Discover the Power of RC Telescopes
Ready to take your research to the next level? Get ready to discover the incredible capabilities of RC telescopes. Whether you’re a university researcher, a scientist, or just someone fascinated by the cosmos, these large astro telescopes are about to revolutionize the way you explore the universe.
So, what’s the buzz all about? RC telescopes, short for Ritchey-Chrétien telescopes, are the unsung heroes of astronomical observation.
With their advanced optics and precision engineering, the deep space observation instruments offer unparalleled clarity and resolution, allowing you to see deeper into space than ever before.
But that’s not all — this sky observation instruments not just for gazing at distant stars and galaxies. The professional astronomical telescopes are also invaluable tools for research purposes, including tracking space debris, monitoring celestial events, and even discovering new cosmic phenomena. Whether you’re studying exoplanets, mapping the universe, or searching for signs of extraterrestrial life, ASA RC telescopes provide the clarity and precision you need to make groundbreaking discoveries.
And the best part? These big telescopes aren’t just for professional astronomers. Thanks to advancements in technology and accessibility, RC telescopes are now within reach for universities, research institutions, and even amateur astronomers. With user-friendly interfaces and customizable features, anyone with a passion for the cosmos can harness the power of RC telescopes to unlock the secrets of the universe.
Differences between RC and CDK
| ASA f7 f2.5 RC | CDK | |
|---|---|---|
| On axis planetary performance without corrector |  |
not possible |
| On axis planetary performance with corrector | |
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| Off axis performance with corrector | |
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| Off axis performance without corrector | |
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| Central obscuration | |
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| Spectral range without corrector | |
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| Can be upscaled to very large fields | |
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| RC technology in affordable price/performance ratio | |
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Large Ritchey-Chrétien telescopes 0.6m to 2.5m by ASA
History of Ritchey–Chrétien (RC)
The RC design was created by George Ritchey & Henri Chrétien in 1910, and is a variant of the Cassegrain telescope. The RC uses a hyperbolic primary mirror and a hyperbolic secondary mirror. Perhaps less well-known is the fact that the RC’s two-mirror design has the smallest off-axis aberrations of any two-mirror design. It is the design most commonly used in professional telescopes including the Hubble Space Telescope, the Keck I & Keck II telescopes, and the
ESO Very Large Telescope.
History of Dall Kirkham (DK)
The Dall Kirkham design was created by Horace Dall in 1928 and uses an elliptical shaped primary and pure spherical secondary mirror. These mirrors are easy and inexpensive to produce. The ‘CDK’ design that we will discuss later therefore represents a corrected Dall Kirkham telescope.
Apples-to-Oranges Comparison
The CDK promotional literature compares a corrected Dall Kirkham to an uncorrected Ritchey–Chrétien. Any conclusions drawn from this comparison are quite frankly, not useful. Meaningful comparisons we will explore include:
• an uncorrected Dall Kirkham and an uncorrected Ritchey–Chrétien
• a CDK and a corrected RC*
*Please note that ASA routinely supplies our Ritchey–Chrétien telescopes with a two-lens corrector. The corrector is optional with an RC, while the corrector is effectively mandatory with the CDK! Read on to find out why.
Comparison One:
Uncorrected DK vs.
Uncorrected RC
The example is calculated with an f2.93 primary mirror and f6.5 system focal ratio (similar to the design values used by our competition). As we will demonstrate later, this optical configuration is less than ideal as it requires a large central obstruction. For now, we will use this design for comparison purposes and suggest better design later.
Results:
• Both systems perform perfect in the field center (assumed the optics are perfectly finished)
• The off-axis performance is 6x better for the RC
• The DK off-axis performance is completely useless even for small field sizes and CCD
• RC can be well used for CCD sensors up to 40mm diameter without a corrector
Comparison Two:
Corrected DK (CDK) vs. Corrected RC (CRC)
As a first step we will now add a two-lens corrector to the two systems above and examine their performance again. With a modern Raytracing Software like Zemax you can choose a glass catalogue like Schott, define the location for the corrector and Zemax needs less than a minute to find the optimum solution. The quality depends a little bit on the location of the two-lens corrector so we assumed the optimum location.
Results:
The off-axis errors of the original Dall Kirkham are too large to be corrected effectively with a two-lens corrector. The RC on the other hand, provides seeing-limited performance over a 70mm diameter field, with a simple two-lens corrector.
The overall off-axis performance of the corrected Dall Kirkham can be improved if the elliptical shape of the primary mirror is changed while maintaining the inexpensive spherical secondary. This is what some companies undertake to reach a sufficient off-axis performance. Below, we will examine such a system against an RC with two-lens corrector (the same RC system as described in Comparison Two). In this case we will reduce the box size to 50 microns to magnify the errors.
Comparison Three:
Modified Corrected DK (CDK) vs.
Corrected RC (CRC)
The CDK in Comparison Three has a corrector that cannot be removed as the system will not work without it even in the field center.
Please note that systems with permanent correctors installed have several disadvantages:
1) The wavelength range is limited due to chromatic errors but also due to the transmissivity of the optical glasses used which blocks wavelengths below 400nm. These systems cannot be used in UV!
2) Every lens in the light beam reduces contrast and adds ghost images even if the coating is perfect.
3) If the field flattener cannot be removed, it is more difficult (and compromising) to add a dedicated reducer.
Results:
Both systems will perform well on this CCD size with some slight advantages for the RC.
The significant disadvantage of the modified Corrected Dall Kirkham (left side) is the fact that it will not be possible to use it without corrector. In this case, since the shape of the primary has been changed, the system will suffer from severe spherical aberration in the field center if you remove the corrector. If you have such a system, you can try it without the corrector and you will not find a satisfying focus.
The RC on the other hand can be always be used without a corrector. The versatility of the RC is that it can be used for high resolution planetary targets and imaging objects without spectral restrictions, or widefield imaging with a reducer when need appropriate. An RC with a removable corrector is the best of both worlds.
