Ready to take control of your camera? In the previous two tutorials we touched on the settings that contribute to photographic exposure – ISO, aperture, shutter speed – and the relationships between them. In this concluding part we will explore various ways you can control exposure and be sure you are creating exactly what you want to create.
Stepping in at the deep end, manual exposure mode requires you to set ISO, aperture and shutter speed to achieve your desired exposure. So you control everything – but the camera’s inbuilt light meter can still guide you – check your manual to see how exposure information is displayed on your camera.
Some people will find manual the most creatively satisfying shooting mode to work with. The beauty of digital is that you can shoot away until you get the settings just right – but if you are inexperienced you might take time finding the best combination and risk missing the shot altogether! Back at the paddling end of the pool, fully automatic exposure (possibly augmented by a range of specific scene options such as portrait, landscape, macro, snow, action etc) may do a good job some of the time, but may also get it wrong – and if you’ve read this far these are the very modes you are seeking to escape!
Between auto and manual many cameras offer two modes that allow you to alter ISO and either aperture or shutter speed creatively whilst the camera still determines the exposure by adjusting the other setting for you.
Aperture priority is the mode of choice for many photographers. I use it for most location photography since depth of field is usually of primary importance to me. If your subject is stationary this is usually the mode to use.
Shutter priority comes into play when you are shooting moving subjects such as the local fun run, your dog bounding across a meadow, fast flowing water etc. You will want to control the amount of motion blur in the image – using the shutter speed.
Blur can also occur when your hand moves whilst shooting – this is called camera shake. You would think that holding a camera still for one second wouldn’t be difficult – try it and look at the resulting picture on a computer. A tenner says its blurred. Even with VR (vibration reduction) lenses you will likely need shutter speeds of under half a second to avoid camera shake. So use shutter priority mode to be sure of a fast shutter speed when shooting hand-held (or, better still, purchase a monopod or tripod to support the camera).
In manual, aperture priority and shutter priority you normally adjust the aperture and/or shutter speed via the camera’s command dial(s) – details vary with camera make and model, so check your manual for precise details of how to work in these modes.
Whatever the shooting mode, ISO can be left on auto-ISO although I only use that in situations where light levels are changing very rapidly – such as a live performance under theatrical lighting.
Under most circumstances, you check and (if necessary) adjust ISO manually when you start shooting a scene, then leave it alone until the light level changes significantly (for example, when moving outside from indoors).
Set the lowest ISO you can, as that will render the best quality image. In low light environments where a tripod cannot be used you may need to increase the ISO.
You have probably noted that the camera still exerts some control over exposure in every shooting mode apart from manual.
What if the camera gets it wrong?
What if your interpretation of a scene does not correspond with the correct exposure determined by the camera?
In other words, how do you achieve your optimum exposure without switching to fully manual mode?
There is another feature that overrides the camera’s choices in automatic or semi-automatic modes, and that is the exposure compensation button.
With this function you force the camera to increase or decrease overall exposure. This can usually be done in increments of 1/3 or 1/2 stop. Adjustments of up to plus/minus 3 – 5 stops can be made, but each stop is a doubling or halving of the amount of light hitting the sensor – so this is a control that usual responds best to a gentle touch.
In automatic modes you don’t know which setting (aperture or shutter speed) the camera will alter to affect compensation. In aperture priority the camera will change the shutter speed when exposure compensation is invoked and in shutter priority it will alter the aperture. In manual mode it does nothing at all.
It is important to remember that exposure compensation remains set until you physically unset it. If you forget to do this after shooting, and then just switch on and start shooting a few days later, you will probably end up with some very badly exposed shots indeed!
Check your manual again to see how you implement exposure compensation on your camera.
When playing back the images you shot there are two further features digital cameras provide that make achieving optimum exposure easy for creative photographers – the highlights view and histogram view (names may differ on your camera; rotate through viewing options until you find the functions described below; very basic cameras may not offer these features).
If you over-expose a scene the brightest areas may be reduced to pure white. The highlights view shows such clipped highlights as flashing areas in the LCD display. It will, however, not tell you when there is shadow clipping (where dark areas are under-exposed to pure black). This is probably because clipped highlights are generally considered to be more undesirable than clipped shadows.
The histogram view is a more sophisticated tool. It takes the form of a graph depicting the range of tones (shadows – mid-tones – highlights) within the image.
If the graph bunches at the far left of the horizontal axis, or does not reach the right edge, you may have under-exposed the scene. If it bunches at the far right, or does not stretch to the left edge, you may have over-exposed the scene. Adjust ISO, aperture or shutter speed to compensate, and shoot again – unless such under- or over-exposure was your intent. This tool is just a guide – there is no such thing as the perfect histogram.
This has been a very small introduction to a very big subject. Until you put things into practice it will probably remain a bit of a blur; learn to control exposure by playing with the functions described above. Shoot a scene (any scene, but ideally one where you do not immediately achieve great results) with a variety of settings and compare the results – it will all start coming into focus.