Shaky GSO Crayford focuser

I have just upgraded the R&P Focuser on my TS152/F6.5 telescope. Of course after this purchase it will be too cloudy for the next (insert number) weeks for me to test it out. However quickly looking at it shows a lot of movement between the focuser and the drawtube, especially when I tightening the securing screw. The movement is so great I cannot believe that this focuser could be usable in this condition, is there something I’m missing regarding using this focuser.

Any advice or insight would be most welcome.

Martin - can you give us more details on the focuser? A website perhaps?

And how does the movement increase when the securing screw is tightened down? That seems counter-intuitive...

Any lateral movement in a focuser is not a good sign but I'm not familiar with the design you are using I'm afraid...

Cheers
Dave

Hi Dave,
The Focuser is supplied by Telescope Services, I suspect it is a GSO focuser, this is the Web page.
www.telescope-service.com/ATM/focusers.html#REFok

If you look at the picture on the website there are two thumb screws on the bottom of the focuser the one nearest the eyepiece ( the top one in the photo) pushes the roller against the drawtube so it will move when the focusing knobs are turned. The lower thumbscrew (I assume) pushes against the drawtube to prevent it from moving when focus is achieved. It's the action of tightening this securing thumbscrew that move the drawtube laterally, once tigthened the drawtube is rock solid.

I must do i write up of how I did the upgrade soon - it involves hammers (well one hammer), I'm sure it'll make interesting reading. Before you mention it the hammer had nothing to do with the above issue :lol: .

Thanks for the help.

I'm not sure if the SCT version is the same as the Newtonian version - the newt version explains the following

There are two large thumbscrews . The upper thumbscrew locks the focuser.
The lower thumbscrew regulates the tension of the focuser - at the easiest setting the focuser moves ultra-smooth. At tighter settings you can use heavy accessories without sacrificing much of the incredible smoothness of motion.

Try increasing the tension using the lower thumbcsrew and see if that gets rid of the slop when tightening down the locking (upper) screw.

If you still see a lot of play (a millimeter or so), I'd have a chat with TS and see what they say.

Cheers

Dave

Hi Martin,
I had a similar problem with a cheapo focuser a year or so ago, when I tightened up the locking screw it did make the focuser solid but one thing I found was that when it was tightened the draw tube was no longer square witrh the optical axis, it was lowered and tilted, so in order the collimate the scope for the focuser, I had to de-collimate it, I dismantled it and found it to be unfixable this compromised the image quality.



I considered replacing the focuser with another, but decided to get a SCt adapter bracket and use a borg 2" helical focuser instead, The SCT adapter is very handy as I can put many SCT bits'n pieces on the back of the scope now.

The amazing thing about this is that the SCT adapter is not a commercial product, it was custom made by a guy in the US who had the exact same scope with the exact same problem, I made an extensive search of the web before I found this on astromart.com, what are the odds :shock: . I costed getting it made here, and was quoted over 100 euros. This is the astromart add.

www.astromart.com/classifieds/details.asp?classified_id=382995

Hi Dave (McD),
As you suggested tightening up on the friction thumbscrew eliminates any visible slop.

Now I have to wait for a starry night in order to check that the slop is actually gone and the collimation of the new focuser.

I'll let you know how things go.

Hi Dave (L),
Hopefully Dave McD's suggestion will work and it's a case of my using the focuser incorrectly rather than anything being wrong with it. Glad you were able to resolve your problem.