Friday, 14 November 2014

How to... Using the camera on 'PASM' and taking control of your photography

How to...

(skip these pages if you know)

I've had an email requesting my 'How to' on NOT using the Auto setting on cameras all the time. In order to answer that, one must understand 'exposure'...

Getting the right amount of light is very often taken care of by the electronics in the camera. The exposure, as it is called, is gained by the interaction of the size of the hole in the lens and the time the shutter is open. This is very simple, big hole small time, small hole long time. Of course, the reality is, someone came along and called the hole size an ‘f’ number and yes, the hole is not kept open for long so that’s in fractions of a second...
So, f2.8 for 1/500th of a second is ‘the same’ as f5.6 for 1/125 of a second. Before this information makes you think, ‘this isn’t for me’, it needs to be said, you can simply accept this is the case and move on.
These f numbers are not really understood by experienced photographers, other than, low ones come with big holes and let you have the person in focus and the background out of focus, larger f’s do the reverse. f16 will get the foreground and background in focus at the same time.

  1. Getting the correct exposure is achieved by the relationship of ‘f’ number and shutter speed
  2. High shutter speeds require a larger aperture or lower ‘f’ number to let in more light. Used to freeze motion
  3. Small apertures (larger ‘f’ number f16 for example) giving larger depth of focus, are compensated by longer shutter speeds
  4. Large apertures such as f2.8 lead to defocused backgrounds and small depth of focus

A lot of cameras have a dial that has PASM on it.

  • Program is used to get the camera to decide what it thinks is a good combination between the 'f' stop and the shutter speed.
  • Aperture Priority is used when you know better and wish to choose how deep your focus is. Shallow artistic depth of focus requires low numbers f2.8 for example. The camera sets the corresponding shutter speed to achieve the correct exposure.
  • Shutter Priority is when you know better and wish to cause blur by using a long exposure time to, for instance, blur a waterfall. Equally you may wish to freeze a sports car by using a fast shutter speed, like a thousandth of a second. The camera will open the lens hole more if you use a fast time to let more light in, and of course, lessen the depth of focus.
  • M is for Manual. This is when you take total control. Your choice of depth of focus and your choice of shutter speed. To get the exposure right you will need a bit more knowledge or a bit of... luck!

To round this up, as you go through the f-number scale, each step equates to a halving of the light, so f2 is twice the light of f2.8 and so on. Shutter speed is easier to understand as 1/15th second is twice 1/30th. The f stop scale runs 1.4 - 2 - 2.8 - 4 - 5.6 - 8- 11 - 16. 

...start using your camera on something other than 'AUTO'

This article is taken from my iBook from a couple of years ago. If your knowledge makes this something that offends, then sorry, equally you might know someone that may find it useful, in which case pass it on.

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