Equinox 80 focuser adjusting...?

[AndyUK]

I've had my Equinox 80 for quite some while, but the MN190 never let it on the mount... until about 6 weeks or so ago. Although I've used it a few hours since then, I've never been satisfied with the shape of the stars - They seemed fairly eager to leave the frame in one particular corner, and two of the others weren't 100% to my eye either, but the 4th corner seemed fine.

After suspecting a gamut of possible causes, I cut out a paper template today, marked the centre, and shone my Hotech laser collimator down it - The attached 2 frames are what I got (one is where I rotated the Hotech 180 degrees).

Now, I think this MAY be telling me two things:

1. The focuser isn't straight. Now, if that is the case, I've searched the net high and low to try and find out how to adjust the focuser without dismantling the entire thing - There's a number of screws on the bottom of the focuser, but which ones do what? (I REALLY don't want to b*gger it up and make it even worse!). (And would I be right in thinking that this level of misalignment would cause eggy stars in one corner?)

2. As both images aren't both 100% identical, would I be right in thinking that, perhaps, the Hotech has lost its collimation slightly as well (bearing in mind that this beam has only travelled the length of the Equinox 80?). Unfortunately I don't have a reliable way of testing this at home (I've heard a lathe is very useful!)

Anyone's help would be greatly appreciated...

[AndyUK]

Anyone...? Has nobody needed to adjust a stock Skywatcher Equinox focuser...?

[Merlin66]

Andy,

None of those screws!

You need to use the three screws which hold the focuser to the OTA...

Just loosen them slightly and tweak the focuser until the laser dot hits the target; then gently re-tighten then - check if OK - job done.

[AndyUK]

Ah - Thanks Merlin! I think I'd nearly deduced that myself... having tried adjusting a few of the potentially obvious ones this morning and none of them having ANY impact whatsoever! The laser's still attached to the OTA - I'll have a crack at this when I take my next tea break... Cheers!

[Magnum]

Hi Andy, my equinox 66 had the same problem, the cause was that the drawtube was not centred in the focuser, there was a bigger gap under the tube than at the top. I didn't take any photos so I will try and describe the fix with the aid of some other peoples photos.

On the 66 The focuser is not attached to the scope by the screws but infact by the large chrome locking ring I think the 80 is the same but im not 100%, just unlock it then keep unscrewing it until it separates.

The rest of the focuser is identical but just a bit smaller

Once you have the focuser of the scope you can start to disassemble it,

on the underside of the focuser, remove the chrome thumbscrew and loosen the tension adjustment screw in the middle and the 4 allen screws that surround it, next there is a small access hole next to the dual speed focuser wheel, turn the focuser until you see a small grub screw through the hole then use an allen key to loosen it a bit you can now pull on the OPPOSITE wheel and withdraw the focuser shaft. NEVER pull on the dual speed wheel or you will damage it.

The draw tube can now be taken out of the focuser.

Now remove the 2 allen screw from the top side of the focuser, this will release the curved bearing plate that can be seen in the photo. this is what the draw tube runs along with the 4 bearings.

To centre the tube what I had to do was pack out this plate slightly with a piece of coke can. Roughly cut out a square of coke can slightly bigger than required, then bend it round the out outer curve of the bearing plate then carefully cut it to the exact size of the plate its important that this be exact as inside of the focuser has a ridge witch means that the plate only rests on its front and rear edges. now just cut out 2 notches for the retaining screws to pass through, then put plate back into the scope with its new spacer sheet.

The bearings will now be slightly raised slightly and cause the draw tube to run perfectly in the centre of the focuser.

Now reassemble in reverse order, once all back together use the central grubscrew to adjust the tension of the focuser until operates smoothly without slipping, I never use the locking *** as it alway causes the tube to tilt a bit.

Sorry I didn't take any photos and apologies for my poor instructions, but if you get stuck send me progress pics and I will guide you through it.

Lee

[AndyUK]

Blimey - Thanks ever so much for this.... but perhaps I should have mentioned I find that even spelling DIY can be tricky somedays....?! That doesn't exactly look like something I'll be able to do this afternoon so I can take it out tonight!

I'm going to have to give this a serious read through quite a few times, but it looks as though I may be heading back to plan A here though - A moonlite (with its plethora of adjusting srews) is looking VERY attractive at the moment, even though it would cost £355... I do find it bizarre that there's no way to adjust the stock focuser without having to insert a bit of tin inside it though - How odd .

I think I'll get the MN190 back out and put the Equinox back in its case for the next few weeks until I can afford one, but thanks for all the info - Hopefully it will be useful for someone else with a similar issue

[Magnum]

Andy why not have a look first and check the centring of your focuser tube, you may be lucky and find its perfect already.

try and measure the gap between the focuser draw tube and the body of the focuser, it needs to be the same gap all the way round, you could use some card or even a toothpick to insert into the gap.

If the gap is even all the way round then its fine and I would leave alone.

Lee

[AndyUK]

Hi Lee - I did unscrew the large chrome focus locking ring (it has helluva long thread on it, doesn't it?!) and had a look down the focuser. I've no doubt that the focuser does need to be shimmed as you've described and it probably isn't actually that difficult (for someone who knows what they're doing!).

However, when I screwed it back on again, the dot did appear to have moved maybe a mil or two back towards the centre... but it's still a way out, and I obviously don't want to "force" the focuser tube down!

Your instructions make total sense though having looked down the focuser and at the dismantled focuser picture... (But I'm still bemused why SW didn't allow for some form of adjustment here, but I guess that's another conversation!). I think the next few sessions will be with the MN190 though, but the job doesn't actually sound as daunting as it initially looked...Maybe it will be doable after all (but only with a bit of peace and quiet!)

[Magnum]

How much off centre is the tube? mine would get worse as I did the tension screw up.

Although mine is now central and corner stars are even, I still suffer with the other problem which is focuser sag, no matter how tight I adjust mine, with the leverage of the flattener and camera, the tube will flex up and down with not a lot of force, which i believe is the cause of my differential flexure. If they had spaced the bearings further apart from front to rear, the whole focuser would be much more rigid.

Lee

[Merlin66]

Lee,

I had similar problems hanging a spectroscope/ camera(s) etc behind my SCT..

A separate support bar was the answer...

[AndyUK]

I've tightened up the tensioner a reasonable amount as, like you, I don't really want to be tightening up the focus lock screw underneath which might slightly shift the framing or, more importantly, the focus - Maybe that is shifting it out (I'll have another look sometime)

However, by the sounds of it, that moonlite is sounding even more like my best solution (as again, at least I'm then able to adjust it any which way I want...)

A separate support bar was the answer...

Wow - That's one helluva contraption you've got there...!

[ollypenrice]

Re the laser, you have everything you need to test it perfectly. No need for a lathe.

Take 2 pairs of big nails and knock 'em into a piece of flat timber so that each nail in the pair crosees its partner to form an X. The two X thingies need to be nearly as far apart as the cylindrical body of the laser is long. These are the vee blocks on which you will rotate the laser. Mathematics tells us that these are just as accurate as any vee blocks ever made, if not quite as robust or as elegant. Then you shine your laser at a distant wall. (OK you've spent all your cash on imaging gear but you still have a wall, right? No? Then use the neighbour's!) If the wall is a decent distance off you have a prodigiously accurate test bed.

Sarah had all sorts of fun with aligning her focusser. The three screws system of SW is.. let's be polite here...optimistic.

Olly

[Merlin66]

How many nights do you want to loose, fighting a sagging focuser??

(It looks bigger than it is - 30mm hollow aluminium section and a couple of angles)

[AndyUK]

Cheers Olly - That sounds like my sort of DIY - 4 nails, a block of wood and a hammer - I can do that ! (I still can't believe that focusers are sold without some form of adjustment though - Utter madness..!)

Merlin - Yes, quite.... None preferably! Those eggy stars, although extremely minor, are really quite off-putting... hence the MN190 having just been put on the mount (in hope that the forecast for tonight is correct ).

I think I'll have to give the moonlite some serious thought... ( or do I move to Plan C and consider a new OTA? (One with a firm, but adjustable, focuser of course!)

[swag72]

Sarah had all sorts of fun with aligning her focusser. The three screws system of SW is.. let's be polite here...optimistic.

Never really got it right if I'm honest, the small Atik chip just hides the evidence!!!

Good luck Andy, you know that a new OTA will only give you similar focuser issues. Seems to be the real weak part of the average scopes that are affordable.

[AndyUK]

Good luck Andy, you know that a new OTA will only give you similar focuser issues. Seems to be the real weak part of the average scopes that are affordable

Hmmmm... You're right - Logic prevails... Moonlite it is then...

[swag72]

I know that it sounds utter madness spending more money on a focuser than the scope is worth, I really do get that. But, as it stands at the minute, unless you are able to afford big bucks, you are not going to get an 80mm scope with a focuser than will give you utter confidence.

Well, that's my opinion!!

[MjrTom]

Thought I recognised one of the photos in this thread.

Not an imager par se but have had my fair share of misfortune with the focusser on the Equinox 80. I started a thread a while back on this topic.

http://stargazerslounge.com/discussions-scopes-whole-setups/142836-sw-equinox-80-focuser-problem.html

For what little imaging I get done at the moment I use a Moonlite focuser on this scope with the non focal reducing skywatcher field flattener.

[AndyUK]

Cheers guys - I'm now decided... I'm not going to waste any more effort (or precious nights) on trying to get this stock focuser sorted... only to find that I may then end up with focuser sag (assuming I can get everything together again!). I'll have to go and count the pennies in piggy bank...

[Merlin66]

That's OK...

But how are you going to ensure the new focuser is on-axis and square to the objective????

[ollypenrice]

That's OK...

But how are you going to ensure the new focuser is on-axis and square to the objective????

He's going to buy a Takahashi, TEC or Astro Physics! Or maybe an FLT98 with Feathertouch.:)

Olly

[Magnum]

Sara, Ian kings new ikharus 80 f7 has a better quality focuser and is only £295 but it uses fpl51 glass which the same as our Equinox66 but a step down from the Equinox80 which uses fpl53.

Though I have never had problems with colour fringing when imaging with mine, so I am seriously considering the Ikharus 80. I reckon it looks much more solid than the new ZS70

Lee

[AndyUK]

He's going to buy a Takahashi, TEC or Astro Physics! Or maybe an FLT98 with Feathertouch.:)

Oh how I wish! I would just LOVE a baby Tak (or even an adult one), but at 10x the cost I paid for my Equinox, I think my wife might have something to say about that, unless she could use it for the school run as well...

But how are you going to ensure the new focuser is on-axis and square to the objective

Maybe I'm being naive, but if I can ensure that the Hotech is collimated, then I was anticipating that I could simply use that with the moonlite adjusters to square it all off(?). If it's not quite that simple, then I guess I may be stuffed - I might have to take pot-luck with a new scope and keep returning it until I got one that was aligned! (I'm not sure which would be more frustrating though!)

[Merlin66]

Looking at your laser image, I think the focuser may have to be adjusted upwards...the suggested shim solution would move the focusing tube in the opposite direction?????

Here's an experiment to try:

Get a couple of bottles of water,about 2Kg, tie them together and hang them over the end of the focusing tube (extended to normal operating position) - What happens to the position of the laser spot???

[AndyUK]

Hi Merlin - I sort of tried something similar when I screwed the focuser back on again - With the laser connected if I gently pushed down on the laser at the back, then the dot became more central. So the adjustment required would be to bring the front of the focuser up (and obviously the rear down)