HOW DOES A DSLR WORK?

 

So you finally bought that fancy new DSLR. Congratulations! You’ve spent some time and read up on Aperture, Exposure, Shutter Speed and ISO and are now asking yourself, “how does my camera use all these inputs to create an image?” Well I’m here to explain!

What makes a DSLR unique is the use of interchangeable lenses, the mirror and pentaprism. After a specific lens is mounted, a mirror behind the lens reflects the light upward to a 5-sided prism, or pentaprism, where it is reflected through the viewfinder. When the shutter release is pressed, the mirror just behind the lens flips up to allow a straight path between the light and the shutter. The shutter opens for the required time and the light falls on the Image Sensor.

Now you may be asking yourself, “what is an image sensor and how does it work?

DSLR cameras capture their images on a silicon semiconductor referred to as a “image sensor.” Digital Single Lens Reflex (DSLR) cameras use either a CCD (Charge Coupled Device) or CMOS (Complementary metal–oxide–semiconductor) image sensor. Most point and shoot cameras use a CCD sensor (excluding cameras like the Nikon D3000) while almost all DSLR’s use a CMOS image sensor. CMOS image sensors derive their name from the way they are manufactured. They are cut from a CMOS wafer which is cheaper to produce then a CCD wafer, provides less power consumption, and also allow for more involved circuitry along side of the photosite array.

This sensor is composed of an array of photosensitive diodes called photosites that capture photons (subatomic light particles) and converts them to electrons, much like solar panels convert light to energy. This build up of electrons in each photosite is converted to a voltage which in turn is converted to digital data as a picture element or ‘pixel’. These pixels are then relayed in consecutive order and stored as an image on the camera’s memory as a file. These files can then be viewed on the camera in the LCD screen, or uploaded to a computer where they can also be viewed or manipulated with imaging software.

Each photosite in a CMOS sensor has three or more transistors which has its benefits and its draw backs. The transistors allow for processing to be done right at the photosite, and each pixel/photosite can be accessed independently. Because the transistors occupy space on the array, some of the incoming light hits the transistors and not the photosites, which leads to picture noise. CMOS sensors also function at a very low gain which may contribute to noise.

After the image has been captured by the sensor and converted into a digital form, basic image processing is done in the camera. This includes removing noise and grain inherent in the sensor, adjusting color levels to user taste, and other simple tasks that don’t require the power of a desktop computer. More modern DSLRs have more powerful computers that allow more complex in-camera processing like converting an image from color to black and white. After the processing is done, Presto! You have your final image.

One thing to remember that is quite amazing is that all of this processing is done in just fractions of a second. Many DSLR cameras can shoot 4,5,6 or beyond 7 frames per second all without missing a beat. DSLRs keep getting faster and smarter with each new model, but that doesn’t mean every time a new model comes out your camera is obsolete.

Well that’s it! Hopefully this helps you understand a little bit more how your DSLR works. Here is a quick recap.

 

  • The Lens – A photograph taken with a digital single lens reflex (DSLR) camera starts at the lens. A DSLR lens is really a collection of sub-lenses called elements. Each lens refines and focuses light to create a sharp, high quality image. Lenses on DSLRs can be changed for different purposes. Wide angle lenses can be attached for landscapes. Long telephoto lenses can be used for wildlife or sports photography. Zoom lenses, or lenses that change their focal length between wide-angle and telephoto, are very common and are often included with the camera.
  • The Mirror, Prism & Viewfinder – What makes a DSLR unique is the mirror and pentaprism. A mirror behind the lens reflects the light upward to a 5-sided prism, or pentaprism, where it is reflected through the viewfinder. When the shutter release is pressed, the mirror just behind the lens flips up to allow a straight path between the light and the shutter. The shutter opens for the required time and the light falls on the sensor. In a DSLR what a photographer sees in the viewfinder is almost exactly what is captured by the sensor.
  • The Shutter & Aperture – In a DSLR, the shutter lies between the flip-up mirror and the sensor and the aperture is found in the lens. The aperture controls, by expanding and contracting, the amount of light passing through the lens. The shutter controls the amount of light falling on the sensor by remaining open for a specific amount of time. The shutter and aperture work together to allow a precise amount of light to fall on the sensor.
  • The Image Sensor – The sensor is a matrix of tiny devices that measure the intensity and color of the light allowed to fall on the sensor by the shutter. These devices are called sensor sites and are comprised of a tiny lens, a signal amplifier, and an analog to digital converter. The quality of the final image is primarily a factor of sensor quality.
  • Image Processing – After the image has been captured by the sensor and converted into a digital form, basic image processing is done in the camera. This could include removing noise and grain inherent in the sensor, adjusting color levels to user taste, and other simple tasks that don’t require the power of a desktop computer. More modern DSLRs have more powerful computers that allow more complex in-camera processing like converting an image from color to black and white.

 

 

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