Ever since the arrival of the first commercially viable digital SLRs in the 1990s, there's been a steady stream of technological breakthroughs and new releases. Sales of digital SLRs remain robust, as it's this 'quality' end of the market that is most immune from the threat of ever-improving smartphones; however good smartphones are, if a pro wedding or sports photographer turned up wielding one, they'd get shown the door.

There are SLR cameras suitable for every type of photographer, from novices to professionals, but which one is right for you?

In this guide, we will discuss the main types of SLR so you can make the right buying decision. First, a word of caution. It's not the case that maxing out your credit card to buy a pro-specification SLR will not instantly make you a pro-standard photographer.

However pricey your SLR, you won't get very creative shots if you only know how to shoot in Auto or Program modes; the quality of your lenses also has a massive impact on your photography.

SLRs: your need to know guide

Before we start covering specific types of digital SLR, let's just recap what an SLR actually is. SLR stands for Single Lens Reflex, and an SLR works by using a mirror to direct light from the lens to the viewfinder (what you usually look through before pressing the shutter button).

When you actually take a picture, a 'reflex' mirror swings up to let light directly through to the camera's sensor, so the image can be recorded. Once the shutter closes, the reflex mirror drops back and directs light back to the viewfinder again. After a lot of complicated, split-second image processing, you have your picture.

SLRs are a type of interchangeable lens camera, which is a big attraction.

What types of SLR are there?

One of the key ways of differentiating DSLRs is by sensor type – the sensor being the light-sensitive electronic device inside the camera that records the image. SLR sensors typically come in two flavours, full frame and APS-C format. Full-frame sensors are found in more expensive SLRs, and are called full frame as they are the same size as a 35mm film negative frame.

DSLR sensor
A digital camera's sensor

This means that their light-sensitive pixels ('photosites') can be bigger, which means more light can enter, which can mean a wider dynamic range and less digital picture interference, or noise. The result is higher quality images.

APS-C format sensors have smaller (approx 22x15mm) sensors, which means a full frame sensor has 2.5x the surface area. A full frame sensor has a 1x 'crop factor,' so a 24mm digital SLR lens, for instance, gives the same angle of view as a 24mm film SLR lens. APS-C sensors cover less of the area projected by a lens designed for full-frame.

An APS-C sensor sees a smaller angle of view, with a crop factor of 1.5 or 1.6x, so our 24mm lens gives the same angle of view as a traditional 38mm focal length. Having said all this, it's not simply the case that full-frame SLRs are 'better'.

While full frame sensors deliver large, high resolution image files, and are particularly good for capturing a wider scene in landscapes (thanks to that 1x crop factor), APS-C sensors can also produce excellent results. Some photographers also prefer the longer reach that the extra crop factor gives them. APS-C SLRs and lenses are significantly cheaper too, which is often the deciding factor for many non-professionals.