Would it be possible to make the following changes?
1) Full screen capability like Fu-kwun with more space for image/object: Too little room to show image/object (always out of screen; and unable to show object/image at "infinity")
  (I saw your auto function but would much prefer a fixed screen for ease of comparison)
made a checkbox to hide the top "use"
added input field and slider that are wider in range for exploring u = - infinity[/b][/color]

2) Default uncheck blue line (with option to check it): In practice, we only draw 2 lines to determine the image. 3rd line is merely for checking answer.

[color=blue][b]i check
the better way to learn principal ray is 3, not 2.
i have added a checkbox for 2 ray but the default is 3[/b][/color]

3) Option to add in "eyeball with retina" in background?

[color=blue][b]there is a screen, but i have no added sharp or blur effects as i do not know or seen any EJS that does that.[/b][/color]

4) Disable –ve f (since eye cannot be –ve f and its not in syllabus)

[color=blue][b]i check
the better way to learn f is to have both sides of the lens.[/b][/color]

Additional Objective besides the usual:
1) To show that human eye lens is of variable focal length. We need to stretch/compress our eye to see far/near object
2) People with short sighted have a upper limit to their focal length
3) People with far sighted have a lower limit to their focal length
4) Old people can have both upper/lower limit to their focal length and hence need bifocal lens

need another applet like this one