ST120 v 130PDS

[TSRobot]

Hi. 

I can't weigh up which is best all round for visual observing. Skywatcher Startravel 120mm or Skywatcher Explorer 130PDS to go on my Vixen Porta 2 for quick setup. Both are in my price range new. They never seem to be seen for sale second hand so i presume they are both good. 

Thanks.

[Knighty2112]

I had a Startravel ST120. Good scope, and I wish I’d kept it now. Not sure on the other one, but both would be good either way for visual use. 

[Louis D]

The ST120 will have loads of color fringing and some field curvature, but won't require collimation.  The 130PDS will have no color fringing, but will have coma and will require collimation.  You can flatten the ST120 field with some effort, but correcting the coma in the 130PDS is much easier with a coma corrector.  The color fringing can be masked with filters, but not eliminated (without using an unobtainable Chromacorr).  Collimation has a learning curve, and then it becomes quite easy to do touch-ups.

As you can tell, there are positives and negatives to each scope.

[TSRobot]

Thanks for the help. I've just read Niall English's book on Refractors. He says that the ST120 at F5 can be changed to F10 using the smaller hole in the lens cover. How does this seem work in reality?

[John]

27 minutes ago, TSRobot said:

Thanks for the help. I've just read Niall English's book on Refractors. He says that the ST120 at F5 can be changed to F10 using the smaller hole in the lens cover. How does this seem work in reality?

Well the focal ratio changes to around F/10 but the aperture drops to around 50mm - so you get the resolution and light grasp of a 2" aperture scope, very little CA and the weight and purchase cost of a 4.7" scope. Not sure thats such a good result myself ?

Personally I'd go for the 130 newtonian. Collimation is not difficult and the CA in the ST120 really does restrict it's usefulness at 80x or more IMHO.

 

[Cosmic Geoff]

I have the smaller Startravel 102 mm. It works well enough as a widefield scope but as a general purpose scope is compromised by the noticeable CA. The larger one will be worse in this respect.

[TSRobot]

I accept CA mostly and don't much view moon and planets. I read the science of the planets such as Casino's revelations with utter fascination. But otherwise it's deep stuff I prefer to hunt for or go really wide and rich.

Thanks

[JG777]

I had a 120 ST for a while, nice on clusters and wide field but not so good on very bright stars, planets and moon. I never really warmed to it for some reason even though it's strengths are the type of objects I like. I would take the 130 newt over the ST as collimation isn't that hard once you know how and the overall observing experience is likely to be better. 

[TSRobot]

Thanks for the help. I guess this is going to be a personal choice best not rushed. I'd told myself that whichever comes up second hand first I would buy, but neither seem to me sold very often so must be much loved. I had a Newtonian some years ago and was happy with collimation though I lent my collimator to a friend and never got it back. How often does an F5 need collimation? Isn't it every time out?

[Ricochet]

The collimation on a solid tube Newt shouldn't move that much so as long as you get it right the first time a 30 second check and minor adjustment at the start of each session would be all you need. Of the two I'd probably choose the 130pds.

[TSRobot]

Weighing it up it does seem as advised, that the 130pds wins. Trouble is that the whole country seems to be out of stock suddenly. Only one shop says "generally in stock" what ever that means, but i'll bet i'll have changed my mind again by the time one becomes available  

[Adam J]

Get the 130pds its a much better scope at that price point. Personally the chromatic aberration on anything less than a semi-apo would annoy me too much. 

[Davesellars]

I don't have experience of the 130PDS but I have the 120ST.  For DSOs, the 120ST is a really great performer under decently dark skies.  I'd worry a bit about the contrast being lost in the 130PDS due to the central obstruction but granted it should be considerably better on the Moon / Planets than the 120ST.  One thing that annoys me more than anything is the focuser...  It's just not precise enough although I'm sure it can be improved.

[TSRobot]

Ok. Just ordered the 130pds from Rothervalley over the phone. Very inside my budget, but crucially under 5kgs so can go on my now fixed Porta 2. Seems to me after lots of research and help from all here that the 130pds wins. Just have to learn to stand up to look at the zenith rather than to sit in comfort with a refractor 

[Louis D]

18 minutes ago, TSRobot said:

Just have to learn to stand up to look at the zenith rather than to sit in comfort with a refractor 

That's just a tripod issue.  If you could either splay the legs farther out or get a tripod that can be configured to a lower height, you'd be in a better viewing position to be seated.  I have DSV-2B mounted on a Manfrotto 058B tripod.  I keep the legs splayed wide so I can get a chair between them, to add stability, and to keep the mount low.

[JG777]

44 minutes ago, TSRobot said:

Just have to learn to stand up to look at the zenith rather than to sit in comfort with a refractor 

I found this to be an advantage with my 150 Newt and not having to crouch much for any viewing . I never used a chair when observing with fracs due to the temptation of having a nap ☺

[TSRobot]

Just now, JG777 said:

I found this to be an advantage with my 150 Newt and not having to crouch much for any viewing . I never used a chair when observing with fracs due to the temptation of having a nap ☺

I find it rather relaxing sat looking at zillions of stars around cygnus  with my wide field frac. The cold keeps me awake for sure though 

[TSRobot]

130pds arrived this afternoon thanks to Rothervalley Optics who have been very helpful even when FedEx delivered to my house number but in the wrong street! 

I've not had a newt for so long now. Since my last one I've had an SCT, Mak, SCT and small Achro and I'd forgotten the image is upside down...I thought something was wrong with it at first . It goes very well on my Porta 2. I'd not forgotten how to collimate though which it needed out of the box. The dovetail is shade of green which i like very much, they should paint the whole OTA that color! I noticed the field curvature looking at chimney pots, but i guess you only see that looking at straight lines. The whole universe is curved all over the place by the effects of gravity anyhow. (I bow to physicists)

The eyepiece holders are bit fiddly.  Does anyone know of an improved version to make it easier to swap between 1.25 and 2inch eye pieces in the dark/cold?

Obviously there will be cloud tonight so I won't even bother looking outside or checking the weather.

TSR

[Ricochet]

1 hour ago, TSRobot said:

I noticed the field curvature looking at chimney pots, but i guess you only see that looking at straight lines.

That will be pincushion (and/or barrel) distortion curving straight lines. Field curvature is curvature of the focal plane and results in the edges of the image being out of focus when the centre is focused. 

1 hour ago, TSRobot said:

The eyepiece holders are bit fiddly.  Does anyone know of an improved version to make it easier to swap between 1.25 and 2inch eye pieces in the dark/cold?

I think that there should be a 2" Baader click lock that can be fitted directly to the standard focuser draw tube. There is also a mounting kit to fit a Moonlight focuser to the 130pds. 

[Louis D]

47 minutes ago, Ricochet said:

That will be pincushion (and/or barrel) distortion curving straight lines. Field curvature is curvature of the focal plane and results in the edges of the image being out of focus when the centre is focused. 

And this pincushion distortion should be eyepiece dependent, not a function of the Newtonian's focal plane.  A Newtonian's focal plane is slightly curved, but much less so than for an equivalent focal length refractor.  There will be coma in the outer field of wide field eyepieces at any magnification level unless a coma corrector is used.

[TSRobot]

Looking at the chimney pots I compared my Maxvision 68degree 1.25 24mm, Hyperion zoom set at 24mm and the included 24mm SW kelner 2inch.

The Maxvision won big time! Curves at the edge noticeable as I pan the view past the chimneys a bit, but in focus most of the field. The Hyperion sharp but narrow at 40 degrees. The SW kelner will stay in the box as the outer 25% of the field is a blur, but that maybe F5 related.

Still need to see some stars.

TSR

[Adam J]

1 hour ago, TSRobot said:

Looking at the chimney pots I compared my Maxvision 68degree 1.25 24mm, Hyperion zoom set at 24mm and the included 24mm SW kelner 2inch.

The Maxvision won big time! Curves at the edge noticeable as I pan the view past the chimneys a bit, but in focus most of the field. The Hyperion sharp but narrow at 40 degrees. The SW kelner will stay in the box as the outer 25% of the field is a blur, but that maybe F5 related.

Still need to see some stars.

TSR

Am not much for observing, I mainly image, but I am told that you need a quality eyepiece when observing with an F5 scope.

[RobertI]

Keep us posted on how you get on with the scope. I have the 130P Heritage for visual and am so impressed with the optics that I am considering the 130PDS for the better focuser and possibility to image. ?

[TSRobot]

Hi Rob. Still waiting for a break in the clouds. I'm not an astrophotographer though. It's nice and light, but must be bit heavier than the Heritage version. I weighed the OTA with tube rings fitted and dovetail and it came to just over 4kg. All i've done so far is collimated it, fitted my Rigel finder and put the 6x30 finder and 24mm 2inch Kelner back into box for attic storage. Hope to get some lovely wide views soon.

[RobertI]

4kg is actually is lighter than I thought it would be, definitely heavier than the Heritage though. Good luck with the clouds!