Sized Aperture Masks
observing close objects such as tight double stars with a
Newtonian telescope, the secondary mirror holder's "spider
vanes" can distort the image. Aperture masks eliminate
spider distortions. Varying size openings provide brightness
choices for cleaning up and toning down the image. Aperture
masks increase the effective focal ratio yielding higher contrast
views: a masked 10" f/6 becomes an unobstructed 3"
f/20 telescope; wonderful for brighter detail targets such
as Jupiter and its moons, Saturn, Mars, our Moon, and of course
tight double stars or pairs with wide magnitude deltas.
first views of clean crisp star images were outstanding. Using
my 10" Newtonian on double stars, the secondary spider
created distortions. Using the mask, I can see why refractor's
unobstructed views are so desirable. Alberio showed small
perfectly circular clean airy disks with pure colors. Swapping
the aperture cover, I found stopping down to 50% was best.
Epsilon Lyrae's individual magnitude differences became obvious
showing exquisitely clean separations with perfect individual
airy disks." - Jerome G.
0.125" thick acrylic, one side flat black. Three 3/4"
aluminum posts secures mask around your tube front. Aperture
opening is computed to maximum possible, from primary mirror
edge to secondary holder edge. Example at left is a 4"
opening for a 10" mirror, and a protruding secondary
stalk turning the 10" f/5.7 into an unobstructed 4"