Stops: What Are All Those Numbers

If you are new to photography, or maybe just new to more advanced cameras, you may have noticed something about the numbers on that camera.  They don't go evenly do they, some of them double as they get larger, and well the f/stops, well they're just funky all together.  The reason for all this numerical nuttiness is called stops, and everything in photography is measured in stops.  To understand stops you have to understand that photography is all about light, and more importantly, how much light is hitting your sensor.  All cameras have a sensor, be it film or electronic.  In order to get a properly exposed photo you have to have the proper amount of light reach the sensor and you do that by adjusting the light.

So what is a stop?  A stop is a measurement of light.  As you increase the light by a stop, you have just doubled the amount of light hitting the sensor.  As you decrease the light by a stop, you have just halved the amount of light.  That is the simplest definition.  But this will help you understand the numbers you are seeing.

Camera: Nikon D80      

Lens: VR 18-55mm f/3.5-5.6G

Focal Length: 55mm

Shutter: 1/60

Aperture: f/5.6

Flash: SB-600

The easiest number to understand is the shutter speed.  The numbers you will see are 1, 2, 4, 8, 15, 30, 60, 125, 250...  but this is only the denominator half of the number, so the real shutter speeds are 1/1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250.  These indicate how long the shutter will stay open in seconds and they are separated by stops.  So if your set at a shutter speed of 1/60 and you decrease the shutter speed to 1/30 then the shutter will remain open twice as long and doubling the light (one stop).  If you change your shutter speed from 1/60 to 1/125 of a second then the shutter will only remain open half as long and halving the light (one stop).  Clear as mud right.

Camera: Nikon D80
Lens: VR 18-55mm f/3.5-5.6G
Focal Length: 55mm
Shutter: 1/60
Aperture: f/5.6
Flash: SB-600

If you've shot with film, and probably with digital you've seen ISO numbers, even if you haven't known you have.  ISO 100, 200, 400, 800, 1600...  There are those doubling numbers again.  The ISO number tells you how fast your sensor responds to light.  This higher the number, the quicker the sensor responds to light. So lets say you are shooting ISO 400, if you move to a slower sensor of ISO 200 you will require twice as much light, if you move to a faster sensor of ISO 800 you will only require half as much light.

Camera: Nikon D80
Lens: VR 18-55mm f/3.5-5.6G
Focal Length: 55mm
Shutter: 1/60
Aperture: f/5.6
Flash: SB-600

The confusing number is the aperture or f/stop.  These numbers will look like 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32.  These reference an adjustable hole (aperture) in the middle of the lens.  These numbers represent the diameter of the aperture.  Divide the focal length of the lens (i.e. 50mm) by the number and that is the diameter of the aperture.  So at f/2 the diameter in a 50mm lens will be 25mm.  At f/4 it will be 12.5mm.  And these again half and double the light.  If your lens is set to f/2.8 and you open it up to f/2 you just doubled the amount of light hitting the sensor, go from 2.8 to 4 and you just halved the light.  Simple.

But here is the absolutely best part of this article.  None of this junk matters!  While in future articles we will delve into the more creative aspects of shutter speeds and aperture settings this is just a primer.  I know when I got my first camera I was inquisitive and wanted to know what the heck all those numbers meant, and while there are reasons to know them, it isn't a requirement.  So if you aren't understanding them yet, don't worry about it, in the end it doesn't matter.

Next in the instructional series will be the Exposure Triangle: How To Make Those Nutty Numbers Work

Thanks for reading!