Not really, see this
I'm using diffuser in my scanner and its working great.
P.S. Sorry to bring up the old thread, but I wanted to let everyone know that using diffusers is a great idea actually.
Do you have pictures of your diffuser attached to your DIY scanner?
The example showed is with an professional photography umbrella outdoors, I can't imagine you have that on your scanner.
Or are you using a professional photography kit? (I wish I had the money for it)
I can imagine however that you take pictures outside to get full advantage of sunlight, a white bedsheet will then be enough to get even lightning on all kind of books. Paperbacks but also glossy magazines.
Since summer is coming and I am going to try making my build at the end of this month it will be summer. So I will have plenty of light outside. Put up some white bedsheets for diffusion. I only have to figure out how to avoide the shadows from the columns.
The only thing I am going to use extra on the first and last picture is a Lastolite grey/white ezybalance screen. This way I will now if the light intensity has changed from the sun and adjust accordingly with Adobe Lightroom. http://www.lastolite.us/product/0/LL%2BLR1250/_/EzyBalance_GreyWhite_Card_12%27%27
Fairly easy to tell the software that in overal the picture with the Lastolite are the correct white balance and all other pictures needs to be the same white balance. Even indoors with lower Kelvin values you can get an expectable white balance this way.