In part one we covered off the Aperture control and what effect it has on Depth of Field.
In this post we will cover off the effects of the Shutter and ISO adjustment.
In the days of film photography, ISO referred to the speed of the film used. In simple terms, it classified the "sensitivity to light" rating of the film.
With digital photography, it is a common misconception that ISO still refers to sensitivity. Modern sensors are classed as ISO invariant with the ISO control adjusting the level of amplification applied to the electrical signals captured by the camera sensor. The higher the ISO capability of the camera generally means the electronic processing produces less noise which in turn leads to a cleaner image captured during low light photography. Many modern sensors are more than capable of producing excellent images beyond ISO 6400, going back ten years an image above ISO 1600 would almost have been classed as unusable by many.
Most digital cameras start with a base setting of ISO 100 which is designed to emulate the popular ISO 100 film, however modern cameras can sometimes go as low as ISO 50 with mobile devices such as the latest iPhones hitting ISO 20. These are the settings to use when capturing the brightest scenes as it lowers the level of signal amplification of the sensor to its minimum setting. As the amount of available light starts to decrease, increasing the ISO will ramp up the amplification of the signal processing electronics resulting in more of the detail being captured by the sensor becoming visible.
The image below shows the effect of ramping up the ISO, note that to maintain the same exposure the shutter speed has to be doubled with. each doubling of the ISO rating. You can see that by the time you reach ISO 12800, noise is becoming quite visible however the photography will be benefiting from a much higher shutter speed capable of freezing motion much better, hence introducing the important link to understand between ISO and Shutter control.
Put simply, to maintain a controlled depth of field (Aperture fixed in place) in differing lighting conditions you have two choices. Adjust the shutter or adjust the ISO. If you are capturing static objects, you can of course lengthen the shutter time keeping the ISO low, however if you have to photograph fast moving objects you have no choice but to shorten the shutter speed hence increasing the ISO to maintain the same exposure otherwise motion blur will be introduced.
Think of the shutter control as your "amount of motion" control:
From the image above it can clearly be seen that when photographing fast moving subjects, short shutter speeds are essential. Fast moving wildlife will require 1/1000s and greater, whereas landscapes can easily be 1/50 - 1/100.
As a general rule of thumb, if your lens focal length is 30mm, keep the shutter speed quicker than 1/30s to avoid blur due to camera shake. Equally, a 300mm focal length requires 1/300s to avoid blur unless using a tripod or a very steady hand!
The following image ties all 3 controls together into a single chart illustrating the effects of all three controls:
Hopefully now you will have a better understanding of the exposure triangle and which control to adjust to capture the image you are looking for.
Please do not hesitate to ask questions at a club night or drop through a message for further information. Lots of information is available online to help explain things further.
Remember to check out our post on night photography for sample settings and which controls to adjust to get different results.