Full frame DSLR: do you really need one?

Full Frame DSLR: do you really need one?

Owning a full-frame DSLR, such as the Canon EOS 5D Mark II or the Nikon D700, is the ambition of many photographers. ‘After all,’ they think, ‘bigger must be better’ – and these cameras, with their supersize sensors, are what all the top professionals seem to use.

Switch to a full-frame DSLR and your pictures will automatically be better – or so the hype goes. But this is only partly true… A full-frame sensor camera just takes different – not necessarily better – shots than Nikon or Canon DSLRs with the more standard APS-C-sized sensor.

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So, what exactly do we mean by ‘full-frame’? A full-frame DSLR from Nikon or Canon or Sony has a sensor that’s the same size as a frame of traditional 35mm film, measuring 36x24mm. The more popular APS-C sensor cameras have much smaller 22x15mm sensors. This means, a full-frame sensor has over 2.5 times the surface area of an APS-C sensor.

Sure, size has certain advantages, but there are distinct drawbacks, too, to making the switch up to a full-frame DSLR.

Camera selection
To upgrade to a full-frame DSLR, prepare to pay a premium. For instance, the street price for a Canon 5D Mark II body is around £1,700, while Canon’s flagship EOS-1Ds Mk III body is £5,250! The added production cost of the bigger sensors means that full frame DSLRs aren’t launched all that often. Today’s Nikon D800 announcement, nearly four years after the release of its predecessor, the Nikon D700, is a shining example of this.

Because full frame DSLRs are less frequent, though, this means you don’t get as much choice as with APS-C.

Image quality
The biggest advantage of full-frame is image quality and image size. Both the Canon EOS 5D Mark II and 1Ds Mark III full-frame DSLRs, for instance, come equipped with 21.1-megapixel sensors, and crucially these sensors are over two-and-a-half times bigger – and have much larger individual pixels (or photosites) – when compared to APS-C cameras.

It is not the number of pixels that really counts – APS-C models such as Canon’s EOS 7D and EOS 550D have almost as many photosites, thanks to their 18-million pixel count – but the size of the photosites is crucial to image quality.

Bigger individual light sensors capture more light – and this means that less electronic noise is created. You notice this most as you increase the ISO setting – with this noise creating a coloured mosaic pattern that is particularly noticeable in shadow areas.

Crop-factor effect
The size of the sensor also changes the amount of the scene captured by the camera. Although APS-C and full-frame cameras can share many of the same lenses, the visual effect they provide is different. It is the angle of view that actually changes – as the smaller sensor covers less of the image projected by the lens.

This is known as the crop factor – which compares the angle of view with that seen by a traditional full-frame 35mm film SLR. With full-frame DSLRs the crop factor is 1x – so effectively can be forgotten. A 24mm lens gives the same angle of view as a 24mm lens before the age of digital cameras.

Full Frame DSLR: do you really need one?   Full Frame DSLR: do you really need one?

An APS-C sensor sees a smaller angle of view – with a crop factor of 1.6x. This means the same 24mm lens actually captures the angle of view of a traditional 38mm focal length setting (24×1.6=38). So if you want to capture sweeping wide-angle vistas, a full-frame camera allows you to take in more of the scene in front of you than an APS-C model with the same lens.

The flip side is that the crop factor effect of APS-C cameras becomes an advantage when shooting distant subjects.

Full Frame DSLR: do you really need one?   Full Frame DSLR: do you really need one?

A 200mm telephoto lens gives the same view as a traditional 320mm lens, when the 1.6x crop factor is taken into account – great for getting close to the action in sports or wildlife photography.

Less lens choice
Full-frame cameras used to offer a real advantage when shooting landscapes or indoors in tight spaces. However, lens makers have combated this by developing zoom lenses with shorter focal lengths exclusively for use on APS-C-sensor cameras.

Standard APS-C-style zooms offer an 18mm setting, equivalent to the view given by a full-frame 28mm lens. Super-wide lenses offer settings of 10mm – equivalent to, or with an effective focal length (EFL) of, 16mm. These lenses cannot be used with full-frame cameras (as they would produce dark corners) – so APS-C users actually get a wider choice of optics!

Blurring backgrounds
Portrait photographers love full-frame DSLRs, as the larger the sensor a digital camera uses, the smaller depth of field (DoF) you get. This means that you can throw backgrounds and foregrounds more out of focus – for artistic effect and to draw strong attention to the subject. The reason for this is that the amount of depth of field depends of three different factors: the aperture, the subject distance, and the focal length.

Use full-frame, and the actual focal length you use for a particular composition changes. You use a 28mm lens setting, say, rather than the 18mm you would need with an APS-C camera – and this difference in focal length means less depth of field.

In practice, this means that wide apertures on full-frame cameras provide noticeably more defocused backgrounds than on APS-C cameras. Look at our portrait photos below and you’ll see that a full-frame DSLR at f/5.6 produces a seemingly similar amount of depth of field and background blur to an APS-C camera at f/2.8. The f/2.8 shot on the full-frame DSLR creates a very shallow DoF for knocking backdrops out of focus to make your subjects really stand out from their surroundings.

Full Frame DSLR: do you really need one?   Full Frame DSLR: do you really need one?

APS-C cameras are better, however, if you want to maximise depth of field – which has advantages in studio and landscape photography. For example, when using the same angle of view, on an APS-C DSLRs you will be able to get away with using, say, f/14, whereas on a full-frame DSLR you may have to use f/22 to ensure your scene is sharp from foreground to background.