Astrograph Telescopes are optical tube assemblies that are specifically designed for astrophotography, or taking images of objects in space. Astrographs, as they are commonly referred to, often have fast focal ratios which make them very efficient at gathering light and large image circles that have been corrected for optical aberrations. These types of telescopes will give you best performance when it comes to taking deep space images. To get some more information about the different types of telescopes, please read down below.
Apochromatic Telescopes are a type of refracting astrograph that bring light of three different frequencies to a common focus. You will need a field flattener or a reducer-flattener with this type of telescope but it will get you incredibly bright and clean images. Apo's, as many refer to them as, have great correction of chromatic and spherical aberration. This design is usually used by more experienced astronomers.
Petzval Telescopes are the highest end of refracting telescopes in terms of clarity. They use a 4 lens optical system they are exceptionally well corrected, they have very fast focal ratios, and they are the easiest to use of all astrographs in the world of astronomy. Petzval's almost always come with a higher price tag and we recommend them to the most serious astrophotographers because of that.
RC Telescopes, as they are commonly referred to, only use hyperbolic mirrors to eliminate optical errors like coma and chromatic aberrations off-axis while producing the flattest focal plane possible without lenses. Since they only use two reflective surfaces, Ritchey Chretiens are also very efficient with light compared to most other telescope systems that use 4, 6, or event more surfaces that will reduce the amount of light hitting the focal plane.
Some may say that the Dall-Kirkham design is the closest to optical perfection that you will find on the market today. They have incredibly large image circles with very small spot sizes. These usually tend to be very expensive telescopes and can be much larger in size. They are commonly used for scientific research, imaging, and also viewing.