more feedback!

1) Wow! Thanks bro you are truly amazing! :))
The blue ray is not quite correct. I've attached a picture for your reference.

[color=blue][b]seems to have fix it now[/b][/color]

2) u, h and F are in steps of 10. Could you change them to steps of 5.

3) Just found 2 new bug.
a) When F = 0, there is no lens.
Maybe for the slider, can skip F=0. If they want to key in, let them be.

[color=blue][b]change the value turn to 5 instead of 0 when 0 is selected[/b][/color]

b) When F = 40, u = -10, the green ray is too short (doesn't cut F)

[color=blue][b]done! made it always reach the xminimum and xmaximum[/b][/color]