11" SCT optical tube, CG5/AVX dovetail

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This 24” long aluminum optical tube weighs only 27.5 lbs., making it easy to transport. It has an 11” aperture, a 2800mm focal length, and a focal ratio of f/10. An optional focal reducer is available to bring the focal ratio down to f/6.3 for CCD and 35mm photography. Optical performance is guaranteed to be diffraction-limited.

Advanced high transmission Starbright XLT optical multicoatings are standard equipment. This coatings package includes high reflectivity multilayer aluminum mirrors enhanced with titanium dioxide for high reflectivity, plus a unique combination of magnesium fluoride and hafnium dioxide antireflection coatings on both sides of the Schmidt corrector lens. The corrector lens itself is made of high transmission water white float glass instead of conventional soda lime glass (which has 3.5% lower transmission) used in other telescopes.

Starbright XLT multicoatings visibly increase the contrast on subtle lunar, planetary, and nebula details when compared with a scope with standard multicoatings. They also give you higher light transmission for brighter deep space images and shorter exposure times during CCD and 35mm photography. Across the total visual/photographic spectrum from 400nm to 750nm, independent laboratory tests show the new Starbright XLT coatings are 16% brighter overall than even the original industry-standard Starbright multicoatings.

The optical tube comes with a big 9 x 50mm straight-through achromatic finderscope and mounting bracket. The finder has a wide 5° field of view. It focuses by loosening the trim ring behind the objective lens cell, screwing the lens cell in or out to focus, and tightening the trim ring to lock in the correct focus. Also standard is a removable 1.25” visual back that holds visual accessories such as a star diagonal, tele-extender, etc. A 1.25” prism type star diagonal is also standard, as is a 1.25” 40mm Plössl eyepiece. This eyepiece provides a magnification of 70x. Its field of view is 0.68° across, over a third wider than the full moon. Dust covers for the optics are also supplied.

A 1.75” wide dovetail slide bar runs the length of the tube for mounting the optical tube on a Celestron AVX Advanced Series go-to mount, or any mount using a Vixen-style mounting dovetail.

Highest Useful Magnification:
This is the highest visual power a telescope can achieve before the image becomes too dim for useful observing (generally at about 50x to 60x per inch of telescope aperture). However, this power is very often unreachable due to turbulence in our atmosphere that makes the image too blurry and unstable to see any detail.

On nights of less-than-perfect seeing, medium to low power planetary, binary star, and globular cluster observing (at 25x to 30x per inch of aperture or less) is usually more enjoyable than fruitlessly attempting to push a telescope's magnification to its theoretical limits. Very high powers are generally best reserved for planetary observations and binary star splitting.

Small aperture telescopes can usually use more power per inch of aperture on any given night than larger telescopes, as they look through a smaller column of air and see less of the turbulence in our atmosphere. While some observers use up to 100x per inch of refractor aperture on Mars and Jupiter, the actual number of minutes they spend observing at such powers is small in relation to the number of hours they spend waiting for the atmosphere to stabilize enough for them to use such very high powers.
Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

Focal Ratio:
This is the ‘speed’ of a telescope’s optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.

Fast f/4 to f/5 focal ratios are generally best for lower power wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to higher power lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio – so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio.

This is the ability of a telescope to separate closely-spaced binary stars into two distinct objects, measured in seconds of arc. One arc second equals 1/3600th of a degree and is about the width of a 25-cent coin at a distance of three miles! In essence, resolution is a measure of how much detail a telescope can reveal. The resolution values on our website are derived using the Dawes’ limit formula.

Dawes’ limit only applies to point sources of light (stars). Smaller separations can be resolved in extended objects, such as the planets. For example, Cassini’s Division in the rings of Saturn (0.5 arc seconds across), was discovered using a 2.5” telescope – which has a Dawes’ limit of 1.8 arc seconds!

The ability of a telescope to resolve to Dawes’ limit is usually much more affected by seeing conditions, by the difference in brightness between the binary star components, and by the observer’s visual acuity, than it is by the optical quality of the telescope.

0.41 arc seconds
Visual Limiting Magnitude:
This is the magnitude (or brightness) of the faintest star that can be seen with a telescope. The larger the number, the fainter the star that can be seen. An approximate formula for determining the visual limiting magnitude of a telescope is 7.5 + 5 log aperture (in cm).

This is the formula that we use with all of the telescopes we carry, so that our published specs will be consistent from aperture to aperture, from manufacturer to manufacturer. Some telescope makers may use other unspecified methods to determine the limiting magnitude, so their published figures may differ from ours.

Keep in mind that this formula does not take into account light loss within the scope, seeing conditions, the observer’s age (visual performance decreases as we get older), the telescope’s age (the reflectivity of telescope mirrors decreases as they get older), etc. The limiting magnitudes specified by manufacturers for their telescopes assume very dark skies, trained observers, and excellent atmospheric transparency – and are therefore rarely obtainable under average observing conditions. The photographic limiting magnitude is always greater than the visual (typically by two magnitudes).

This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
The weight of this product.
27.5 lbs.
Heaviest Single Component:
The weight of the heaviest component in this package.
27.5 lbs.
Based on Astronomy magazine’s telescope "report cards", scopes of this size and type generally perform as follows . . .
Terrestrial Observation:
Observing terrestrial objects (nature studies, birding, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial observing. Scopes with apertures under 5" to 6" are generally most useful for terrestrial observing due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes. 
Lunar Observation:
Visual observation of the Moon is possible with any telescope. Larger aperture scopes will provide more detail than smaller scopes, thereby getting a higher score in this category, but may require an eyepiece filter to cut down the greater glare from the Moon's sunlit surface so small details can be seen more easily. Lunar observing is more rewarding when the Moon is waxing or waning as the changing sun angle casts constantly varying shadows to reveal craters and surface features by the hundreds.  
Very Good
Planetary Observation:
Very Good
Binary and Star Cluster Observation:
Very Good
Galaxy and Nebula Observation:
Very Good
Terrestrial Photography:
Photographing terrestrial objects (wildlife, scenery, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial photography. Scopes with focal ratios of f/10 and faster and apertures under 5" to 6" are generally the most useful for terrestrial photography due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes.
Lunar Photography:
Photography of the Moon is possible with virtually any telescope, using a 35mm camera, DSLR, or CCD-based webcam (planetary imager). While an equatorial mount with a motor drive is not strictly essential, as the exposure times will be very short, such a mount would be helpful to improve image sharpness, particularly with webcam-type cameras that take a series of exposures over time and stack them together. Reflectors may require a Barlow lens to let the camera reach focus. 
Planetary Photography:
Star Cluster / Nebula / Galaxy Photography:
2 years
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1. Kevin on 5/16/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
12 years ago or so I purchased a Celestron 8"SCT from Astronomics and still have it to this day. I have used this telescope regularly for all these years and have no complaints with it. Back in 2010, I built a 10'X16' roll off roof observatory on my property in Mayslick KY. This site has fairly good skies with a limiting magnitude of about 4.9 to 5.5 depending on the seeing for any particular evening. After its completion, I began to lust after a bigger scope and began saving for an 11" Celestron. Well, that dream finally came to be true a week ago as I received my C11 and proceeded to install it on my Orion Atlas EQ-G mount in my observatory.

I must say at this point, that to truly understand a review of any telescope, one must have some experience with another telescope of any kind, preferably with the same optical design. Therefore I feel that with my 12+ years of using the C8, I am more then qualified to tell you that the difference between the 2 scopes is like night and day (Pun Intended). Objects appear much brighter, on the order of maybe .5 to .7 magnitude, much crisper focus (when properly collimated), and, when used with the 6.3 reducer/corrector, much sharper images out to the edge of the field. I must say that saving for and finally purchasing this telescope was more then worth the wait!

First light was yesterday, in the wee hours of the morning (May 15th 2013 at 3:00AM). After performing a 3 star alignment (which, by the way, was surprising in and of itself by how easy it was to find and center the 3 stars of the alignment), my first object was M51, the Whirlpool Galaxy. Now I have looked at this object for countless hours, thru other telescopes of varying sizes and quality, over the many years I have been involved with this wonderful hobby, but I must tell you, that upon first viewing M51, it literally took my breath away! Both M51 and its companion, NGC5195 were brighter and showed more detail then I have ever seen, barring those in a photograph. The spiral arms were clearly visible and the connection point between the 2 was plain to make out. The only thing missing was color, but we all know that this is not possible due to the limitations of the human eye on extended objects. I must have sat there for 10 or 15 minutes just gaping at this beautiful specimen that was displayed in my 15mm Televue Panoptic eyepiece.

Tearing myself away, I then went to M13 (my other most loved DSO) and again I was dumbfounded at the resolution of this fantastic globular cluster. Not only were there more clearly visible outer stars but I was able to discern stars almost to the center! I'm telling you, this thing looked 3D to my eye!!! Now, I've photographed M13 many times with various cameras and modified web cams, and only a couple of them could rival the real time image that now appeared before my eye. It is not to say that the C11 will provide images that can rival photos on a regular basis, but on this night, on M13, it certainly came close. I am now looking forward to trying my hand at imaging thru this scope to see how well it will do photographically. I firmly believe that it will deliver wonderful images in that medium as well as it does visually.

I observed many more objects that early morning until the sky began to brighten at around 5:30AM, much to my dismay, for I was in no way finished enjoying this incredible work of modern telescope technology. This telescope is built very well for a mass produced product, with fit and finish that I believe have no rivals for its class. The focus has a very positive feel and I could not perceive any noticeable image shift due to mirror slippage. With my C8 this was something that occurred quite frequently. Everything about this telescope exudes quality, attention to detail, and modern design.

If you are considering upgrading an older, smaller telescope, I believe that you will mot have any buyers remorse about spending the money on the Celestron C11 SCT telescope.

Oh, and by the way, the folks at Astronomic are some of the best in the business as far as product knowledge and customer service are concerned. They will go out of their way to make sure that you are satisfied with your purchase. I should know, I have been one of their satisfied customers since the early 90's and have bought just about all of my astronomical gear from them and I will continue to do so. Kevin "Scopefreak" Vaught
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We haven't recommended any accessories for this product quite yet... check back soon or call one of our experts (1-405-364-0858).
  • Starbright XLT multicoated optics
  • 40mm 1.25" Plössl eyepiece (70x)
  • 1.25" visual back
  • 1.25" prism-type star diagonal
  • 9 x 50mm straight-through finderscope
  • Dust covers
  • Dovetail bracket for mounting on Celestron CG5 and Advanced Series go-to, Meade LXD75, and Vixen Sphinx and Great Polaris mounts
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Celestron - 11" SCT Optical tube

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Celestron - 11" SCT Optical tube
 AstronomicsAstronomicsAstronomicsAstronomicsAstronomics (Average: 5.00 | Users: 1)  Only registered users can submit ratings - Register Here
Our Product #: C11OTA5X
Manufacturer Product #: 91067-XLT
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MSRP: $4059.95

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This 11" aperture aluminum Fastar optical tube has ultra-high transmission Starbright XLT multicoatings and a dovetail bracket for installing it on Vixen style saddles like those included in the newer Advanced Series mounts as well as the older CG5s.

. . . our 38th year