Focuser shift?

[Pompey Monkey]

I have had the new scope running all night (OK, 2300-0300) for the last two nights. both mornings I found the subs to have degenerated into rather less-well focussed images than I hoped for. At first I thought I had my first telescope that suffered from severe focus drift due to temperature change...but the temperature only changed 3-4 degrees maximum over the course of the sessions.

Then I found out about the SubFrameSelector in PI and I managed to do some simple analysis:

Attached is a graph of the FWHMs of my subs from the last two nights. I got the initial focus better on the second night (another story!), but both show almost constant de-focusing drift over the course of the night.

I now suspect the focuser is slowly unwinding.

What do you guys think? Am I right?

 

[Pompey Monkey]

FWIW, it turned out to be focuser slip. I tightened the lock a bit tighter and it maintained focus for hours on end

[ollypenrice]

This is why I like my Heath Robinson tangent arm microfocuser, which you might remember. It puts the micro back into micro and prevents slippage. It is also a partiularly beautiful piece of fine engineering worthy of Cartier's the jewellers, as you an see (if not wearing your glasses...) Ahem.

On the other half of the tandem is a standard Tak microfocuser. It's rubbish, I tell you!

Olly

 

[Pompey Monkey]

Yep, I remember. Although I did not get a close look at it at the time. But your picture, as they say...

I'm just about to embark on the path of electronic focusing (diy, of course) in another small step towards full automation. Hopefully the stepper motor will keep things in check

[opticalpath]

1 hour ago, ollypenrice said:

This is why I like my Heath Robinson tangent arm microfocuser, which you might remember. It puts the micro back into micro and prevents slippage. It is also a partiularly beautiful piece of fine engineering worthy of Cartier's the jewellers, as you an see (if not wearing your glasses...) Ahem.

On the other half of the tandem is a standard Tak microfocuser. It's rubbish, I tell you!

Olly

 

Now that is my kind of DIY, Olly!  I bet it works a treat.  Function over form every time.

Adrian