The VMC200L is a 200mm catadioptric optical tube. The use of a meniscus corrector in front of the secondary mirror means that light is corrected twice on the optical path. The result is that spherical aberration and field curvature are well corrected. The VMC200L’s primary mirror is f2.5 and the compound optical system is f9.75 making the system much more compact and portable than many competitive models. An additional key feature is the rack and pinion focusing that is placed behind the primary mirror. The use of this focusing system eliminates the image shift associated with most other Schmidt-Cassegrain systems. This is especially important when using high power magnification and for astrophotography. When focusing, the image is stable and easy to adjust.