Finder problem

[robindurant]

I cant get my Dobsonian finder to point accurately at Stars

I set it up on a star. say at 45deg alt but when I slew to another say higher or in another direction its out of line. Go back and it still on line with the original

On my EQ6 mounted 80mm Scope I have no problem, spot on wherever I point it.

Is it something to do with whether its a AltAz or Equitorial

Can anyone help me.

Robin

[NGC 1502]

Hi Robin. Hmmm....cant see it having to do with the mount EQ or Alt-az. If the finder is aligned with the tube it should be ok whatever the mount.

Are you using the same finder on two scopes ? Maybe when it's mounted on the Dob, there is some slack in the finder shoe, so it shifts when the tube is at different positions ?

Hope you sort it, Ed.

[tyler_jrb]

I agree with ed it is most likely that it is not tightened or fit properly and moves when it is say at a higher position.

[themos]

could there be some flexure of the optical components in the Dob, primary or secondary?

[robindurant]

Hi Themos

You may have got the answer. All components on the Dob are firmly fixed so there is no slack, however, my Dob is a SW 250mm Flex Tube and the struts may be flexing at different angles.

What do you think

[themos]

I have to admit it's not very likely, but then again I've never heard of such a problem. The finder's magnification is tiny in comparison so the induced misalignment must be considerable.

[JamesF]

Wouldn't the eyepiece show signs of the problem if the struts were flexing?

In fact, could it be the ep/focusing tube/secondary mirror assemblies that are actually the problem rather than the finder?

James

[NGC 1502]

the struts may be flexing at different angles.

If the struts are flexing, then the collimation will shift, so you could check that at different tube elevations to either confirm or eliminate it as the problem.

Regards, Ed.

[themos]

Loose optics in the finder?