None collimateable primary mirrors?

[InterstellarTim]

Hello again all,

I’ve been rethinking my next scope choices and for the price of a previous setup I can get a larger aperture and GoTo Mount by moving away from refractors (shocker :))

ive since seen the StarWatcher Explorer 130PS AZ GTi and the SkyWatcher Star Discovery 150i WiFi as immediate options that jumped out at me and both improve on aperture of the 127L refractor I was looking at and are cheaper but both are noted as having non collimateable primary mirrors. What are the pros or cons of this? This seems like the best of both worlds to me as Collimation was a reason I was staying away from reflectors, am I missing something? Would the optics be poorer to that of a similar aperture reflector that did use collimateable primary mirrors for example? 

[johninderby]

Lack of collimation of the primary causes many to call it the work of the devil and unatural but in reality with a small scope doesn’t seem to be a problem. The optics are the same.

Edited June 30, 2020 by johninderby

[Chris]

Has John said, the optics are the same. I've used several factory fixed primary mirrors and they have all performed well arriving and remaining collimated

[Zermelo]

Hi,

you may be interested in a thread I kicked off recently, as I was in a similar position and ended up buying the 150i:
https://stargazerslounge.com/topic/356514-advice-please-choice-of-next-scope/

You can still adjust the secondary on the 150i. As it happens, when I did get hold of the scope it was slightly off collimation, but close enough not to need tinkering with the secondary, see: https://stargazerslounge.com/topic/357345-how-far-off-collimation-is-this/

As others have said, the mirror itself is the same, decent-quality parabolic that SW use in their more rexpensive models. And as you have identified yourself, if the primary doesn't actually need adjusting, then that's certainly a plus in my book. The 150 is a clever compromise to be sure; the mirror and the tripod are more than you might expect, while the focuser is probably the weakest feature; but for the price I paid, I'm happy so far. Be aware that instructions for the GoTo are a bit confusing, as those supplied are for the non-wifi version of the mount. There are many threads in these forums that are helpful with the various alignment procedures.

 

[ScouseSpaceCadet]

I've owned a 130PS and currently possess (a somewhat customised) 150i. The 130PS was used for many months. Primary collimation was fine on delivery and remained so. Secondary collimation was infrequent. Collimation of the secondary is a simple process taking a minute or so at most with either a collimation cap or cheshire.

The 150i tube I picked up cheap relatively recently and made some improvements, while keeping it significantly lighter than a standard 150p.  

The mirrors are the same quality as their "vanilla" Sky-Watcher counterparts.

The 150i after a tinker :

Edited July 1, 2020 by ScouseSpaceCadet

[Zermelo]

16 hours ago, ScouseSpaceCadet said:

I've owned a 130PS and currently possess (a somewhat customised) 150i. The 130PS was used for many months. Primary collimation was fine on delivery and remained so. Secondary collimation was infrequent. Collimation of the secondary is a simple process taking a minute or so at most with either a collimation cap or cheshire.

The 150i tube I picked up cheap relatively recently and made some improvements, while keeping it significantly lighter than a standard 150p.  

The mirrors are the same quality as their "vanilla" Sky-Watcher counterparts.

The 150i after a tinker :

Hi ScouseSpaceCadet , if you have time could you identify the kit you've added here? And do you have any idea how much weight it added?

[InterstellarTim]

Are they “bobs knobs” to replace the collimation screws?

i think I’ll be going for the SW Explorer 150p on an AZ4 Mount as this is regarded as a great grab n go setup and as the mantra goes ‘the best scope is the one that gets used the most’

[ScouseSpaceCadet]

Bear in mind the telescope was picked up very cheap as a customer return...

A Sky-Watcher 9x50 RACI finder scope I already had, with a black bracket sourced from an SGL member. 

 

Bob's Knobs cost too much. 35mm knurled thumbscrews replaced the collimation grub screws. Collimation is now tool free and less fiddly.

https://www.wdscomponents.com/en-gb/adjusting-screw-steel-metric-wds-605/c-385/p-495/v-5926

 

A TS-Optics 1.25" Crayford focuser. 4x m4 counter sunk screws bought separately. I used 16mm length but 10mm would probably do. 

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p7836_TS-Optics-1-25--Newton-Crayford-Okularauszug-aus-Metall-mit-T2-Anschluss.html

It's not a straight swap. A Dremmel, hand tapping tool & dust free towel were needed. The draw tube hole required widening, with four screw holes drilled and tapped. The towel was stuffed down the tube to protect the primary. The white dots below are just for illustration. They're not in the exact positions

 

A Sky-Watcher 21cm dovetail bar attached to Orion 182mm tube rings. (Sky-Watcher are cheaper but they're white)

https://www.harrisontelescopes.co.uk/acatalog/skywatcher-medium-dovetail-bar.html

https://www.amazon.co.uk/dp/B0000XMXZW?tag=duc08-21&linkCode=osi&th=1&psc=1

 

The screw holes left behind after removing the small integral dovetail were filled with plastic covers. They were slightly too small for the holes so were secured with a couple spots of UHU glue.

https://www.ebay.co.uk/itm/8mm-x-4mm-Hole-Plugs-Plastic-Blanking-Masking-Finishing-Inserts-Black/221912851461?hash=item33ab096405:g:WYYAAOSwNkJaKBJC

 

The weight with the 9x50 & Celestron XCel LX 25mm eyepiece is 5.2kg. With a standard plastic red dot finder and a 25mm Celestron XCel LX eyepiece, 4.75kg.

 

Edited July 2, 2020 by ScouseSpaceCadet

[Alfian]

@ScouseSpaceCadet that's a neat setup and a useful list of bits used. I remember doing a focuser transplant on my Tal1 which involved similar surgery. One of those careful "measure twice (or so) cut once" jobs that seemed a bit daunting at the time but not so in retrospect. As to a fixed primary, I have a 114p which I bought mainly for the Skywatcher Avant mount. Collimation hasn't been a problem at all which surprised me as its an F4.3 scope. Even after a  few modifications it only needed just a very minor tweak of the secondary. A surprisingly good little scope for the money.

[DaveS]

It's not just low-end 'scopes that have non collimateable primary mirrors.

The Primary mirror and corrector elements of my ODK12 are also factory set, and TBH I'm glad they are. Adjusting secondary collimation and spacing is quite enough, doing it for the primary, corrector elements and focuser would be a nightmare.

[Ian Sykes]

On 01/07/2020 at 20:53, Zermelo said:

Hi,

you may be interested in a thread I kicked off recently, as I was in a similar position and ended up buying the 150i:
https://stargazerslounge.com/topic/356514-advice-please-choice-of-next-scope/

You can still adjust the secondary on the 150i. As it happens, when I did get hold of the scope it was slightly off collimation, but close enough not to need tinkering with the secondary, see: https://stargazerslounge.com/topic/357345-how-far-off-collimation-is-this/

As others have said, the mirror itself is the same, decent-quality parabolic that SW use in their more rexpensive models. And as you have identified yourself, if the primary doesn't actually need adjusting, then that's certainly a plus in my book. The 150 is a clever compromise to be sure; the mirror and the tripod are more than you might expect, while the focuser is probably the weakest feature; but for the price I paid, I'm happy so far. Be aware that instructions for the GoTo are a bit confusing, as those supplied are for the non-wifi version of the mount. There are many threads in these forums that are helpful with the various alignment procedures.

 

The Skywatcher star Discovery 150 is one to avoid in my opinion. My experience with one that my brother bought has caused me to warn potential buyers. The plastic primary mirror housing that has NO collimation screws to adjust the mirror is the claim about no collimation required is verging on the ridiculous IMO. My brother's was out of collimation straight out of the box. This didn't inspire any confidence in their claims. I was asked by my brother to set up the Go to and telescope as soon as it arrived at his home. I was really [removed word] off that it needed collimating out of the box especially with no screws to do so. There's three side screws holding the mirror housing and with an hour's tinkering i managed to collimate it. This is a ridiculous situation and is caused by Skywatcher savings on weight and costs on the design and manufacture. It's said that it's for beginners so as not to need them having to collimate ever. This will result in the quality of their images deteriorating over use. And moving the scope around. Heaven forbid that it's dropped or knocked over/bumped etc. And a beginner having to try and collimate using the side screws then they will probably throw the towel in regarding Astronomy as a pastime.

Edited November 24, 2020 by Ian Sykes
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