Historically a problem encountered by beginners is understanding apertures and shutter speeds. Manufacturers have come to your aid by evolving automated exposure controls; aperture priority, shutter priority, program, matrix, spot, multi segment + different names for the same function by different manufacturers. The cure is now more complex than the problem.
Aperture/ shutter speeds - ½ and third stops.
The concept of apertures and shutter speeds is fairly easy to understand. Let me draw a parallel:
Buy a camera - cost £100, but you need to save up for it.
£50/wk for 2wks
£ 2/wk for 50wks
£25/wk for 4wks
£ 4/wk for 25wks or any combination in between.
This is a combination of Quantity and Time:
Quantity is aperture
Time is shutter speed
Let’s look at them individually and take the easier one first
- Numbers range from at least 1 to 1000 + B (or "Bulb")
- Fractions of a second 1/30 or 1/60 or 1/125 or 1/250 each more or less double or half its neighbour
- Numbers range from f2 to f22, eg. f4 or f5.6 or f8 or f11
- Apertures are also doubles/halves, but not obvious.
You will make mistakes!!
Let's say the ‘Correct exposure’ for a scene is 125th sec @ f8.
1 stop 60th @ f11
1 stop 250th @ f5.6
2 stops 500th @ f4
2 stops 30th @ f16
3 stops 1000th @ f2.8
3 stops 15th @ f22
All these combinations will give the same exposure - but not the same effect.
Scale refers to sensitivity of CCD - the higher the number the quicker the response.
Low number - 25 ISO slow
High number - 800 ISO fast
100 200 400 800 etc. also doubles/halves.
Higher number leads to grain/digital noise
Definition - Exposure is the amount of light allowed to reach a CCD via a combination of aperture and shutter speed.
Conclusion - Aperture and shutter speed is the way light is controlled to enable an exposure to be made.
by Neil Blair