Aperture - Photography

Basic overview

Aperture is measured using focal length. Also known as f-stop (e.g. f/1.8, f/3.5, etc etc).

The aperture is a measurement of the amount of light that can enter. It is inversely proportional. Meaning a smaller f-stop, means a larger opening and a larger f-stop, means a smaller opening.

The lower the f-stop, the larger the aperture. The larger the f-stop, the smaller the aperture.

Understanding aperture

With that being said, you can understand aperture in this manner:

• 50mm f/1.8
• 50mm f/3.5

An aperture of f/1.4 means you can open up the aperture to the maximum of f/1.4. You can always close the aperture up more but you can not open up the aperture more than what is defined.

So between the above two lens definitions, f/1.4 will allow more light in than f/3.5. As such in lower light conditions you will want a lens which has a lower f-stop.

A term people use to describe a lens with a low f-stop or large aperture is "fast lens". They essentially mean that you can take a picture at a faster shutter speed. The shutter is actually part of the camera so "fast lens" may not seem technically correct but as far as what is achieved, it's correct enough.

As a final mention, you can still shoot at a fast shutter speed even with an insanely high f-stop or small aperture. You most likely won't let enough light in to adequately expose the sensor / film, but I felt that it needed to be said. Just so you don't think you "can't" do it, you will just need more time to get a good exposure / shot. So smaller aperture basically means slower, larger aperture means faster. Hence again, fast lens, lower f-stop (i.e. larger aperture).

Depth of field

Aperture also controls depth of field. The smaller the aperture, the longer the depth of field. The larger the aperture, the shorter the depth of field.

If you have two objects at separate distance and a lens with a large aperture, regardless of where you focus, some of the items may be out of focus. If you have a small aperture, they may all be in focus. Consider how people "squint" their eyes to see something sharply. You're focusing the light entering your eyes, to a smaller opening to get a sharper picture.

Now the best reason to get a lens with a large aperture (lower f-stop) is to let in more light. This in turn allows you to take shots at higher shutter speeds and or lower ISOs. You can always close up the aperture more, but you can not open up the aperture beyond what the lens says.

Bokeh is the art of using blur to an artistic advantage. When you open up the aperture, you get more bokeh (i.e. less depth of field). Bokeh can be covered later but the primary focus should be on depth of field and how aperture correlates with it.

• Large aperture (i.e. smaller f-stop)
  • Short depth of field
• Small aperture (i.e. larger f-stop)
  • Long depth of field

What to walk away with

It makes sense to know that your lens controls most all other settings so aperture unlike the others, directly controls what you can do. The others can be modified at will but cannot change the aperture. A critical defining factor.

• Large aperture (larger opening)
  • Small f-stop
  • Shorter depth of field
  • Faster shutter speeds
  • Lower ISO speeds (i.e. less grain)

• Small aperture (smaller opening)
  • Large f-stop
  • Longer depth of field
  • Slower shutter speeds
  • Higher ISO speeds (i.e. more grain)

Remember with stability (i.e. steady hands / tripod) you can adjust shutter speeds and or ISO speeds accordingly. However in situations such as sports shoots, where the shot is in motion, you will want a larger aperture to have a faster shutter speed to avoid motion blur (if that is what you want).

The aperture cannot be opened up more than what the lens is defined as, but it can always be closed up more. So if within your affordability range, get a lens with a larger aperture (i.e. smaller f-stop). This is what really factors in on the price of a lens by the way.