Common Lens Error No. 10: Vignetting
Most lenses produce images with slightly darkened corners when they are used with the aperture wide open.
Although this vignetting is technically a flaw, it can be attractive and some photographers even add it post-capture to help draw attention to the subject.
If you want to avoid it, however, you need to close down the aperture a little.
Vignetting can also be caused by an ill-fitting lenshood that hasn’t been twisted into the correct position, or a stack of filters that has been screwed onto the end of the lens.
These may cause excessive shading or even extend into the edges of the frame – especially with wideangle lenses.
For the best results use a hood that is specifically designed to be used with your lens.
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Common Lens Error No. 11: Soft images
If you are partial to scrutinising your images at 100% on a computer screen you’ll notice that the focus point in shots taken with the aperture wide open or closed right down isn’t as sharp as in those taken with a mid-range aperture.
If you want to get the best from your lens its worth shooting a sequence of images of the same subject and focus distance at every aperture.
Then examine the shots at 100% on-screen and find the shot in which the subject looks sharpest.
Once you’ve found it check what aperture the image was taken at – this is the lenses optimum aperture.
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