I’d like to kick off with one of the more confusing components of any digital SLR camera, aperture. Aperture isn’t even really a feature of the camera: it’s a feature of the lens. It is a measurement of the opening in the lens. This opening allows light to pass through the lens – that light eventually strikes the digital sensor, which then captures an image. The aperture of a lens is never completely closed: it is always either narrow or wide open. Furthermore, aperture is a variable setting that can be adjusted by the photographer.

Back in the good old days of manual film SLR cameras, aperture was always set by turning a ring on the lens (right where it attached to the camera). Today, this mechanical system has been replaced with an electronic one.Many modern digital SLR lenses no longer include an aperture ring. This is because with a digital SLR, you set the aperture using the camera body: electronic contacts allow the camera to communicate with the lens so when you select an aperture on the camera, it adjusts the lens aperture accordingly.

If you do happen to have an older film lens that is compatible with your digital SLR, you will have to lock the aperture ring on the lens (this is often done by turning the ring to the narrowest lens aperture). Once the aperture ring is locked, then the camera will be able to communicate properly with the lens.

Now for the fun part: the aperture numbers themselves. Part of the fun is that in order for them to make sense, you have to think of aperture numbers as fractions, even though they aren’t displayed that way. Here’s why: the larger the aperture number, the smaller the opening in the lens. Aperture numbers follow a pretty typical scale, and you can always tell when an aperture number is being referenced because it starts with “f/”. The aperture scale goes something like this:

f/2.8, f/4.0, f/5.6, f/8, f/11, f/16, f/22

From left to right, the opening in the lens is getting progressively smaller. An aperture of f/2.8 means the lens is wide open, while at f/22 it is quite narrow. This is why thinking about apertures as fractional numbers might help (unless you’re really bad with fractions). For example, if you compared the fractions 1/4 and 1/22, 1/4 is the larger of the two and therefore represents a larger opening of the lens. This is enough aperture numerology for now. In the next post, I’ll tackle the issue of stops of light and will describe how the standard aperture scale can be broken down further.

By kind permission of Chris Roberts of

http://www.digital-slr-guide.com/

In the last post, I provided an introduction to aperture.

Here’s a quick summary of that information:

• Aperture indicates whether the opening in your lens is wide open or narrow
  
• Your digital SLR communicates with the lens via electronic contacts
  
• You can control the width of the opening by changing the aperture setting from the camera
  
• A small aperture number (2.8) represents a WIDE opening in the lens
  
• A large aperture number (22) represents a NARROW opening in the lens
  
• Aperture numbers follow a standard scale called f-stops.
  

The aperture f-stop scale looks like this:

f/2.8, f/4.0, f/5.6, f/8, f/11, f/16, f/22

Now, this particular scale shows each aperture number changing by something called a full stop of light. When the aperture changes by a full stop, the amount of light landing on the camera’s sensor is either doubled or halved.

Example:

• f/2.8 lets in twice as much light as f/4.0
  
• f/4.0 lets in half as much light as f/2.8
  

Once you realize that the lens aperture can be changed by full stops, a question arises: what about half stops? Yes, aperture numbers can also be broken down into a half-stop scale:

f/2.8, f/3.5, f/4.0, f/4.5, f/5.6, f/6.7, f/8.0, f/9.5, f/11, f/13, f/16

While a simple half-stop scale might make the most sense, most digital SLR cameras are actually set up by default to change aperture in third-stop increments:

f/2.8, f/3.2, f/3.5, f/4.0, f/4.5, f/5.0, f/5.6, f/6.3, f/7.1, f/8.0, f/9.0, f/10, f/11, f/13, f/14, f/16

Let’s take a quick break from the numbers and talk about HOW you actually change the lens aperture using a digital SLR camera.

• First, you have to set the camera in a mode that allows you to change aperture – a good one to start with is “Aperture Priority” mode (often marked as “A” or “Av”)
  
• In order to change the aperture value, you have to spin the main command dial which is located near the shutter release under your index finger
  

All main command dials don’t just spin freely: they “click”. Let’s say that your digital SLR is one of the many where aperture numbers are broken down into third-stops. Let’s also say that currently your aperture is set to f/8.0. Now, if you want to OPEN the lens by a full stop, you click the main command dial three times in one direction to go from f/8.0 to f/5.6. If you want to NARROW the aperture back down to f/8.0, you click the main command dial three times in the opposite direction.

The reason that you have to click three times is because of the third stops.

• f/8.0 to f/7.1 = +1/3 stop of light
  
• f/8.0 to f/6.3 = +2/3 stop of light
  
• f/8.0 to f/5.6 = +1 full stop of light
  
• f/5.6 to f/6.3 = -1/3 stop of light
  
• f/5.6 to f/7.1 = -2/3 stop of light
  
• f/5.6 to f/8.0 = -1 full stop of light
  

Before we wrap things up on aperture control, a word about customization: the factory default setting for most digital SLR cameras is to use a third-stop aperture scale. However, some cameras allow you to customize the scale and change from third-stops to half-stops if you so desire. Both work equally well, the third stop scale just provides you with a slightly finer level of aperture control.

By kind permission of Chris Roberts of

www.digital-slr-guide.com

In the past two posts, I’ve been talking about aperture, and how you’re able to control this setting on your digital SLR camera.

Here’s the high-level overview of aperture:

• Aperture indicates whether the opening in your lens is wide open or narrow
  
• Your digital SLR communicates with the lens via electronic contacts
  
• You can control the width of the opening by changing the aperture setting from the camera
  
• A small aperture number (2.8) represents a WIDE opening in the lens
  
• A large aperture number (22) represents a NARROW opening in the lens
  
• Aperture numbers follow a standard scale called f-stops
  
• Changing an aperture value by a full stop either doubles or halves the amount of light passing through the lens
  
• Aperture values can be changed in either half stop or third stop increments
  

Here’s the standard set of aperture numbers:

f/2.8, f/4.0, f/5.6, f/8, f/11, f/16, f/22

In this post I’m not going to go into as much detail about the aperture setting itself (that’s been pretty well covered) but instead I’ll explain why all lenses are not created equal, and how aperture comes into play.

There are two key points about lenses that are required to begin with:

1. Virtually all lenses can be set to the same narrow aperture (f/36)
   
2. Not all lenses can be set to the same wide aperture
   

When it comes to lenses, this second point is a limitation of some lenses and this limitation has a name: maximum aperture.

Let’s compare two lenses that are equivalent when it comes to focal length: both are 18-55mm zooms. Let’s say that lens A has a maximum aperture of f/4 while lens B has a maximum aperture of f/2.8. Now, BOTH lenses can be set to narrow apertures (anything between f/4 and f/36), but the f/2.8 lens can open up much wider than the f/4 lens. In fact, the lens with the f/2.8 maximum aperture can let in twice as much light as the lens with the f/4 maximum aperture.

The practical take-away here is that if you tend to enjoy taking photos in REALLY dim light (cloudy days, building interiors, etc.) then you’ll want to look for a lens with a very wide maximum aperture.

The most common aperture numbers that you’ll see on kit lenses are f/3.5 and f/5.6. The reason that there are two numbers is because the maximum aperture CHANGES depending upon the focal length of the lens. At 18mm the maximum aperture of a kit lens is a wide f/3.5, but if you zoom to 55mm that maximum aperture narrows down to f/5.6.

Now that you’ve got a better understanding of maximum aperture, let’s discuss why using the maximum aperture isn’t always such a good idea.

When it comes to image sharpness, lenses don’t perform as well at extreme apertures as they do with apertures in the middle of the range. Example: a 50mm lens set to f/2.8 or set to f/36 won’t capture images that are nearly a sharp as when you use apertures f/8 and f/11. Now, some lenses are better than others at maintaining sharpness throughout the entire aperture range – this is why they cost well over $1,000 USD.

For anyone who doesn’t have this type of budget for lenses, you’ll just have to live with the fact that your lens probably won’t be ultra-sharp at very wide and very narrow apertures. If you take photos with plenty of light, then you won’t have any problem using apertures between f/8 and f/16 all the time. However, if you enjoy taking shots in dim light, you’ll often find yourself using the maximum aperture of your lens.

When shots don’t turn out quite as sharp as you hoped for, maximum aperture can be one of the culprits.

By kind permission of Chris Roberts of

http://www.digital-slr-guide.com/