8" Dob - Focuser broken or normal?

[1kmodem]

I bought a 2nd hand 8" bintel dob and new to telescopes so I am not sure whether the focuser is broken or this is how they work...

When the scope is upright the focuser knobs move the EP part in and out like a camera focuser, but when viewing on say a 45 degree angle it just falls in and I have to manually pull it out to where I want it, then lock them in with the 2 screws.

I've tried tightening 1 screw and turning the focuser but its locked.

Here are some pictures of my scope inside and outside.
pic #1 - inside the scope
pic #2 -1. is the focuser knobs 2. is the locking knobs
pic #3 same as #2 without flash

Any help is much appreciated.

168758

168759

168760

[Marios]

If your tension screws wont stop the focuser from sliding down under gravity you have a problem. Take it down to Bintel in Melbourne for a look over it wont cost you anything.

[erick]

Some years ago I wrote:

The GSO Crayford has two finger operated screws under the body - the knurled screws. The one closest the body of the telescope is a lock. When you screw that in tight, the draw tube is locked and the adjustment wheel just spins. Loosen that off - you don't really need to worry about it (*). Just make sure it doesn't fall out and get lost during transport. If you want, remove it entirely and put it away somewhere.

The screw closest to the eyepiece sets the force with which the drive mechanism contacts the draw tube. Too loose and the drawtube slips under its own weight. That sounds like what is happening to you. Just keep tightening it up to reach the minimum tightness at which the draw tube doesn't slip under its weight. Of course, with different weight eyepieces in the focusser, you may have to adjust this tension. The objective is not to have it too tight - puts undue pressure on the various bearings contacting the drawtube. It can also change its behaviour with temperature so you might need to adjust it as the temperature falls.

(* update - this applies for visual. If you were putting a camera or video cam in, you may wish to lock it at focus.)

Does this help?

The thread is:

http://www.iceinspace.com.au/forum/showthread.php?t=36706

Cheers, Eric

[1kmodem]

oh, its not collapsing when tightened.

Thanks Erick, exactly what I was after, I did try minimal contact on the locking knobs, maybe I just have to play around it with more. Only my first real attempt tonight, after the other night failed...collimated and ready to go then Clouds!