Skywatcher Heritage 130p secondary mirror mount - help?!

[chiefgibbon]

Hi,

I'm just getting started and have bought a Skywatcher Heritage 130p - it seems to offer a good way to start for not too much money, it fits in the limited space I have to store it and it's easy to take somewhere dark (not my back garden unfortunately ).

Having tried it out I was pretty dissapointed, the image is more magnified but much less clear or bright than my old binoculars. Having read the manual section on collimation (yes, I really did read the manual!) I decided just to check if it looked OK, and found that it does not at all - I can see only about 1/3 of the primary mirror in the secondary. On closer inspection the secondary mirror holder is way off centre (by about 1cm); the single arm holding it is way off perpendicular to the ring it screws into (don't know the proper name for this bit I'm afraid!).

I've contacted the online shop I got it from and am awaiting a reply - they're reputable so I'm not expecting any trouble. But I'd appreciate some advice.

In every other respect this scope is perfect for me, but this way of mounting the mirror looks like a design weekness to me. If it were a 3 or 4 spoke spider this wouldn't happen and would be fixable if it did. So if I get it replaced but at some point in the future it gets knocked out of alignment, the way it's designed it won't be correctible and the scope will then be useless? Am I wrong - can it be readjusted? I am assuming the secondary mirror mounting arm screws straight into a fixed thread so has no adjustment capability apart from a small amount along the arm axis? Where the spider mounts to the outside ring there is a lock nut, which I have not undone; but if I did would I find I could correct the angle to perpendicular so the mirror would be in the right place - is there something cleverer behind the lock nut than a fixed thread?

I've no problem with adjusting stuff from time to time - but I do have a problem with things that ought to be adjustable but are not . I know this is an inexpensive scope, but this looks to me like a compromise too far.

Any experience of this problem or thoughts? Any advice very much appreciated.

chiefgibbon

[AlexB67]

Hello, welcome to the forum

You are not alone. You are going to have to collimate it I am afraid. I agree it is a weakness in this scope. I was going on about recently in another post taking it on a holiday and had some concerns this parts comes undone rather easily in transport when the scope gets thrown around a bit. I am sure this is not supposed to happen, it is supposed to be collimated on delivery. Some say they had if off as well on delivery, but also heard others saying it was perfectly positioned upon delivery with no collimation needed.

You are going to need a few tools and tighten that strut, that's what I did, measure that the height of secondary is centred okay, though you do not have to be 100% accurate to begin with. The other slight weakness in this scope is the focuser design, no matter how accurate you collimate it, once you get it to a reasonable level, you'll find in time that part will be largest source of error anyway.

All that said and done, it is not as bad as it sounds, the scope can deliver great views. There are many levels in collimaton you can go to, but to begin with I'd start here

and follow that procedure with a collimation cap. Learning about collimation can be fun later with other tools, but you can get it close enough with a bit of time and patience in that scope using the above procedure. There are more detailed guides, astrobaby amongst one of the most commonly mentioned, but it may be a bit overwhelming at first to take in all that.

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

The above video will get you going.

With regard to the single arm/strut. I forgot now how I did it exactly. It can be adjusted and I got it right in the end, there are two parts to it, a threaded bit but also a screw nut, Use both to get it tightened, it's a bit of a fiddle I admit.

Another thing I would be inclined to do, assume the secondary tilt is okay, do not touch the centre screw and tilt screws to begin with straight away, as that bit is unlikely to have come undone in transport. Just concentrate on the strut and the centring. If you think the secondary is centred in place but the reflection of the primary in the secondary is still off, you'll need to go further and follow the procedures in that video.

Good luck.

[chiefgibbon]

Hi AlexB67,

Thanks for the links, certainly clearer than the manual! Doesn't look too difficult a procedure, I'll give it a go tomorrow night.

So is the nut on the strut a lock nut that I need to loosen then somehow rotate the strut itself - or some other arrangement? I assume I don't need to rotate the entire secondary mirror mount . I think my biggest worry is that the strut arrangement is going to become non-fixable before I've had my monies worth from the scope and am ready to buy (and find space for) a bigger one! I guess it would always be possible to drill through and fit a longer strut with a nut on both sides or something.

Hmm I was a bit surprised at how primitive the focuser is, especially compared to some of the nice old manual focus camera lenses I have, but I guess it will do the job...

[AlexB67]

From reading your post initially it was the strut I thought that had come undone. Without seeing the scope exactly and what you are faced with I am a little uncertain to give a definite answer as to what the problems are. It could be a combination of things, it is also possible that it is in fact the center screw of the secondary mirror assembly is not tight enough also, and that somehow the secondary rotated about that axis, ( instead of the strut axis I was thinking about, either would also cause the collimation to go off.

I would be inclined to take a bit of time, not yet touching anything too soon too quickly, absorb the video and try and determine what is off and try and deduce from there. It looks very nice and clear in those pictures in the video, but you may find in fact that when you actually see it is a bit confusing with all the reflections going on through a cap. Easy to be a little confused by it all at first, I certainly was a bit, but nothing to be scared about.

Also perhaps have a chat with the seller if you need to, I certainly did when I bought mine when I had the same troubles.

Read around about collimation a bit. If you happen to have a 2x barlow with a 1.5 lens at the end, you can unscrew that, stick the coli cap in the barlow, stick that in the focuser, screw the focuser all the way in so it is nice an snug without minimal slop. The bottom outline of the barrel of the barlow will give you a nice circular outline (so it is a kind of extension tube, it should have no lenses in it when removing that lens at the end, as is the case with mine when I do that), that helps to see the centring of the secondary, otherwise I found it quite hard.

The cap is not really designed for centering and adjusting the secondary anyway, though you can have a decent stab at it, especially with that barlow trick I found it helped a lot, very handy. Though you can have a fair go with the cap alone anyway.

I would not be worried, you'll get it up and running, it can be fixed up. I highly doubt it is a case of having to return it.

[chiefgibbon]

Sorry I should have posted a photo to start with, it's hard to describe clearly what the problem is in 3D especially given that I don't know the correct names for everything... hopefully the attached phot makes it slightly clearer what I'm talking about!

[Prador]

I dont know if its because of the angle but to me it looks like the strut holding the secondary mirror is bent. The strut seems to take a bend to the left immediately after locknut.

Is there any evidence on the strut that it has suffered an impact?

Can you put a 12" ruler (or any suitable straight edge) on the focuser so it is perfectly parallel along the optical axis of the focuser tube and see if the secondary strut is in line with it?

[chiefgibbon]

The secondary strut is not in line with the focuser, that's a good clear check thanks. However it doesn't look bent, I think it may have been inserted cross threaded. It is firm, it doesn't waggle about or anything. I'd be happy to undo the nut and see what happens but the manual doesn't say anything about this and I don't want to damage it.

The box arrived with a bit of a bash on the outside but nothing too bad, there's no sign of impact on the scope at all and the dust cap was on when it arrived so I don't think anything could have hit it in transit.

[AndyWB]

Yeah, I'd get it exchanged. I wouldn't worry about it in the future - that strut is pretty stiff and the secondary isn't that heavy. Certainly, mine hasn't always had the best treatment (I'm still learning!) and it is fine. I agree with you - I think it looks cross threaded to me.

I don't think it's a general problem, though - mine arrived from China with the collimation bang-on.

FWIW, I don't think my secondary is exactly central, but it is inline with the focuser, so that should be okay.

[AlexB67]

yeah agreed, looking at the pictures now it seems warped indeed. In that case return it I'd say. I expect you may be able to fix with a few tools, but there would be a risk of further damage so better to return.

[chiefgibbon]

Thanks all, I really appreciate your advice. I'll do as suggested and get it exchanged.

cg

[AlexB67]

Hope you have better joy with the next one. I guess you must be really disappointed . I would not let that put you off the scope, as far bang for buck goes in aperture and optics, it is a nice all-rounder for planets and DSOs and with a few extra eyepieces in time added to the collection it is hard to beat. Not that I own anything else, but it came in as the winner for the price for what I wanted and could afford at the time anyway

[chiefgibbon]

Yep I am dissapointed not to be able to use it until the replacement arrives but will be glad to get it sorted properly. Especially in view of nice clear skies recent evenings! I'll report back how I get on with the replacement!

[Torin]

Hi, I had a similar problem when I bought mine, you won’t lose anything by giving collimation a go and you'll learn how to do it without worrying you might break it. If collimation doesn’t work then take it back. Collimation worked for me though and I'm very happy with the scope. Give it a go and good luck!

[chiefgibbon]

Well, the seller was very helpful and sent a replacement without fuss, which I got the other day.  I'm pleased to report it looks spot on this time to my inexpert eye, I'm sure the collimation bug will get me some time soon but for now it looks fine.

Tried it out for the first time on Sunday (as you'd expect it's been pretty cloudy here since I got it  ), mainly looking at the moon, and was entranced at the deteil you can see.

So big thumbs up and thanks again to all for your advice.

[ChuckM66]

I received my Sky-Watcher 130p telescope a couple of days ago and it looks like my unit suffers from the same problem - Loose and bent strut. I'm working with the seller to maybe replace the damaged parts or possibly return the unit.

I am completely new to this, but while waiting for resolution with the seller, I tightened the strut and went through the collimation procedure in manual using a makeshift collimation eyepiece. I think I was successful in aligning the optics -- making significant adjustment to both secondary and primary mirrors.

Here are my questions:

Assuming I've got the optics aligned, the secondary mirror assembly still isn't centrally located in the ring because of the bent strut. Will this prevent this telescope from performing to its greatest potential?

I could try to straighten the strut to improve the secondary mirror central position. Should I even bother?

Any advice or insight would be appreciated.

Thanks,

Chuck M.

Georgia, USA

[andyb505]

I bought a Heritage 130p a few months ago and the strut on mine is not bent in any way and the secondary mirror is in a central position.

I think your should replace the strut or the scope. Having used mine quite a few times I don't think there is any need to strengthen the strut, assuming it is straight.

Andrew