Can I make my own Expodisc?

Question

I've been contemplating the purchase of an Expodisc to finally be rid of most white balance corrections. The price is a little steep for me, however. I was wondering, is there a way to make something similar to this using materials that one might find 'off the shelf' at a store like Home Depot?

I've tried lenses (prismatic diffusers) from lighting fixtures combined with various translucent plastics without much luck.

Note, the price is not that steep, I'm just one who sticks to a very strict gear budget and I like the satisfaction of making my own stuff.

Answer

From what I understand about Expodisc, it is a rather carefully engineered filter. It is designed to transmit a diffuse 18% of visible light, corresponding to a standard 18% gray card. Unless you have a way to precisely measure the light passing through materials that can be found at the likes of Home Depot, and can ensure that the resulting light is properly diffused, I am not sure you'll have any luck.

I would either buy a set of gray cards, or just bite the bullet and get the Expodisc.

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