CELESTRON C8 PDF

Buy Celestron C8-A-XLT CGE 8″ f/10 Schmidt-Cassegrain Telescope (OTA Only) featuring 8″ (mm) Schmidt-Cassegrain OTA, mm Focal Length, f/ High quality Celestron C8 SCT optical tubes are an ideal upgrade for large aperture chasers. Buy now on sale from Celestron’s Official Australian Dealer. View the night sky or terrestrial landscapes with the Celestron C8-A SCT, an unmounted Schmidt-Cassegrain telescope with premium StarBright XLT coatings !.

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I spent a lot of time carefully comparing both scopes, but the upshot was that the refractor was streets ahead of the C8 in almost every way. Since then many people have told me my original C8 must have been a dud, that a typical modern C8 is a much more competitive telescope.

I love a factory-fresh unboxing! SCT optical configuration, from celestron. The SCT design has many advantages in terms of compactness and light weight the corrector is thinner and lighter than that in a Maksutovfor example.

However, that compactness requires steeply curved optical surfaces — the primary mirror is F2 – which can be hard to make well and close tolerances are required if performance is to be good. Another disadvantage of the design is the large central obstruction.

A large obstruction does reduce contrast, but the main effect in my experience is to worsen performance in poor seeing. That means the potential for striae and inhomogeneities varying from sample to sample.

C8 Primary and baffle tube seen through the almost-transparent XLT-coated corrector. Theoretically you could get celestrob 1. celewtron

Discontinued Celestron C8 with Wedge and Tripod

One big advantage of a long focal length is that you can get high powers without using complex, expensive eyepiece designs — Plossls and Orthoscopics are adequate. Early C8s had an cekestron corrector, but this one has velestron multi-coatings as you can see in the photos. StarBright XLT employs multi-layer mirror coatings and multiple layers of magnesium and hafnium fluoride on the corrector plate. Celestron also use a better, more transmissive glass for the corrector than in previous models.

Overall, Celestron claim Those screws are your collimation adjustment. The secondary mirror housing is removable, so you can plug a camera and doublet corrector in at prime focus to image with the focal ratio of the remarkably fast F2 primary mirror.

Because of the square function relating f-ratio to exposure time, that means 25x shorter exposures! Celestron no longer make Fastar hardware, but oddly still support the architecture which is nowadays implemented by third parties like Starizona.

Build quality looks more mass-produced than the original C8, but is actually very good — typical recent Synta in fact.

This version ceelestron a grab handle at the back which is very convenient.

A plastic dew-cap is provided, but unlike the original push-fit C8 cap, this one twists and locks in place — a good compromise between push and screw-on types. C8 Focuser, standard 1. Like many Cassegrainsthe C8 focuses internally by moving the main mirror. This has advantages over an external focuser — it keeps the tube sealed, the eyepiece in one place and allows lots of focus travel. As we will see, this C8 unlike some earlier versions suffers from neither of these issues: The C8 is light enough to go on most small mounts.

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The accessories delivered with the C8. The C8 OTA comes with a very gold! The eyepiece is a nice multi-coated Celestron E-Lux Plossl and the mirror diagonal looks decent quality too.

In Use — Astrophotography. The following snap of M37 with an inset enlargement of the stars in the left corner reveals slight miscollimation and substantial off-axis coma, even on the smallish APS-C M37 through C8 with enlargement of comatic stars in top left corner. In Use — The Night Sky. Cool-down is slower than a typical doublet refractor, but not as lengthy as a Maksutov which has a much thicker corrector plate.

The focuser is very smooth and precise.

It has minimal image shift and what there is only manifests itself at high powers. Focus is the same in both directions, unlike some moving-mirror systems where the sweet-spot has moved when you back out.

I found the focuser very easy ccelestron use when imaging with a DSLR. This is in marked contrast to my own original orange-tube C8 and a Meade LX that I tried since, both of which had very mushy, imperfect focus over a wide range of settings.

Celestron C8-A XLT SCT Optical Tubes

Poor scopes often have imprecise focus because spherical aberration makes parts of the optic focus light to a slightly different point than others. In this respect the C8 underperforms a good APO especially a well-corrected triplet. A dew-shield would be your first C8 accessory. This explains the snappy focus and much of what follows in this review. The C8 was however slightly out of collimation from the factory.

The whole Moon easily fitted in the field and revealed both the crescent and Earthshine. Upping the magnification to x with an 11mm Plossl showed numerous shadow-filled craters scattered across bright Oceanus Procellarum and lots of detail in the larger craters like Kepler and Marius.

Wrinkle ridges and bright rays showed up to great effect and contrast and sharpness were first rate. Although the Moon was low in the pre-dawn, seeing was good and I lingered over the Aristarchus Plateau which was just off the terminator. In good seeing the C8 delivers wonderful views of the Moon. Venus low in the late afternoon sky of Christmas Day showed the thinnest sliver of a bright crescent.

The C8 showed it to perfection with none of the nasty flare or chromatic aberration you sometimes see.

Even so, at x the gibbous disk was sharply defined and both the polar cap and Mare Acidalium were easily seen I always seem to catch Mars with Mare Acidalium in view for some reason. Near the zenith and in good seeing, Jupiter revealed a wealth of detail at x with an 11mm TV Plossl. Numerous belts and partial belts in the polar regions were seen, as were variations in the width and tone of the NEB and SEB and small dark storms in the polar regions.

Though the view was broadly similar, there was more detail on offer than in the mm APO set up nearby; in particular the C8 delivered more contrast than the smaller aperture, making detail easier to pick out. On another occasion, even when low in the early morning pre-dawn sky, Jupiter showed a lot of detail in steady seeing.

The Great Red Spot was right on the limb and the thickened region of vortices down-wind from it was easily seen. Nearby, Ganymede was just coming off transit as a perfect disk.

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Saturn was still very low cleestron the dawn sky at the time I was doing this test, even so in good seeing the view was cleestron. The Cassini division, ring shadow and darkened polar hood were easily visible and there was a hint of banding in the hood as well.

Again, the view was crisp and sharp with no aberrations and snappy focus at ceoestron. Overall, the C8 makes a very fine planetary scope in good seeing. Whilst viewing them, I noticed some stray-light reflected from bright stars when right on the field stop. However, M37 revealed a lot more stars than in a smaller aperture and its characteristic central flower-like shape.

Teleskop-Express: Celestron C8 Schmidt-Cassegrain (8″ – orange design) – Optical Tube Assembly

Off-axis aberrations do mar the view of extended objects, such as clusters, compared to a better corrected design. Globular clusters — like M56 and M15 – look good at medium magnifications in the C8 and their outer parts resolve. Castor was an easy split, but in mediocre seeing stars bloat more than they do in an unobstructed aperture making tight doubles harder to split.

Star colours seem less strong than they do in good refractors, perhaps because the light is distributed into a broader point-spread function. Planetary nebulae generally look good in the C8, where aperture counts and off-axis aberrations are less important. So the Ring and Dumbbell nebulae and to some extent the Crab look brighter and more defined with a clearer shape than they do they do in say a typical small refractor.

The people who told me that a modern C8 is a very different i. Whilst the two are very similar in design, none of the components are the same and indeed the current model is made in China by Syntanot in the U.

But functionally the main difference is not down to the design of the tube and castings, or even the multi-coated corrector, but is simply a matter of optical and mechanical quality. So the new C8 gives excellent views of many types of object, but particularly the Moon and planets, which reveal lots of detail through the C8 in good seeing.

Even image-shift — long a source of frustration for C8 owners — is very well controlled and the focuser is a pleasure to use, both visually and for imaging. The C8 does still have some downsides to be aware of: It cools slowly and the exposed corrector dews-up easily. The long focal length and narrow baffle tube limits maximum true field to about a degree.

Off-axis aberrations are worse than some other designs: The C8 underperforms in poor seeing, noticeably so compared to an unobstructed aperture. Star fields lack that brilliancy you get with a fine APO. Collimation clearly has a tendency to shift in transport. Despite being far more portable and easy to mount and use, it is also true that the C8 still underperforms a good long focus Newtonian of the same aperture though to a lesser degree now that it has such good optics.

Updated by Roger Vine