Courses in Astrophotography

The Ultimate Planetary Telescope?

A review of my Celestron C14 telescope.

By Damian A. Peach.

Introduction.

After some pretty bad experiences over the course of 2004 using large Maksutov’s (which thermally were a disaster under this northern temperate climate) I finally decided I had to explore some alternative options for a primary telescope. Both my sold C11 and the C9.25 telescope I had been using were excellent telescopes, and delivered superb views and images. After some deliberating, I finally opted to go for the largest of the Celestron line – their C14 Schmidt Cassegrain.

Now having owned one of these telescopes for about 18months at the time of writing, I can now give a good review of this telescope having used it from some excellent locations, and through apparitions of all the major Planets.

Some vital stats.

The C14 is the largest of Celestrons line of Schimdt Cassegrain telescopes. It has an aperture of 356mm (14”), and a central obstruction of 32% (by diameter.) The OTA is physically somewhat larger and heaver than the C11, weighing in at a hefty 40lbs for the OTA (compared to 28lbs for the C11.) This means the mounting the C14 OTA requires quite a substantial mount for it to be reasonably stable. The C14 focal ratio is also slightly different, being an F11 system (rather than an F10 one such as the smaller models.)

First light and intial impressions.

First light with the telescope was obtained during the summer of 2005. Mars was just starting to climb to a reasonable altitude in the dawn sky, headed for opposition some months later. Initial star testing sessions indicated smooth optics, with a good star test. At high power in good seeing, a nice sharp airy disk was present. Its also worth mentioning a second C14 owned by a friend also has very nice optics. No thermal problems were apparent after keeping the telescope outside for several hours before observing (and much of the time the telescope is kept outside anyway.) Early morning views of Mars were very impressive under good seeing. Though the Planet was only 10 arc secs apparent diameter, significant amounts of detail could be seen. One of the most notable things is the lovely colour saturation a large aperture gives, and Mars revealed a lovely ruddy orange tone. Early Mars images at this stage showed impressive detail on the small disk.

Thermal Considerations and comments.

The C14 is a large telescope, and thermally, it could be a nightmare if certain rules are not obeyed. Firstly, I have found for this telescope to perform to its potential it has to be kept outside, or close to the ambient air temperature. If you tried to observe with this telescope bringing it from indoors, in most temperate climates it would simply never cool down.

On evenings were the temperature drops sharply, even when kept outdoors, the out of focus star pattern with present a weak thermal plume. On such nights, it may take and hour or so for this to dissipate. On other evenings, where the temperature drop is much lower, the out of focus star pattern presents a lovely set of clearly defined rings surrounding a central dot. Even at sunset it can present this undisturbed pattern on evenings where the temperature change is not steep and rapid.

Using the telescope in the tropics is completely different, and it operates with no thermal issues whatsoever.

Viewing Mars in 2005-06.

During the great apparition of Mars during 2005-06, I was able to take over 130 nights of images using this telescope, so have a very good idea of what it is capable of when working on the red Planet.

Mars on November 19th, 2005. Apparent diameter 19 arc seconds. A Wealth of detail can be seen in these images. C14 @ F41. Lumenera CCD camera.

The C14 is simply in love with Mars. I have really not seen anything that does as well on what is often a small and challenging target. While other scopes will start to lose the finer albedo markings only a couple of months after opposition, using the C14 it is really a very different matter. A Mars apparition is long longer about the opposition period, but about 7-8 months worth of high resolution viewing and imaging.

Mars on April 22nd, 2006. Apparent diameter 5 arc seconds. These images show that even when Mars is very distant the C14 continues to show a considerable level of detail.

The views and images with Mars close to opposition are really something. Tiny albedo markings are visible, while the colour visible on the disk is wonderful. The C14 will produce very detailed images of Mars even when it subtends only 5 arc second diameter. All of the familiar markings are visible, and that lovely ruddy colour is maintained. With a diameter of 8-10 arc secs, significant detail is still visible, and minor Martian features such as Gomer Sinus, or the projections around Juventae Fons remain clearly visible on images.

Viewing Saturn in 2006.

Saturn tends to be a very critical object for the most stunning views to be had. It really requires good seeing for pleasing images, and needs decent aperture (8” or more) for very good resolution. The C14 again excels on Saturn. The resolution it can deliver its really notably better than telescopes in the 20-25cm category, especially on the critical detail in the ring system.

Saturn on April 11th, 2006. My best ever image of the Planet, and probably my best ever view of Saturn at the eyepiece.

The views of Saturn through the C14 at Barbados in 2006, and also at home in March 2006 were simply staggering. On April 11^th2006 at Barbados, the view was probably the best I have ever seen it. Under long periods of near perfect seeing, the C14 really showed what it can do, and reveals a wealth of detail across the globe and rings. The resolution it delivers on the Saturn images I’ve taken exceeds what the excellent 9.25” telescope can deliver. The Cassini division has a sharper edge, and looks wider, while the critical Encke division looks narrower and finer due to the C14s better resolving power. The 14” also makes Saturn an easier target due to its good light gathering power. Colours on the Planet when observing visually are, as with Mars very lovely indeed. It is hard to really convey the view under excellent seeing through this telescope, but the image from that memorable nigh on April 11^th is presented above to show the magnificent spectacle.

Viewing Jupiter in 2006.

My only viewing of Jupiter so far was done at Barbados in April 2006, since the Planet is not well placed from my home site. Jupiter being a larger target and certainly the most dynamic of all the Planets is a wonderful target with almost any telescope.

Jupiter under excellent seeing conditions in the C14 reveals a wealth of fine detail across the Planets cloud tops.

The C14 as you would expect, delivers staggering views and images of the giant Planet under good seeing. The colour saturation is lovely as with the other Planets, while the level of detail visible on the disk in very good seeing is simply more than anyone could ever hope to draw accurately. The tiniest details pop into view, while targets such as the GRS show internal swirls, and colour variations.

Imaging Jupiter with this telescope is also a real treat. The Jovian moons show nice colour shades on their small disks, and Ganymede easily shows surface markings under good seeing. Even Io reveals clearly its bright equator and darker polar regions under very steady seeing. Filtered work is very straightforward with this telescope, as since Jupiter is a larger object, lower focal lengths produce good image scale, allowing faster frame rates or lower gain settings. It also makes the use of narrow band filters easier.

Lunar viewing.

The Moon is a great target for almost any optical device butt the resolution delivered by the C14 is really impressive. Firstly, I think it is really on a scale up from what the 25cm apertures show, revealing some of the Moons finer details in superb clarity.

Lunar performance from the C14 is wonderful under excellent seeing. This view of the Alpine valley clearly reveals the famous rille along its centre as a clear channel with shadow along its length.

Features such as the rille in the Alpine Valley aren’t just detected by this telescope, but it is actually resolved as a proper sinuous channel. The lunar surface in good seeing is resolved into a mass of sub kilometre detail, that you could literally spend a lifetime studying. More minor craters in the 20-30km size range suddenly become resolved well enough to become very interesting craters in their own right. Larger craters such as Clavius or Petavius show a whole new perspective at the resolution the C14 can deliver. A downside to this however is that the long focal length of the C14 means that its really a telescope for high resolution regional study rather than views of wider areas.

Looking further afield.

The large aperture of the C14 really does lend itself to Deep Sky observing. Views of objects such as M57, M27, M17, M4, etc are wonderful under a dark sky. It does particularly well on globular clusters with its excellent resolving power. M13 is resolved to the very core, with pinpoint stars filling the entire field. On one night next to a friends 7” F/9 Apo, there was just no comparison, with the 14” easily delivering a brighter and more well resolved view.

It isn’t all good!

While the C14 is an amazing telescope for Planetary observing, you’ll notice in many of my comments the words “good seeing”. This telescope simply will no perform if the seeing is not steady. As an estimate from my home site, I would say perhaps only a handful of nights each year are steady enough for the C14 to resolve to what it is capable of.

This begs the question that at typical amateur locations is it really worth having a telescope of this aperture for planetary work? The answer for most observers is probably not. I think most nights at typical amateur locations, a 25cm telescope will reveal all that there is to see/image. Only on those nights when the seeing is excellent will the larger aperture of the C14 reveal views and images of a quality that only a large telescope can. For a committed planetary such as myself it is worth the extra aperture. If you are prepared to travel to excellent locations, or indeed are fortunate to live at a location where the seeing can be frequently stable, the extra aperture of the C14 is worth having. For those wanting an all purpose ultimate telescope, again the C14 will more than meet expectations.

For me, as a dedicated Planetary observer the C14 has delivered my best images to date, and has proven for me at least, the extra aperture was well worth having. Though on many nights its performance is limited due to the seeing conditions, on those rare nights of superb seeing, this telescope is capable of delivering views of the Planets that will astound and amaze.