photo
Pentaprism
A multi sided prism housed in the roof of a SLR camera so that the image that's seen by the lens can be viewed through the viewfinder above the lens
Camera Shutter
controls the amount of time the sensor or film is exposed to light. typically DSLR cameras allow for exposures from 30sec long to as fast as1/8000 of a sec. Shutter speeds can be adjusted in small increments from 1/30 to 1/125th of a sec. With each incremental adjustment half the amount or twice the amount of light is exposed to the camera sensor. As the shutter speed increases the amount of light reaching the sensor decreases. As the shutter speed decreases the amount of light reaching the sensor increases.
Sensor
A DSLR camera's sensor sits inside the camera body, on the other end of the camera's lens. When the shutter button is pressed, the mirror moves out of the way and allows the light passing through the lens to fall on the sensor. The sensor records the light, and the rest of the electronics inside of the camera convert that light information into a photograph. Where older cameras had film, a digital camera has a sensor.
Lens Elements
Each of these elements aims to direct the path of light rays such that they recreate the image as accurately as possible on the digital sensor. Wide angle lenses have small focal lengths, while telephoto lenses have larger corresponding focal lengths.
Aperture
The aperture controls the amount of light that reaches a digital camera sensor. An aperture acts much like the pupil of an eye. It opens wider as light decreases to let in more available light. It gets smaller when light increases to reduce the amount of light entering the eye. The diameter of an aperture is measured in f-stops. A lower f-stop number opens the aperture and admits more light onto the camera sensor. Higher f-stop numbers make the camera's aperture smaller so less light hits the sensor.
Focusing Ring
The ring used to adjust the lens so that the subject appears sharp on the camera sensor.
Diopter
Your camera has a small dial or slider right next to, above, or below the viewfinder. That's a diopter adjustment. It actually controls the focus of the viewfinder (not the lens). The diopter allows you to adjust the cameras viewfinder so the image you see through it looks nice and sharp. Because everyone's eyes (and prescriptions) are different the diopter is put in place to help compensate.
Camera Mirror
reflects the image coming through the lens towards the pentaprisim