Yesterday we shot a lot of plates under constantly changing skies, from direct sun to heavily obscured by clouds. It was a pain in the butt, so this morning I have been looking at UV meters to try to determine if it would be useful to get one for wet plate. My (hour of) internet research has enabled to be definitively state that UV is not relevant for wet plate, as wetplate is only sensitive to visible light. Here is why I can can confidently state this with a level of certainty only the internet can provide:
• There are three types of UV: A, B, and C.
• UV C cannot penetrate the atmosphere.
• UV B is 290 – 320 nanometer, but does not penetrate glass so cannot get through your lens to the collodion.
• UV A is 320 – 400 nanometer, and can get through glass (unless it has a UV coating). 95% of the UV that reaches earth is UV A
• According to Lund Photographic the spectral sensitivity of collodion is 403 to 521 nanometers. According to the internet violet (color) begins at 380 nanometers and extends to 450. This means that there is a disagreement between the description of UV A extending to 400 nanometers and the description of violet beginning at 380 nanometers, but both would agree that by the time you get to 403 nanometers you are in the visible spectrum.
• So, collodion is sensitive to almost all of violet, all of blue, and half of green, so a lightmeter that measured only this section of the visible light spectrum could be accurately used to predict wet plate exposure.
I rest my case!
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