Unfiltered Cassegrain Astrograph Rankings
Decoding Cassegrain Specs
Listing 154 Best Off-Axis Telescope Modifications for Astrophotography
Schmidt-Cassegrain telescopes, or SCTs, are the most popular of the Cassegrain bunch and the most affordable for a given aperture. Most can be reduced to f/6.3 using a thread-on reducer, and some can be converted to f/2 with a Starizona HyperStar system. The Celestron RASA telescopes are basically permanent HyperStar conversions. An f/2 Schmidt camera allows for short exposure times but can be hard to focus and may be incompatible with many cameras, particularly monochrome or DSLR cameras. Additionally, image scale is limited.
Regular SCTs have a somewhat hazy outer field of view by default, which must be corrected with a reducer-flattener, also making them more reasonable for deep-sky imaging. Aplanatic SCT designs offer better performance for deep-sky imaging, though there isn't much difference in planetary performance. The Celestron EdgeHD and Meade ACF designs are both aplanatic SCTs, though the EdgeHD has superior optical and mechanical qualities with a greater selection of available accessories; ACF telescopes cannot be used with HyperStar, though standard SCTs from both Meade and Celestron work with the HyperStar system.
Ritchey-Chretien telescopes provide a sharper and flatter field than SCTs by default, often achieving a larger image circle, and usually come with superior focusing systems and other mechanical aspects that make them better for deep-sky imaging. Collimating them can be challenging, they're pricier, they need a field flattener like refractors for deep-sky imaging, they produce diffraction spikes like in a Newtonian, and they're subpar for visual or planetary imaging due to their large central obstructions.
Classical Cassegrain telescopes aren't really intended for deep-sky imaging (though some can be used for it anyway). Vixen's VC and VMC telescopes are a variation of the Classical Cassegrain using small corrector lenses similar to those found in aplanatic SCTs. Like Ritchey-Chretiens, you get diffraction spikes in your images, they're usually slow in f-ratio, and fewer accessories are available to support them for deep-sky imaging use.
Maksutov-Cassegrain telescopes should be avoided for deep-sky imaging, as none of them offer fast focal ratios, large image circles, or the ability to use a reducer. However, they require minimal collimation and can achieve stunning planetary images.
Uncensored Cassegrain Rankings for Deep-Sky Imaging
Budget Cassegrain Telescopes under $1k
Celestron C6 XLTType: SCT
Rank $839.95 at AgenaAstroBuy from HighPointMade in China
Meade 6" ACFType: Aplanatic SCT
Rank $949 at HighPointBuy from AgenaAstroMade in China
iOptron Photron 6"
Type: Ritchey-Chretien
Rank $499.95 at HighPointBuy from AgenaAstroMade in China
GSO/AstroTech 6′′ Classical Cassegrain
Type: Classical Cassegrain
Rank $599 at AgenaAstroBuy from AgenaAstroMade in China
Explore Scientific FirstLight 152mm Mak-Cassegrain
Type: Maksutov
Rank $749 at Explore ScientificMade in China
Mid-Range Cassegrain Telescopes ($1k - $2k) for Deep-Sky Imaging
Celestron EdgeHD 8
Type: Aplanatic SCT
Rank $1599 at HighPointBuy from AgenaAstroMade in China
Apertura/GSO/TPO/Orion/AstroTech 8" f/8 Ritchey-Chretien
- 4.5 starsType: Ritchey-Chretien
- $1399.95 at HighPointBuy from AgenaAstroMade in China
iOptron Photron 8" (Ritchey-Chretien)- 4.5 stars
Rank $1699.99 at HighPointBuy from AgenaAstroMade in China
Apertura/GSO/TPO/Orion/ AstroTech 8" f/8 Carbon Fiber Ritchey-Chretien- 4.5 stars
$1349.95 at AgenaAstroBuy from HighPointMade in China
Celestron 700 Maksutov- Partially Recommended
$999.95 at OPTCorpMade in China
Sky-Watcher Skymax 180- Partially Recommended
$1299.99 at OPTCorpMade in China
Orion 7′′ Maksutov- Partially Recommended
$1349.99 at OPTCorpMade in China
High-End Cassegrain Telescopes ($2k+) for Deep-Sky Imaging
Celestron RASA 800- Type: Schmidt CameraRank $2999 at HighPointBuy from AgenaAstroMade in Japan
Celestron C9.25 EdgeHD- Type: Aplanatic SCTRank $2999 at HighPointCheck Amazon PriceMade in Japan
Meade 10" f/8 ACF- Type: Aplanatic SCTRank $3299.99 at HighPointBuy from AgenaAstroMade in China
Apertura/GSO/TPO/Orion/ AstroTech 10′′ f/8 Ritchey-Chretien Optical Tube- Type: Ritchey-ChretienRank $3195.95 at HighPointBuy from AgenaAstroMade in China
Meade 10" f/10 ACF- Type: Aplanatic SCTRank $2399.99 at AgenaAstroBuy from HighPointMade in China
Planetary Imaging Cassegrain Rankings
Compact Planetary Cassegrains under $1k
iOptron 150mm Maksutov Cassegrain- Type: MaksutovRank $848 at HighPointCheck Amazon PriceMade in China
Classical Cassegrain (GSO/AstroTech 6′′ Classical Cassegrain, Celestron 5" Schmidt-Cassegrain - all $599-$699)
Mid-Range Planetary Cassegrains ($1k - $2k)
Celestron C9.25 XLT- Type: SCTRank $1899.95 at AgenaAstroBuy from HighPointMade in China
GSO/AstroTech 8" Classical Cassegrain- $1099 at AgenaAstroMade in China
Celestron 700 Maksutov, Sky-Watcher Skymax 180, Orion 7′′ Maksutov (all $999-$1299)- Partially RecommendedType: MaksutovMade in China
Celestron EdgeHD 8- Type: Aplanatic SCTRank $1599 at HighPointCelestron C8 XLT (SCT) - 3.9 starsRank $1349.95 at AgenaAstroBuy from HighPointMade in China
High-End Planetary Cassegrains ($2k+)
Celestron C11 XLT- Type: SCTRank $3199.95 at AgenaAstroBuy from HighPointMade in Japan
Celestron Cedeos 11- Type: Aplanatic SCT
Rank $4299 at OPTCorpMade in China
Vixen VC200L, Vixen VMC200L (both $2349-$2799)- Type: Classical CassegrainMade in Japan
Meade 10" f/8 ACF- Type: Aplanatic SCTRank $3299.99 at HighPointBuy from AgenaAstroMade in China
- Schmidt-Cassegrain telescopes are often reduced to f/6.3 using a thread-on reducer, but an f/2 Schmidt camera allows for short exposure times and is found in the Celestron RASA telescopes, yet can be hard to focus and may be incompatible with many cameras.
- Celestron's EdgeHD and Meade's ACF designs are both aplanatic Schmidt-Cassegrain designs, with the EdgeHD offering superior optical and mechanical qualities and a greater selection of available accessories.
- Ritchey-Chretien telescopes provide a sharper and flatter field with larger image circles compared to Schmidt-Cassegrain, but they require field flattener for deep-sky imaging, produce diffraction spikes like in a Newtonian, and are subpar for visual or planetary imaging due to their large central obstructions.
- Maksutov-Cassegrain telescopes should be avoided for deep-sky imaging due to their slow focal ratios, small image circles, and lack of ability to use a reducer, but they can achieve stunning planetary images requiring minimal collimation.
- For those new to astronomy, budget-friendly deep-sky telescopes include the Celestron C6 XLT (SCT), Meade 6" ACF (Aplanatic SCT), and iOptron Photron 6" (Ritchey-Chretien), all available for under $1k.
- Advanced and high-end deep-sky telescopes include the Celestron RASA 800 (Schmidt camera), Celestron C9.25 EdgeHD (Aplanatic SCT), and Apertura/GSO/TPO/Orion/ AstroTech 10" f/8 Ritchey-Chretien Optical Tube, all available for $2k+ and offering advanced performance for deep-sky imaging in the field of space-and-astronomy, as well as machine-based manufacturing technology.
