# Illustrator

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## How to construct a Fresnel zone plate

### Mar 21, 2012 5:13 AM

Does anyone know of an easy way to draw a binary Fresnel zone plate such as the one shown here?

In this case the size of the innermost circle is immaterial but each successive ring (black or white) must be of equal area to the previous one.

I am searching for a quick way that does not involve too many complicated calculations.

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Mar 21, 2012 6:38 AM   in reply to Steve Fairbairn

Steve,

Basically, the ratios of W values are just the square roots of the natural numbers, 1>2>3>4 etc.

Square root of 1 = 1

Square root of 2 = 1.41421

Square root of 3 = 1.73205

Square root of 4 = 2

If you start somewhere in the row, you will have to use quotients by dividing the latest number by the first one (it is 1 when you start with the 1). So it is much easier to start with 1 and then just delete the innermost one(s) if desired.

So almost any small calculator can do it for you. You may save the innermost width in the memory and multiply that by the square roots as you go, or you may use copies of the first circle and just multiply the W/H by the square roots as you go.

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Mar 21, 2012 9:03 AM   in reply to Steve Fairbairn

You are welcome, Steve. Neither did I, before I grabbed a pencil and drew a few rings and looked at them.

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Mar 21, 2012 11:28 AM   in reply to Steve Fairbairn

Building a lighthouse, Steve?

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Mar 22, 2012 4:18 AM   in reply to Steve Fairbairn

Shall we have the pleasure of seeing the pattern(s), Steve?

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Mar 22, 2012 7:08 AM   in reply to Steve Fairbairn

Nice and strange. Thank you, Steve.

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• 448 posts
Feb 20, 2012
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Mar 22, 2012 8:32 AM   in reply to Steve Fairbairn

Great! May I ask what it's application is/what you're using it for?

You've given ideas. Recently became obsessed Shepard Fairey's work and this technique is a nifty way to create some interesting elements/pattern fills, kinda like he does.

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• 448 posts
Feb 20, 2012
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Mar 23, 2012 9:44 PM   in reply to Steve Fairbairn

Oh, is that what we're called? Sweet. Greetings, fellow werewolf. Crap of mine.

Looking through Fairey's stuff, look how he uses layered patterns to create interesting "dither" textures with just one color print; very cool.

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