the other two and is something which will be useful to learn and apply once you get out of automatic or program mode on your camera. But it’s not all there is to it? There are other things to think about if you then want to take pictures of its too dark and you can’t change anymore as there just isn’t enough light for the camera to be able to take a suitably exposed image no matter what settings you try and use. What we’re talking about here is using artificial light such as flash, reflective or artificial light. We’ll look at these shortly in future articles but for now we’ll call it a day and chat later. Bye for now.