note that the object must be on the left of the lens.

the assumption is the light source is always shining from left to right!

Physlets®, i.e., the Java applets themselves, are a registered trademark of Wolfgang Christian.  

can you explore and find out the focus length of the lens?

[color=blue][b]Hint: [/b][/color]
an object placed exactly at the focus length of the lens will result in an image at infinity!