Last Updated October 18, 2003
Two weeks ago I had the chance to compare the viewing of Mars through a 5" scope Vs my 12.5". I soon realized the 5" gave just as much detail and contrast as my 12.5"er. My friend Tim was using an Apodizing mask on his 5" scope. The views were amazing because the Apodizing mask moved the diffraction spike from the object to a region further away leaving a nicely defined plant with great contrast!
Tim has built his mask by following the simple instructions in the April 2003 issue of the RASC Journal. I followed the same procedure and made one for my 12.5" scope. I've included some photos below for you to look at.
This design uses simple window bug screen material. I used a fiberglass type but one could easily have also used the aluminum alternative both of which are available.
Using a piece of card board I drew a cross in the middle marking the central point of the card board. I then drew two extra lines one at 45 degrees and one at negative 30 degrees. Using a compass I drew three circles each at the aperture specified in the chart below and used them as a template to cut out the inner portion of the 3 masks.
I then aligned the straight lines in the window screen as shown and glued them together with some nail polish to ensure that the three screens do not shift during final assembly. After the nail polish dried I stapled the mask to a thin Lexan ring which I cut precisely to the size of my secondary cage. This process resulted in a flexible mask which attaches quickly and easily to the back side of my secondary cage using 4 pcs of Velcro.
I chose to install the mask on the bottom side of my secondary cage while Tim installed him on the top of his tube assy. Simply personal preference. I store the mask on the bottom of my rocker box out of the way but still accessible.
A = 55 % B = 78 % C = 90 % D = clear aperture of the mirror. "E" is the outside secondary diameter
Return to my Home Page of Projects
