Monday, 9 July 2012

ISO, Shutter speed and Aperture!!!


Good morning interweb, well it is as I start writing this but may well be the afternoon or even evening by the time I finish. 
Quite a weekend all round really. Remembrance of the people killed in the 7/7 bombings, work, and the discovery that Andy Murray is Scottish after all and not British.
I have managed to get a few shots in the can as they say with a Canon 7D camera and Lightroom has hoaved into view on my processing radar.
A few people have been asking one or three questions about photography etc this weekend so I thought I may give a bit of a simple guide to the basics of how it all works with these new fangled digital works of the devil camera thingies.
The very bare basics of digital photography are this, you have a camera with a sensor inside it instead of film.
That sensor is exposed to light thus creating an image which is recorded in a digital file.
For us to get a correctly exposed image we have to control how the sensor reads that light and how much light we expose the sensor too.
To control how much light falls on the sensor and how the sensor reads that information we have 3 main attributes which we can control.
ISO, shutter speed and aperture. All 3 work together and affect one another as their respective attributes are changed.
Lets take a look at each of these in turn.
ISO, this is what was called ASA in the days of film photography and in the digital world is responsible for how sensitive we make the sensor in the camera to the light that falls on it.
The figures are pretty similar to that of ASA and so an ISO of 100 would be fine for shooting outside on a nice sunny day but would be of no use at all in a dark room or at a concert for example. With film the higher the ASA rating the more “grain” was visible, with ISO, the higher the number the more “noise” is introduced to the photograph.
Shutter speed, This is what dictates the amount of time that light is allowed to fall upon the sensor to allow the sensor enough time to record an image. For general use this is measured in fractions of a second and a good rule of thumb to prevent camera shake (blurred images from movement whilst the shutter is open) it is advisable to always use a shutter speed at least equivalent to the focal length of the lens in use. For example if you are using a 100mm lens then you should really be using at least 1/100th of a second shutter speed or have the camera on a tripod.
Aperture, this is where most people at first start to get confused.
This is not helped by the fact that the bigger the number the smaller the hole or “aperture” that the light is allowed to travel through. The size of the aperture also has a bearing onto the depth of field of the photograph or in other words, how much of it is in focus from front to back.
For instance if you set your aperture to F22, a very large part of your image from front to back would be in focus and the reverse, at F2.8 only a very short range from front to back would be in focus. This is also dependent on where you focus the camera.

OK so now we have the basics how do they all relate to one another .
Say we were outside on a nice sunny day and we set our camera to ISO 100 and a shutter speed of 1/200ths in its Tv mode (in this mode you set the shutter speed and the camera sets the F stop to allow for a correctly exposed image). We press the shutter button part way down and the camera takes a reading of the light available in the scene and tells us it will set the F stop to F8 to get a correctly exposed image.
But we are taking a photograph of a landscape and require much more depth of field (more of the image in focus from front to back) so we require an F stop at around F16.
To achieve this our 3 settings all interact in a predictable way.
We could set the ISO to a higher level to make the sensor more sensitive to the light falling on it or we could adjust the shutter speed to achieve the same result. For every notch we lower the shutter speed the Fstop increases in a linear fashion and the same is true in reverse. So ignoring the stupid .5 parts of F stops if we take the shutter speed down from 1/200th to 1/160th, the F stop would go from F8 to F9. We repeat this process till we get the aperture to F16.
Obviously there are at times other factors to take into account but getting the basic understanding of what is going on will go a long way to help you getting more from your photography and helping you get the results you want.
I will hopefully be putting up some more basics classes or if anybody would like to know a little bit more about any aspects of photography that I may know about just send me a message asking and if I know anything about it ill put up a post.
But till then, here is some drivel, Do not remove a fly from your friend's forehead with a hatchet and remember this, The reason most people never reach their goals is that they don't define them, or ever seriously consider them as believable or achievable. Winners can tell you where they are going, what they plan to do along the way, and who will be sharing the adventure with them.
Peace out yall, THE BAGSTAXXX

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