How far behind the pinhole should you place the viewing screen?

[yo_man]

Homework Statement

You want to photograph a circular diffraction pattern whose central maximum has a diameter of 1.0 cm. You have a helium-neon laser (lambda=633 nm) and a 0.12-mm-diameter pinhole.
How far behind the pinhole should you place the viewing screen?

Homework Equations

The Attempt at a Solution

I'm not understanding how to go about doing this/starting this question

 

[rl.bhat]

Half angular width of the central maximum = lambda/d, where d is the slit width.
And half angle = radius of the central maximum/distance of the screen.

 

[yo_man]

so I do 633 nm/1 cm --> of course I will convert to uniform units
and half angle is 0.5 cm/x

but how do I use these?
and should i be using the 1 cm or the .12 mm?

 

[rl.bhat]

633*x^-9/0.12*10^-3 = 0.5*10^-2/x

 

[yo_man]

so I did that and it's not right. so then I tried using 0.12 x 10^-3 instead of 0.06x 10^3
and I solved for x, and it's not right...

 

[rl.bhat]

x = 0.5*10^-2*0.12*10^-3/633*10^-9 = 0.95m