I have a question about the colored filters used for the telescopes. Here I will give an example for the filters of the big telescopes, but I assume that it applies also to the smaller personal telescopes. The range of the visible light goes from about 400nm to about 750 nm. Where the "blue" has a range of 400–475nm. Now, when we look at the list of some "blue" blocking filters for the Blanco 4m telescope for example, we see that it allows a transmission in the http://www.ctio.noao.edu/spectrographs/filters/blocking/Schott/wg345.gif" [Broken] which would not really be blocking the blue... Is there anything that I'm missing here?