When a digital camera takes pictures, the straight line will be a little radian. How to correct or avoid it?

This belongs to lens distortion, which is unavoidable for any lens, but the distortion of a good lens is slight. Generally speaking, barrel distortion is easy to appear in wide-angle segment, and pincushion distortion is easy to appear in telephoto segment. Therefore, unless it is a special occasion, generally try to avoid using the wide-angle end and telephoto section of the lens, such as a lens of 28- 1 12mm, and you should try to use the middle section of 35-80 mm ... But for a large zoom lens, it is more difficult to control the distortion within a certain range because both the wide-angle and telephoto are required. Because distortion is an inherent property of the lens, it is related to its design and manufacture, so when you buy a camera, you should look at the evaluation and understand its distortion degree. Some camera built-in software can correct lens distortion, and some software can also do this (such as light and shadow magician), but this can only be regarded as a way to make up for it.