Omegon Primary Mirror 254 mm f/8 Ritchey-Chretien Mirror Set

Omegon Prime Mirror 254 mm f/8 Ritchey-Chretien Mirror Set: primary mirror and secondary mirror for DIY installation

A Ritchey-Chrétien uses two hyperbolic mirrors instead of the parabolic primary mirror of a Newtonian or the spherical mirrors of a Schmidt-Cassegrain. This combination completely eliminates coma, so that stars remain round right to the corners of the field of view. That is why this is the design of virtually every professional observatory.

This set includes the optics, not the tube. It is intended for builders who are building a truss structure themselves or who want to retrofit an existing tube with new optics. This 10-inch size is the entry-level model in the series and the most manageable of the four.

Quartz glass for a stable focus

Both mirrors are made of fused silica, also known as quartz glass. That material hardly expands with temperature changes.

That is exactly what long exposures are all about. A mirror made of ordinary glass slightly changes shape during the night as the temperature drops, and then the focus drifts. Quartz holds its shape.

Coating with 94 percent reflection

Both mirrors have an aluminum layer with a protective layer of silicon dioxide over it. The reflection is 94 percent per surface.

In a two-mirror system, that counts double: the light bounces twice before it reaches the camera. As a result, every percentage point of increased reflection per mirror has a stronger impact than in a single-mirror system.

Focal length and scale

At f/8, the focal length is 2000 mm. This provides a large field of view, suitable for small deep-sky objects such as globular clusters and compact star clusters.

Please note that a long focal length places high demands on tracking. Accurate mounting and autoguiding are not a luxury, but a prerequisite.

Included

• Hyperbolic main mirror of 254 mm
• Matching secondary mirror
• Both with aluminum and silicon dioxide coating

Featured accessories

For aligning a Ritchey-Chrétien, a collimation eyepiece is the recommended tool: a laser does not suffice here because both mirrors are hyperbolic and the alignment is more sensitive.

For whom yes and for whom no

• ✓ Experienced builders assembling an RC truss structure
• ✓ Astrophotographers who want coma-free images right to the corners
• ✓ Anyone who wants to equip an existing tube with better optics
• ✗ Beginners: this is optics without tube, mount, or focuser
• ✗ For those who want to perceive visually: an RC is a photographic design
• ✗ Setups without autoguiding: the focal length is too long

Specifications

You can find more telescope parts for this brand on the Omegon brand page.