Yesterday’s Topic: The Exposure Triangle
Before we dive too deep into other subjects, I thought it best to explaining how your DSLR camera works. We’ll use this image for reference:
Without getting too technical on the number of elements, the types, the exact configuration of the pentaprism and such, light comes in through the lens. The lens will have a number of elements, some made of glass and sometimes some made of acrylic or other materials. All these elements (think of them as type of lenses, like a contact lens) help to focus the light. A focus ring on a camera, as well as the auto-focus capabilities of the camera, will move one or more elements front to back ever so slightly in order to achieve focus. As light comes into the camera it is flipped vertically because of the convex shape used to concentrate the light into the sensor area (think of looking at your reflection in the inside part of a spoon). Remember, you’re taking a foot tall bunny and trying to shrink it down to the size of the sensor. Poor bunny.
Before the light passes out of the lens and into the camera body, it goes through the aperture which, as you read before, can reduce the amount of light passing through to increase Depth Of Field. It then hits the reflex mirror (DSLR stands for Digital Single Lens Reflex, meaning it only has one lens and a reflex mirror that pops out of the way, as we saw on Shutter Speed) and bounces up. Next, it passes through the focus screen. To put it mildly, different cameras are different. On average, the focus screen is a matte finished transparent screen often with a LCD overlay to show actual focus points. This screen is the same distance away from the mirror as the sensor and this is the main reason the SLR became so handy, as there was not a need to keep film out of the way, focus, put film in, expose, remove film in the days of large format cameras (those ones with the big bellows come to mind).
After passing through the focus screen, the light will bounce around the pentaprism (crudely drawn in this diagram, here’s a better version on Wikipedia) which will flip the image the correct way for presenting at the eyepiece. Tada! Some cameras will have a light meter above the eyepiece, reflected with a transparent mirror. Other cameras will have the light meter behind the main mirror, which is also semi-transparent.
When you press the shutter release (or ‘button’ as a lot of people call it) your camera locks in the focus and light metering settings before flipping up the mirror. As explained in the Shutter Speed post, it then activates the shutter (and closes down the Aperture to the appropriate size) to let light hit the sensor, which has had its sensitivity set by the chosen ISO. The shutter closes, the mirror drops back down
Most cameras come to life when the shutter release is pressed half way down. At that point auto-focus (if engaged) and light metering become active. These two functions control most of the camera when in Auto and Program mode. Indeed, Shutter and Aperture modes follow suit and we’ll cover these modes a bit later in the month as well. If a lens has vibration reduction or image stabilization, it will turn on as well.
After light hits the sensor and the image is captured, it will drop the information into a buffer. A buffer is a holding pen for information. Inside the camera are one, two or more processors, just like in your computer, smart phone and, eventually, toaster. The processors need a bit of time to crunch the raw information from all those millions of pixel sensors. The buffer allows for a space for incoming images to hold up until the processors can work. Even shooting at three frames a second, processors aren’t fast enough to keep up on a one for one basis, so the buffer helps with the backlog. Just like waiting in line at Disneyland. Think of your buffer as those long, long, swerving holding pens….errr….lines.
To keep with that analogy, if more people come into the line than the ride can load at one time, eventually the line gets full. Pretend when the line got full and passed the entrance to the ride, that no one else was let in. That’s what happens with the buffer. Shooting at eight frames a second will fill a buffer pretty fast and the shooting speed of the camera will slow to the point where a new picture can only be taken when another has been written to the memory card and removed from the buffer. Don’t worry though, they keep coming up with faster and faster processors (although they also keep coming up with bigger and bigger sensors which fill more space!).
Information is processed before it hits the buffer, making JPEG files, with their smaller size, take up less space in the buffer. Again, different cameras are different. If you are shooting in RAW mode, the information will essentially be written to the memory card untouched while a companion file is saved along with it. This companion file has all the information about the image when it was shot, including what the white balance was, which shooting mode was used, the metering mode at the time, how sweaty your palms were as the rhino was charging your truck….
In JPEG mode, the RAW information will be compressed to save space. Some cameras have another processor that just compresses files, creating the JPEG files. I discuss RAW vs. JPEG here. For now it will suffice to say that RAW files can be 3-5x larger than JPEG and that’s why they take longer to handle.
Lastly, the information will be written to a memory card and your image is saved!
I know this information might be basic to some of your and thank you for bearing with me, as I want to make sure the basics are covered. We’ll begin to pick up speed from here and and get into the meat of how to take better photographs.
Experiments For You To Try
Now that you know how your camera works, try these experiments at home:
Next Up: How to hold a camera
31 Days To Better Photography is a series written by professional photographer Peter West Carey on The Carey Adventures.Com. The series is designed to unravel the mysteries of photography so you can take better pictures. Subscribe here to receive all the updates and bonus material. Your comments are always welcome.