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CATADIOPTRIC TELESCOPES

	Catadioptric telescopes combine a corrector lens and mirrors.  The two main type of catadioptric telescopes are the Schmidt Cassegrain  telescope (a/k/a SCT) and the Maksutov Cassegrain telescope.  The SCT is becoming the most common astronomy telescope purchased.  In this author's humble opinion, these all the best all-purpose telescopes that there are.  Light first enters through the correcting lens in the front of the tube assembly.  It is then passed to the primary concave mirror in the back of the telescope.  The light then bounces to the front of the telescope where the light hits the secondary mirror, which then sends it through a hole in the primary mirror in the back and out to the telescope eyepiece. This telescope has many advantages.  Like the reflecting telescope, the primary mirror can be quite large because it is well supported, so weight is not much of an issue.  You can achieve a longer focal length, which means that you will achieve greater magnification.  Further, this type of telescope will eliminate the chromatic aberrations associated with reflecting telescopes.  The optical tubes are typically short considering the large size of the aperture. Despite how great these telescopes are, they too have their disadvantages.  The optics need to be aligned, or collimated perfectly to achieve a high quality image.  Many people you will talk to will tell you that these telescopes do not need to be aligned often once they are aligned.  However, even a 1/20 turn of one of the collimation screws can make a big difference, so it is advisable to check it often and make fine tune adjustments as necessary.  It takes a fair amount of trial and error.  Another big disadvantage is that the primary mirror has a hole in it and the secondary mirror resulting in some light loss.  These telescopes also tend to be more expensive than other telescopes of similar aperture.   Refracting Telescopes Back to Telescopes Main Reflecting Telescopes

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