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Lens review

2009-05-29
 

Canon EF 35 mm f/1.4L USM

5. Chromatic aberration

Here, another interesting thing happens, and it’s one of the reasons why we won’t test the lenses on the Canon 5D camera. The voice of reason would dictate that the aberration on a full frame will be higher than on An APS-C sensor. The graph below shows something different, though, because the aberration at smaller apertures in the case of the 20D is significantly higher than in the case of the 5D, being on the borderline between medium and high levels. On 5D it reaches the low and medium borderline.

Canon EF 35 mm f/1.4L USM - Chromatic aberration

This effect can be understood if we stop for a while and think how the chromatic aberration happens and how we measure it. When pixels are larger, the chromatic aberration is more difficult to register and, additionally in our methods it is measured by determining the size of an area, expressed in pixels, between the resolution graph for blue/cyan and for red. When the pixels are bigger, there are less of them in this area – thus a lower result and a necessity to redefine the scale. Fortunately the full frame EOS 1Ds Mark III has exactly the same pixel density than the 20D and that camera is a natural candidate for the full frame measurements. The use of that reflex camera will make the conversion of the MTF values and the chromatic aberration values unnecessary. There’s one question, though – when we will be able to afford it…but it’s quite another story.

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Canon EF 35 mm f/1.4L USM - Chromatic aberration

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