Ritchey-Chrétien & Dall-Kirkham Telescopes

RC, DK and Corrected DK

• Ritchey-Chrétien: Two hyperbolic mirrors remove coma. The field is still curved, so a flattener is recommended for APS-C sensors and larger.
• Corrected Dall-Kirkham (ODK): An elliptical primary and spherical secondary with a lens corrector near focus. Gives a flat, coma-free field over a large sensor and is easier to collimate than an RC.
• Super Cassegrain (SCA): SharpStar's design adds correcting optics for a faster focal ratio and wide flat field.
• Truss or closed tube: Truss tubes are lighter and cool faster. Closed tubes resist stray light and dew better for portable use.

What These Telescopes Demand

At 1600 to 3000 mm of focal length, tracking errors and seeing are magnified. Expect to use off-axis guiding, a mount with real margin and an electronic focuser with temperature compensation. Collimation is precise work, especially on RC designs.

What We Plan With You

• Image scale: Long focal length with small pixels oversamples most skies. We check your camera and suggest binning or a reducer if needed.
• Mount and guiding: We size the mount for the tube's length and weight and plan off-axis guiding.
• Corrector and spacing: We confirm the flattener or reducer and its exact back-focus.
• Collimation support: We explain a reliable routine for your design so you are not chasing it every night.

RC and Dall-Kirkham Telescopes: Frequently Asked Questions

Is an RC good for a first imaging telescope?

It is not the easiest start. Long focal length is unforgiving. Most imagers learn on a small refractor, then add an RC for galaxies.

Can I observe visually with an RC?

Yes, but the large central obstruction lowers contrast on planets. These are designed primarily for imaging.

How often does an RC need collimation?

A well-built RC holds collimation for months if it is not knocked around. A quick star test each session tells you if anything moved.

Ready to image galaxies at long focal length?

Send us your mount, camera and sky conditions. We will tell you which tube will work for you.