- by Thomas "TJ" Gillespie
What does the A stand for on my camera / camera dial?
A stands for aperture and setting your camera to A places your camera in aperture priority.
What is aperture in photography?
Aperture and f-stop are used nearly interchangeably but I will define them uniquely for clarification.
Simply put, the lens of a camera is the eye of the camera. Just as your eye has a pupil and an iris, so does the camera lens. The size (diameter) of your pupil is determined by the amount constriction or dilation of your iris. When the “iris” of a lens is dilated the “pupil” is said to have a large aperture. Conversely, when the “iris” of a lens is constricted the “pupil” is said to have a small aperture. The “iris” of a lens is made of up blades. The blades create the size of the hole which is determined and measured by a ratio called f-stop.
What is f-stop in photography?
Technically, f-stop is a ratio and is found by dividing the focal-length of the lens (as expressed in millimeters: 35mm, 70mm, 105mm, etc...) by the diameter of the “pupil” (see aperture in previous question). If the focal-length is 100mm and the diameter of the “pupil” is 25mm, then100/25 = 4. Therefore, f-stop would be focal-length (f) over the number of times the diameter of the aperture fits into (f). In this case 4, making f-stop f/4.
What does aperture do?
Aperture, also known as f-stop, controls depth-of-field (how much stuff will be focus) and the rate at which light will flow to the digital sensor.
The smaller the aperture, like f/11, f/16 or f/22, the greater the depth-of-field (more stuff will be in focus) but the lower the flow rate of light to the digital sensor. The larger the aperture, like f/1.4, f/2 or f/3.5, the shallower the depth-of-field (less stuff will be in focus) but the higher the flow rate of light to the digital sensor.
What is aperture priority?
Aperture priority is a setting that tells your camera to keep the aperture set at a fixed size regardless of how much or how little light you are photographing in. Only the shutter speed and, on some cameras, ISO will change in the camera’s effort to properly expose the photograph.
Why would I photograph or take photos in aperture priority mode?
There are a many answers as to why you would take pictures in aperture priority.
In the photography class we will address the answer that focuses on controlling depth of field. A larger aperture (bigger hole but smaller number) will give you a shallower depth of field. A smaller aperture (smaller hole but larger number) will increase the depth of field. In the How do I use my DSLR camera class you will learn when to use a small, medium or large aperture.
Purchasing a spot in my group photography class at my online store will automatically get you reserved on the date you selected during your purchase. You will receive subsequent emails from me regarding your specific class.
All students can retake scheduled group sessions for free, unlimited, for 1-year after first instruction. Only limitation is that class sizes never exceed 10 and classes are first come, first serve.
Find me on:
- Great starter book
- Medium sized travel book. Beginner - Intermediate
- Capturing the Eye, Fall Colors and Unreal Blur (PDF)
- Portraits, Flowers and Silhouettes (PDF)
- Unusual Point of View, Glowing Light, Stopping Action and Showing Action (PDF)
- Ultimate Field Guide to Photography (PDF)