agree, you get point! I am working now, so can't write in Chines

For xialibaraen: In most time you don't need to correct it, however, when you want to enlarge the picture to 16x20 or bigger, then it will be a problem. Also if this picture is for commercial use, then you have to use a large format carmera, which alow you to adjust the angle between lenth and film back, as old time I know.However today you can use PS to solve this issue.Thank you for the trying it and let us know.