Digital Photography - Advantages of Full-Frame Digital SLR

DSLR cameras are typically equipped with either an APS-C size sensor or a larger, full-frame sensor. Full-frame cameras are generally bulkier, more expensive and require larger, full-frame lenses. If you've been wondering what advantages a full-frame dSLR offers and whether the benefits justify the bulk and expense, this article will explore the strong points of full-frame sensors.

Nearly all 35mm film cameras were designed for a frame size of 24x36mm. There were a few quirky SLRs that used a different film size, and medium format SLR cameras used much larger 120mm film. Overall, however, the typical film SLR standardized on a frame size of 24x36mm.

The first dSLRs created a dilemma for camera-makers. It was difficult to build a sensor the size of a 35mm film frame. Availability of larger sensors was limited, and the quality of some early 35mm size frame sensors was questionable.

For this reason, dSLR makers adopted a sensor the size of the APS-C film frame, which measures 15.7x23.6mm. APS size sensors were simpler to make and while smaller, offered sufficient quality for most users.

By the time digital technology evolved to where it became practical to build reasonably priced full-frame cameras, APS dSLRs had become the standard. While the majority of dSLRs still use the APS size-sensor, full-frame cameras appeal to photographers for several reasons:

Image quality

Since an APS image will require more enlargement than a full-frame image to obtain a specific size, prints from a full-frame image will almost always be superior. For small photos, the difference is marginal, but 8x10 and larger prints are noticeably superior from a full-frame camera.

Improved Dynamic Range

Dynamic range refers to the ability of a camera to capture detail in both the shadows and the highlights. Manufacturers use different methods of processing images inside the camera, so it is difficult to compare dynamic range between brands. Overall, however, smaller sensors capture less dynamic range. This means prints from the full-frame dSLR have better tonal range.

Less Image Noise

Many photographers assume a manufacturer can cram any number of pixels into a sensor, so sensor-size is irrelevant to pixel count. In reality, sensor dimensions determine the size of the individual pixels. For a sensor of any given pixel depth (megapixel rating) full-frame sensors will contain larger photo-sites (pixels). Larger pixels collect more light, so there is less need to amplify the signal. Amplification translates into heat, which increases image noise. When you compare sensors of the same pixel count, a full-frame sensor will generally control image noise better than its APS cousin.

Availability of Wide Angle Optics

Cameras with an APS-C sensor are often referred to as "crop" cameras, because the smaller sensor captures a reduced portion of the image compared to a full frame sensor. In other words, an APS size sensor crops the image that a full-frame camera would deliver.

This magnifies the effective focal length of the lens. A 200mm lens on an APS-C camera will capture an image roughly equal to a 300mm telephoto on a full-frame dSLR.

At first this might seem to be a big advantage, and many wildlife and sports shooters choose crop cameras for this very reason. They get a longer focal length without the need to invest in super-telephoto optics.

Of course the focal length magnification applies to all lenses, so it becomes difficult to find suitable wide-angle lenses for an APS sensor camera. They can be had, but they are rare and expensive. Fast wide-angle primes are particularly hard to come by. So those who shoot landscapes, interiors or other wide-angle subjects will find a full-frame dSLR offers a major advantage.

Greater Selective Focus Options

Selective focus, the ability to isolate subjects from the background, is closely coupled to shallow depth of field. Although a number of elements affect overall DOF, selective focus increases as you get closer to your subject. Because the smaller sensor magnifies the image when compared to a full-frame camera, you have to move farther away to get the same composition.

The result of this is that for any given focal length, you will see less selective focus with an APS-C sensor, because you need to shoot from farther away to achieve the same image crop. Long telephoto lenses are capable of delivering nice selective-focus effects on an APS-C camera, but on the whole, you will achieve greater, more pleasing selective-focus with a full frame camera, particularly with shorter focal-lengths.

Ability to use lenses at their designed focal length

On a 35mm camera, a focal length of 35mm is considered a wide angle, while a "normal" lens has a focal length of 50-60mm. Telephotos start at around 85mm.

Because of the crop factor, a normal lens on a APS camera would have a focal length of 35mm, while a 50mm lens is equivalent to a 75mm lens. An extreme full-frame wide-angle of 16mm would only offer the view of a 24mm lens when coupled to the APS-C camera.

This might seem to be an exercise in semantics, but many photographers have favorite lenses, and are distressed that they cannot use them as they could on a film camera. This problem is compounded because they may not be able to find a suitable lens to give them the same effects on an APS-C camera. High-speed 50mm lens are quite common, but it is difficult to find a 35mm f/1.4 optic. In other words, very fast "normal" lenses are practically nonexistent for APS-C cameras.

Whether any of these factors are relevant to you will depend on your subject, your final application and your style of shooting. For many photographers, the APS-C sensor will provide all the quality and composition ability they need. For others, however, full-frame sensors offer superior images and special effects that cannot be duplicated with a smaller sensor.

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Tom Bonner is the author of the Sony Alpha DSLR - A300/A350 Digital Field Guide, published by Wiley Publishing.