Above the beginner shelf sits a set of instruments designed around a camera rather than an eye, and their prices only make sense in those terms. An astrograph is judged on the flatness and cleanliness of its field, not on how much it shows.
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What an apochromat corrects
Three elements, at least one of extra low dispersion glass, bringing three wavelengths to a common focus. The result is a star image with no colour halo across a wide field, which is the requirement a camera sensor imposes and an eye does not. The cheapest apochromatic refractor in this index prints $498.00.
What an astrograph is
A telescope optimised to produce a flat, well corrected field across a sensor rather than a sharp point on axis. That usually means a fast focal ratio, a large image circle and a field flattener designed for the instrument. Photographically it beats a visually excellent telescope of the same aperture.
Ritchey-Chretien, and why it appears at this end
An RC is a cassegrain variant with two hyperbolic mirrors, free of coma across a wide field, which is exactly the defect that limits fast newtonians photographically. Professional observatories use the design, and amateur versions are inexpensive relative to an apochromat of equivalent field quality, which is why they are common on imaging setups.
Questions people ask about refractor
What is an apochromatic refractor telescope?
A refractor whose objective brings three wavelengths to a common focus using specialised glass, giving colour free star images across a wide field.
What is an astrograph telescope?
One designed for photography rather than visual use, judged on field flatness and correction across a sensor rather than on aperture.
What is an RC telescope?
A Ritchey-Chretien: a cassegrain with two hyperbolic mirrors, free of coma across a wide field, widely used for imaging and in professional observatories.