transmission grating
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John Barby
Feb 16, 2015, 4:07:06 PM2/16/15
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Has Anyone Tried The Transmission Gratings From Edmund Scientifics? The Groove Density Is Close To The Dvd Spacing And Is Parallel.
Terry Relph-Knight
Feb 17, 2015, 6:59:58 AM2/17/15
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Hi John,
Yes I've tried it, and I believe a number of other people have too. The Edmund Scientific holographic gratings are available with either 1,000 lpi or 500 lpi. Using a DVD-R gives you 1,351 lpi. The claimed dispersion angles for the Edmund gratings are given as 36 and 19 degrees. Presumably for an incident at normal to the grating and for the limit wavelengths of 400 and 700nm. I don't believe these specifications because they do not agree with any calculated values. I have asked Edmund to explain their specifications and they have never replied. The calculated dispersion angle for a 1,351 lpi DVD-R under the same conditions is 38.35 degrees. With an incident beam at anywhere between 30 and approaching 90 degrees to the normal the dispersion angle for DVD-R falls to around 24 degrees. The dispersion angle affects how much of the web cam sensor is covered by the diffracted light form the grating.
Using a DVD-R does give you a wider dispersion angle so at least potentially greater resolution than the 1,000 lpi film. When the DVD-R grating is correctly aligned the curvature really isn't a problem since Spectral Workbench takes a sample through one point in the curve. DVD-R material is readily at hand and is stiffer than the holographic film. It is a good idea to remove the blue dye from the DVD-R material.
The Edmund gratings are apparently made by Anchor Optics a division of Edmund. I have tried both DVD-R and Edmund and have settled on using DVD-R gratings.
Yes I've tried it, and I believe a number of other people have too. The Edmund Scientific holographic gratings are available with either 1,000 lpi or 500 lpi. Using a DVD-R gives you 1,351 lpi. The claimed dispersion angles for the Edmund gratings are given as 36 and 19 degrees. Presumably for an incident at normal to the grating and for the limit wavelengths of 400 and 700nm. I don't believe these specifications because they do not agree with any calculated values. I have asked Edmund to explain their specifications and they have never replied. The calculated dispersion angle for a 1,351 lpi DVD-R under the same conditions is 38.35 degrees. With an incident beam at anywhere between 30 and approaching 90 degrees to the normal the dispersion angle for DVD-R falls to around 24 degrees. The dispersion angle affects how much of the web cam sensor is covered by the diffracted light form the grating.
Using a DVD-R does give you a wider dispersion angle so at least potentially greater resolution than the 1,000 lpi film. When the DVD-R grating is correctly aligned the curvature really isn't a problem since Spectral Workbench takes a sample through one point in the curve. DVD-R material is readily at hand and is stiffer than the holographic film. It is a good idea to remove the blue dye from the DVD-R material.
The Edmund gratings are apparently made by Anchor Optics a division of Edmund. I have tried both DVD-R and Edmund and have settled on using DVD-R gratings.
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