Comparing Compact and DSLR Cameras

A Camera Must Fit YOUR Needs

You should always choose the right camera to fit your needs, but in order to decide which camera that is, it is important to understand the differences in the kit which is out there on the market. There are significant differences in the way Compacts and DSLRs work and some situations demand specific kit.

It’s important to realise that whilst the final output of “a picture” from digital and film cameras is similar, digital cameras are little more than small computers with a lens on the front. Analogue (film) cameras work in very different ways. Both are limited by the laws of physics.

Differences Between The Compact And The DSLR:

1. Basic Mechanics

Nikon DSLR without lens (but with large battery pack attached). You can see the mirror inside.

The most obvious difference between Compacts and DSLRs is the ability to change the lens of a DSLR, which allows much greater creativity at the expense of time and effort to do so. Additional lenses come at a cost of course, both of money and of the inconvenience lugging them around.

With a DSLR the image is previewed in the view finder courtesy of a mirror which sits in front of the sensor. This mirror is flipped up when the shutter button is pressed, letting light hit the sensor instead. For an instant, you can’t see the image as it’s being shot – but the camera needs no power or electronics for you to be able to see the image in the view finder. What you see is what the sensor is going to see.

A digital Compact camera’s sensor is always getting the light from the lens, and electronically shows you a preview on a small screen. It consumes power, generates heat and the preview can be hard to see in bright light conditions. What you see is what the electronics think you’re going to see.

2. Lens Properties

In the process of making a digital picture, the first thing light does is bounce off the subject and head down the lens of your camera. This is where the first significant technical difference is; the lens in a compact may cost £50 and be attached to a £200 camera. The lens of a DSLR may cost 10 to 100 times that – or more, with a corresponding increase in the quality of light reaching the sensor. Quality of manufacture, materials, lens coatings, number of glass elements and physical size all affect the quality of light.

Nikon DSLR with several larger lenses. This DSLR has a battery pack attached, so looks far bigger than it otherwise would be - don't panic!.

During light’s journey down the lens, it passes through the aperture. A DSLR lens is often physically much bigger than a Compact camera’s, and can accommodate a much larger mechanical aperture. This makes a huge difference to the amount of light making it through to the sensor and to the depth of field the lens is capable of producing.

Size DOES matter – especially in terms of lenses. The larger physical size of a DSLR lens allows greater distance between the lens glass elements and the sensor, creating an increased focal length. This in turn allows a shallower depth of field which means some of the subject can be in-focus, while the background is merely a blur. A shallower depth of field affords much more creativity, allowing the photographer to use this to separate subject from background and is seen by most people to create a more pleasing image. The smaller size of a Compact’s lens means the bokeh (amount of blur for the out-of-focus parts) is minimal, due to the light simply not having enough room to spread out on its path from lens to sensor. Everything seems more in-focus. This is a pro in terms of simplicity, but a con in terms of creativity.

In mobile phone and miniature cameras, the lens and sensor are tiny – measured in mm. There is no room for light to spread at all, therefore the focus options in these and other miniature cameras is very limited.

3. Physics

Chromatic Aberrations on one of the spires of York Minster

Light of different wavelengths (colors) is bent at different angles by both the optics and the aperture resulting in color fringing towards the edge of an image – an effect known as chromatic aberration.

All cameras generate this effect, but higher quality components and larger sensors minimise it to the point where the effect is smaller than 1 pixel, therefore it cannot be seen. It’s not a case of 1 factor making a huge difference between Compacts and DSLRs, it’s the accumulation of a dozen small differences which can add up to something noticeable. Smaller apertures add further to any chromatic aberration already created by lower quality lens components.

Compact cameras deal with lower amounts of light as everything is so much smaller. This means that anything which degrades the light getting to the sensor has a relatively larger effect.

4. Sensor Size

The next significant difference between the two happens when light hits the sensor. Compact camera sensors are much smaller by necessity, It’s compact camera! Common sizes for Compact sensors are 1/8th or ¼ inch. A DSLR sensor can be an inch square or more (35mm is the standard “full frame” sensor size) – allowing far more points of sensitivity to be built onto it – known as light buckets. The more buckets, the more light is collected, the less electronic amplification has to be done to make the image.

5. Where Digital And Analogue Cameras Differ

Once light has been collected on the sensor, it’s passed to the electronics in order to turn it into an image and here’s where there’s another difference. For analogue cameras, the only difference between a Compact and an SLR Single Lens Reflex) is the lens type and quality, and the negative size.

SLR (left), Compact Camera (right). Both cameras use 35mm film, so the area of film hit by the light is exactly the same.

In a digital Compact camera, a reduced quality of light from the lens has reached a reduced size of sensor, which has collected much less of it. It’s then handled by a relatively low-cost set of electronics.

In both Compacts and DSLRs, the term ISO is still used but rather than referring to the sensitivity of the film as with analogue film cameras, it refers to the amplification of the digital signal received from the sensor. Higher quality electronics in a DSLR get to work with an already far superior sensor signal – resulting in a technically higher quality image with greater range of light against dark, and color fidelity. This is known as the Tonal or Dynamic Range. The Dynamic Range of DSLRs can be 6 or more “f-stops”, the range of a Compact only 1 or 2. For comparison, the human eye can be thought of as having a range of about 30 f-stops.

6. Final Output Of A Picture

Compact Camera

Most DSLRs have the option to adjust the compression used for the final output image (usually a JPG) – many offer uncompressed or RAW image output. The less compression is used, the more accurately the image can be reproduced on screen or in print. Only a few Compacts offer the facility to output as a RAW image as to transfer all that uncompressed data to the memory card is slow and expensive in terms of processing power. A Compact camera is designed to be a relatively quick and easy to use device. It’s designed to compromise the final output quality for the speed of being able to take several photos in quick succession, without worrying too much about settings.

A DSLR contains dedicated electronics purely for final data transfer to memory card. The higher up the price range you go, the more capable a camera’s electronics become. It may also include dedicated chips for focus, one for monitoring the battery, one for tracking objects and so on. All these jobs are likely handled by one “general purpose” chip in a Compact.

The accumulation of all these small differences results in Compact cameras being suited to one kind of shooting, DSLRs being suited to another.

7. Noise

Much "digital noise" is visible on this picture when zoomed in like this. This can easily happen if you are shooting on a high ISO.

Shooting with a Compact in low light conditions often leads to a "noisy" image with poor color definition. This is due to the much lower amount of lower quality light reaching the sensor, which has to then be amplified significantly by a relatively cheap set of electronics. In good sunlight, the difference between an image from a Compact and a DSLR may not be too noticeable, depending on what was being shot. If the image is of a landscape and depth of field is not so much of an issue, then even more so.

In low light, there are 2 ways to avoid a poor signal to noise ratio being amplified onto the image: Increase the aperture size and allow more light through – or – increase the exposure time. The aperture size is limited by the physical size of the Compact’s lens, and longer exposure times increase the risk of motion blur or camera shake.

There’s No Hard And Fast Rule

A Puffin at the Farne Islands, England - taken with a DSLR

Compacts usually win out in terms of convenience and portability - they're ideal for slipping into the pocket and taking with you wherever you go. DSLRs allow you much more creativity and greater image quality, but are bigger, heavier, (usually but not always) more expensive and more delicate bits of kit.

The image quality produced by a DSLR will be far superior (at the expense of convenience and simplicity) but without exception, equipment and technical quality is of secondary importance to the image content. Photographers make the image, not the camera. You can take an awful picture with a DSLR and prize winner with a cheap Compact.

Camera manufacturers are constantly making leaps forward with their technology and electronics, hugely improving the algorithms and software which enhance the image from the sensor and turn it into a JPG. A 2015 mobile phone camera produces significantly better images than a 2005 Compact camera. A 2015 Compact, likewise, could out-perform a 2005 DSLR in some areas such as low light conditions, but not in terms of the depth of field effect afforded by the DSLR’s bigger lens and sensor.

It’s worth remembering that there’s a grey area in-between the two categories of DSLR and Compact camera. Some larger Compacts are big enough to allow a very similar quality picture to a smaller DSLR. Some DSLRs are cheaper than some Compacts. Some cameras blur the distinction yet further. They have no reflex mirror and are therefore not “SLR”s, instead using the electronic sensor preview - but have an interchangeable lens system.

How a camera will be used most of the time dictates what kind of camera will be best.

That said, for those serious about photography we would recommend investing in a DSLR. That is not to say you can't take decent images without one. All cameras have their place, but a DSLR gives you far better quality, with so much more creative freedom. You can take pictures with a DSLR which you couldn't hope to take with a compact.

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