Quote Originally Posted by mikewhi
Hi Mr. "127" (btw, whatever happened to 000-126? We all know about 007)
Well 126 died a horrible death sealed in a little plastic cartidge...


Quote Originally Posted by mikewhi
I'm not that tecnhical that I could plot this, so I need help intrepreting the graphs. Are you saying that for the first scan with EFKE 25 that the only light passed thru the filter is the small area under the red curve that crosses over the 3rd and 4th section of the graph? All other light is either blocked by the filter or is not rendered by the film?
Basically yes.

The white curves are the response of the film vs frequency. The vertical lines mark 400,500,600nm - the approximate divisions between uv,blue, green and red. Efke 25 doesn't respond to much above 600 (ie in the 4th section), as it's basically insensitive to red.

A 25 filter is the top red line, so if "white" (thats a whole other ball game!) light where to hit the filter, only the stuff under the curve would reach the film.

Combine those two lines and you get the lower red curve. That is the effective light which reaches the film and then actually has some effect on it. The area under the final curve is what matters, but for this combination it's not very big.

I compared the area under the original film curve, with the final curves area to estimate an exposure compensation.

However to do this properly you need to take into account the original light, which isn't exactly "white". Ideally you'd have a spectrum for the light, multiply that by the spectrum of the subject, multiply that by the filter, then by the film to give a final spectrum. Compare that with and without the filter, and you have a totally accurate exposure compensation.

Ian