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The Celestron C11 vs. C14: Which is Right for You?

Celestron C14 and C11 OTA. Credit: Celestron

In the 50 years since it was introduced, the Celestron C14 has garnered a reputation as a go-to scope for high-resolution planetary imaging. What about the C14’s smaller sibling, the Celestron C11? I’ve owned both and will share my experiences with them here.

Size

Photos will not prepare you for the size difference between the two models. They appear almost identical in pictures, and three inches doesn’t seem like much of a difference. But nothing could be further from reality! While the difference in aperture is only 27%, the C14’s volume is double that of the C11.

The C11 mounted on a Losmandy G11 mount. Credit: Rouzbeh Bidshahri
The C14 – At first glance it’s difficult to differentiate the C14 from the C11 pictured above. But note the extra 11-lb (5-kg) counterweights on the mount to accommodate the greater weight of the C14. Credit: Rouzbeh Bidshahri

The C14 also has a much larger surface area, which makes it more susceptible to the impact of wind. Adding a dew shield doubles the length and creates more wind pressure.

The C14 with dew shield next to the 6’ 2” (187cm) author. Credit: Rouzbeh Bidshahri

Weight

The relative weights of the two telescopes match their size differences as well.

I find the C11 very easy to handle, with several options for cases to transport it when needed. Its weight of 27.5 lbs. (12.4 kgs) is quite reasonable for 11 inches of aperture.

On the other hand, the bulk and heft of the 46-lb (21 kg) C14 make it quite difficult to handle and transport. The C14 is it better suited for more permanent setups, though motivated users can still transport, if necessary.

More importantly, a mount to carry the C14 has to have the capacity to handle twice the weight and bulk of the C11.

My Losmandy G11 can easily carry the C11. For the C14, I upgraded the motors and gearboxes, and extended the counterweight shaft but eventually decided the higher-capacity Losmandy Titan mount was more suitable.

The Losmandy G11 used for the C11 by the author on the right and the Losmandy Titan on the left used for the C14. Note the three 26-lb (12kg) counterweights needed for the heavier C14. Credit: Rouzbeh Bidshahri

Cost

For most users, the substantial price difference between the C11 and C14 can be the deciding factor. The current price of the C11 is $3,200, while the C14 is $6,500. And that’s before considering the cost difference in the mounts required.

Thermal Management

The thermal mass – the amount of material and the trapped air that can store heat – is also related to the weight and volume of the telescope. When observing the planets at high resolution, you want the temperature difference between the internals of the telescope to be as close as possible to that of the cooler ambient air.

The C11 cools down much faster than the C14 and requires less attention to thermal management. Unlike the C11, the C14 has two small vents, but I found them inadequate for acclimatizing the large thermal mass of the telescope. C14 users need to take extra measures, like longer cool down periods or insulating the entire tube to keep the internal tube thermals at bay.

The almost identical-looking C11 and C14 rear cells with rear cooling vents on the C14 but not the C11. Credit: Rouzbeh Bidshahri

Focuser

Both telescopes have a knob on the rear for focusing by moving the primary mirror. I found mirror flop – unwanted tilting of the primary mirror – to be less of a problem in the C14 than the C11. Also, the C14 comes with two shipping mirror lock screws that can be removed and replaced by custom mirror locks, as I did. This helps considerably in holding the primary mirror steady.

Both the C11 and C14 have the larger 3.28” SCT thread on their focusers, which is much more stable than the standard 2” SCT thread of smaller telescopes. Both have 5.975 inches of back focus.

C14 with custom mirror locks installed. This is not possible on the C11. Credit: Rouzbeh Bidshahri

Optical Layout

The optical designs of the two telescopes aren’t identical. The C14’s focal ratio is f/11, while the C11’s is slightly shorter at f/10.

The longer f/11 focal ratio means a typical 2x Barlow lens turns the C14 into an f/22 system, perhaps a bit too long for some cameras with smaller pixels. I use the 2” Astrophyiscs advanced Barlow at 1.8x to get the focal ratio down to f/20 when needed.

Furthermore, the secondary mirror of the C14 is slightly smaller relative to the primary compared to the C11. The C11 has a 34% secondary obstruction versus the 32% obstruction of the C14. A smaller obstruction is preferable as it helps with contrast, though the 2% difference is minimal.

Typical Ritchey-Chrétien (RC) and Corrected Dall-Kirkham (CDK) telescopes have central obstructions in the 50% range, which is one of the reasons the SCTs usually perform better for planetary imaging where higher resolution is desirable.

The large aperture of the C14 and the relatively small secondary compared to RC and CDK designs. Note the almost invisible corrector plate with its excellent anti-reflective coatings. Credit: Rouzbeh Bidshahri

 Performance

Performance is what it all boils down to. On paper, the Rayleigh’s resolution of the C14 is better, at 0.39 arcseconds vs. the 0.5 arcseconds of the C11 (lower is better). Under real sky conditions, however, the actual resolution difference is less evident. When atmospheric seeing is poor, there isn’t much difference in resolution. Some argue that larger apertures are actually affected more by poor seeing (the blur caused by turbulence in the upper atmosphere).

The example below is from a night with medium to good seeing where the C14 can really spread its wings. Seen here is Jupiter at 7,260mm of focal length with details inside the Great Red Spot. Europa is to the left of the planet.

Jupiter with relatively good seeing at high magnification with the C14. Credit: Rouzbeh Bidshahri

There is also a difference in image scale. With a 2x Barlow lens, planets are substantially larger with the C14. This is a welcome result given how small the planets are.

Size of Jupiter on the sensor of the ASI290mm with a 2x Barlow lens on the C11 at the top and the C14 below. Credit: Astronomy Tools

An even bigger difference between the telescopes is the light collecting area. Those three extra inches of aperture mean the C14 has 62% of extra light collecting area compared to the C11. I find this useful for imaging Saturn, which is much dimmer than Jupiter. I can lower the focal ratio of the C14 to f/16 while retaining the same image scale as the C11 at f/20. The planet is thus the same size on the screen but 35% brighter. This allows a lower gain (creating less noise) or shorter exposures allowing a higher capture frame rate. In either scenario, the extra light is helpful.

The example below is Saturn with mediocre seeing. The extra focal length and aperture of the C14 allowed me to eliminate the Barlow lens and still get a respectable image size of 4035 mm.

Saturn under poor to mediocre seeing using a lower f/ratio with the C14 than on the C11. Credit: Rouzbeh Bidshahri

Final Thoughts

So, which is better?

Although the C14 is much larger and costs more than twice as much as the C11, the difference in the resulting image is not quite as dramatic as those factors.

To decide, the user must consider all the factors, including portability, mounting, and thermal management. Even more important, however, are the local atmospheric conditions and the skill level of the user. If either are lacking, the C14 likely won’t offer much extra in the results.

Ultimately, a more advanced user with good seeing will definitely be able to achieve better results with the C14. I personally ended up selling the C11 and keeping the C14.

On the other hand, the old adage also holds true: the best telescope is the one you use most often!

MSRP: C11: $3200, C14: $6400

Website: www.celestron.com

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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