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Introduction to Ritchey-Chretiéns

Ritchey Chretiéns, or RCs for short, utilize a two-mirror design to bring an image into focus, and are therefore categorized as reflector telescopes. The Ritchey Chretién design is a fantastic choice for imaging distant deep sky objects such as galaxies and small nebulae. If your primary goal is long focal length, deep sky astrophotography, then the Ritchey Chretién design may be the ideal telescope for you. Like Newtonians, the secondary mirror in an RC is also held up by four struts known as spider vanes — this is what causes stars to appear cross-shaped in images. Unlike Newtonians, RCs are designed to eliminate coma, which can cause stars to become misshapen near the edges of the image. RCs are very well-corrected telescopes, meaning you won't need to spend extra money on a coma corrector or field flattener for imaging. This makes them a great choice for the imager who wants a plug-and-play telescope right out of the box.

Ritchey-Chretiéns for Research Purposes

For researchers, the Ritchey Chretién design is one of the best options out there. RCs do not suffer from coma, and only suffer from astigmatism. Although astigmatism can elongate stars off axis, the center of the star remains in a position that keeps it measurable for star positions. The lack of refractive lens elements allows this telescope design to detect wavelengths broader the visual spectrum making them very useful for measurements in the ultraviolet (UV), near-infrared (NIR), and infrared (IR) wavelengths. RC telescopes are also very modular, field flatteners are available for expanding the corrected image circle, reducers can be integrated for faster focal ratios, and barlows can be used for longer focal lengths. With all these properties within one telescope, it's easy to see why RCs are extremely desirable among researchers and advanced astrophotographers.

Ritchey-Chretién Weaknesses

RCs are great for long focal length deep sky imaging and research, but they are less ideal for visual use or planetary imaging. The reason for this is because RCs usually have a large central obstruction, which is how much light is obstructed entering the front of the telescope due to the size of the secondary mirror. The large central obstruction reduces contrast a significant amount, which makes the RC inferior to say, Schmidt-Cassegrain Telescopes for planetary imaging or visual observing. This is not to say that you can't use an RC for either application, but just that an RC's strong suit is deep sky imaging.

Ritchey Chretiéns are fantastic telescopes for research or for imaging galaxies and other distant deep sky objects for amateur use. RCs range widely in price depending on their aperture and quality of their components. If you need help picking out an RC, get in touch with our friendly and helpful Sales team!


FAQs

Still have questions? We have answers.

Are Ritchey Chretién Telescopes good for astrophotography?

Yes, Ritchey Chretiéns are a fantastic choice for deep sky astrophotography! Their long focal lengths make them particularly good for for distant targets such as galaxies and small nebulae. In addition, they are very well corrected optically, meaning you don't need additional accessories. RCs are not ideal for wide field deep sky work. They are also not as good as other telescopes like SCTs for planetary imaging due to their lower contrast as explained above, but you can still absolutely use one for capturing the planets just at reduced contrast.

Do Ritchey Chretién Telescopes need to be collimated?

Yes, as with all reflector designs, RCs do need to be collimated and usually somewhat frequently. Any laser collimator should work, but we recommend getting one that matches the size of your focuser, which is 2" in most cases. You can watch our video on how to collimate a high-end Ritchey-Chretién here.

What kind of mirrors do Ritchey Chretien telescopes use?

RC telescopes use hyperbolic mirrors to eliminate optical errors like coma and chromatic aberrations off-axis while producing the flattest focal plane possible without lenses.

Why are some Ritchey Chretién Telescopes priced low and others high?

Ritchey Chretién telescopes come in a wide variety of prices. On the lower end, this is primarily because the telescope will come with lower-end components, such as the focuser. Lower-end RCs may feature a "fixed" primary mirror design. Collimation is also important on a Ritchey-Chretién, and entry-level RCs may be somewhat difficult to collimate for precision imaging purposes. For this reason, if you're planning to use your RC for high quality deep sky astrophotography, plan to spend more on a quality RC.

On the high end, RCs are more expensive because they use a hyperbolic primary mirror design. These become very expensive to produce at large sizes due to the degree of accuracy required to manufacture the mirror. Research-grade RCs can costs tens of thousands of dollars, if not more, for this reason.

Can I use a Ritchey Chretien telescope for visually observing the night sky?

RC telescopes are usually best for imaging because of their lower contrast compared to most other telescope designs. If you plan to use one for viewing you will generally need to use a diagonal with your eyepiece because of the angle of the telescope when looking at the night sky.