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Er, what just happened?

Spec-Chum

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Spec-Chum

Spec-Chum

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Last night I did my usual once over of my scope (operation "cloud cover").

Make sure none of the mirrors had fallen off...check ( always good to see! :D )

Make sure collimation OK...dead on still...check

Make sure tension of spider vanes is OK...all central and tight...check

Make sure spider vanes are straight...che...oh wait, one's a little twisted, so I untwisted it

Double checked collimation OK...What the?? My secondary is now further down the tube. It is almost like I've unscrewed the central bolt, but I check this and it was as tight as ever. All I did was untwist a spider vane, and now my secondary is not central in the focuser and my crosshair is well over to the left of the central donut. Everything is still tight!

Well, puzzled, I set out realigning the secondary again as I don't mind doing this, and actually have it down to fine art now, or so I thought. I now cannot get the secondary central under the focuser unless I completely screw the central bolt as far as it will go, and even then it's slightly too far right as looking down the focuser, it's like I need to tighten the central bolt more. I measure the spider vanes again, they're all central, but the secondary still won't go directly back under the focuser.

I collimated as best I could by getting the crosshair on the donut and having all the primary in view, and it's actually dead on again in that respect but it's bugging me that my secondary was central before I untwisted a spider vane and now it won't move far enough back???

What the heck happened?

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Paulus17

Paulus17

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So the twists in the vanes shouldn't be there then Russ??

They are only very slight and hardley noticeable,but i did wonder about em when i first tried collimating??

At the moment mine is spot on,or at least i think it is,with the twist in.

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Spec-Chum

Spec-Chum

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I think we may be on about different things mate, the twists I mean are when the vane is not exactly edge on to the primary. Is that what you mean?

It doesn't affect anything collimation wise (well shouldn't!), but I always make sure they're exactly edge on, to minimise light loss (if there even is any!)

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Paulus17

Paulus17

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I think we may be on about different things mate, the twists I mean are when the vane is not exactly edge on to the primary. Is that what you mean?

It doesn't affect anything collimation wise (well shouldn't!), but I always make sure they're exactly edge on, to minimise light loss (if there even is any!)

Yep thats what i'm on about.

Just checked mine and it's just the one that has a noticeable twist in,that i can see,so i will try and take it out later.

So more fun no doubt to come.

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Spec-Chum

Spec-Chum

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I'd certainly have thought that they should always be edge-on and not twisted. If I saw one twisted I'd assume it was not assembled correctly or damaged.

James

By twisted I mean very slight twisted, such as when you turn one of the thumbscrews and the vane twists slightly before the screw starts to turn. It really is nothing major and I really can't understand how that can affect the position of the secondary.

I'm half tempted to remove the secondary and completely start again. It's looking a little grubby anyway...but that's for a different thread lol

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jamespels

jamespels

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Spec-Chum, how did you untwist the spider vane? Usually, just undoing the tension nut very slightly will untwist the vane as the vane will move slightly before the nuts starts to turn. If you backed off the nut a way, the tension in the OTA may have changed, meaning that when you tightened it up again it was slightly off-centre even though you hadn't touched the other three. The first time I reassembled my spider / secondary (following fitting a new focuser), it took me ages to get it properly centred at the right tension - I had it nicely centred at one point but the end of the OTA was looking distinctly square...

Another option is that something was a little over-tight somewhere and "pinged" back, though I would expect something to be loose if that had happened.

J.

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umadog

umadog

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You want your spider vanes untwisted. They should present as small a profile as possible to the primary mirror. The larger the profile (due to twists) the larger the diffraction spikes will be.

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Spec-Chum

Spec-Chum

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Spec-Chum, how did you untwist the spider vane? Usually, just undoing the tension nut very slightly will untwist the vane as the vane will move slightly before the nuts starts to turn. If you backed off the nut a way, the tension in the OTA may have changed, meaning that when you tightened it up again it was slightly off-centre even though you hadn't touched the other three. The first time I reassembled my spider / secondary (following fitting a new focuser), it took me ages to get it properly centred at the right tension - I had it nicely centred at one point but the end of the OTA was looking distinctly square...

Another option is that something was a little over-tight somewhere and "pinged" back, though I would expect something to be loose if that had happened.

J.

I just grabbed and untwisted the actual vane, didn't touch any of the bolts. I also think something "pinged" also, but I didn't hear or notice anything and it was all tight again afterwards. 1 theory I have was one the bolts was tightening against the OTA and me untwisting the vane made it central to it's screw hole again, so it fell forward a couple of mm.

Whatever has happened is still there as I couldn't get the secondary central again after it happened, so I'm fairly sure it's a spider vane issue. I'm just not sure how or what yet...

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umadog

umadog

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You may never figure out what happened. :( The best thing to do is to re-align and make sure everything is fairly tight (don't go crazy). If that's the case, it really shouldn't move like that again.

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Spec-Chum

Spec-Chum

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Speccy, I'm sure you have a gremlin in your scope!

I reckon your Mrs is tweaking bits Baader she enjoys the peace and quite when your putting it right :D

You know you talk about telescopes too much when 'bet' autocorrects to 'baader' haha

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