Calculating equivalent apertures
    A common question among ATMers seems to be about the value of enhanced coatings (those with greater than 88% reflectivity) versus standard (88% reflectivity - Aluminum with overcoating) coatings. Add to that the problem of multiple optics (do you coat both the primary and the secondary with enhanced coatings?) and you have quite the problem. Here is a calculator that will let you test your setup before you send your mirrors off to the coaters. Many thanks to Larry Manuel for his help in creating this calculator.
    In the table below, enter the aperture (diameter) of your primary mirror in any unit you want. Enter the reflectivity of your primary and secondary mirrors as a percent (for example, enter 88 for 88% not 0.88). Click on any other field to calculate the output.
  Primary Aperture
Common Reflectivities:
 Standard = 88%
 Semi-enhanced = 91 - 94%
 Enhanced = 96 - 99%
 Beral = 91%
 		Primary Reflectivity %
Secondary Reflectivity %
Equivalent Aperture:
Improvement over standard coatings %
   What's it mean?
   

This document, its contents, and its Web representation are Copyright ©1996, Michael Lindner and others. For complete copyright information, including allowed uses of this FAQ, please see Section 8. Initially created on Thursday, September 12, 1996 by Tim Poulsen.