By CNET Asia staff,Larry Loh
12/02/2007
URL: http://asia.cnet.com/digitalliving/tips/0,3800004921,61988858,00.htm

Why a digital SLR?

	Canon EOS 30D

Things used to be so much simpler in the world of film photography. If you were a serious hobbyist, film SLR cameras were the way to go as compact film cameras simply didn’t have the features and speed to match.

With the advent of digital photography technology, however, the lines are blurring. These days the mid- to high-end compact digital cameras (also known as prosumer) are giving the digital SLR cameras a serious run for their money. The popularity of this group has also benefited from the higher price tag placed on the dSLRs, with buyers opting for slightly fewer features at a lower cost.

The world is changing, though

		Digital SLR Superguide Part 1: Why a dSLR? Part 2: Choosing a dSLR

Giant leaps in research and development, along with economies of massproduction, have led to more affordable and better dSLR cameras being introduced into the market.

For those hovering on the edge of a buying decision there are some questions still being posed: Is this the right time to buy a dSLR? What do you need to get quality images? What should you expect and which dSLR is right for your needs and budget?

If you’re asking these questions and more, this guide is for you.

What is a dSLR?
dSLR cameras are all the rage these days. Sales have been going through the roof and the demand is increasing by the day. However, many users have not been able to realize the full potential of their dSLR, not being aware that dSLRs are advanced tools for photo-taking and do not always feature the same level of automation as their prosumer counterparts. A dSLR requires some training and experience to realize its potential.

So let’s start at the beginning: What is a digital SLR?

SLR stands for Single Lens Reflex. What this means is there is a mirror behind the lens which reflects light coming into the camera through the lens onto a ground glass screen above. The view through the lens can be seen through the viewfinder with a five-sided glass prism (a pentaprism) being used to turn the image the correct way round.

As the shutter button is pressed the mirror lifts up out of the way to allow the light to reach the lightsensitive area of the camera, where the image is captured. In the traditional world of film, the negative or slide film is the medium that captures the image, but in digital terms the film is the CCD or CMOS sensor.

As a general rule SLR cameras also feature an interchangeable lens system where different lenses can be used, as opposed to compact cameras that usually have a single fixed lens.

What does this all mean for the photography novice? The very design of a SLR camera means that it allows for increased accuracy and greater versatility. By looking through the lens that takes the picture, composition and framing can be more accurate and the system gives a wider scope of options. The metering and focusing systems are usually more accurate as well.

There are several manufacturers which carry a good range of digital SLR cameras (or dSLRs for short). These include Canon, Fujifilm, Nikon, Olympus, and Pentax.

dSLR camera features



More details

What's the difference?
To compare the main difference between the various types of digital cameras available in the market today, here's a quick snapshot.

Types of digital cameras




Comparison of sensor sizes
Having compared the difference between the various cameras and sensors, what does this translate to for dSLR users? Here are some of the advantages and benefits of digital SLR technology, as well as drawbacks.


* Sensor sizes reflect full size equivalent to 35mm film

Advantages of a dSLR

Users of compact digicams would certainly have experienced this before–-the action is happening right in front of you, the right settings are selected and the image is composed. You depress the shutter button, but the camera, due to its complex electronic system and slower processor, takes much longer than expected to respond. By the time the image is captured, the action has already happened and moved away.

dSLR cameras have a significant advantage in this area. As the viewfinder is optical and not dependent on electronics, response time is much faster and there’s considerably less shutter lag (the time it takes from the moment the shutter button is pressed to the moment when the image is finally captured). The Single Lens Reflex action also aids in quick composition and framing of the photograph’s subject,allowing you to quickly whip up the camera and take a fast shot of the action. This is known as WYSIWYG: What You See Is What You Get. Looking through the viewfinder you see exactly what you are photographing. Removing the lag or delayed response from the electronic viewfinder (EVF) of compact cameras is a big plus for dSLR cameras.

dSLRs typically employ only the latest in processor technology, and this translates into faster responses in the electronics. Image processing is faster and written to the storage medium quicker than most compact models, resulting in faster image reviewing and on-camera processing. This means that dSLRs are able to clear their image buffer quickly, freeing up the camera for the next available shot.

The larger image sensor of a dSLR means it has less electronic noise, and therefore can be used at higher ISO values without producing pictures with noise. For example, most prosumer cameras allow up to only 400 or 800 ISO speeds, but on most dSLR cameras values up to 1,600 ISO are the norm, with some models boasting ISO values of up to 3,200 or 6,400. This is an advantage for low-light photography, especially for action or sports photography where fast shutter speeds are needed to freeze the action. Focusing also tends to be faster on dSLRs. However, there is nothing which inherently requires the compact cameras to have slower focusing, and the gap is narrowing in the newer models.



The bigger sensor of dSLRs also means better image quality. A dSLR with a bigger sensor may have a smaller pixel count than some prosumer-level cameras, but the image it produces would have a much wider dynamic range and greater image resolution. Thus, while the megapixels of a dSLR may limit it in terms of printing out large-size prints, the image quality produced by the dSLR will be of a high quality. dSLRs also generally boast bigger and faster image file buffers. This allows the camera to continue shooting even when the CPU is busy processing previous files taken. Compact digital cameras, on the other hand, have much smaller buffers and this restricts the camera in terms of fast shooting, as the buffer has to be cleared before being able to continue shooting.

Change is good
With the use of the interchangeable lens system, the dSLR makes available a wider range of focal lengths. This is especially the case at the extreme end, where huge telephoto or ultra-wide lenses are available. This also means that dSLRs are able to use lenses with wider apertures: Ideal for shallow depth-of-field (DoF) or fast and low-light shooting conditions. The larger sensors and relative lens aperture sizes allow for a greater DoF range compared to prosumer cameras, i.e. f/2.8 lens on a prosumer camera may not produce equivalent results to an f/2.8 lens on a dSLR lens.

So far most SLR lenses have been designed for use with 35mm film cameras. This means that if the dSLR’s sensor size is smaller than the size of a 35mm frame it will affect the focal length of the lens. This is called the "crop factor". To give an example, the EOS 30D has crop factor of 1.6. In practice, this means that a 100mm lens on a dSLR will have the same angle of view as a 160mm on a 35mm film camera. This is great for getting the most out of your zoom lenses, but it does mean that you will need to make sure that you have a good wide-angle lens for landscapes and the like.

The ability to use different lenses offers the greatest flexibility in taking images. There is no reliance on zoom by wire focal system on digicams, and focus control is fast and easy. Focusing is achieved by the lens itself mechanically and not electronically controlled by adjusting buttons on the camera. It results in a very natural way of managing the desired settings, with one hand controlling the camera settings and the other handling lens focusing. Precise manual control is also simple to achieve with the dSLR and lens.

Pictures in the RAW
An additional boon for dSLRs is the use of the RAW digital format. This is by far the most versatile image format for the best image quality and control and is typically only available in top-end prosumer cameras and dSLRs. The RAW file format allows very precise control over exposure, white balance as well as a host of post-processing options even after the shot has been transferred to the computer.

Other aspects to consider
Despite the obvious advantages, dSLR cameras may not suit all needs. They do have drawbacks to consider.

Many prosumer cameras have zoom lenses of a large aperture, such as f/2, which would be extremely expensive, or just impractical to use on a dSLR. The lenses on prosumer cameras are designed specifically for their CCDs, and generally perform better at large apertures than comparable lenses on dSLRs. On typical consumer-grade SLR zoom lenses, the user has to stop down to f/5.6 to get the equivalent level of sharpness or invest in a professional-grade lens. The main reason for the difference is that the space taken up by the mirror in a dSLR requires a complex retrofocus design to get a wide-angle view.

By the very nature of its design and structure, a dSLR lets you view the shot only after you have taken it (the Olympus E-330 is an exception because there's an second sensor that projects live view on the camera), while a prosumer camera lets you view the scene through its LCD or electronic viewfinder. This same design also doesn’t allow any dSLR to have a video capture mode, which is a common feature on many digital cameras.

Most prosumer cameras are much more compact and lighter than dSLRs, which is a big advantage when traveling or for casual picture-taking. For example, the Canon Digital IXUS 850 IS weighs in at a mere 150g, including batteries, while the Canon EOS 30D weighs a much heftier 700g with the lightest kit lens. The size also forms another factor since dSLRs are much bulkier in terms of form factor and equivalent accessories.

Prosumer cameras are often sealed units with a fixed lens, so there’s no worry about dust getting on the sensor. With interchangeable lens dSLRs, dust is a problem and requires frequent cleaning, which is a delicate and timeconsuming task.

A prosumer camera lets you take extreme close-ups, often as large as 1:1 with its built-in lens. With a dSLR, you have to buy a rather expensive macro lens, and carry it around with you. In addition, the prosumer cameras with a wider depth of field and smaller sensors are very useful for macro photography. A prosumer camera doesn’t have a moving mirror, which is a source of vibrations and noise in dSLRs, and therefore it can be used at a lower shutter speed and with less camera shake, which is critical in extreme close-ups or in locations where silence is important.