Skywatcher 130 vs 130p

[bcsteele]

Hi all,

After many years I am getting back into astronomy - with my limited budget (around £200) and looking at the info scattered around - especially on these forums, I have settled on getting a Skywatcher 130.

I was going to get a 130p as the mirror is better -however I understand it isn't quite so good at high mag, and as I want to view planets, perhaps the 130/130m  is better ???

Some advice would be helpful please.

Thanks in Advance

Bry

[Schorhr]

Hello Bry,

I am not familiar with all the variants, but if a mirror is not clearly specified as parabolic, stay clear of it.

Spherical mirrors will work if the focal length is high enough (and has a theoretical Strehl of 0.80 or higher).

A 130 900 will not have 0.80;

100*e^-(2*pi*( (130/2)^4/(2*900)^3/16/0.00056)/3.5)^2 = 68.65

And this is not factoring in obstruction, roughness of the mirror, bad edges and other errors, but it purely the theoreticly possible.

I copied the formula from a german board, so one of the geniuses here may be able to make a more accurate statement. Consider it as a approximation.

Either stopped down to 120/900 (less resolution or darker image) or with ~990mm focal length the mirror would have >=0.80.

If the focal length is long enough, the spherical abberation is not as much of an issue, thus all the 114/900 and 76/900 telscopes seem to have a spherical mirror.

Danger- Some short tube (Catadioptre) like the 130/1400 or 114/1000 have a lens to reach that focal length, and are about half as long as their actual focal length would suggest. Those usualy have spherical mirrors, and the barlow type lens will not fix all issues... Instead introducing more problems.

Not to b confused with Maksutovs for example, they are so short as the secondary sits infront, reflecting the light through the center of the mirror.

I have a Heritage (130/650), and reading into the subject, the mirror qulity seems to vary. Sky-watchers 130/650 probably all have the same type mirror.

You should be able to magnify 150-200 if it's allright, good models may work a bit higher, but seeing is often a problem then.

I reccomend you consider getting a 150/1200 dobsonian as it will have a 2" focuser for wide angle eyepieces at low magnification, it can be used with cheap eyepieces and still produces a sharp field of view, and collimation is easier.

150mm aperture will benefit from higher resolution and light gathering power, so if the seeing conditions are great you can even magnify higher before the image gets bad, and even below 200x the exit pupil will be larger, so you'll see fainter details, especially on Deep Sky Objects.

Personally I find tracking planets on a dobsonian easy if you use a 60 or 70 degree wide angle eyepiece, even at 200-300x.

The problem with most kits is the EQ-2 mount (or some sell a fake EQ-3, that's not the neq3/eq-3-2 but the Astro-3 Mount that's just a bit better then the EQ2)

I Even found the 130/650 on Astro3 a bad combination. What use is the equatiorial mount if at high magnification it's vibrating/shaking all over the place? Not a suitable combination for imaging or even visual over ~100.

If you want to go low-budget, consider a Heritage 130p, as it leaves you with some spare cash for eyepieces ;-) And you can still put it on a EQ-3 later, or on a Az Synscan or Nexstar SLT Goto mount later.

If planet's is your main target, the 6" may be the best choice- if you can store/transport it. Though a good EQ mount is not light either...

At focal ratios of f/8 or f/6 the cheap 20-27gbp 66degree aparent field of view wide angle eyepieces work great.

Plössl <10mm have a horrible short eye relief, so don't buy any Plössl Kits for example.

[Beardy30]

I have had a 130 for a couple of years good starter scope the p is for parabolic and worth the extra spend they r good scopes but I would advise you consider a dob 150p I wish I had due to the simplicity a dob gives you.

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[LouisJB]

I can recommend the 130P, I'd personally avoid any non-parabolic, don't trade ideas of magnification against image quality, you can always magnify with eyepieces.

None of the 130s are going to be perfect for planets but you can get probably up to 200x with a 130mm depending on seeing which should show some detail of Jupiter and Saturn.

It's something I've yet to try myself but for general use the 130P appears great, almost portable too.

The 150P naturally a little better (30% more light and 750mm instead of 650mm focal length). If I were starting I'd pick the 130P again as a small portable wide-field tube to keep even when you've also later purchase something much more expensive for more specific uses.

[Beardy30]

Sound advice

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[AlexB67]

While I do not know from practice never having tried the spherical mirrors versus parabolic, in practical terms it apparently does not significantly affect the views at 5 inch or below aperture for it be really visible, but perhaps someone who has actually compared them for real can say something more about that.  At higher aperture it is best avoided though as the issues grow with aperture.

[Schorhr]

It really depends, even a 12" could work as spherical mirror, but you'd need a 3m ladder :-)

Over 6" it bcomes inpractical.

I have compared a few spherical 130/900 (.78) and the Heritage (parabolic, else it would be 0.07!) and the difference is minimal. But it will have less contrast and I would not reccomend any shorter 5" with a spherical mirror.

[Alfian]

Hi Bry,

I have the Celestron 130EQ (but in hindsight I think the Skywatcher although very similar is a better overall package) and although it doesn't specify that it s a parabolic mirror, I am informed by others that know, that it is parabolic - so I would be extremely surprised if the any of the Skywatchers were not!

All that said - if you have a particular yen to view planets - I'd look to something with a longer focal length than the 130s F5. I have a little F12.9 102 Mak and the views of Jupiter  and particularly the moon is so much better than my 130EQ. The other thing with the 130EQ is the mount itself. Once you get the hang of an EQ mount you really appreciate them, but the EQ2 (similar to my cG3) is only just sufficient for the scope - which sometimes has its frustrations.

The suggestion of Schorhr re the 150 Dob is a much better idea. More light, easier to deploy and use, a 2" focusser which is a real bonus, and its an F8 - which in my book is a really sweet spot. It will give you pretty decent views of planets - yet it will also afford reasonably wide views (eyepiece providing). At just over £200  (£209 at FLO)

http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-150p-dobsonian.html

If you were dead set on an EQ mount - you could take a look at the TAL1

http://www.opticalvision.co.uk/astronomical_telescopes/tal/newtonian_reflectors/tal-1

A heavy chunk of russian engineering - thats a few years old now - but has something of almost a cult reputation for quality build and really good optics. - and also around £200.

[Schorhr]

Hello Alfian,

that's odd, I find the Planetary views of the Heritage 130p better then with the 4" Mak- Other eyepieces or bad Mak mirror on my side?

[JamesF]

I'm pretty sure the Skywatcher 130 and 130M (both 900mm focal length) have spherical mirrors.

James

[AlexB67]

As far as I know I believe this to be the case also James.  It is how I recall it anyway and this review would confirm that,

http://www.stargazing.org.uk/reviews/Explorer%20130M%20EQ2.html

At around f/7 this difference of parabolic versus spherical at this aperture is supposedly quite negligible. I would think  a better eyepiece with that spherical and mirror, and a poor eyepiece  with the parabolic, I'd imagine the former would be the winner overall.  I don't think it is a massive thing to get  that hung up on in this range of SW scopes at that sort of aperture.  Whether the shorter focal ratio of say the heritage or the  longer one would be more to ones liking would be more of a deciding factor  in combination of what eyepieces to use for me I think, since the f/7 would be that bit more forgiving. On the other hand the f/5 Heritage gives those low mag wide angle views that I like so much  that comes with a cheap price tag.

[Alfian]

Hi, Paraobolic/spherical ? I'm happy to be be corrected if thats the case - but the acid test is how well they work - and it seems that they do. The Tal1 - I'm pretty sure has a spherical but at F7.3 (I think) its probably not an issue - and clearly that works just fine.

As to the Skymax 102 - I'm a bit astounded! Could be that your Heritage 130 is better than my 13OEQ (that wouldn't surprise me actually) or maybe your 102 is a bit out. When I first got my Mak - I have to say that the airy disks were as good as they could be - really impressed and I've never been less than impressed with it since. At 102mm it is clearly better on brighter images. I bought it mainly for lunar work - and for me its perfect at that.

[Special K]

Hi, the 130P got my vote after much searching around and research into Parabolic or not.  From what I recalled, only the 130P is Parabolic but there were some informed posts on the forum that cast that fact into some doubt.  You're in the right ballpark with your budget if you want a 130 and I think the Skywatcher has a more substantial mount than the Celestron.  I've not compared mine with a spherical mirror to see a difference but there is very little difference in cost so it seemed best to buy the 130P and I didn't care about a motor.  My thinking was to go Parabolic to get the best I could.  I like the EQ mount and it really isn't any effort at all.  So long as you got a view of Polaris from your viewing site, you're fine.  And if you're in a hurry the alignment doesn't need to be perfect.  However, the suggestion to look into a Dob could be a good idea and that mount makes a lot of folk happy.  You get more OTA as less money needs to go into the mount and therefore get more light gathering with a larger scope, like the 150 suggested.  It's all a matter of preference.

Regarding magnification the rule of thumb is no more than twice the aperture, so 260x with this is an absolute ceiling.  I'd say 130x is a more practical ceiling and rarely go beyond that.  With a 5mm BST eyepiece (which is much more pleasant than the factory 10mm and 25mm you'll get in the kit), you'll have a lot of fun.  That EP, or any of the other BST's, are just under £50.  Having said that, the supplied eyepieces are more than enough to get you started.  Enjoy the new scope!

[JamesF]

From what I recalled, only the 130P is Parabolic but there were some informed posts on the forum that cast that fact into some doubt.

Plenty of UK retailers claim that the 130P is parabolic.  I'm not sure they, nor the importers, would be desperately keen on the situation likely to ensue were it found to be otherwise.

James

[LouisJB]

only the 130P and the (non-existent anymore?) 130PM (M=motor) have parabolic mirrors, the normal parabolic tubes are 650mm and the spherical 130 and 130M are 900mm. I think there was a special version of the P with a shorter tube for photography, but I can't recall what that is called. I'd expect that is notionally 650mm also, minus a tiny little bit! 

Lots of reviews on the internet do mention poor image quality of the spherical versions and lots of people seem to really like the parabolic versions.

[Special K]

Plenty of UK retailers claim that the 130P is parabolic.  I'm not sure they, nor the importers, would be desperately keen on the situation likely to ensue were it found to be otherwise.

James

Sorry James, I didn't word this the best:  The 130P is definitely Parabolic and there are no doubts about that, but there have been some posts based on communication with SkyWatcher that the other models such as 130M are also Parabolic.  The doubt is whether non 130P models are indeed parabolic or not. 

[AlexB67]

I thought the convention would likely be 130p parabolic always, 130 or 130m spherical and m for motor.  I'd imagine, usually if there is a selling point to be made  that adds a positive marketing whistle the manufacturers would want to emphasize that.  So for the 130 and 130m they take it away.  I mean anyone ever seen a 130s or 130ms 

As another point of interest, even if in practical  terms the spherical and parabolic differences are negligible at this aperture and ratio, perhaps sales figures have revealed that these tags actually matter, because many will buy into it, parabolic must be better,  so I'll buy that instead.

I must admit for me it was certainly a factor starting out reading up on this range of scopes. I better get the parabolic one but people much more knowledgeable than I revealed it is really no big deal afterwards, and from some figures I recall seeing too some time back I forget the details of now, but the point that stuck in my head was it was no real biggy for this range of scopes at that aperture and ratio.

[JamesF]

I think there was a special version of the P with a shorter tube for photography, but I can't recall what that is called. I'd expect that is notionally 650mm also, minus a tiny little bit! 

There is a 130P-DS which has a slightly shorter tube and a dual-speed focuser.  Or perhaps it's more accurate to say that the distance between the primary and secondary is smaller.  The focal length of the primary mirror is still the same, which means the focal plane is further "out" of the focuser tube, making it easier to get the sensor of a camera to the focal plane.

James

[JamesF]

Sorry James, I didn't word this the best:  The 130P is definitely Parabolic and there are no doubts about that, but there have been some posts based on communication with SkyWatcher that the other models such as 130M are also Parabolic.  The doubt is whether non 130P models are indeed parabolic or not. 

Ah, right, I see.  The only reference google can find me for someone actually saying "the mirror is parabolic and here's why" rather than repeating the assertion "I've heard that the mirror may be parabolic" really doesn't convince me.  If the 130 and 130M really were parabolic I'd expect them to be sold as something like a 130PL, just as the longer focal length version of the 150P is sold as a 150PL.  It would not however surprise me if it is actually quite hard for the average person to tell the difference between a spherical and parabolic mirror of the 130's aperture and focal length.

James

[bcsteele]

Hi Folks

Thanks for all of that -

Reading through the posts it looks like the consensus is for the 130P (with or without a Motor)

However serious thought should be given to a 200 Dob as well

oh and Schorhr I'm sorry but most of that first part of your post was just simply lost on me with all those numbers, but I appreciate your effort!

And thanks to everyone else that posted!

I'l give an update once I have made a purchase - No hurry, Pembrokeshire is all in cloud right now

[bcsteele]

ah, the 200 dob, may be just out of my price range, perhaps the 150p  dob

[LouisJB]

I doubt you'll regret that choice.

If you get the version on the EQ2 you can always add a motor with basic controller later, as an add on for basic tracking for visual observing. You might find (as I did) then you like EQ mounts and tracking and go upgrade it, because it doesn't take long to realise regardless of what tube you have to really getting the most out of it the mount is also a crucial thing, especially if you do plan to take any images with it.

Good luck.

[Schorhr]

Hello Bry,

perhaps you can get a 8" / 200mm dobsonain used? Sometimes they sell for 200 or even less.

After all the 130p/m discussion:

What are you wanting to observe, what are your expectations, how dark is your observing spot or do you have to travel?

I strongly reccomend to stay clear of the EQ-2 mount, it won't work well, especially at high magnifications. EQ mounts are nice, but for photography something stable is required, and visual the dobsonian will beat the stability easily.

At least the 130/650 will also still be mountable on a cheap goto or simple az mount, if you don't neccesarily need an EQ mount but wan't a portable and higher telescope ;-)

[LouisJB]

I think even a basic EQ2 is better than the equivalent cheapo alt-az, at least you can polar align and let run with a motor. It's usable, especially if well balanced. I've used mine with much fun at the limit of tube magnification. It all went wrong when I started trying to put my DSLR on it, but at least I was able to dabble. The EQ2 is definitely wobbly but given you get one for £30 more than the 130p heritage it's a lot more versatile and is still useful for many visual situations.

I won't get into the dobsonian debate. It will come down to various trade-offs in that price range but I do think a smaller wide-field on a simple eq mount makes for a good starter package, probably why they sell that setup and it's so popular.

[Schorhr]

Hello Louis

Will you get into focus with the 130p?

I can only get into focus with the 130/650 flextube if I shorten the tube length.

No, we don't have to argue about dobsonian or EQ mount, and if the EQ-2 is popular or not, but everybody has different perception and expectations regarding stability. It would be unwise to recommend it to beginners without mentioning that it's a compromise, as with most of the telescope bundles available.

I tried imaging on the Astro 3, and while more stable then the EQ-2, it was not really usable. Visual I found it troublesome over 100, perhaps 150x magnification. I had to focus more on not nudging the eyepice with my eye then on anything else. But th height of the mount is a big plus...

With short time photography, even a £170 altAz goto mount is more suited with this kind of tube IMHO, even though due to the AltAz tracking the exposure will be limited to perhaps 20-30 seconds depending on the height and total focal length. Stability was okey-ish though.

No doubt an EQ mount has many benefits, and I would think a NEQ-3 would give better results. Visually, it does not matter if EQ or AltAz/Dobsonian. The whole tracking at 200x and up is a piece of cake either way.

The 80£ saved on a EQ mount and motor is allready half-way to a decent EQ mount for such a telescope! :-)