Can't focus on stars my Skywatcher Heritage 130p

[John]

A spherical mirror can work well at F/8 or slower but at F/5 the spherical figure will not give as sharp images as a parabola because the light will not be bought to focus at close enough to the same point. This applies regardless of the aperture.

I'd be surprised if a respected brand claimed that a mirror was a parabaloid if it wasn't.

[Mak the Night]

A spherical mirror can work well at F/8 or slower but at F/5 the spherical figure will not give as sharp images as a parabola because the light will not be bought to focus at close enough to the same point. This applies regardless of the aperture.

I'd be surprised if a respected brand claimed that a mirror was a parabaloid if it wasn't.

Thanks John, I had suspected there was more to it than I knew. I'd always assumed parabolic mirrors kept the OTA at a more manageable size as the apertures got bigger. It makes a lot of sense that the focal ratio has a lot to do with determining what kind of primary is employed. My Explorer is f/6.9 (I think) which is closer to f/8. I don't think that there is any discernible difference until you get apertures that are 150mm or over, or so I was told. I doubt if I could tell the difference anyway.

AFAIK the Celestron AstroMaster 130 actually does have a parabolic mirror, its f/l is 650mm. Celestron do promote the idea that it has a 'superior' parabolic mirror in their advertising though, suggesting that it is better than a spherical mirror. It's probably just a marketing strategy to make you choose it over the SW Explorer, which appears to be its main rival in the 130mm Newtonians.

According to this review (below) the Sky-Watcher 130 P gave sharp edge of field views even with the supplied EP's, which the reviewer attributes is possibly to its parabolic mirror. 

http://www.firstlightoptics.com/user/skywatcher_explorer_130p_review.pdf

[Psychology]

I use a skywatcher 2x barlow with my Heritage 130p and don't have any trouble. I can't make out the red spot but the bands are visible. It did take me  a few observing sessions to get used to the telescope though, for example M13 was just a bright blob, but with practice I can start to see detail.

[Mak the Night]

There may be a difference with the give-away Barlow and the standard Sky-Watcher 2x Barlow that can be purchased separately. Any weak link in the light train will drastically alter the viewing quality. I basically only use my TeleVue Barlows now. Jupiter's Great Red Spot moves with Jupiter's rotation and is not always visible. The last time I saw it was in daylight (dusk) conditions at around 21:45 early June (4th I think) with Jupiter at a 29.9° elevation (Cancer) and Jupiter set properly at 01:14 although I couldn’t see it then due to woods being in the way. I did observe Saturn about an hour later rising (Libra) at 16.9°. IIRC Antares was also visible just below it (all with the Explorer 130, a 20mm Celestron erecting EP, 15mm Celestron Kellner, 25mm TeleVue Plossl and a 3x TeleVue Barlow).

[Psychology]

You may be right as I bought mine seperately.

[Mak the Night]

You may be right as I bought mine seperately.

It stands a good chance. Personally, I think the Sky-Watcher 25mm MA and the diagonal give-aways are perfectly usable, even the 10mm MA isn't as bad as people often claim IMO. However, the give-away 2x Barlow is unusable in my experience, for exactly the same reason as the OP states, it just can't be brought into focus. It has a completely plastic body with a metal band posing as the draw tube.

Here's mine with the 25mm MA inserted:

Note that it has two thumb screws. 

This is the Celestron Universal Barlow from FLO: http://www.firstlightoptics.com/celestron-eyepieces/celestron-2x-universal-125-barlow.html

And this is from Sky-Watcher's website: http://www.skywatcher.com/product.php?cat=26&id=150

These are very similar, but don't have removable Barlow elements unlike the Celestron Universal Barlow. I'm guessing the Sky-Watcher Barlow 2x (D) in the Sky-Watcher website link above also has a removable element. Note that both Barlows below have barrel undercuts and only one thumb screw.

This is my Celestron 2x shorty Barlow originally from an AstroMaster Kit, it doesn't feature an undercut, unlike the one on FLO's page, but does have a camera thread like the Sky-Watcher Barlow 2x (D) on their page. I should imagine both the SW and Celestron Barlows with detachable elements and camera threads are from the same manufacturer (GSO?).

Except for the give-away plastic SW Barlow featuring two thumb screws, all the other Barlows in my jpegs work perfectly well.

[Stub Mandrel]

Interesting. My (secondhad) Skywatcher scope came with a Barlow that appears to be the alloy-bodied version of the Celestron x2 with a t-mount thread on it.

Seems to work OK to me:

[Mak the Night]

Interesting. My (secondhad) Skywatcher scope came with a Barlow that appears to be the alloy-bodied version of the Celestron x2 with a t-mount thread on it.

Seems to work OK to me:

Nice picture! I think the T-mount Celestron x2 Barlow is quite well made, it feels quite robust and has a detachable element. I reckon that Barlow with your telescope wasn't the original give-away. 

Edit: OTOH if your scope in your signature is this ~ http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150pl-eq3-2.html

According to FLO it comes with 'X2 Deluxe Barlow Lens 1.25" (with Camera Adaptor)', which I am pretty sure is identical to the Celestron Universal Barlow, which I am also pretty sure is identical to mine which came included with the Celestron AstroMaster Kit. 

They could all be rebadged Guan Sheng Optical, although the 2x Barlow on their website lacks a camera adaptor.

http://www.gs-telescope.com/content.asp?id=120

[Stub Mandrel]

Edit: OTOH if your scope in your signature is this ~ http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150pl-eq3-2.html

According to FLO it comes with 'X2 Deluxe Barlow Lens 1.25" (with Camera Adaptor)', which I am pretty sure is identical to the Celestron Universal Barlow, which I am also pretty sure is identical to mine which came included with the Celestron AstroMaster Kit.

Yes, it's a 150PL so that would explain it.

[Alonsos]

I've bought a dob 200p and initially although I was told it would not need collimating on inspection the spider arm chrome screws were loose, one in particular as were the primary adjusters, so eventually had spider out & found one of the 3 threads was damaged so that got fixed ,then put it all back,spent hours looking at collimating videos and understood what to do,then proceeded to actually collimating it ,easier said than done ! Ha but it's all looking sweet now ,I went out last nite to try it, the moon was Wow ! But stars were a lot better than when I first had the scope BUT is the goal to get stars as perfect dots in a perfect world or will they always be sort of a very slight flare ,I defocus and get that equal sort of donut ring talked about & aware of seeing conditions etc ,I can't see I could collimate any better ,the eyepieces used were 10 mm & 25 mm which came stock with 200p would I do better getting a ( more expensive ) eyepiece ? Ep or whatever

Regards

Take care you lot !

[Stub Mandrel]

I see stars as pinprick dots with the standard skywatcher EPs, I don't think I've ever seen what I would describe as flare. Are you seeing four 'spikes' around bright stars,which is something caused by the scope's spider?

[Alonsos]

Ta for that

ime seeing not 4 spikes but general flare to one side or the other

Perhaps Ime being to critical, I would put a pic on here but any pic I want to use the site says to large , too much content ha