Creating parabolic line

[plowry01]

I need a small linear parabolic "trough" reflector, it seems they cannot be bought. I think I'll need to cut a parabolic frame and line it with reflective material. 

So what I'm trying to do is create a line parabola with the focal point in line with the ends of this line. Presumably I have to use the "conic curve" tool but I do not know how?

[plowry01]

I think I worked it out, drew a line for the diametre. Drew a 45 degree line down from one of the ends. Drew a line from the centre of the first line to meet the angled line. Drew a "conic curve" over the first line and pulled it down to meet the end of the vertical line / angled line. Set rho value to 0.5. I don't know if it's perfect or not but it looks right.