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Schmidt Cassegrain Telescopes, or SCTs for short, utilize folded optics to allow for long focal lengths in a compact telescope design. This makes them one of the most compact telescopes per aperture — much shorter than refractors or reflectors of a similar aperture. There are two primary manufacturers of Schmidt Cassegrain Telescopes: Celestron and Meade, which are both well-respected brands within the telescope industry. SCTs are known for their long native focal ratios, usually around f/10. You might think this makes them too slow to be used for anything other than planetary viewing or imaging, but read on to find out why this isn't the case!

SCTs are a great choice for beginners, namely because of the mount many entry-level SCTs come with. Although you won't see many SCTs under the $500 mark, you can find many under $1000, including the highly-regarded Celestron Nexstar SE series. These SCTs come standard with a computerized go-to mount that automatically point to objects at the push of a button. Because SCTs have such long focal lengths, using a go-to mount to automatically point at objects is basically essential. Without a good go-to mount, it becomes difficult to find objects in space because it can be like looking through a straw at such a long focal length. Thankfully, though, all SCTs that come with a mount have the go-to feature these days.

The benefits of Schmidt Cassegrain Telescopes don't stop at the beginner level — they can be excellent scopes for intermediate and advanced users as well. This is especially true for both planetary and deep sky astrophotography. For planetary, SCTs are the preferred choice of some of the world's best planetary imagers. This is largely in part to their affordability for a long focal length telescope with a small central obstruction. They also pair very well with Barlow lenses, which give the extra magnification required for planetary viewing and imaging. This allows you to get approximately an f/20 telescope with just a 2x Barlow, leading to great quality images of the planets, moon, and the sun (when paired with a proper solar filter).

For deep sky imaging, many astrophotographers opt for the Celestron EdgeHD series or the Meade ACF series. Both of these offer a wider image circle than the "standard" level of SCTs, meaning you can use a larger sensor camera on these telescopes. It's also important to note that most entry-level SCTs come with an alt-az mount, which don't lend well for deep sky imaging. If you're hoping to do deep sky imaging with an SCT, consider buying one that comes with an equatorial mount or buy the SCT telescope and equatorial mount separately.

One might think that SCTs are too slow to give good results for deep sky imaging. At their native f/10, it takes longer to gather the required light for faint deep sky objects. Fortunately, SCTs also pair very well with focal reducers. The most common focal reducers for SCTs reduce them down to an f/6.3 or f/7 focal ratio with a well-corrected field. However, some SCTs have a secret weapon up their sleeve. If your Celestron SCT is "Fastar compatible," this means you can take advantage of something called the Hyperstar system. The Hyperstar, an additional accessory made by Starizona, allows the focal ratio to be reduced down to a blazing fast f/2! This means your exposures can be 25x shorter than the exposure lengths required for the native f/10. For deep sky astrophotographers looking to do wide field imaging, the Hyperstar is a fantastic upgrade for compatible SCTs. The only drawback to the Hyperstar system is that it cannot be used visually.

When you combine all of the possible focal ratios for SCTs, you can have what many believe to be the most versatile type of telescope. You can use SCTs at f/20, f/10, f/7, or (imaging only) f/2 with the right accessories, making them a fantastic all-around telescope. No other telescope type can perform as well at such a wide variety of focal ratios. This, combined with their compact design make them wildly popular with observers and imagers of all skill levels.

FAQs

Still have questions? We have answers.

Are Schmidt Cassegrain Telescopes good for astrophotography?

Yes, Schmidt Cassegrains are a fantastic choice for astrophotography! SCTs excel at both planetary and deep sky imaging, especially when paired with the right accessories like a Barlow lens for planetary imaging, and a focal reducer or Hyperstar system for deep sky imaging. All in all, SCTs can be used at f/20, f/10, f/7, and f/2 (on certain models), making them extremely versatile for all types of astrophotography.

Do Schmidt Cassegrain Telescopes need to be collimated?

Yes, Schmidt Cassegrain Telescopes do need to be collimated. Fortunately, unlike Newtonians or other reflectors, SCTs need to be collimated much less frequently. This means you may only have to collimate an SCT 1-2 times per year, as opposed to every observing session.

Why are some Schmidt Cassegrain Telescopes priced low and others high?

Schmidt Cassegrain Telescopes come in a wide variety of prices. On the lower end, SCTs are usually paired with a go-to mount for beginners. These are great telescopes for observing small objects like the planets and craters on the moon. They're also a solid choice for education and public outreach because they come with a go-to mount that tracks the sky, meaning you can tell the hand controller where to point them and they will stay centered on their target for hours.

On the upper price range of SCTs, they often come with one of two features, or both: a larger aperture, or a series of extra optics near the focuser that allow for a flatter field across the whole image circle for astrophotography. The latter telescopes are known as the EdgeHD series from Celestron and the ACF series from Meade. If you're looking to do serious deep sky imaging with an SCT, you'll want to aim for either of those. These higher-end SCTs are often sold as just the telescope only that allows buyers to pair them with a proper German Equatorial Mount, which are required for serious imaging.