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Mirror Masks


12" and 6" masks shown.


Detail of flat black and gloss sides.

Mirror Masks
$20.00 In stock.

Mirror masks can help improve telescope performance by correcting for Turned Down Edge (TDE). If you would like a mirror mask that aslo eliminates diffraction anomolies induced by mirror clip overhang, we can create a custom design for you.

Masking the mirror's outer 1/8" where typically TDE occurs, theorhetical limiting magnitudes are slightly reduced while assuring a sharp image:

Limiting magnitude
Mirror diameter
Without mask
With mask
6.0"
13.61
13.43
8.0"
14.24
14.10
10.0"
14.72
14.61
12.0"
15.12
15.03

Constructed of 1/8" thick black acrylic, masks are stiff, light weight and have a non-reflective matte side. 0.25" holes 120 degrees apart allow you to precisely center the mask at the mirror edge. Attach using small Velcro dots on top of mirror clips.

Mirror diameter
Mask I.D.
Mask O.D.
6.0" (152.4mm)
5.75"
6.75"
8.0" (203.2mm)
7.75"
8.75"
10.0" (254.0mm)
9.75"
10.75"
12.0" (304.8mm)
11.75"
12.75"
12.5" (317.5mm)
12.25"
13.25"

Order - $20 each. 
Primary Mirror size:
Shipping invoiced separately: $6 in US(2 masks max), $15 to Canada.

Prototype 10" mirror mask.

Current design example 10" mask.
Turned Down Edge

Authoritative optical tester Dick Suiter discusses masking mirrors (see #2) to improve image quality.

"Turned down edge (TDE) Outside of proper parabolization, edge problems are the most common maladies afflicting mirrors. A turned down edge, or TDE, is a narrow zone, no more than 1/8 inch [3mm], at the extreme edge that turns downward, focusing long. If the zone is wider then it is called a rolled edge. Rarely the extreme edge will turn upward, focusing short. This is called a turned up edge." - Mel Bartels