Takahashi Fs102 has a cell screw loose

[Sunfish (Ray)]

The pull screws on my Tak come loose after a few years. I tighten them by hand to stop the rattle. Now the push screws have come loose and undone themselves. Should I make them just a tiny bit tighter. ?

I have tried to check centering of the focus tube and collimation but the process is inconclusive without a Tak collimation scope. A laser does not fit the Baader clamp eyepiece holder tightly enough to be reliable.

[iborg (Philip)]

Hi Ray


I expect someone will be able to give you a better answer, but, I suggest snugging the screws in firmly, after a putting a drop of locktite on the threads.


There are different 'strengths' of locktite, I suggest just a mild one, in case you want to loosen or remove the screws in the future.


Philip

[ab1963 (Andrew)]

Hi Ray
I wouldn’t even think of touching it until one of the Tak experts chime in and definitely don’t start glueing things down....

[Rainmaker (Matt)]

Until the Tak experts get here I suggest you snug the screw up tight . Then check the collimation by focusing on a bright star, preferably on a tracking mount. Use an eyepiece that gives you at least 200x and look at the shape of the first diffraction ring. If it is concentric with the Airy disc your collimation is ok. If not, you can adjust by the push pull screws.

Choose one set of push-pull as the reference set and do not adjust that pair, use the other two sets in very small increments and check the star shape to see if your adjustment made it better or worse.. .

[Sunfish (Ray)]

Thanks for those replies. I took it out for a star and image test and for the first time the CFN cloud prediction was totally wrong.

I tried the Merlin laser collimation reflection method but my laser is not powerful enough to provide a reflection without a mirror on the cell. So I will just have to wait until the skies clear or get a Cheshire.

[Sunfish (Ray)]

Still cloudy.

I changed the battery in the laser collimator and now I do get a reflection off the rear of the lense, a little off centre.

I have checked the laser collimation and it seems a few mm off over 6m in one plane . Less perhaps than can be adjusted out or the tolerance of any eyepiece holder. Not sure. Tiny fractions of a millimeter adjustment at that focal length.

The focus tube seems to be consistently 1mm off the centre of the lense cell and can not be adjusted out.

The question remains as to whether reflection from the back of the lense is an adequate collimation adjustment tool or simply an indicator that collimation may be required. Any thoughts?

[sharpiel]

Some time ago, a user on here collimated his own Takahashi toa130, a feat most of us fear to do. He did it with a laser collimator. I think his user name was tempestwizz, though I now can't find the thread. It was more than 12 months ago and I can't search back further than that. Perhaps you'll have more luck. He'd be a worthwhile resource to consult.

Edit: here is the link. Hope it helps you.

http://www.iceinspace.com.au/forum/s...d.php?t=164082

[multiweb (Marc)]

That's unfortunate. I wouldn't use a laser. A star test shoul tell you if it's correctly aligned. There is always a small error with how you secure a laser in a scope of any kind. Also don't use loctite. It's a one way street. Even the blue type is quite hard. A dab of nail varnish is enough to set and it's easy to dissolve with acetone.

[fsphotography (Frank)]

You could use a Cheshire collimating eyepiece.

[Sunfish (Ray)]

Thanks for the suggestions. All helpful.

The stars were out very briefly with some high cloud but enough for some star tests. The out of focus rings look good. Evenly spaced and concentric with a 12.5. With a 4mm ortho, the scintillation made the out of focus rings a little mushy but centered.

Perhaps I caught the loose screws before the pull screws moved and changed the cell position. Just hand turning the push screws up to the face seemed to have kept the cell in a reasonably correct position. The cell was set previously and before my time to match the focus tube.

I made a 50mm cheshire and the reflections seem centered , although it would take a collimation scope to fine tune those tiny circles.

Changing a spacer and going back to optimum backfocus also minimised the field tilt which seems to be somewhere in the train as it follows the OAG around.