What is Peripheral Illumination Correction all about?
The following is from Cannon USA. http://learn.usa.canon.com/resources/articles/2011/whats_new_eosline_peripheral_article.shtml
Virtually all camera lenses are designed so that the volume of light transmitted to the image sensor tends to decrease somewhat from the center of the image to the corners. Many different terms are used to describe this phenomenon, such as “vignetting,” “light fall-off,” “unevenness of illumination,” etc. Most experienced photographers are well aware of this common lens performance characteristic, and some take advantage of it for creative effects. Vignetting, for example, has been a popular artistic technique for centuries. It draws attention to a well-lit main subject by darkening the areas surrounding it. Intentional vignetting can be effective in a wide variety of photographic applications, including landscapes, portraiture, and advertising photography to name a few.
However, there are many other shooting situations where uneven peripheral illumination can be very distracting and undesirable. Examples include aerial photography, sports photography, seascapes, and any other kind of composition where consistent, even illumination across the frame is preferred. For these situations, the less falloff there is in an image, the better. Generally speaking, uneven peripheral illumination or light falloff is at its worst at the maximum aperture of the lens, whatever that happens to be. It could be f/1.2 with a fast prime lens, f/2.8 with a professional zoom lens, or even f/5.6 with a consumer-grade zoom lens. In most cases, peripheral illumination is also affected by the distance setting – it gets worse at infinity because the entire coverage of the lens is being used, but it gets better at closer distances because the lens is projecting a larger image towards the image sensor and as a result the sensor is effectively seeing a cropped view. In almost all cases, uneven peripheral illumination quickly diminishes as the aperture of the lens is stopped down. For most high-quality lenses today, uneven peripheral illumination is no longer a concern once the lens is stopped down by a couple of f/stops or more.
Just had two fantastic weekends at the Pee Wee Boys and Bantam Girls BOX Lacrosse Championships.
I have always been just fascinated with the sport mode on my Canon REBEL cameras. Outside, with the zoom lens, the pictures were always crystal clear and if shot on the large setting, cropped with no distortion.
Since upgrading to the Rebel T2i, I found that the images did not seem quite as clear outside, and at the Pee Wee Boys Championship was really disappointed that most of my zoom pictures seemed way out of focus and blurry due to the poor inside lighting. While reading up on the why, I found some little known information (to us amateurs, anyway) about the peripheral illumination setting on the DSLR cameras. Checking the Menu settings on my camera, I found that my Canon zoom lens, although compatible to my camera, as all Canon Lenses are, is too old and is not supported by the peripheral illumination feature. Even working with the Canon software did not improve the images to a great extent.
Even after editing this is really grainy and out of focus.
At the girls Championship, I thought I would play with the semi-auto focus settings and see if I could get any improvement. Using a 6400 ISO setting, the improvement was astronomical! Not only did I get some great shots, but when I cropped them, I saw very little distortion. I also re-adjusted the light settings slightly and got even more improvement.
Much better detail, color and less blur.
Another step in the learning process!