Collimation help please

[Celeste]

Hi guys,

 

Long time no see, but things haven't been too great around here ATM. The lovely Graham is sorting my HEQ5 for me (thanks so much) So now my attention is on my scope. One of my sons mates was twiddling the screws on the spider vane, I didn't think much of it, but it seems when I last used the scope something must have been moved. I have tried using my laser collimator but it doesn't seem to want to center on the dot. Normally, I can get it spot on in the middle, but not now I have god awful shaped stars when I try to image, with weird shaped diffraction spikes, urgh. Possible bent vanes, or simply out of focus? (I used bahtinov mask) I found Astro baby's guide, which is easy for me to understand but she says that some scopes have the vanes on an offset, my scope is a Skywatcher 150P-DS and I have no clue if that scope is offset or not....how can I find out? I have measured the vanes and they are off, only one way though. Do I center it or not? Other than that, I have some white and coloured card to see if the mirror is a circle (knowing my bad luck it won't be!) and then I can go from there. 

Sorry seems I am rambling, and hopefully it's not going to be too hard to fix. If the vane is bent though apparently it's not worth sorting...how can I tell? they *look* ok?

[Daz Type-R]

Hi Nicky, sorry things have not been too good for you, hopefully they will improve soon.

 

First off I would give your sons mate a clip round the ear for mucking about with things he shouldn't

 

Secondly, the offset or not to offset is a tough one, which as far as I understand it, is down to choice.

 

if you use a sight tube (like a Cheshire) to collimate, then you automatically set the secondary to be either offset or not, as that presents the full face of the secondary to the primary and ultimately to the focuser.

 

But reading your post above, you have been using a laser, so to get somewhere in the general ball park of good collimation, I would start by making all the spider veins an equal length, then follow the guide you have been using.  That should sort it for you or at least, get you very close.

 

If you are still having issues, let us know and we will see what we can do.

 

HTH.

Edited May 3, 2016 by Daz Type-R

[Doc]

The offset is built into the secondary, you do not need to put it there.

 

You need to make all the spider vanes the same length so adjust the knobs on the outside of the tube until all are equal.

 

Then collimate your secondary using your laser until your red dot is in the centre.

 

Then do your primary as usual.

 

Hope things improve for you Nicky and do what Daz says, clip your son's mate around the ear hole 

[Brantuk]

If you'd like a hand with it Nicky, I'll happily take a look if you want to pop over my place with the OTA.

(pm me for address)

[Celeste]

Thanks Guys, I read it as some scopes vanes are offset themselves, not the secondary....makes sense now! I have tried to take a pic down the focus tube but I can't seem to keep my camera still enough lol. I did measure and centered the secondary, used the laser got the dot in the middle as best it will go (damn thing moves slightly) and set the primary too. I need a clear night now to retest, but as I said I did all that before but it was still out. Something seems amiss....I think my camera angle doesn't help but it looks kinda...not right to me. Maybe I need to get a cheshire

[Doc]

You can only see two mirror clips Nicky. If you cannot get the third one to appear by using the three collimation screws then you will need to centre the secondary by slightly undoing the centre screw and moving the secondary around until all three are visible and try to get the secondary looking as circular as you can and not oval shaped.   Only slightly undo the screw not fully and when turning it do not touch the front of the mirror only the sides of the mirror.

 

 

 

 

Edited May 4, 2016 by Doc

[Celeste]

Ok I have taken a few better images. What do I need to do to correct this? 1st is straight down the focus.....2nd has paper in so you can see the secondary....I can see from these it is off.

 

[Doc]

That's better you can see all three mirror clips. The secondary still looks more oval then circular, I think it needs tilting slightly. You can also tell this by looking at the second picture. The primary isn't sitting directly under the secondary.

[Celeste]

Thanks Doc...I will have a look at that later, gotta feed the rabble first. I haven't ever touched the tilt or really had to move much when collimating before.......so how come it's all out now? I think that kid did more than twist a screw. BTW he is only 8yo so I can't be too mad at him.

[Doc]

Have a look at a collimation guide I wrote a little while ago.

 

Collimation Guide

 

[+DaveJW]

Nice  collimation guide Mick.

[+Bino-viewer]

Thats a handy reference guide you've done there Mick.

Thanks for sharing.

 

Could it be 'pinned' somewhere....?

 

 

[Doc]

Will do Rob.

 

I've placed it here:

 

 

 

Edited May 5, 2016 by Daz Type-R
Link was incorrect

[Celeste]

Doc when I click the link in your reply it takes me to create new topic....Thanks so much though I will have a play with the secondary more today see what I can do

[Daz Type-R]

32 minutes ago, Celeste said:

Doc when I click the link in your reply it takes me to create new topic....Thanks so much though I will have a play with the secondary more today see what I can do

 

I have amended Micks post, the link should work now.

[Celeste]

Thanks, I found it  

[Doc]

Cheers Daz.