Angela Nicholson looks at the Canon EOS 7D and EOS 5D Mark II to see whether full frame still holds an advantage over APS-C-format cameras
Image sizes of the 5D vs the 7D
At 300ppi, prints of images from the Canon EOS 5D Mark II measure 47.55×31.7cm, while those from the EOS 7D measure 43.89×29.26cm. This means both cameras are capable of producing images that make good A3 (29.7x42cm) prints.
When A2 (42×59.4cm) prints are required, the resolution of the EOS 5D Mark II’s images must be dropped to 240ppi, while those from the EOS 7D must be printed at around 223ppi.
At lower sensitivities it is impossible to distinguish between images from the two cameras when they are enlarged in this way. At higher sensitivity settings, however, the EOS 7D’s images are more granular and chroma nose is visible. The amount of noise isn’t objectionable, but the EOS 5D Mark II images are smoother.
Canon 5D vs 7D – Optics and focal length
Image: These two sequences were taken from exactly the same spot to demonstrate the impact of the 1.6x focal length multiplication factor across the 16-35mm focal length range
As an APS-C-format sensor is smaller than a full-frame device, it effectively crops the image when a full-frame lens is mounted. The result is similar to using a longer focal length optic than the one actually mounted on the camera, so the effect is often referred to as focal length magnification. With Canon’s APS-C-format DSLRs such as the EOS 7D, the focal length magnification factor is 1.6x, but with Nikon and Sony models such as the D300S and Alpha 550 it is 1.5x.
For enthusiast photographers who started out with 35mm film cameras, the focal length magnification of APS-C-format DSLRs can be a source of some frustration, as a much-loved 24mm optic on an EOS 7D produces the framing that we would expect to see at around 38mm. However, at least APS-C-format cameras use the central area of 35mm-format lenses, and this can benefit image quality.
In recent years manufacturers have addressed the magnification issue by producing much wider optics specifically designed to work with the smaller-format cameras. Canon’s shortest focal length, for example, appears in a zoom lens for the APS-C format: the EF-S 10-22mm f/3.5-4.5. This has an RRP of £990 and it produces images similar to a 16-35mm lens on 35mm format.
A list price of just under £1,000 is not to be sniffed at, but full-frame users who want the same framing will find they have to shell out considerably more for the EF 16-35mm f/2.8L USM, which is listed at £1,400, or the EF 16-35mm f/2.8L II USM at £1,790. Although these two lenses benefit from Canon’s superior L-series build quality and a wider (constant) maximum aperture, full-frame users may prefer to opt for the EF 17-40mm f/4L USM, which has a more manageable RRP of £940.
At the other end of the focal-length spectrum, the APS-C format’s magnification factor allows photographers to frame distant subjects more tightly than full-frame photographers can with the same optic. This means that on the EOS 7D, the £960 EF 200mm f/2.8L II USM offers framing not too far off what is seen with the EF 300mm f/2.8L IS USM, which has a list price of £5,630. The shorter length lens isn’t stabilised, but at 765g it’s less than a third of the weight of the 2.55kg 300mm optic, and as it’s almost half as long it is easier to hold still anyway. It also takes up a lot less space in your bag and is easier to carry, so you are far more likely to take it out in the first place.
The focal length magnification factor is also useful with close-up and macro photography, as subjects appear larger in the frame at the same focusing distance. As such, a lens that achieves 1:1 magnification effectively produces images with 1.6:1 or 1.5:1 magnification, depending upon the APS-C camera of choice.
Image: A wideangle optic (16mm on full frame) and a low angle were required to capture these dramatic cloud formations