Skywatcher 130 PDS - Twisted Spider Vane ?

[Spaced Out]

Ok.... so I’ve pushed the primary forward by (I’m guessing) 8mm or so on the adjusters, a quick test on a bright star and the problem is still there.

The lock screws still have a bit of thread visible now (about 5mm), not sure if I should push it any further or if it would make much difference if I did ?

I’ve tried using an eyepiece on a bright star to see how that looks but I’m finding it really difficult to make the spikes out clearly. Probably my tired old eyes !

Is there an easy way to assess if the focuser is tilted somehow ?

[Spaced Out]

Right I’ve fumbled about with the primary and moved it down the tube to the point where it fell off one of the screws ! I managed to get this screw back in and tighten it up a little, so the mirror is now as far forward as I can safely get it, still I have the split spikes on the left side of the image !

At this point I’ve decided to take the nuclear option and strip the scope down. I will lop off a section of the focuser tube (i’ve marked on the tube where the focus point is for the DSLR & MPCC) and centre the focuser. While I am at it I shall clean the mirrors, flock the scope and get the blackboard paint out too.

Once rebuilt and collimated if I still have this issue I may just chuck it in the bin !

Any advice on this little project ? I’ve just watched the astronomyshed YT vid on mods which has explained the dismantle/re-assemble process quite well, it’s spurred me on a bit.

With regard to chopping the focusser tube, I’m only going to use this scope for imaging so I am happy to try it, how much should I be lopping off ? Is it still OK to have a bit protruding into the scope at the point of focus ?

[tooth_dr]

17 minutes ago, Spaced Out said:

Right I’ve fumbled about with the primary and moved it down the tube to the point where it fell off one of the screws ! I managed to get this screw back in and tighten it up a little, so the mirror is now as far forward as I can safely get it, still I have the split spikes on the left side of the image !

At this point I’ve decided to take the nuclear option and strip the scope down. I will lop off a section of the focuser tube (i’ve marked on the tube where the focus point is for the DSLR & MPCC) and centre the focuser. While I am at it I shall clean the mirrors, flock the scope and get the blackboard paint out too.

Once rebuilt and collimated if I still have this issue I may just chuck it in the bin !

Any advice on this little project ? I’ve just watched the astronomyshed YT vid on mods which has explained the dismantle/re-assemble process quite well, it’s spurred me on a bit.

With regard to chopping the focusser tube, I’m only going to use this scope for imaging so I am happy to try it, how much should I be lopping off ? Is it still OK to have a bit protruding into the scope at the point of focus ?

 

Frustrating Gary, but I think it'll work out ok for you.  I dont think it's too bad though and certainly good enough to master your imaging/processing on this scope.

[spillage]

I would strip it down flock it, put it back together and get everything right and then look at doing the focus tube after re-testing.

[Adam J]

Honestly I am now out of ideas, spikes are almost universally caused by protrusions into the light path. It could still be a twisted spider but you have checked that. 

So...strand of spider silk in the light path?

Perhaps a primary mirror clip? 

Its an interesting one, i doubt flocking will help. 

Hope that you get it resolved. 

 

[des anderson]

Sorry can`t  offer any advice, but the image is out of this world, excuses the pun. Des

[Spaced Out]

19 hours ago, Adam J said:

Honestly I am now out of ideas, spikes are almost universally caused by protrusions into the light path. It could still be a twisted spider but you have checked that. 

So...strand of spider silk in the light path?

Perhaps a primary mirror clip? 

Its an interesting one, i doubt flocking will help. 

Hope that you get it resolved. 

 

Hey don’t worry and thanks for the help !

My gut feeling is that it is probably focuser tube intrusion, it does stick quite a way in ! However I’m going to follow the advice here, I will centre the focuser and re-collimate first. If that doesn’t fix it then I’ll chop the focuser tube down.

I’m sure the flocking won’t resolve this issue but I was thinking of flocking/darkening the tube and mirror cleaning anyway so I figured why not do it all while I’m fiddling about with everything !  

23 hours ago, spillage said:

I would strip it down flock it, put it back together and get everything right and then look at doing the focus tube after re-testing.

Good advice, thanks !

[Ricochet]

1 hour ago, Spaced Out said:

I’m sure the flocking won’t resolve this issue but I was thinking of flocking/darkening the tube and mirror cleaning anyway so I figured why not do it all while I’m fiddling about with everything !  

While you're stripping and flocking make yourself a baffle to block the edge of your mirror. I mounted mine on top of the mirror clips but others have simply laid theirs on the mirror under the clips. Make sure there is a gap between the edge of the baffle and the inside of the tube. Here's a picture of my oversized proof of concept test baffle:

 

[Spaced Out]

Well, time for an update.  

I've tried a number of things to resolve this issue without success, I’ve rotated all of the spider vanes round by one to see if it was a single vane issue, I removed the coma corrector, rotated the camera around lots, removed and centred the focuser the best I could, turned the focuser upside down, hacksawed the focuser tube down to reduce intrusion and in the end totally stripped and rebuilt the scope 3 times.

The result...... my scope is now flocked and matt blacked, but I still have the problem ! On the plus side I think I have narrowed down the issue to some sort of focuser tilt ?

Turning the focuser upside down reversed the issue in the image so from that I assume it must be a focuser problem ? I rebuilt the scope 3 times and centred the focuser as carefully as possible each time, but the problem remains.

When collimation is as good as I can get it and I look through the collimation cap I can see the cap reflected but also the edge of the focuser tube at the top right side, suggesting the tube isn’t central ? When I look through without the collimation cap at the spider vanes, the vertical vanes are clearly a touch wider than the horizontal vanes which are a very fine line, if I move my head slightly to the left the vertical vanes narrow up nicely the same as the horizontal ones.

I’m a newby and still feeling my way around here so please correct me if I am wrong, but from this I am assuming that the focuser or focuser tube is tilted somehow ? Every time I have rebuilt the scope I have carefully centred the focuser the best I can using the 3 collimation screws. I am wondering if there are further tilt adjustments available for the focuser/focuser tube to line it up perfectly with the secondary ? There are few more allen screws on the bottom of the focuser but not sure what they all do tbh !

[Waldemar]

Well, at least there is one consolation:  By the time this issue is solved you can remove the L plate... you will be an expert at this!

[Ricochet]

Have you measured and marked the point directly opposite the focuser and then used a sight tube or laser to confirm the focuser is pointing at it? Also I would definitely use a cheshire/sight tube to centre the secondary mirror, a simple collimation cap is probably not accurate enough. 

Unfortunately, I do not have one of these focusers to know what the different screws are all for. 

Edited November 21, 2017 by Ricochet

[spillage]

3 hours ago, Spaced Out said:

Every time I have rebuilt the scope I have carefully centred the focuser the best I can using the 3 collimation screws. I am wondering if there are further tilt adjustments available for the focuser/focuser tube to line it up perfectly with the secondary ? There are few more allen screws on the bottom of the focuser but not sure what they all do tbh !

I have not got access to my 130 but my 150 has only 3 allen screw on the focuser. Have you worked out the orientation of the issue.

If you know which side of the focuser is giving the issue then:

I would be tempted to take all three grub screws out to the point that they do not make any adjustments so you are at point zero, undo the focuser and maybe using the plastic from a milk container pack one side out with a couple of slithers and see it it makes it better or worse. Try all four sides and if that make no difference then make adjustments on the grub screws.

Just one more thought, have you tried rotating the veins around??

spill.

 

 

[Spaced Out]

16 hours ago, Ricochet said:

Have you measured and marked the point directly opposite the focuser and then used a sight tube or laser to confirm the focuser is pointing at it? Also I would definitely use a cheshire/sight tube to centre the secondary mirror, a simple collimation cap is probably not accurate enough. 

Unfortunately, I do not have one of these focusers to know what the different screws are all for. 

Thanks for your reply.

Yes I measured and marked the point directly opposite the focuser and used a cheshire to centre it. Difficult as 2 of the collimation screws are hard/impossible to reach with the focuser tube in ! I used a collimation cap with a small central hole to centre the secondary because this was the advice I have read online, I'll try using the cheshire instead tho.

[Spaced Out]

15 hours ago, spillage said:

I have not got access to my 130 but my 150 has only 3 allen screw on the focuser. Have you worked out the orientation of the issue.

If you know which side of the focuser is giving the issue then:

I would be tempted to take all three grub screws out to the point that they do not make any adjustments so you are at point zero, undo the focuser and maybe using the plastic from a milk container pack one side out with a couple of slithers and see it it makes it better or worse. Try all four sides and if that make no difference then make adjustments on the grub screws.

Just one more thought, have you tried rotating the veins around??

spill.

 

 

Thanks, I'll give this a go.

Yes I rotated the spider vanes around but no change, it was only when I turned the focuser upside down that I saw the problem reverse itself. Also looking directly through the centre of the focuser at the spiders the vertical vanes definitely look a touch thicker than the horizontal ones, then when I move my head slightly to the left they narrow up and look fine, I'm guessing this all points to an off kilter focuser of sorts ? 

[Spaced Out]

16 hours ago, Waldemar said:

Well, at least there is one consolation:  By the time this issue is solved you can remove the L plate... you will be an expert at this!

Thanks, I'm feeling frustrated that my little problem persists but I've certainly learnt quite a bit so far going through this whole process. The things I used to be really scared to touch (like collimation, moving the secondary about etc..) don't seem scary any more. That's got to be a step in the right direction !

[Skipper Billy]

At least you now know what the problem is - fixing it should be easy !!

If you watch this series of excellent videos - all 9 parts ! (but they are quite short) you will have everything just perfect !

https://www.youtube.com/watch?v=zd-fl9SEYHw

Have fun!

 

[spillage]

I would say that if you move your eye towards the front/back then put a bit of packing at the front/back accordingly.

Did your measure the holes diameter for the focuser divided by 2 plus the measurement from the edge of the scope to the start of the hole. Just wondering if the focuser needs moving forwards? its been a while since I have stripped mine and cannot remember how much movement you have.

[Deorbiting]

Here is what my spider thing looks like I just bought my telescope I really don't what to do and If it affects my telescope too much?

[wimvb]

11 minutes ago, Deorbiting said:

Here is what my spider thing looks like I just bought my telescope I really don't what to do and If it affects my telescope too much?

Gently bend it back, then recollimate. Image a bright star to see how it affects the diffraction spikes.

[cuivenion]

On 04/11/2017 at 12:48, Ricochet said:

While you're stripping and flocking make yourself a baffle to block the edge of your mirror. I mounted mine on top of the mirror clips but others have simply laid theirs on the mirror under the clips. Make sure there is a gap between the edge of the baffle and the inside of the tube. Here's a picture of my oversized proof of concept test baffle:

 

Hi, I'm wondering what the purpose of this baffle is? Is there any before and after images showing it's effect?

[Ricochet]

7 hours ago, cuivenion said:

Hi, I'm wondering what the purpose of this baffle is? Is there any before and after images showing it's effect?

I am not an imager, but in the thread that convinced me to finally get round to it an imager posted the comparison below. This image was taken with a smaller baffle resting between the mirror clips and the mirror. I tried the larger, above mirror clip method to try to also redirect air from the fan behind my primary mirror over the face of the primary mirror to disrupt the boundary layer, I'm not sure that it has really made any difference in that regard. I can see the same reduction in diffraction visually on planets, and while on stars the effect is not so obvious, they are smaller and more point like. In general the background sky seems darker and I think that I can see fainter stars, although I have not made any measurements to confirm that.

My suspicion is that the diffraction is cause by the rough, unpolished bevel around the edge of the primary, but it could also be due to deviations from the ideal curve at the edge of the polished zone.

 

 

[cuivenion]

Thanks for that, useful info.

[Francesco Bisi]

Excuse me, could you tell me the distance of the spider's rays, are all four equally spaced?

Thanks

Edited October 28, 2019 by Francesco Bisi

[Cornelius Varley]

1 hour ago, Francesco Bisi said:

Posso chiedere un aiuto, le misure precise dei raggi dello spider del 130/650 pds

Posso chiedere aiuto, le misure precise del raggio del ragno di 130/650 pds

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[BrendanC]

I know this is an old thread but I may have a similar issue:

So, shout out to @Spaced Out if you're still around - did you ever resolve this, and if so, how?