15 December 2008

Peripheral Illumination Correction

The perfect lens. Oh how nice that would be. Sadly, it's just not possible. Well, not unless you're a multi millionaire and are willing to pay many millions for each lens. Even then optical physics gets in the way and there would have to be compromises. Oh, and if you had "the perfect lens" you wouldn't be able to carry many of them!

So, with that in mind, Canon introduced a feature to DPP a while ago to help correct the problem of corner shading. Essentially they used testing and optical data to work out how a lens responds on a particular camera and then it can be corrected automatically. Simply go to the DPP NR/Lens/ALO tab and choose tune next to Lens Aberration Correction.

Now, that's all well and good, but what about in camera? Well, since they've got the data, there is no reason why, in theory, it couldn't be put into the camera. And that's what they've done with the DIGIC 4 processor. So, on the EOS 50D and EOS 5D Mark II there is a Peripheral Illumination Correction option in the menu that allows you to enable or disable it.

Obviously it only works with Canon lenses, and currently it's only working for around 40 lenses. 26 are pre-loaded into the camera and the rest, up to a maximum of 40 at a time, can be added using EOS Utility.

What you should remember about this is that it's nothing to do with AF Microadjustment, which we'll look at in a future post.

What does it look like? Well, the images below should give you some idea.

Oh, and in the image that has darker corners, it's not vignetting! Vignetting is a hard corner and has different causes. This is a softer corner and is caused by light not striking the pixels in the corners of the frame squarely.




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