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Celestron Advanced C11 SGT XLT Telescope ?


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Hi Essex,

What do you plan on using the scope for? Imaging or Observing? This scope is heavy, it will push the CG5 Mount to its limit. With an F/10 ratio, combined with an overloaded mount, I would choose differently for imaging.

For observing, this scope would be great. A focal length of 2800mm is ridiculous (in a good way). Planets will look amazing in this scope, as well as most DSOs. The CG5 has a good Go-To system, works well. Just get a dew shield, SCTs build up moisture.

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I have had a C11 for a while now and must admit that so far haven't been impressed with it's performance considering the price tag.However the scope did appear to be slightly out of collimation showing a distinct flare in the diffraction pattern on the top right hand side so I attempted to do a re-collimation which ended disastrously with damaged collimation screw heads Purchasing Bobs Knobs and another attempt at collimation produced these diffaction patterns either side of focus but I havent had the chance to give the scope a proper re-test yet.Myself I am still tending to use my 8 inch Newtonian with 3x Barlow for Planets most of the time which is much lighter and easier to collimate and unless the seeing conditions are exceptional I'm not convinced larger diameter scopes like the C11 will give significantly better results.Having said this I have seen some cracking images on SGL produced by others using a C11 or above which is why I purchased mine in the first place.Choosing the best scope for you in your local conditions is quite a minefield.

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Hi Essex,

What do you plan on using the scope for? Imaging or Observing? This scope is heavy, it will push the CG5 Mount to its limit. With an F/10 ratio, combined with an overloaded mount, I would choose differently for imaging.

For observing, this scope would be great. A focal length of 2800mm is ridiculous (in a good way). Planets will look amazing in this scope, as well as most DSOs. The CG5 has a good Go-To system, works well. Just get a dew shield, SCTs build up moisture.

Hi And thanks for your reply

I was going to use the scope for viewing firstly and maybe at a later date try imaging

The KIT is offered for sale by Celestron the C11 on the CG5 mount

It does say in the sales list the combined weight is 90 lbs with the heaviest part being less than 30 lbs , so for me if the C11 was 30 Lbs I could manage that , I assume the other 60 lbs is the mount and the tripod :)

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I have had a C11 for a while now and must admit that so far haven't been impressed with it's performance considering the price tag.However the scope did appear to be slightly out of collimation showing a distinct flare in the diffraction pattern on the top right hand side so I attempted to do a re-collimation which ended disastrously with damaged collimation screw heads Purchasing Bobs Knobs and another attempt at collimation produced these diffaction patterns either side of focus but I havent had the chance to give the scope a proper re-test yet.Myself I am still tending to use my 8 inch Newtonian with 3x Barlow for Planets most of the time which is much lighter and easier to collimate and unless the seeing conditions are exceptional I'm not convinced larger diameter scopes like the C11 will give significantly better results.Having said this I have seen some cracking images on SGL produced by others using a C11 or above which is why I purchased mine in the first place.Choosing the best scope for you in your local conditions is quite a minefield.

Hi Catweasle

Thanks for your reply

I thought I had found a scope for use at home and away at star party's , not so sure now , will have to look and see If I can find any reviews / tests , I was about to press the button :)

They give it a big write up as well . sounds amazing

Celestron's C11 is an extremely popular larger Schmidt Cassegrain that is both a large aperture telescope, and yet easily manageable by one person, hence portable. The same Starbright XLT coated optics as all other SCTs in Celestron's range means very bright, contrasty and well resolved DSOs, as well as planetary colour contrast that is immediately obvious. The natural progression for a C8 owner, at the eyepiece the C11 demonstrates a very worthwhile upgrade, with more resolved detail, higher contrast on extended nebulous objects, and galaxies show structure more easily. A superb optical tube for those wanting true laege aperture performance.

There has been much said and written regarding the optics in the SCT. Essentially, the combination of a spherical primary, an aspherized secondary and a Schmidt plate (a thin glass plate, plano (flat) on one side, and with the Schmidt curves on the other), creates a wavefront that is free from Lower Order Spherical aberration (LSA), free from Higher Order Spherical aberration (HSA or zones), a diffraction limited field free of coma and astigmatism, and the field free of Chromatic aberration (CA).

The design has much greater freedom from off-axis coma than the equivalent focal ratio Dall-Kirkham

Much greater freedom from off-axis coma than the focal ratios usually found in Newtonians

Does not suffer from the tube currents common in open tube Cassegrain focus designs, such as the Dall-Kirkham, the Klevsov, the sub-aperture meniscus Maksutov and the standard Cassegrain, nor does it require regular cleaning of the primary optics because the closed tube keeps dust and debris out

It has a smaller secondary than the photographic Ritchey-Chrétien

It has none of the chromatic aberration associated with achromatic refractors.

There are other ways to design a catadioptric system at f/10 using the full aperture Schmidt type correcting plate, by generating a different aspheric curve on the secondary. However, for production purposes, the difficulty lies in producing a diffraction limited instrument using a different aspheric curve on the secondary, on a consistent basis. Regardless of theoretical advances that other designs may promise, the key lies in the consistent diffraction limited performance that is actually realised when a catadioptric telescope is factory produced. Celestron***8217;s original tried and tested method has worked and worked very well over the decades, one of the main reasons astronomers continue to trust Celestron's optical designs. Many competing catadioptric telescopes have found it difficult to match the optical consistency of Celestron.

The Celestron Schmidt Cassegrain design is also beneficial for planetary imagers over other catadioptric designs such as the Maksutov Cassegrain (both the standard Gregory type and the separate secondary configuration), due to the cooling times of the thick meniscus lens on Maksutovs. Maksutovs often show correction errors for long periods of time whilst cooling. On the larger instruments (greater than about 180mm) this can be quite protracted. The problem is often due to the differential cooling periods of both the primary mirror and the meniscus. For planetary imagers, this can sometimes mean an unproductive night waiting for spherical aberration to reach a minimum. The Celestron Schmidt Cassegrains cool at a much faster rate, which means a much longer period of observation with the telescope at optimum correction.

Celestron***8217;s Schmidt Cassegrains offer the amateur astronomer or the optical enthusiast the complete ***8220;owning a telescope***8221; experience. The apertures range from five inches to fourteen inches and focal lengths between 1250mm and 4000mm. They are the scope of choice for planetary imagers, and deep-sky imagers because of the range of image scales. They represent the ideal observing instrument with medium to large apertures, medium to longer focal lengths for the comfortable use of higher magnifications, a large diffraction limited field free of aberrations, and rear eyepiece positioning for relaxed long periods of observing. The closed tube design keeps the important optical surfaces clean and prevents image-destroying tube currents seen in some Newtonians. The primary mirror focusing system permits close focusing with minimum spherical aberration, whilst enabling the observer to vary image scale, and all of this potential and performance in a closed compact easy to handle optical tube assembly.

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The KIT is offered for sale by Celestron the C11 on the CG5 mount

It does say in the sales list the combined weight is 90 lbs with the heaviest part being less than 30 lbs , so for me if the C11 was 30 Lbs I could manage that , I assume the other 60 lbs is the mount and the tripod :)

From what I can tell, 33lbs is the 3 x 11lb counterweights, Mount/tripod is 31lbs, a C11 weighs 27lbs :eek: The mount is allegedly good to 35lbs on the dovetail.

The celestron catalogue gives this setup as 91lbs

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