Non-collimateable primary mirror?

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Non-collimateable primary mirror?

Postby Newbie Jimmy » Wed Aug 22, 2018 9:25 pm

Hi,
I'm looking to buy a telescope and really like the idea of the Sky-Watcher Star Discovery 150i f/5
It has Wi-fi (which I wouldn't normally go for) but it also has the capability to be manually moved to look elsewhere and afterwards it will slew back to where you were originally looking.
Other Wi-fi enabled telescopes I've seen such as the Astro Fi series do not have this capability and can only be moved by the Wi-Fi connected tablet or laptop.

My question though please is that in it's description it says "NOTE: The 150i telescope has a non-collimateable primary mirror"

Would someone be able to explain to me please what if any the pitfalls of this could be?
Thanks
Jimmy
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Re: Non-collimateable primary mirror?

Postby Gfamily2 » Thu Aug 23, 2018 12:32 am

Newbie Jimmy wrote:Hi,
I'm looking to buy a telescope and really like the idea of the Sky-Watcher Star Discovery 150i f/5
It has Wi-fi (which I wouldn't normally go for) but it also has the capability to be manually moved to look elsewhere and afterwards it will slew back to where you were originally looking.
Other Wi-fi enabled telescopes I've seen such as the Astro Fi series do not have this capability and can only be moved by the Wi-Fi connected tablet or laptop.

My question though please is that in it's description it says "NOTE: The 150i telescope has a non-collimateable primary mirror"

Would someone be able to explain to me please what if any the pitfalls of this could be?
Thanks
Jimmy

Hi Jimmy
There's a discussion on the Cloudy Nights forum about this very telescope - with a video review.

Without having watched the video, or read all the comments, it seems as though the intention is that it is made such that primary collimation should not be necessary, but small primary mirror adjustments are possible.
The secondary can be collimated in the usual way.

https://www.cloudynights.com/topic/5259 ... -or-is-it/

It sounds like it could be good - my first concern was that it was a Bird Jones design - which can sometimes be as good as 'not collimatable', but the OTA seems to optically be a straightforward Newtonian design.

ETA
A Positive
As computerised scopes in this price range go, this has a reasonable aperture - there's always a certain amount of the budget that goes on the mount and the rest goes on the scope, and it looks as thought Sky Watcher are hitting the point where a standardised wifi connector and a downloadable app means they don't need to spend as much as on a handset and wired connection, so more can be spent on the scope.

And it is worth remembering is that with this package you're buying both a mount and a scope.
The mount can be used with another scope and the scope can be used on another mount. And if you like this hobby, you will get another scope and there's a moderate chance you'll buy another mount.

Two Negatives
#1
To use this scope, you'll be using your phone or tablet. These have batteries that run down, particularly at the end of the day - so make sure you re-charge them before you head out to observe.
The phone or tablet will also mean you'll be using the screen as a handset - so you'll also likely be looking at the screen - whereas with a 'trad' handset, you'll be using real 3d buttons you can feel and use without looking.
And you don't have to unlock the handset if you've not used it for 5 minutes like a phone, which can mean you muck up your dark adaption when you wake it up

#2 It's worth being aware as well that the capability for imaging will be limited with this scope. You'll probably not be able to get a focussed image on anything other than a smart phone through the eyepiece, and the mount is unsuitable for anything other than very basic imaging.

But as a visual use scope on what looks like a versatile mount it's worth considering.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
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Re: Non-collimateable primary mirror?

Postby Aratus » Thu Aug 23, 2018 1:09 pm

Newbie Jimmy wrote:
My question though please is that in it's description it says "NOTE: The 150i telescope has a non-collimateable primary mirror"

Would someone be able to explain to me please what if any the pitfalls of this could be?
Thanks
Jimmy


A Newtonian telescope needs to have all its optical components lined up properly to give the brightest sharpest image. 'Collimation' is the process that does all that. It normaly involves 3 screws on the main mirror which you can adjust to bring the mirror to right angles with the tube. Different temperatures acting on the mirror mount, simply moving the telescope about, or knocking it can upset the collimation. From what I understand, Skywatcher have mounted the mirror in such a fashion that it will never move, whatever happens to it. Thus having lined it up at the factory, it no longer needs to be collimated.

If it is true, then there are no pitfalls. It can only be good news. (I have no reason to believe that it is not true.) If it is adjusted at the factory, sturdly held with materials that are not effected by temperature changes, then it should work fine. Time will tell.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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Re: Non-collimateable primary mirror?

Postby Newbie Jimmy » Thu Aug 23, 2018 8:24 pm

Gfamily2 wrote:Hi Jimmy
There's a discussion on the Cloudy Nights forum about this very telescope - with a video review.

Without having watched the video, or read all the comments, it seems as though the intention is that it is made such that primary collimation should not be necessary, but small primary mirror adjustments are possible.
The secondary can be collimated in the usual way.


Hi, thanks very much for your reply
The video is for the model pre Wi-Fi, but it has the same ability to 'slew back to target if moved.
This is done on the scope in the video by using the handheld GoTo , but I'm wondering how I would do this on a Wi-Fi enabled scope? Maybe from the Sky portal app do you think?

The scope in the video with the handheld Go To is no longer available to buy as new as far as I can tell, as it has been replaced with the wi-Fi version :cry:
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Re: Non-collimateable primary mirror?

Postby Newbie Jimmy » Thu Aug 23, 2018 8:25 pm

Aratus wrote:
'Collimation' is the process that does all that. It normaly involves 3 screws on the main mirror which you can adjust to bring the mirror to right angles with the tube. Different temperatures acting on the mirror mount, simply moving the telescope about, or knocking it can upset the collimation. From what I understand, Skywatcher have mounted the mirror in such a fashion that it will never move, whatever happens to it. Thus having lined it up at the factory, it no longer needs to be collimated.


Thnakyou for explaining this - I now understand :)
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Re: Non-collimateable primary mirror?

Postby Newbie Jimmy » Thu Aug 23, 2018 9:00 pm

I have been thinking about this scope and am not sure if the Wi-Fi aspect really appeals. I imagine I'll have to look at my bright phone or tablet in a dark field which will cause eye glare. Plus I'll be relying on phone/tablet battery life too.

I am unable to find online a version of the non Wi-Fi Sky-Watcher Star Discovery 150p currently for sale as new as i think it's been discontinued and replaced by this Wi-Fi version.
However, i have managed to find an Orion Starseeker IV 150p telescope that looks almost identical? (this thread wont allow me to post the link to Amazon)
Is this scope the same do you think as the previous Sky-watcher version?
Jimmy
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Re: Non-collimateable primary mirror?

Postby Gfamily2 » Fri Aug 24, 2018 1:19 am

Newbie Jimmy wrote:I have been thinking about this scope and am not sure if the Wi-Fi aspect really appeals. I imagine I'll have to look at my bright phone or tablet in a dark field which will cause eye glare. Plus I'll be relying on phone/tablet battery life too.

I am unable to find online a version of the non Wi-Fi Sky-Watcher Star Discovery 150p currently for sale as new as i think it's been discontinued and replaced by this Wi-Fi version.
However, i have managed to find an Orion Starseeker IV 150p telescope that looks almost identical? (this thread wont allow me to post the link to Amazon)
Is this scope the same do you think as the previous Sky-watcher version?
Jimmy

It certainly looks very similar (the OTA looks the same, and the handset is the same shape and appearance as the v4 SW Synscan handset at least), and they all seem to come from the same factory in China. However, it has to be said that the Orion price is quite a bit higher, but for a 150mm Newt on what seems a reasonable mount with relatively high 'usability', it's not bad

It's interesting that the blurb on the astroshop.eu site for the Orion says that it's good for astrophotography, given the comment I made in my earlier post.
Normally Newtonians are not great for this, because the primary image falls inside the focuser, so you can't get it on the dSLR sensor. If you're interested in imaging, I would strongly advise you to to get assurance before buying that they can be used with dSLRs.

Oh, and the ability to link is supposedly dependent on how many posts you've made, not many more and you'll be able to link - away
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
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Re: Non-collimateable primary mirror?

Postby Gfamily2 » Fri Aug 24, 2018 2:00 am

Just found this...
https://www.365astronomy.com/SkyWatcher ... scope.html

Get in there quick if you're interested!
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
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Re: Non-collimateable primary mirror?

Postby Aratus » Fri Aug 24, 2018 11:30 pm

vega1972 wrote:
Therefore I can't see why a Newtonian telescope can't be made to keep a decent image throughout its lifetime. Or is this simplistic?


New materials and manufacturing techniques could make it possible. It might simply be that people have always accepted that Newtonians need to be collimated as a universal fact, and have therefore never seriously tried to overcome the problem. Perhaps the addition of collimating screws and their moveable mounts just makes the design more unstable, and is therefore has been a self fulfilling prophecy all these years. The jury is out on this one, and it will be interesting to see the 'verdict'.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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