The Complete Idiot's Guide to Aperture

I've actually received quite a few notes asking me to make this a news article so people could hit the favorite button and save it, so here it is:

Defining Aperture - I know many of you know everything there is to know about aperture. This is for those of you who don't, because I know you're out there. For this journal, I am not going to write in many technical terms, I'm going to try to explain it as easily as I can...so here it goes. A simple definition of aperture is an opening through which light travels. In photography, this is a very important word. When taking your photographs, aperture can be controlled to decide how much light reaches your camera's sensor. Just about all DSLRs and higher end point and shoots have an Aperture Priority (AV on Canon cameras, and AP on Nikon cameras) mode. This setting is the easiest way to experiment with aperture. Aperture priority is not a fully automatic mode, as it allows you to choose your aperture (F number), and gives the camera permission to choose your shutter speed, and if you'd like, even your ISO speed. Picture looking straight up at the sun. If you look at the sun with your eyes wide open, you're going to get a lot of sunlight into your eyes. If you look straight up at the sun, but put your hand over your eyes and only peek out through a small opening through your fingers, you will not get as much sunlight into your eyes. In photography, your eyes in this scenario would be the camera's sensor, while your hand would be the aperture. Shooting "wide open," or at the smallest possible F number (usually F/2.8 to F/5.6), means your camera is allowing the most possible light into the sensor. When you shoot wide open like this, you are forced to use a faster shutter speed, to compensate for the amount of light you're taking in. Shooting at a larger F number (larger than F/8 or so), means your camera is allowing less light into the sensor. Here, you will be forced to use a slower shutter speed, to compensate for a lack of light.

Depth of Field - Now I'm sure many of you have seen comments on images here on DA that say things like "Great DOF!!!" DOF stands for the depth of field. What this is, is the area of the image that is in focus. Simply put, in most situations, smaller F numbers mean that only a small portion of your image will be sharp (shallow depth of field), while larger F numbers mean that a large portion of your image will be sharp.

In order to achieve the affect some call "bokeh," or a blurry background, you want to use a small F number to separate your focal point from it's background. Photographs of birds or insects, with a blurred out background have a "shallow" depth of field. The photograph below taken by ~BogdanBoev, was shot at F/6.3, and as you can see, the background is completely out of focus and blurred away, while the birds are extremely sharp.



On the contrary, there are instances when you'd like most of your image, from the foreground right through to the background to be in focus. In these situations, such as a landscape, you want to use a larger F number. This will give you a larger depth of field, and place most of your photograph into focus. The photograph below taken by *fubecando, was shot at F/11. as you can see, details in the foreground, as well as the background, are sharp and in focus.



Exposure Time - Aperture will also effect your exposure time, making exposure a necessary element to consider when choosing your aperture (F number). A smaller F number allows the most light into your camera's sensor, therefore needs a fast shutter speed. This is good for action shots, and other times when you need to freeze the moment. A larger F number allows less light into your camera's sensor, and therefore requires a longer shutter speed. This is good for times when you'd like to capture movement, smooth out moving water, or many other instances where a longer exposure time is best.

The image below, shot by =Dalberti was taken at F/13. With the aperture cutting off some light to his camera's sensor, he was able to smooth out the moving water by leaving his shutter open for 2.5 seconds.



On the contrary, the image below shot by ~Neutron2K, was shot at F/4.0. This allowed lots of light into his camera, and gave him the ability to use a quick shutter speed of 1/1600 of a second to really freeze all of that awesome action.



The Sweet Spot - Lenses for your DSLRs most definitely have an aperture "sweet spot," or, an aperture that produces the sharpest possible images. This is usually a couple F numbers (stops) from your maximum aperture (smallest possible F number). Simply put, if your lens's maximum (smallest F number) is F/5.6, then your lens's sharpest aperture will probably be between F/8 and F/11. In most DSLR lenses, if you can, try and avoid the extreme apertures. I know F/32 is there, but definitely try to avoid that. Also, if you're shooting wildlife and want to use a fast shutter speed, try stopping down (using a larger f number) if you have the light available. You might be surprised how much sharper your telephoto lens is at F/8 than F/5.6.

Automatic and Program Mode - However great Automatic (AUTO) and Program (P) modes may be for snapshots, they definitely don't choose the correct aperture in most situations. If you don't want to shoot at full manual, try starting with Aperture Priority (AV for canon, and AP for nikon). Automatic mode or programed automatic mode, will normally not choose large F numbers, because the camera doesn't think these apertures will allow enough light into the sensor. If you want to shoot a landscape with a large depth of field, you will have to switch into a manual or semi-manual mode, because if not, your camera is going to choose too small of an F number, and you risk your image being improperly focused, and details you would have liked to be sharp, will not be.

Hopefully this helps some of you