Celestron C11 | Jim's AstroLog

I am quickly building an exceptional capability to image wide field objects, some of which appear much larger than the Moon. I hope to someday be be able to engage in a wider spectrum of astrophotography, to include planets, and smaller deep space nebulae and galaxies.

My Losmandy GM-8 mount has the payload capacity to easily handle photography with my TeleVue NP101 4″ refractor along with a guide scope, and two cameras, all of which are best suited for wide field photography because of the main telescope’s short focal length. I could add a goto control panel and servos to this mount for about $1600, but I can find anything that is suitable to be viewed or photographed with this instrument with the technique described in Finding Barnard’s Star. I have a Celestron 11″ reflector that I can put on this mount, but it is so near the mount’s maximum capacity, even before adding a guide scope and cameras, that it is unsuitable for astrophotography. So this set of facts drives the need for a mount with greater capacity, and sticking with the Losmandy line, with which I am already very comfortable, I will get the Losmandy G-11, which is about $3200 with goto. The Celestron’s longer focal length, and hence its much narrower field of view, and the planetary and exceedingly dim deep space objects that I seek warrants the goto capability.

Before I make that plunge, I need to finish checking out the used Celestron that I bought last year. I took a few shots of Jupiter and Mars in April (all images in this paragraph can be found in the Gallery) that didn’t turn out very well. For comparison, look at the Jupiter and Saturn images that I took with the 4″ NP101 in 2012 and 2013. Dew was a huge problem on the night of the Jupiter pictures I took with the C11. I am hoping that improper focus is the only remaining problem in the Mars picture. Summer set in before I could gain enough experience with this instrument and start the tedious work of eliminating problems. Jupiter is quickly becoming an early evening object again, so I can resume this work in December or January.

I can claim some success with my Jupiter images. The dimensions in pixels in the full res images is almost exactly what I had calculated before taking the photographs, and is what is needed to capture the detail that I am looking for. Check out the Jupiter images that James Willinghan took with a 12″ Meade, and posted to the Howard County Astronomical League (HAL) Facebook page (June 2013) to get some idea of what I am trying to achieve. While you’re there, you check out the progress on the observatory that the club is building in some of the more recent postings. I somehow became the only mug that is clearly identifiable in the banner image. I can also be seen in some of the pictures taken when we cleaned and repaired the dome (Sept 2014), and when we set up the telescope to check out (April 2014) dimensions and clearances required. I have only posted one photo (Nov 2013) on this page so far.

As a last resort after trying everything within my capability to eliminate problems, I will have Marty Cohen at Company Seven check for optical defects, and make needed repairs if the telescope is worth putting more money into. I bought it second hand, and for almost nothing, just to get some experience with reflector telescopes. If the Celestron is not worth saving, then I will buy a new telescope, probably the Meade 12″, at the same time that I buy the new mount.

In January 2014, I made it another step closer to becoming one of those amateur astronomers who has x number of telescopes…that his wife knows about. Celestron marketed the C11 Ultima, a 280mm f/10 telescope, in the mid-1990s, and I picked one up second hand at Hands on Optics for a very reasonable price. And by the way, I recommend that anyone interested in a telescope or binoculars stop in and see Gary Hand, because you never know what you might find there. The telescope had been installed in an observatory, and as a result it was somewhat exposed to the elements for a number of years and it needed some work. I cleaned the exterior surface with a premium car polish, and it looks as good a new with the exception of some minor scratches. The V-style dovetail plate was loose because the attachment screws were too long, and therefore would not tighten. I was able to easily repair this. In the short term, I wanted access to a larger SCT reflector to gain experience with a longer focal length and bigger aperture instrument, and to learn how to collimate a reflector. I have been able to take it out just once, and I can see that I have a lot to learn. In the longer term, there may be some potential for more work on the the telescope. I doubt that the mirrors have ever been resurfaced, so that is a possibility. The multicoating on the corrector plate glass is in pretty bad shape. I hear that this is an expensive repair, so I might just have to live with it. And finally, I may install a cooling fan, which will help the telescope reach an equilibrium temperature with the outside air faster. The telescope weighs 22 lbs. Since this approaches the maximum capacity of my mount, I am already thinking about my next major purchase.

Jim's AstroLog

Tag Archives: Celestron C11

Rationalizing a GOTO Telescope Mount

Trying out a used Celestron C11

The Astronomical Musings of Jim Johnson