![]() A Schmidt-Cassegrain telescope (SCT) in its usual configuration consists of a short tube with a concave spherical primary mirror, a full-aperture corrector lens, and a smaller convex secondary mirror located on the optical axis near the center of the corrector plate. The main goal of Celestron was to provide consumers with an affordable mirror-based telescope that has a wide aperture and focal length at a consumer-friendly price. The Celestron Edge HD is a smart iteration of a normal Schmidt Cassegrain design. The Edge HD, unlike a ‘normal’ Schmidt Cassegrain telescope, produces aberration free, flat field images This is due to the fact that the Edge HD is a reflector (mirror-based) telescope instead of a lens-based telescope, which is cheaper to produce. As an example, in the price range of an Edge HD (about $1349 in the USA, or €1745 in Europe), you’ll be looking at refractors that have an aperture of about 110 to 130mm, and a focal length of about 800 to 1000mm, whereas the Edge HD offers you with a whopping 200mm aperture and a 2000mm focal length. This is where refractors (lens-based telescope) get expensive for consumers. However, in order to zoom in on smaller objects such as the planets in our solar system, or some of the smaller deep-sky targets, a telescope with a bigger aperture and a longer focal length is needed. In my case, I already own a widefield apochromatic refractor – my TS 80MM F/6 Photoline APO refractor – which I use for wide(r) field astrophotography with great satisfaction. So it often comes down to looking at the best option – given the goals you have in mind. Each telescope has its own pros and cons. The Edge HD offers a bigger aperture and longer focal length than APO refractorsĬhoosing “the right” telescope can be hard, and actually I’m convinced that there is no such thing. Finally, I’ll share my “first light” experiences using the Edge HD on the moon and some of our planets. In this blog, I’ll first share my thoughts on what kind of telescope I was looking for, and what advantages the Edge HD had to offer over other telescopes in a similar price range that convinced me to buy an 8″ Edge HD. Another advantage is that the Edge HD can be turned into a multi-purpose telescope (planetary, small DSOs, or widefield) with some aftermarket add-ons. Where normal Schmidt Cassegrain telescopes suffer from off-axis coma and field curvature, the Edge HD comes with a lens-based system that corrects for these issues, offering the user a sharp edge-to-edge, high-quality resolution image with pinpoint stars. The Edge HD is famous for its astrophotography capability. Moreover, the Edge HD 8″ is relatively light (6.3 kg / 14 lbs) and short (432mm /17″) which makes it easy to carry outside, set up, and store. One of the main reasons why I bought the Celestron Edge HD 8″ (800) telescope is that it provides a long focal length (2030mm) and a big aperture (203mm / 8″) at a relatively affordable price ($1349). ![]() For smaller DSO’s and planets, a long(er) focal length and a big(ger) aperture are a must.
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