Saturday, November 07, 2009
	.: Apodizing Mask    This home-made lyot mask is used to cut through the seeing much like an aperture stop. It can help steady planetary observing on less than perfect observing nights. When used on a scope, it removes the first diffraction ring of the airy disk at the expense of fattening the central part of the disk. It works best on large aperature Newtonian scopes and helps with enhansing detail on planets and split double stars—small Newtonians and SCTs have too large of a secondary mirror obstruction for the mask to be effective. The only drawback is that it causes a rainbow effect to appear around your object. The following specs come from Improving Your Reflector Telescope Performance on Planets, Astro Techniques (Steve Waldee Web site no longer available). Constructing the mask is very simple: Use three layers of standard fiberglass window screening material. All three screens are cut to the diameter of the telescope. Central holes are cut into each screen in the following diameters: 1st screen: 90 percent, 2nd screen: 78 percent and 3rd screen: 55 percent. The size of the holes in a 10 inch telescope would then be: 9 in.; 7.8 in.; and 5.5 in. Position each screen section so that their patterns are rotated by a successive offset of 30 degrees providing a relatively randomized blocking effect of the screen. Sandwich all three screens between two pieces of lightweight wood or cardboard and secure into place (see diagram below). The dimensions are not very critical—just adapt to your own scope. To use, simply place the mask into the front of your scope resting it on top of the secondary spider. ©2006, article originally published by Steve Waldee. ©2006, The Astrogirl Homepage. All right reserved.	Recommended Resource