Digital Single-Lens Reflex Camera

Digital single-lens Reflex camera

How a DSLR Camera captures an image

BY: KATIE KOVALCHIK

INTRODUCTION

A digital single-lens reflex camera combines the optic mechanisms of a singlelens reflex camera and the imaging sensor of a digital camera. The reflex design scheme is what differentiates a DSLR camera from other digital cameras. These are discussed in more detail further into this document.

The process of capturing an image with a DSLR camera occurs in a stepwise sequence; beginning with light traveling through the lens and ending with a stored image on the memory card.

This guide will describe the photo-taking processes taking place inside the camera. The process includes the following elements • camera lens • reflex mirror • focal plane • digital image sensor • pentaprism • viewfinder The order of elements follows the sequence that light takes through the camera.

AUDIENCE + SCOPE

This guide educates photography beginners using digital single-lens reflex (DSLR) cameras. Beginners of DSLR photography will learn more about the camera and the image capturing process. This description will not serve as a replacement to the manufacturer manual accompanying a DSLR camera, but will enhance the photographer’s knowledge of the camera components and how it functions.

2

Figure 1: Camera lenses

CAMERA LENS

A camera lens is an optical lens used in conjunction with a camera body to create images. On a DSLR camera, the versatility comes from the interchangeable lenses. Different lenses can have different focal lengths1, apertures.2, and other properties, which are further explained in this guide.

The aperture in the camera lens is how light travels into the camera body to create an image.

Photographic lenses are most often represented in millimeters (mm), which correlates with the focal length of the lens. For example, a standard lens is a 18mm-55mm lens, meaning the lens can be used at a wide angle of 18mm, (useful for a landscape) or used at 55mm (more zoomed in), which is typical for portrait photography. The higher the millimeter number, the more magnifying capability a lens has.

1 FOCAL LENGTH | description of magnification capability 2 APERTURE | the hole or opening through which light travels through the lens 3

Figure 2: How light travels through camera lens and body

REFLEX MIRROR

As light travels through the aperture in the lens, it hits the reflex mirror and is deflected four times before we see it in the viewfinder (Figure 2). When you are looking through the viewfinder, the mirror is down and ready to reflect the image to the viewfinder. As you trip the shutter3 button, the reflex mirror flips up, allowing the light coming through the aperture to hit the image sensor on the focal plane (Figure 3). This is why your view of the image disappears when you press the shutter button.

The reflex design scheme is the primary difference between a DSLR camera and regular digital cameras. The reflex mirror can either reflect the image to the viewfinder (what you see when you look through) or it can flip out of the way so that the image is recorded on the image sensor.

3 SHUTTER | device that allows light to pass through the lens for a determined amount of time to expose the digital image sensor to capture a permanent image 4

The alternative is a camera design where a viewfinder with its own lens, such as a disposable camera or compact digital camera. In a disposable camera, you look through a viewfinder that is not connected with the image capturing process. The disposable camera viewfinder frames the scene you are looking at and does not represent what the camera lens is seeing.

Focal Plane

Figure 3: How a scene is transferred to the focal plane

FOCAL PLANE

The focal plane is the area in a camera where light is focused. As seen in Figure 3, the focal plane is on the back of the body of the camera. The image that passes through the aperture in the lens is projected onto the focal plane. This is the same surface of which the digital image sensor is mounted.

Â

5 Â

Figure 4: The digital imaging sensor inside of the camera body

DIGITAL IMAGE SENSOR The digital image sensor converts light into a digital file. Once the shutter is tripped, the reflex mirror flips out of the way so the image can come through the lens and travel to the focal plane, where the image sensor is located (Figure 3).

This sensor is an integrated circuit chip4. The chip converts the light (image) coming into the camera body into electrical signals, which are turned into images.

The main type of sensor in a DSLR camera is a charge-coupled device5 (CCD).

In the CCD sensor, each point struck by light creates an electrical charge that activates every sensor at once and stores the charge. The charge is then converted into data, which is then stored to the camera’s memory card.

The digital image sensor is the primary difference between a digital camera and a film camera. The DSLR sensor stores the images digitally, while a film camera stores photos on photographic film through a chemical process triggered by light exposure.

4 INTEGRATED CIRCUIT CHIP | a set of electronic circuits on one small plate that acts as a control board for a device 5 CHARGE-COUPLED DEVICE | device for the movement of electrical charge, usually from within the device 6

Figure 5: Diagram of a pentaprism reflecting an image

PENTAPRISM

A pentaprism is a five-sided reflecting prism6 that deflects light at a 90° angle.

As you can see in Figure 5, the image is reflected within the prism two times, which keeps the image from being inverted7. The quality of the pentaprism is evident in how close the stored image is to what you preview in the viewfinder.

VIEWFINDER The viewfinder is what allows the photographer to see what the camera is seeing. This element lets you preview the image and compose the shot. When

6 PRISM | in optics, a prism is a transparent element with flat surfaces that refracts, or changes the direction of light 7 INVERTED | put upside down or in the opposite position, order or arrangement 7

the reflex mirror is in standard position, it reflects the light up through the pentaprism, which corrects the image so it is seen correctly in the viewfinder.

As stated before, the DSLR camera relies on the single-lens reflex system to reflect a true image through the viewfinder. This differentiates a single-lens reflex camera from a regular digital camera. A regular digital camera cannot be considered a ‘single-lens’ camera because it has a lens for taking the picture and a lens through which the photographer views the seen.

Modern viewfinders not only show you the expected image, but also offer possible focal points8, light metering9 and what mode the camera is in. This allows the photographer to edit different camera settings while viewing the composition.

CONCLUSION The digital single-lens reflex camera is an exciting upgrade from a regular digital camera because of enhanced quality, control and capability when it comes to photography. These enhancements are a direct correlation of the improved mechanisms within the lens and camera bodies. The benefits of knowing more about the DSLR camera will lead to better photography because of a well-rounded understanding of the camera system. While a DSLR camera is a significant investment, it has the potential to be a lifelong hobby and educational experience.

8 FOCAL POINT | where the image is focused on and most clear 9 LIGHT METERING | how the camera is reacting to the light intensity 8

CITATIONS CONTENT "CCD vs. CMOS." Teledyne DALSA. N.p., n.d. Web. 04 Mar. 2014.

"Digital SLR Camera Basics." Nikon. N.p., n.d. Web. 04 Mar. 2014.

Shankland, Stephen. "How Nikon Bettered Canon with Full-frame SLRs." CNET News. CBS Interactive, 17 Dec. 2007. Web. 04 Mar. 2014.

IMAGES Cover: http://graphics.stanford.edu/courses/cs178-11/canon-1000D-cutaway.jpg Figure 1 http://upload.wikimedia.org/wikipedia/commons/9/9b/Photographic_lenses_f ront_view.jpg Figure 2 http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/imggo/slr2.gif Figure 3 http://www.vantagephotography.com/blog/wpcontent/uploads/2009/02/focal -point.jpg Figure 4 http://www.the-digital-picture.com/Images/Other/Canon-Digital-SLR-CameraSensor.jpg Figure 5 http://labman.phys.utk.edu/phys222core/modules/m7/images/pprism.gif

9 Â