How does the power of a lens affect its ability to focus light?

[Khashishi]

Well then my guess was wrong, but I'm not surprised.

 

[Drakkith]

Well, you're correct in that you need to take the aberrations into account to determine how well the image is focused at the focal plane, which will affect how fast the OP burns through paper.

 

[NascentOxygen]

So I've been doing some experiments, using bottles filled with various liquids and timing how long they take to burn paper which is placed at the focal point (where the light was focused).

This is an interesting investigation---is it something you thought up, or is it in a science program you are studying at school?