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Dobsonian Mounts

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Manual or Digital setting circles.
1 mount for 2 telescopes? Yes!
Stands to raise height
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Image Sharpening Masks

Primary
:  Fix Turned Down Edge.  
Imaging: Remove mirror clip flare.
Aperture: Eliminate spider spikes. 
OOptimized Mirror Cells

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Clamshell & Rotating Rings

For Dobsonian mounts
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For Equatorial mounts
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Mirror Masks

12" and 6" masks shown.

Detail of flat black and gloss sides.

Fix Turned Down Edge (TDE)

Mirror masks can help improve telescope performance by correcting for Turned Down Edge (TDE). If you would like a mask that also eliminates diffraction anomalies induced by mirror clip overhang, or have a different diameter mirror, we can create a custom design for you. For example, a customer asked writing: "The star test shows that my new GSO Dobson has some TDE. GSO uses metric dimensions and the diameter of the mirror is 200 mm not 8 in (203 mm)."

If your mirror has TDE, masking the outer 1/8" (where TDE usually occurs reduces your theoretical limiting magnitude but assures a sharper 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
Mirror options:
Primary Mirror size:
Custom mirror diameter:

Shipping invoiced separately: $6 in US(2 masks max), $15 to Canada. Please e-mail us for cost to other destinations.

Prototype masked mirror clip intrusion.

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