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Intro to SLR Cameras
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SLRs are no longer just for the advanced photographer. Many now have automated features similar to compact cameras, so you can get the resolution and performance of a SLR and still be very easy to use. This being true, there still are many features that are only available on a SLR. This SLR section will dive deeper into some aspects of digital photography and discuss some of these features not available on compact digital cameras. If at anytime you feel that the information is going over your head or not deep enough into a subject, feel free to e-mail us with questions and we will be delighted to provide you with more information.
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| SLR means "Single Lens Reflex." The image viewed through the viewfinder is the image that the lens sees. The ability to see through the lens is important because you see what the lens sees. This is accomplished with the use of a mirror and a prism. Light enters the camera through the lens, which resolves the image. Behind the lens the light bounces off a mirror, goes up through a prism, which changes its direction, and then into your eye. When the shutter is fired, the mirror flips up out of the way to expose the sensor to light. This same principle is the reason why there is no live preview on the camera’s LCD screen. Typically using the viewfinder will help you get better composition and sharper images. |
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Advantages
SLRs are more robust cameras than compact point and shoot. Major advantages are the ability to interchange lenses, greatly increased resolution, the ability to see through the lens and increased performance. Increased performance includes: very little or no shutter lag, a much more robust metering and focusing system, and the ability to override any of the cameras automatic settings to create images exactly how you want. The trade off is, you loose the some of the portability compared to a compact camera. A photographer may carry a kit of a couple lenses, a flash and maybe an assortment of accessories |
Not only do digital SLRs typically have a higher resolution than compact cameras, currently ranging from 6 to 14 megapixels; the imaging sensor is also larger. (To learn the basics about sensors, see the digital basics section) This allows for larger pixels. Larger pixels have less noise, can be pushed to higher speeds, and have a larger surface area to gather light. The result of this is images with better color, sharper textures and edges, and a larger gamut range. When post processing images, the gamut range will define when there is detail in the shadows and highlights. The wider the range, the more you can adjust your images for color and exposure afterward. Larger pixels are more efficient at gathering light. Better information, in the end, will render better quality images.
You may ask, why don’t all cameras have larger sensors, if they are better? Large sensors are more expensive to produce and cannot physically fit into smaller cameras. SLR sensors illuminate a larger area an require a lens that can accommodate the larger illumination area. Big sensors also consume more battery power. |
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SLRs have performance. Most compact digital cameras have some sort of shutter lag. This means you have to wait from the time you press the shutter button until camera actually takes the picture. SLRs typically do not have this problem. When you press the button you get a picture and sometimes more than one picture. Many SLRs can shoot in burst modes. This means that when you hold down the shutter, the camera takes pictures continuously until the card is full or the camera has reached its burst limit. The buffer is what controls the burst limit. A buffer is internal memory where the camera temporarily stores pictures while transferring the data to the card. When the buffer is full, the camera cannot take any more pictures until it transfers enough information onto the card to make space for another picture.
Shutter speed is only one aspect of performance. The autofocus systems play a large and unnoticed role. The autofocus system can really define how fast the camera operates. Auto focus works on contrast and lines. Better quality systems can focus quickly on smaller lines or lower contrast. The lens can also make a difference. Many lenses now have internal focusing which means that the focusing motors are built inside the lens instead of in the camera body. This can drastically increase performance while focusing. Most SLRs share 3 common autofocus modes:
1) Single servo auto focus will focus on the subject once each time the shutter button is pressed. SLRs will not take a picture until the frame is in focus in this mode.
2) Continuous server auto focus will continually focus on subjects as they change or as the scene changes as long as the shutter button is pressed half-way. In this mode, the camera bases the focus on depth of field and will continually fire once it finds an object in that focus range.
3) The third is manual focus. Lenses have focus rings, turn it until the image looks in focus. Usually the camera will tell you if it thinks that the subject is in focus, but in this mode it will not focus automatically.
Last is exposure metering. More accurate metering systems will give you a more even capture of the light in the scene. Even exposure in a scene will help to avoid blown out highlights or shadows without detail. Metering systems have points in the frame where readings are taken. The camera then averages these readings together to get the exposure. The goal for a good system is to average in a way that gives the scene a dynamic look, not flat, and keeps the scene in the good exposure range. Cameras also have different types of metering modes, but most cameras typically share 3:
1) Average (matrix) metering uses all the points in the viewfinder to make an exposure. Individual readings then get averaged.
2) Center-weighted uses the spot in the center of the viewfinder and in most cases 30% of the surrounding area.
3) Spot metering only takes a reading from the area inside the center spot of the viewfinder. This mode is the most critical because the camera is basing the exposure off of the smallest area of the frame.
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