Custom Sized Aperture Masks

When 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.

"My 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.

Mask is 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" f/14.25.