C11 FeatherTouch Micro-focuser Upgrade - what have I done wrong?

[DRT]

I recently purchased a FT Micro-focuser upgrade for my C11. As instructed by the guidance on retailer's websites I went for the CPC version as my OTA has the three-pointed star configuration on the back of the mirror cell.

I followed the instructions, including some YouTube videos and it took only a few minutes.

I have just mounted the OTA to look at the Moon to test the focuser. After installation it was turned fully clockwise (as instructed), so the mirror was fully backed out. Turning the micro-focuser anti-clockwise to move the mirror up the cell results in a "clunk" every couple of turns and the mirror doesn't appear to be moving.

 

Any ideas?

[brantuk]

Uh oh! Sounds like the thread inside is overshooting the bar that moves the mirror. When I did my CPC FT upgrade I remember setting it to half way along the full throw before installing the focuser. I could be wrong of course but that's what it sounds like to me Derek.

[DRT]

16 minutes ago, brantuk said:

Uh oh! Sounds like the thread inside is overshooting the bar that moves the mirror. When I did my CPC FT upgrade I remember setting it to half way along the full throw before installing the focuser. I could be wrong of course but that's what it sounds like to me Derek.

Yikes!

I'm not even sure I know what that means?

Any suggestions on what I should do next? 

[brantuk]

Well if I'm right (or if I'd done that on my Sct) I would reverse the installation - put the old unit back on, and wind it to the middle. The mirror mountings sit on a threaded bar and it's moved up/down the tube when you turn the focuser.

I'll dig out my old instructions and double check for you Derek - I have to get them out soon cos I'm putting the original focuser back on mine - but I'm pretty sure it wasn't fitted at the end of the throw (fully backed out). I simply calculated the middle by counting turns form one end to the other then divide by two.

[Peter Drew]

I think Brantuk is right with his diagnosis, the threaded portion of the bar that advances the mirror carriage is a right hand thread, by rotating the microfocuser anticlockwise the male screwed component is not engaging. Sounds as though the instructions are back to front ???  

[DRT]

21 minutes ago, Peter Drew said:

I think Brantuk is right with his diagnosis, the threaded portion of the bar that advances the mirror carriage is a right hand thread, by rotating the microfocuser anticlockwise the male screwed component is not engaging. Sounds as though the instructions are back to front ???  

Or I read them upside down?

Thanks, guys, I will give this a go in the morning.

[DRT]

Fixed!!!

I couldn't wait until morning so decided to get the toolbox out and try to see what was wrong.

I removed the three screws that fix the focuser to the back of the OTA. I then tried to unscrew the focuser from the threaded rod and it came away in my hand. The brass nose of the focuser that contains the female thread that goes onto the threaded rod attached to the mirror cell had become unscrewed from the barrel of the focuser. I removed the brass nose from the rod, screwed it back onto the focuser and nipped it tight with an adjustable wrench. I then re-threaded the focuser onto the rod and screwed it on until the mounting plate was about 1cm away from the back of the OTA. I then pushed the focuser (and the mirror cell) in that final cm and re-fixed the three screws. 

It now works perfectly and I briefly achieved sharp focus on the Moon 

And, of course, it has now clouded over 

 

Thanks for your help guys

 

[Highburymark]

Glad you got it sorted Derek

[brantuk]

Glad you're sorted now Derek.

[Stu]

Nicely done Derek.

I'm interested to know how these work. Given that they still work the mirror, I'm guessing that image shift still happens, but is it just easier to deal with because of the micro focus?

[Racey]

Stu

On my EdgeHD the Feathertouch does nothing significant other than offer the precision of having the 10:1 gearing in addition to the usual 1:1 when adjusting focus  

The mirror shift is marginally improved particularly if one is careful about the direction the mirror is moved into focus. But the mirror locks on the EdgeHD are the only way I can address that with any chance of elimination...

Simon

27 minutes ago, Stu said:

Nicely done Derek.

I'm interested to know how these work. Given that they still work the mirror, I'm guessing that image shift still happens, but is it just easier to deal with because of the micro focus?

 

[Merlin66]

I fitted the micro focuser to my C9.25 and another to the C11 when I upgraded.

Great piece of gear that works very very well.

yes, it does "minimize " the mirror slop due to the enhanced bearing effect on the push/pull threaded rod on the mirror cell. 

(Just a note: the Celestron design for the mirror movement and attachment is completely different, and in my opinion based on using many Meade SCT much more robust)