Strange Focuser/Autofocus Problem

Sequence Generator Auto Focus
1

I’m having a bewildering issue with autofocus and am hoping someone has some ideas as to what could be happening. My scope is a CFF135 with a Feathertouch FTF3215 and Starlight Instruments Handy Motor on it, controlled by an Optec FocusLynx controller. I’ve been using this for 2+ years without issue.

Recently I have started getting autofocus failures that are now happening more and more often. On taking a closer look, the autofocus images do not show stars as points but rather as little lines, in most cases 2-3 star widths long. This effect is most pronounced when the focuser returns to the focus point to take a validation image. The validation image shows lines instead of stars and the autofocus run fails because of it. So something somewhere is shifting. This happens while the scope is actively guiding or with guiding off.

I noticed that there was a little bit of binding in the focuser drawtube travel and so I took the focuser apart, cleaned and re-greased it. Now the focuser is buttery smooth yet firm. There is no lateral shift in the drawtube that I can detect. But unfortunately the problem still persists. I’m really at a loss to figure out what the problem is.

Any thoughts?

2

If you take a 5 second exposure while moving the focuser what do you get? Seems if everything is nice and tight you should only get a circle but if things are shifting you’ll get a line of increasing width.

Also seems odd that you’d have that much movement after the focuser reported it was done moving.

Jared

3

I’ll try that tonight Jared.
It is extremely odd to have that much movement after the focuser reports it is done moving and this is a recent development. It’s not a mount tracking issue either. I have a tandem setup and the other scope focuses just fine.

4

Tonight I took a 5s test image while racking out the focuser. As Jared suggested, I got a short line of increasing width.

I noticed that the motor was making a clicking noise while rotating, which seemed odd. So I took the motor off and it appeared like there were some internal parts that were “loose”. After a bit of trial and error I got everything in the motor snugged tight and put back on the focuser. So far tonight I’ve had several successful focus runs without issue. Fingers crossed!

1 Like