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Canon EOS 350D / XT vs EOS 5D: Lenses

When it comes to using lenses, there’s one big difference between the Canon EOS 5D and the models which come below it. The EOS 5D has a full-frame sensor which means lenses deliver exactly the same field of view as they would on a 35mm film SLR. In contrast, the physically smaller APS-C sensors used by the 300D / Rebel, 350D / XT, 400D / XTi, 10D, 20D and 30D models result in every lens having its field of view reduced by 1.6 times; this has the effect of multiplying the focal length by 1.6 times.

While this would appear to give the 5D the advantage, at least in terms of wide angle lenses, there’s actually benefits to having a body with a smaller sensor. Most crucially, smaller sensors avoid the outer areas of a lens where it doesn’t perform as well. So if you were to fit a lens designed for use on a full-frame body, the camera with a smaller sensor will almost certainly deliver superior optical results, especially towards the edges of its frame. This is clearly illustrated in this page from our Canon EOS 30D review.

Of course this benefit only applies if you attach a lens corrected for full frame, and it must be said the vast majority of lenses used with Canon’s APS-C bodies are only corrected for their smaller frames. But it does none-the-less give owners of these bodies a premium lens option if desired.

In contrast, the 5D’s full frame sensor is forced to use the extremes of every lens and shows up poorer models warts and all; it also won’t work with any EF-S lenses. And even if you fitted a top-end L lens to the 5D, you’re still more likely to suffer from worse vignetting (light fall-off in the corners) than an equivalent EF-S lens on an APS-C body. Towards the corners of the 5D’s large frame, the light rays are also striking the sensor's micro-lenses at a shallower angle, which further accentuates the problem. This is clearly illustrated in our results pages.

In the favour of full frame though, while you may not be able to use EF-S lenses, you do have a much larger range to choose from, and again, each will deliver the same field of view as they would on a 35mm body. This is surprisingly reassuring for photographers trading up from 35mm who have an existing collection of lenses, but clearly means much less for anyone upgrading from an APS-C digital body; indeed any EF-S lenses they’d bought would become redundant. For a more detailed discussion on the pros and cons of full frame, check the Verdict of our Canon EOS 5D review.

Canon EF-S 17-85mm versus EF 24-105mm

In this feature we’re not just comparing the Canon EOS 350D / XT against the Canon EOS 5D in terms of body alone, but also the kind of general purpose zoom lens you’re likely to use on each. So for the 5D we’ve chosen the EF 24-105mm f/4.0L IS USM, and for the 350D / XT gone for the EF-S 17-85mm f/4-5.6 IS USM; the latter is also a popular choice for 20D, 30D and 400D / XTi owners, for whom all of the following comparisons equally apply.

In terms of coverage on their respective bodies, each lens has a slightly different range. Once the smaller sensor is taken into account, the EF-S 17-85mm delivers an effective range of 27-136mm. On paper this is clearly slightly less wide than the EF 24-105mm, but considerably longer. To see what difference these really is in practice though, we shot the same scene with both lenses fitted to their respective bodies within moments of each other, and used a tripod to ensure a consistent position.
 
Below are the results with each lens set to their widest positions. As expected the EF 24-105mm delivered a slightly wider field on the 5D than the EF-S 17-85mm did on the 350D / XT. It wasn’t a great difference though, especially as the wide angle on the 17-85mm comes up slightly wider than other 17mm lenses as seen on our EF-S 17-85mm review. That said, fans of wide angle coverage place great importance on those extra few mm, and for them the EF 24-105mm on the 5D will be preferable.