What is an NG lens?

NG means no good, which is a shot that failed when making a movie~~~~~

Usually used when the director will say NG during filming, which means it failed and required Reshoot. There are often stories in entertainment news in Taiwan and Hong Kong. If something goes wrong, or the scene is laughable, or the effect is not satisfactory, the director shouts cut! Ask for a retake.

The following is excerpted from: Shanghai Cultural Celebrity-Ye Yonglie

He (Director Du) asked the film crew members one by one whether it was good or not. As long as one person said "no", he immediately said "Do it again". At that time, Director Du always called the "one more shot" shots "NG". At first, I didn't understand what this "NG" meant. Later I found out that it was the abbreviation of "No good", which means "not good".