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The Celestron C14: The Ultimate Planet Killer?

Celestron C14 Fastar version. Credit: Celestron

If you’ve ever viewed the planets in a telescope, you likely noticed how small they appeared. Capturing fine detail on these small objects presents special challenges, which I covered in my four-part series on planetary imaging here on AGT.

Large aperture is important for planetary imaging and the Celestron C14 is considered the king of aperture for this purpose, while also being compact.

A collection of solar system objects captured by the author with a Celestron C14. Credit: Rouzbeh Bidshahri

The Celestron C14

Th C14 has been around since the early 1970s. With 14 inches (356mm) of clear aperture, it was one of the largest catadioptric telescopes available to amateurs (catadioptric telescopes incorporate both lenses and mirrors). The C14’s Schmidt-Cassegrain (SCT) design folds its long focal length of 3910mm (154 inches) into a very compact 770mm (30 inch) tube.

Schematic of the SCT telescope. Credit: Celestron

SCTs are very sharp on axis, so the center of the field is excellent, but they’re not as well corrected towards the field’s edges. This aspect of the design and their long focal ratios make SCTs less suitable for deep sky imaging than some other designs. For small targets like planets and very small deep sky objects, however, they excel.

Celestron’s Edge HD version of the SCT has a much larger corrected field of view plus a focal reducer, making it far more suitable for deep sky imaging.

Build

The C14 feels very solid. With its compact design, its heft is apparent the first time you lift it! The telescope alone weighs 46lbs (21 kg) even with the tube made from aluminum. The rear cell is a one-piece aluminum casting, reducing cost compared to CNC machining.

The cast aluminum rear cell of the C14 and the handle, focus knob (orange), and vents (top and bottom). Credit: Rouzbeh Bidshahri

An extruded wide CGEM (Losmandy D-type) dovetail and two handles on the back are included. I didn’t find the handles to be very helpful, but I did add another dovetail on top for a much-needed carry handle.

Top dovetail plate installed to attach a carry handle (holes drilled to save weight). Credit: Rouzbeh Bidshahri

Collimation

The C14 was the easiest to collimate of any of the telescopes I’ve used. You just need to get concentric rings on a defocused star image by adjusting the three collimation screws on the secondary mirror. Once adjusted, the C14 holds collimation very well.

I recently reviewed a new software-only collimation product for AGT, SkyWave-Collimator, that provides even more precise results.

Concentric rings with a defocused star, showing correct collimation. Credit: Rouzbeh Bidshahri

While the Philips screws installed from the factory were adequate, I wasn’t comfortable using a screwdriver in the dark near the glass corrector plate, so I swapped them out for Bob’s Knobs tool-free collimation screws ($23).

Bob’s Knobs collimation screws for adjustment of the secondary mirror. Credit: Bob’s Knobs

Optics

The optics of the C14 are where it really shines, literally! The new Starbright XLT coatings offer 95% peak mirror reflectivity and 97.4% transmission through the corrector plate. That yields a total system throughput of about 89%. I wasn’t able to find official information on the type of glass in of the primary mirror, though.

The solid line shows the new Starbright XLT with a total system throughput of 89%. Credit: Celestron

The conical primary mirror is quite thin but reinforced with ribs on its back. This reduces weight and provides for faster cooling.

The secondary obstruction is 32%, reasonable by reflector standards. The secondary is easily removed for cleaning, if necessary (or to add a HyperStar widefield conversation kit, not covered on this article).

The optical quality of the C14 is excellent. I can resolve very fine details both visually and photographically. I was very impressed early on when I captured details within Jupiter’s Great Red Spot from our backyard!

Ultra-high resolution image of Jupiter and the Great Red Spot using the lucky imaging technique. Credit: Rouzbeh Bidshahri

 

A highly magnified image of the Airy disc of a star. Credit: Rouzbeh Bidshahri

Focuser

The C14 focuses by moving the entire primary mirror with a turn of the focus knob on the rear of the telescope. The focus mechanism works well for visual use, with little play or mirror flop (sudden tilting of the mirror).

With a Barlow lens increasing the focal length up to 8000mm (315 inches) for high resolution imaging, however, its best to use a secondary external Crayford-style focuser for the very fine focusing that is needed regularly. Because the tube is metal, and the mirror’s glass isn’t an expensive ultra-low expansion type, focus is prone to drift as temperatures change.

Rear of the C14 with two custom mirror locks and an external focuser. Credit: Rouzbeh Bidshahri

I went further and had custom mirror locks made by Thomas Esmeralda at Zapsteel Custom Machining. These ensure the primary is locked in place, eliminating the possibility of play. Collimation also holds better with the mirror locked in place, avoiding slight tilting of the primary mirror with motion. Celestron has added similar mirror locks as standard on the Edge HD models.

Thermal management

Thermal management is perhaps the Achilles heel of the SCT design. While the corrector plate is beneficial in keeping dust out of the tube and off the primary mirror, the lack of ventilation traps warm air, keeping the system from cooling as nighttime temperatures drop.

The temperature difference between the warm internal and cold external air causes tube currents, turbulence, and a boundary layer of air on the primary mirror, all of which degrade the image.

The C14 came with two small vents on the back, which I felt weren’t adequate. Small fans I installed to force air into the were insufficient.

The larger the SCT model, the more significant this issue becomes. The solution I tried is wrapping the telescope in insulating material to decrease the interaction between the internal and external air through the metal tube. Leaving the telescope in ambient conditions (and out of the sun) for several hours then allowed it to slowly equalize with the ambient temperature.

The C14 wrapped in a layer of insulating foam and then a layer of Reflectix double layer insulation. Credit: Rouzbeh Bidshahri

Dew

Dew can be a problem for SCTs. The glass corrector plate is a notorious dew magnet. A dew shield will help a lot but I would recommend an additional heater installed around the dew shield. I found the flexible integrated heater models from AstroZap work very well ($190). Celestron now has a system designed to integrate into their SCTs.

Final Thoughts

The C14 is a very capable instrument that offers excellent results right out of the box. The large aperture provides light gathering power and resolution. Being compact, even my relatively small Losmandy G11 mount could carry the C14, something that would never be possible with a Newtonian telescope of similar aperture.

To get the most out of the C14, you need to take the time to temperature acclimatize, collimate, and focus perfectly. With a little tweaking and optimizing shown here, you can get a significant performance increase with relatively little extra cost.

It’s no wonder the C14 is a legend I planetary work. I would say you’d be hard pressed to find anything better anywhere near its price range!

 

Plus:

Large aperture

Compact package, easily mounted equatorially

Very sharp on-axis optics

Very easy collimation

 

Minus:

Thermal management is essential

Corrector plate susceptible to dew

An external focuser is needed for fine focusing

 

Images of Jupiter at different wavelengths showing excellent details once everything is set up properly. Credit: Rouzbeh Bidshahri

 

MSRP: C14 XLT $6,499
Website: Celestron.com

 

For more on all aspects of planetary imaging, see Rouzbeh’s four-part series on AGT.

 

About Rouzbeh Bidshahri

Rouzbeh Bidshahri is a mechanical engineer with a lifelong passion for astrophotography. He has tested dozens of telescopes ranging from 3 to 20 inches in aperture and has spent several years optimizing systems for very high-resolution planetary imaging in the sub 0.1 arcsecond/pixel range. He has contributed to several institutions such as ALPO (The Association of Lunar and Planetary Observers). His main area of interest has been designing and operating larger setups, and he is currently focusing on high resolution, long exposure photography for both broadband and narrowband deep sky imaging.

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