Help needed - Crayford focuser

[niko]

Guys,

picture the scene - no viewing for weeks and weeks, lug the 10" up to dark skies, too exhausted the first night to set up, second night aligned the finderscope beautifully, unpacked the as yet untried new (secondhand) pentax 7mm and all go for viewing Saturn and Orion nebula.

Then....focuser knob just turned round and round without moving the cradle in and out.

There's two screws on the side - I assume one is tension and one is locking. I tried hand tightening these without any change.

There doesn't appear to be any ratchet visible. Could something have dropped out, do I need to just tighten the screws more, am I just a dimwit????

Needless to say I'd spent the day painting, it was dark and cold and I just put my tail between my legs, packed up the scope and went inside for a beer.

thanks guys

niko

PS - Oh, it's a Bintel crayford

[erick (Eric)]

Nick, the bottom one (closest the tube) has to be completely loose. The top one is tightened to get the appropriate pressure of the adjustment mechanism on the tube for the weight of eyepiece.

The bottom one is the annoying one since when screwed in, the adjustment mechanism just spins freely - feels weird.

If that doesn't work, then you do have some other problem, but these are pretty simple mechanisms - not much to go wrong.

[astronut (John)]

Niko,
After trying the solutions suggested by Eric, if you don't have any success try this http://www.backyardvoyager.com/gsofocuser.html
It sounds like the screw holding the focuser wheel has either dropped out or loosened.
The link will show you how to service and fine tune your focuser.
I've tried it and it works very well.

John.

[niko]

thanks guys. It is werid because I tried the tension nut in all manner of positions - really loose to really tight without any change.

Guess I'll muster the courage to take it out of the OTA and have a fiddle along the lines of the link.


John - when you say "screw holding the focuser wheel" - do you mean on the focussing knob shaft?


thanks again

niko

[pjphilli (Peter)]

Hi Niko
I had a similar problem to yours when I first got my Meade ED APO 80mm refractor with a Crayford focuser. Even when the tension screw was fully in the focuser was so loose that the camera weight caused the barrel to move out. I asked my suppliers and Meade for an answer which was "return the scope". Great help! and the ONE page instruction book was no help either. I had a look around the scope and found that underneath the focusser were four small allen key screws. It turned out that these must be the "coarse" tensioning adjustment. I backed these off and after turning them in until they just touched I then screwed them in 1/8 of a turn on diagonally opposite screws until a nice range of tensioning could be achieved by the front screw. I don't know if your Crayford is similar but you may have a look around it and get lucky.
Cheers Peter

[Barrykgerdes]

Hi Guys

My first test of the crayford style focuser had the same problem. I worked it out in the end by trial and error. I was going to suggest that silly pastime of reading the manual. So after pouring through the manual I found a little about it with some pictures but I was still much as much in the dark. It certainly wasn't explained as simply Erick did.

Barry

[astronut (John)]

Originally Posted by niko

thanks guys. It is werid because I tried the tension nut in all manner of positions - really loose to really tight without any change.

Guess I'll muster the courage to take it out of the OTA and have a fiddle along the lines of the link.


John - when you say "screw holding the focuser wheel" - do you mean on the focussing knob shaft?


thanks again

niko

Yes!! Look on the edge of the focusing wheel, you'll notice a hole.
Buried deep inside is a set screw. This holds the wheel to the shaft.
If the screw is loose, it will let the wheel rotate without making any focus adjustments.

[niko]

thanks everyone for such accurate and quick responses - I'll have a look at what John suggested tonight and work backwards from there.

Again, many thanks to all

niko