Continuity mistake: When Emma and Mr. Knightly are practising their archery some arrows disappear from the target. After they have both shot 2 arrows, the target is shown with 4 arrows in it. They each shoot one more and the target is shown again - Emma's arrow is shown hitting it yet there are still only 4 arrows in it in total. (00:23:10)
Continuity mistake: When Emma and Mr Knightley kiss for the first time near the end, they are both tilting their heads to the right when the camera angle is from Emma's perspective. Then, the instant the camera changes to Mr Knightley's perspective, they are suddenly tilting their heads to the left.
Factual error: In the wedding scene at the beginning, the new Mrs. Weston is shown wearing a white dress. This was not the convention at that time; white wedding dresses were pioneered by Queen Victoria (1840-1901). The bride would simply have worn her best dress.
Suggested correction: A white dress may very well have been an unmarried lady's best dress at the time, as it was common for young ladies to wear white.
Continuity mistake: Emma is walking home after praying at church. She encounters Mr. Knightley, who has just returned from London. Emma has a shawl. In close-up shots of her face, the shawl covers her right shoulder. In medium shots showing both her and Mr. Knightley, it no longer covers her shoulder.
Factual error: When Emma painted the portrait of Harriet, the paper was stuck to the drawing board with tape. Emma is set in 1815, but sticky tape wasn't invented until 1845.
Continuity mistake: In the scene where Mr. Knightly proposes, he got a haircut. The hair, eyebrows, entire look changes. Seems to have been filmed on different days.