Source for optically flat glass.

Peter De Smidt said:

Hi Sandy,

I too have experienced Netwon's rings when dry scanning with the negative on the platten. I'm glad that there's no problem with glass. I like the fact that your method requires no expensive Mylar. Unfortunately, I doubt that I'll find a sheet of glass .5mm thick, and even if I did it would be very delicate. Still, I may spring for the new Epson 750 scanner, and it's best focus point might be higher. Thanks for sharing your method!

-Peter

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Peter,

The 750 looks very interesting. But I am going to wait to see how effective the scanner is in terms of ration of dpi to lppm. The Epson 4800 is less than 50%. 4800 dpi (at pixel to lppm of 2.5:1) should give about 80 lppm, but by my tests, actual lppm is less than 40. If the 750 increases the efficiency to 65-70% I will consider it a good buy, otherwise will stay with the 4800 until the next generation.

Sandy

I already posted a link to S. I. Howard Glass, Co., (http://www.howardglass.com/) but with the description of the application, their products looks fully appropriate. I don't think you need optical flatness, meaning measured in wavelengths of light. Certainly the scanner manufacturers aren't using that grade of glass.

Their soda lime glass is available in thickness of 0.40, 0.55, 0.70, 0.90, 1.1, 1.2, 1.6 mm, all the way up to 19 mm. Typical prices for thicknesses around 1 mm are $1.15 per square foot. Sizes are various, such as 20 x 20 inches. I think they cut to the size that you want.

Perhaps their B270 super white crown glass is better. They emphasize its optical clearness. It costs a lot more.