My current photography goal is to get comfortable using the Advanced Modes on the Canon EOS 400D. However, for me it is helpful to know some of the theory behind relevant technical terms before I actually try to put anything into practice, so in the next few blog entries I am going to attempt to get a basic grip on some of the technical features I have encountered when playing around with the various Advanced Modes.
ISO - changing the camera’s sensitivity to light
The ISO figure indicates the sensitivity of the camera’s imaging sensor to light. In the Basic Modes examined in the previous blog entry the ISO speed is automatically set within ISO 100 - 400 as appropriate to the light levels. However, when using the Advanced Modes the Canon EOS 400D has the following ISO Speed options: 100, 200, 400, 800 or 1600.
Basically the higher the ISO number you select the more sensitive to light the camera will be and vice versa. Therefore if you are taking photos in a dark room then you should select an ISO figure towards the top of the range (since higher light sensitivity will enable the camera to make the most of any available light there is), whereas if you are in a sunny park you should select a lower ISO figure. This is the very minimum you probably need to know to effectively use the ISO setting in Advanced Modes.
ISO and shutter speeds
Additionally, changing the ISO will affect the shutter speeds that are available for taking the photograph. For example, if you are taking a photo in a low light and you select a high ISO number the camera will allow you to use a faster shutter speed than would have been the case with a lower ISO number. This is because the increased light sensitivy of the camera’s imaging sensor means that the shutter can be open for a shorter period of time and still get enough light to properly expose the picture.
Having a faster shutter speed in such situations is good since it means that the camera will take the photograph more quickly, which really reduces the likelihood of camera shake occurring (particularly useful if, like me, you lack the steady hands of a surgeon and do not carry a tripod around with you wherever you go!). You can clearly see this effect in the two photos below:
Photograph taken in a relatively dark room in P-Mode with ISO Speed of 1600
Photograph taken in relatively dark room in P-Mode with ISO Speed of 100
As you can see the first photo that was taken with ISO 1600 setting is much sharper, whereas the second photo taken with an ISO speed of 100 is blurry.
The shutter speeds in the photos were as follows:
- 1st photo (ISO 1600) - a shutter speed of 1/15th of a second, which is very fast and accounts for the much sharper image produced.
- 2nd photo (ISO 100) - a shutter speed of 0.8 seconds - this is quite a slow shutter speed - I actually had to wait for the camera to take the photograph after pressing the button - in that time clearly my hands weren’t still enough!
ISO and picture quality
One disadvantage to using a high ISO speed is that it may result in slightly grainy images; this may be seen if you examine the full size (original) version of the above 1st photo on my flickr account - therefore it is important to experiment with the whole range of available ISO speeds in order to find the lowest one that works in the light conditions rather than just opt for the highest ISO all the time.
Additionally, according to the Canon Manual using a high ISO speed may cause irregular colours in the image. I don’t think there is such an effect in the photos above, but when playing about with ISO settings previously I have noticed that if you set the ISO speed too high in already light conditions it does affect the colours. I’ll try to get an example up here soon.
