Alt-Azi mount slipping when viewing high altitude objects

[mrdiki]

Hi, now the owner of a Skywatcher 4.75 " refractor.

The mount is an alt-azi type and altitude is controlled by what is called a "friction bolt", basically a nut on the end of a bolt holding the telescope in the up and down position.

I have the telescope well balanced but when viewing objects at a high altitude it starts to slip from position as inevitably the centre of balance of the scope changes. Tried various movements of the scope to re-balance but to no avail and the best way seems to be a good old fashioned spanner and tightening. This is not something that I want to do to often as I am worried about over tightening or even stripping the thread.

Does anyone else have this problem? How do you rectify it? Can you buy a lock mechanism that is simple to fir and similar to the azimuth lock?

Many thanks in advance for any advice.

Richard

[Stu]

Hi Richard,

I use this sort of mount a lot and this is a common problem. The issue is normally that the weight of the eyepiece stands away from the axis of rotation when pointing up at the zenith. Sliding the scope forward in the rings does not help with this at all as you've found.

The only solution that I've been able to find is to put some form of counterweight under the front of the scope, effectively below the line of the scope so that when at the zenith the balance is correct and you don't need to clamp the clutches down hard. I'll try to send a picture when I get the chance.

[John]

If it is the AZ-3 mount, here is a nice modification to address this issue:

http://www.spacegazer.com/index.asp?pageid=97490

[happy-kat]

^ I did that mod to my Az3, easy and cheap to do.

[RT65CB-SWL]

Hi Richard,

What alt-az mount are you using?

I have a Tele-Optic Giro and when the 'scope are balanced I don't get any slippage.

Only me... if I am on frosty, snowy, damp/wet grass!

[Stu]

I've used just about all the different variants of Giro mount, and they all suffer to a greater or lesser degree from imbalance when looking towards the zenith. It is worse with long, heavy eyepieces and when using a Barlow, and the bigger mounts handle it more easily than the smaller ones as their clutches tend to be more progressive. It's there in all of them though, just a fundamental balance problem which the mount can't compensate for.

This is my 'highly elegant' solution which I sometimes use. With clutches completely slack, it stays perfectly balanced even at the zenith. It is made from an ADM vixen clamp, part of an L bracket, and the counter weight and bar from a Star Adventurer mount!

[John]

Thats an interesting approach Stu

I agree that balance is quite delicate with the Giro type mounts.

[Stu]

Thats an interesting approach Stu

I agree that balance is quite delicate with the Giro type mounts.

It works very well John.

Do you think it might have been cloudy recently?