There are a couple of ways to reduce chromatic aberration. One is to use multiple lenses to counteract this effect. The second uses a long focal length to minimise it. This is why early refracting telescopes were made very long.
Chromatic aberration caused by Refracting telescopes.
Reflecting Telescopes
Reflecting telescopes, also knows as reflectors, use bowl shaped mirrors instead of lenses. The mirror called the primary mirror has a surface shaped so that any line across the centre of the mirror is a parabola. A mirror with that shape, called a parabolic mirror (Plano concave) reflects light rays to a sharp focus in front of itself. There a second mirror reflects the rays to an eyepiece.
Astronomers generally prefer reflecting telescopes to refracting telescopes. The weight of a large lens can cause it to bend and become distorted. But a large heavy mirror can be supported from behind. As a result mirrors can be made much larger than lenses, and therefore can gather more light. In addition, parabolic mirrors are useful because they can collect infra red and some ultra-violet rays’ as well as visible light. Reflector telescopes also do not suffer from chromatic aberration, as all the wavelengths will reflect off the mirror in the same way. Also only one side of the reflector telescope needs to be made perfect as the light is reflecting off the objective.
However it is easy to get the optics out of alignment. Often a secondary mirror is used to redirect the light into an eyepiece. This secondary mirror produces diffraction effects, making bright objects appear to have spikes.
Isaac Newton designed one of the first reflectors in 1668 to avoid chromatic aberration caused by lenses. In his design, Newton used a small, flat mirror to reflect light from the primary mirror to an eyepiece at the side of the telescope tube. In 1672, a Frenchman by the name of Cassegrain designed a telescope using a small convex mirror in front of the primary mirror. The small mirror reflected the light through a hole in the primary mirror to an eyepiece behind it. Astronomers today for Optical and Infrared telescopes use this design known as a Cassegrain telescope.
An example of a Reflecting telescope is a Newtonian telescopes (also known as catoptrics). This telescope uses a parabolic
Concave mirror to collect and focus light entering onto a flat secondary mirror. This secondary mirror reflected the image out to the eyepiece.
Catadioptric Telescopes
Catadioptric Telescopes also known as Refracting-reflecting telescopes have a large lens at the front of a tube and a large spherical mirror at the end. The lens refracts light rays slightly to correct the reflective errors caused by a spherical mirror.
There are two popular types of Catadiotptric telescopes: The Schmidt-Cassegrain, and the Maksutov-Cassegrain.
Schmidt-Cassegrain
In this design, the light enters through a thin aspheric correcting lens, then strikes a spherical primary mirror and is reflected back up the tube. There it is intercepted by a small secondary mirror that reflects the light out an opening, where the image is formed at the eyepiece.
This is a best all-round, all-purpose telescope design. It combines the optical advantages of both lenses and mirrors while cancelling their disadvantages. However it is more expensive than Newtonian telescopes. Its also loses some light due to the secondary mirror obstruction compared with refractors.
Maksutov-Cassegrain
A Russian astronomer invented the Maksutov-Cassegrain telescope, by the name of D. Maksutov. The Maksutov design is a catadioptric design with basically the same advantages and disadvantages as the Schmidt. It uses a thick meniscus-correcting lens with a strong curvature and a Secondary mirror that is usually an aluminised spot on the corrector. The Maksutov secondary mirror is typically smaller than the Schmidt's giving it slightly better resolution for planetary observing.
The Maksutov is heavier than the Schmidt is, and because of the thick correcting lens it takes a long time to reach thermal stability.
The Maksutov optical design typically is easier to make but requires more material for the corrector lens than the Schmidt-Cassegrain.
Infrared Telescopes:
An infrared telescope collects infrared (heat) rays from objects in space. Most infrared telescopes are reflecting optical telescopes with an infrared detector instead of an eyepiece. Objects at room temperature give off infrared due to the heat they hold. As a result astronomers must design infrared telescopes so that heat from the telescope itself does not interfere with the radiation from space. An American physicist Frank J. Low designed the first infrared telescope. This device, called a bolometer, was an extremely cold electronic thermometer in a vacuum. When infrared rays hit the bolometer, it warmed up and gave off an electric signal. Today infrared telescopes use electronic devices called array detectors, To form images on a computer screen.
Ultraviolet Telescopes:
Ultraviolet Telescopes are reflecting telescopes with electronic detectors. They are used to study most wavelengths of ultraviolet rays. Which can be reflected just like visible light. But the shortest wavelengths, called extreme ultraviolet rays, are harder to reflect. These rays can only be reflected off a mirror at a small angle called a grazing incidence. Ultraviolet telescopes enable astronomers to study extremely hot objects in space, including quasars and stars called white dwarfs. Astronomers also use ultraviolet telescopes to study how stars form and the composition of gas between stars and galaxies.
X-ray telescopes:
X-rays have shorter wavelengths and higher energy than ultraviolet rays. The simplest X-ray telescopes use an arrangement of iron or lead slats instead of mirrors. These slats block all X-rays except those from one line across the sky. The X-ray photons then enter a detector filled with X-ray absorbing gas, where they are counted.
Gamma Ray Telescopes:
When a gamma ray photon collides with atoms, it knocks several electrons loose from the atom or even breaks up the nucleus of the atom. This collision can produce a shower of subatomic particles and low energy radiation. This radiation travels in the same direction as the original gamma ray and is detected by devices known as scintillators. When radiation hits a scintillator, the instrument produces a flash of light that can be recorded. By measuring the amount of radiation scientists can calculate the energy level of the gamma ray. Gamma ray telescopes have enabled scientists to learn more about some of the least understood objects in the universe, including quasars and pulsars.
Modern Developments in Telescopes
Several Breakthroughs in mirror designs have enabled astronomers to make large mirrors that do not bend or become distorted under their own weight.
One new design is the segmented mirror, used in the Keck telescope (completed in 1992) on the island of Hawaii. The Kecks light-gathering mirror consists of 36 hexagonal mirrors mounted close together. The mirrors form a reflecting surface 10 metres in diameter.
In conclusion I personally believe that reflecting telescopes would be the best option to invest in. As refracting telescopes suffer from Chromatic aberration, and Catadioptric telescopes due to their more complex design cost a fair deal more then reflecting telescopes. Catadioptiric telescopes also lose some light due to the secondary mirror obstruction. Which intern can result in a less visible image.