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How to order secondary mounts


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Available for Cassegrain secondary mirror sizes from 0.75" to 4.00" (19 to 102 mm) in diameter.
Thin stainless steel spider vanes for low diffraction.
Sturdy 4-vane spider design.
Unique simplified collimation procedure.
Larger models feature heavy-duty vane design.
Made from corrosion-proof materials.
Graphite-impregnated flat black finish for low light scatter.

The Protostar Cassegrain mounts accept mirror diameters from 1.30” to 4.00” (33 to 102 mm). The holder has a flat aluminum face for adhesively mounting the optic to. Collimation adjustment uses the same simplified principal as our Newtonian mounts.

Models for mirror sizes above 3.50” (89 mm) in diameter use heavy-duty spider assemblies. Mounts can be ordered with our antidew heater option built into the holder.

Since some Cassegrain telescopes require very precise spacing between the primary and secondary mirror. You can adjust the axial position (i.e., closer or further from the primary) of your secondary mirror with high precision. When selecting the mirror holder size, choose the closest next size smaller holder. Available in a metric threaded version.

Each Cassegrain mounting includes a collimation adjustment tool, mirror mounting spacers, fasteners, and instructions. Made in the U.S.A.

Each kit includes:

spider assy

collimation tool

mirror holder assy

mirror spacers

drill bit (for installation)

mounting hardware


Read how to order secondary mounts...

Detailed Product Images
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Download the installation manual for Cassegrain secondary mounts.

Prices include both spider and mirror holder.

The tube ID ranges shown in the table are for pricing purposes only, and the spiders are not adjustable over this wide range. We make your spider to fit your exact tube requirements. When ordering, please provide the actual tube (or cage) inside diameter. We will make your spider slightly smaller to permit proper vane tensioning.

The dimensions in the table are in inches.

Note: Spiders are custom-made for your inside diameter (ID), and are not adjustable over the ranges shown in the table below. When ordering, provide the information described on the ordering information page.

Secondary size

7.00" to 12.00" tube ID

12.01" to 15.00" tube ID

15.01" to 22.00" tube ID

0.75 - 1.30





























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