Collimation shift issue with portaball :(

[mbaddah]

I hope someone can help me with the following issue. It seems during collimation with my laser and barlow, when aligning the secondary mirror first with my laser collimator, the laser beam will stay in it's place no matter which way i move the scope.

However when it comes to adjusting the primary mirror with my laser and barlow, the returning circle beam seems to shift position as I move the scope around http://www.cloudynights.com/ubbthreads/images/graemlins/frown.gif

I've checked the trusses are tight on... I'm not sure if the primary mirror is actually moving around despite been bolted on tight?

Any help would be greatly appreciated, thank you.

[Robh]

Collimate your primary then fix it using the locking screws. Check your collimation again as the locking screws themselves may vary it. Now move your scope up and down. Does the collimation still change after you lock up the mirror?
I had a similar problem with my 12" Lightbridge. The primary mirror springs were so puny the collimation screws just didn't work properly. In fact, I used the locking screws as the primary collimators. The problem was solved by replacing the springs with heavier ones.
Refer to these recent threads ...
http://www.iceinspace.com.au/forum/showthread.php?t=59148
http://www.iceinspace.com.au/forum/showthread.php?t=58731

Regards, Rob

[mbaddah]

Thanks Rob for those links. Unfortunately the Portaball doesn't use the spring setup like the lightbridge. Had another look and realise the same thing was happening with trying to collimate the secondary mirror as well, i.e. when moving in the altitude motion, the laser dot will be aligned in the primary mirrors centre circle when at 45deg altitude, tilt it to the Zenith and the dot moves one way, to the horizon and it moves to the other.

The laser seems quite secure in the focuser and will only move if I force it to by hand. Perhaps it still could be the laser jiggling around ever so slightly?

[Robh]

Is there any slack in the focuser? Can you collimate the scope with the focuser wound right in?

Regards, Rob.

[bmitchell82]

Im not sure what a portaball is, but have you thought about the mirror cell? most commercial mirrors are held in place with a floating mirror cell. if the mirror is loose and not restrained properly then the mirror could well be slopping in the cell giving you this exact problem.

First though i would check your focuser for focuser slop. give it a bit of a shimmy around and see if it moves excessively.

[Waxing_Gibbous]

M,
Unhappily I have no experience with this great scope.
I can only say If you can't fix the problem, I'll take it off your hands for a reasonable fee!:P
Try the Mag1 website as the new owner is reputed to be helpful and I'm pretty sure there is a Portaball users group on Yahoo.




(Lucky Sod)
Peter

[Satchmo]

Thats the whole idea of the barlowed laser. Makes it insensitive to laser wobble when you are collimating the primary. Simply take the barlow lens off to collimate the secondary and put it on again to collimate the primary. If the little donut shadow returned to the collimator base is moving about as you move the scope then there is some mechanical flexure there in the system. If everything is tight I'd go to the manufacturer. Maybe it needs stiffer mrimary mirror springs though I'm sure there would be some kind of locking bolts somewhere.

Good luck.

[mbaddah]

I attempted to collimate it with the focuser wound right in and out and it produced the same result.



lol! How much is a "reasonable fee" :D Unfortunately I haven't had any responses from the owner despite sending numerous e-mails, not sure if it's going to his spam folder or not :P
I've put in a request to join the yahoo group, hopefully can get some help there.



That's exactly what's happening Mark and it was my initially concern :( I'll contact Mag 1 concerning it and see what they say.

Thanks for the help guys.

[mbaddah]

Well I finally managed to work out the issue I had with the collimation issue and rectify it :) After weeks of tearing my hair out, the issue was so simple to resolve I feel embarrassed
even mentioning it :ashamed:


I was browsing through the mag 1 website, and noticed the trusses were arranged a little differently from the way I had set them up. Sure enough, quick glance at my setup and I realised instantly what the problem was. I had combined the 2 trusses with each other that are neighbouring one another (:doh::screwy:) rather thancombining the trusses in a "V" shape (i.e. the truss further apart). (I hope that description was clear cause I nearly confused
myself :confused2: )


After setting up the trusses in the V shape manner, it felt instantly more stable than before. I put in the farlight laser collimator, screwed everything on tightly and turned it on. I then moved the portaball in all different directions and sure enough, the laser stayed put! Barlowed the laser, adjusted the primary mirror, moved the scope again and it didn't move :D

Here I was thinking of sending the whole scope overseas for Mag 1 to look at! I can go to sleep comfortably now Thanks everyone for your help :thumbsup::thanx: