AstroMaster 130EQ-MD

[gillipies]

Hi all,

Very seriously considering buying one of these. There seems to be a lot of confusion on reviews etc regarding weather or not the mirror is parabolic or spherical. It seems that Celestron's official line is its spherical but customer reviews seem to suggest otherwise.

Can anyone shed any light? Is it even that important on a scope like this? If i was to get a parabolic scope i my price range i'd have to sacrifice aperture size to be able to do it ... which is more important?

[John]

With a focal ratio of F/5 it really has to be a parabola to produce decent images. I can't really believe that Celestron would market an F/5 newtonian that did not have a parabolic mirror

[gillipies]

Hmm, maybe not a good option then? I did just find this hidden away in the support bit of their website;

''http://www.celestron.com/c3/support3/index.php?_m=knowledgebase&_a=viewarticle&nav=0&kbarticleid=2543

The AstroMaster 130 has a spherical mirror.

Telescope mirrors are described by their figures in terms of the curvature of the optical surface. A spherical figure is one type of curvature which is like a section of a sphere’s surface, while a parabolic figure is another more complex curve. This curvature determines how the light is focused by the mirror.

A spherical mirror will reflect light coming from a distance and not bring all the rays to the same point or focus. Light striking outer parts of the mirror will focus closer than light striking the inner parts of the mirror. This effect and the blurriness it causes in an image is called spherical aberration.

A parabolic mirror will reflect light coming from a distance and bring all the rays to the same point or focus. It has no spherical aberration. However, a parabolic mirror does have another effect called coma. It can be seen off to the side in images formed by the mirror.

The difference between the two curves and the resulting aberration also depends on focal ratio of the mirror. Larger f-ratio mirrors (bigger than f/8) will be nearly identical whether made as spherical or parabolic.

Overall, parabolic mirrors are preferred for reflector telescopes, but parabolas are a harder curve to make and cost more to manufacture.

The AstroMaster scopes are less expensive designs and use spherical mirrors.''

[John]

I'd look at alternatives like the Skywatcher 130P then. An F/5 newtonian with a spherical mirror is not going to be a very satisfactory instrument.

[John Togger]

I believe the AM130 does have a parabolic mirror. There appears to be a bit of confussion over this, not helped by Celestron themselves. A member here recently posted up an email thread between themselves and Celestron on this subject (was it you Tribal Wolf?) and a reputable dealer just last weekend concurred that they do have parabolic mirrors.

Happy to stand corrected though.

[Gina]

I have one of these scopes that I bought off Amazon well before I found SGL. It was a cheap first scope to see if my lifetime wish to get into astronomy was well founded. Once I started using it I was well and truly hooked I soon found all it's faults and it was useful in showing me where things needed improving. The MD seemed an afterthought being poorer than the rest so I made my own and got better results. Next was the mount/tripod - very wobbly and made it almost impossible to focus - touch the focuser and the whole thing wobbled. So (since I wanted AP) decided to invest in a very good mount with tripod. Reckoned to be the most important bit of kit for AP. That made the focuser quite usable. The scope was certainly very much better but still didn't give a very sharp image. I concluded that this was due to a spherical mirror. If it really IS parabolic in spite of the manufacturers saying otherwise then I don't think it's of a very high standard. But then the whole kit of scope/mount/tripod/MD only cost me £130 so I didn't expect much.

The SW 130P is described as parabolic and I would expect it to perform better but I can only go by other people's views as I haven't got one or looked through one myself so I can't say if it's a better buy.

That's my personal perspective. It must be considered that I always knew I would want images as I have had a lifetime in photography including doing all my own chemical processing in the old days.

[Imd]

I believe the parabolic question came from the following article:

http://www.celestron.com/c3/support3/index.php?_m=knowledgebase&_a=printable&kbarticleid=2543

perhaps the design has changed since this article was written. However, if people who are using it enjoy what they see then the scope is surely fit for this purpose.

I hope you thoroughly enjoy your new scope.

[dag123]

As I have said before in a few posts, mine can split the double-double in Lyra and the supernova in M101 a while back.

While there are a few minor gripes, I certainly think it is value for money.

dag123