Perhaps you have a shiny new DSLR, or maybe you have had it a while and have just used it on Auto. Perhaps you would like to have a little more control of the camera, and if so this Blog is aimed at you. Here, I will attempt to explain what is involved when you shoot without Auto taking control.
First of all, let’s talk Exposure. We always need to achieve “correct exposure.” Cameras (or phones) set to Auto will make a good stab at getting the exposure correct most of the time. The trouble is, whilst the exposure may be accurate, the camera may not have chosen the best shutter speed or aperture for the creative effect you had in mind. For instance with sport, you may want to freeze the action or you may want to blur it. With landscape, you may want everything in focus or just one flower. To achieve these results you have to select the correct shutter speed and aperture. Don’t worry, this is easier than you may think.
Before explaining about shutter speed and aperture, it is worth noting that many DSLRs will have Programme (P) modes that are pre-set to shoot in the style you choose. A little bit like the modern car that has a Sport button which changes the essential settings to power the vehicle into the nearest tree. With the Programme Modes, you will need to check your handbook to understand which modes offer what.
However, if you are going to jump in the deep end and drive that camera yourself, here is what you need to know.
There are THREE factors that effect exposure and they must be controlled together to give you creative expression.
1. ISO (International Standards Organisation) Previously ASA, and even earlier BSA, but they are all the same. If we are dealing with film, the ISO of a particular film tells us how quickly it responds to a given amount of light. Film that responds quickly is known as a fast film and will have a high ISO of 400 or 800. These films would be chosen to shoot in low light or to shoot action. The disadvantage is, the higher the ISO the grainier the image becomes.
Film that responds less quick is called a slow film (who would have thunk it!) and while this will need longer exposures than a fast film, it delivers much better quality. These films will have an ISO of 50 or even ISO 25.
With digital photography the film is replaced with a sensor that has the ability to respond at different ISO speeds. So, if you are shooting at a wedding on a bright day, you can turn the ISO down to 100 and get lovely crisp images with smooth tones. But when you want to shoot the Dad dancing later, you will have to turn up the ISO to 1000 or even more. The only problem you encounter here is the same you encountered with film. With higher ISO speeds the image quality deteriorates due to excess “noise.” (Small grain-like flecks of colour disrupting the image.)
So, choose the lowest ISO you can use in any given situation.
2. Shutter Speed. Everyone knows the shutter button is on top of the camera and when you press it, the camera takes a picture. True, but lots of things happen once you press the button. First of all, when you look through the viewfinder on a DSLR you are looking at a mirror angled at 45 degrees and that reflects the view of another 45 degree mirror that sits behind the lens. This mirror allows you to look through the lens, but it sits between the back of the lens and the digital sensor. It is actually in the way.
So when you press the shutter button, the first thing to happen is the mirror flips up to give the light access to the sensor. However, the shutter is still closed, and must open to allow the light to make the exposure on the sensor (or film.) We determine how long that shutter stays open by selecting the shutter speed.
Once more. You press the shutter button. The mirror pops up. The shutter opens for the required time. The shutter closes. The mirror pops back down. And with a top end camera that can happen 8 or 9 times per second! (That is why they make such a great noise!)
Choosing the shutter speed will determine the results you achieve. Let’s say we are shooting on a tripod, so the camera is absolutely still. We are shooting racing cars going past. If we choose a very fast shutter speed of 1000 (that is 1000/th of a second) the action will freeze. If however we choose a slow shutter speed of 1 second, the cars will be a blur trail. At night they will just leave those light trails so familiar in cityscapes.
If you would like control of your shutter speed, the camera can still ensure you obtain correct exposure if you select the shutter priority mode. This is usually marked on the control dial as either TV or S. After setting the camera to Shutter Priority, you can now decide if you want a slow shutter speed, say to blur a waterfall or a fast speed to freeze action. You can control the Aperture the camera selects by increasing or decreasing ISO.
3. Aperture. The lens has an iris diaphragm which is set at various “apertures.” They are marked in logarithmic order, usually along the lines of f2.8, f3.5, f4, f5.6, f8, f11, f16, f22. The higher the number the small the aperture (hole) that that diaphragm makes. This has a profound impact on the image. If we shoot a landscape at f22 we produce an image where everything is sharp, from sheep fence at the front of the picture to all the sheep in the field. (Maximum depth of field.)
However, if we choose to shoot at the lowest number on the lens (f2.8 in this case) we say that lens is then “wide open.” The diaphragm is totally open and has not “shut down” the lens. A wide open lens produces an image where only the actual point that was focussed upon is in focus. So in our example, the sheep fence is in focus, but the sheep behind are all out of focus. (Limited depth of field.)
To control Aperture and allow the camera the get the exposure right, select the Aperture Priority Mode which will be marked as A on your control dial.
The best way to master the information I have given you here is to practice. If you are shooting for fun, try to shoot in TV mode then switch to A mode. Increase and decrease the ISO and discover what happens. Shooting images is a bit like playing a musical instrument, you have to put the work in to make it play the tune you like.
With the information you have here and with practice, you ought to be able to figure out how to shoot in Manual Mode M. If you can figure that out, it would be a very good thing as it would prove that you understand the fundamentals, but for those with better things to do that figure that, I will Blog about shooting in M at a later date.