APT new behaviour on change of filter focuser moves right out then back in

[g__day]

I don't know how I manged to confuse APT so badly (I swapped its assigned Camera and focuser to let it auto focus my colour camera and Moonlight focuser. Then I reverted everything back to the mono ZWO camera, filter wheel and focuser.

Now there is this weird behaviour during a filter change (with a relative offset of say 20 - 90 from the refernce Luminance frame). It had to move from 4097 to 4047 when the imaging plan changed to Red - but it didt that by moving out to around 5997 (which must be near its limit) then comming all the way back to 4047!?!

I even noticed this on a best of two runs auto focus - and some times it tries to send the focuser past its limits and kills the imaging plan as the focuser can't get to wherever in limbo it is trying to send it!

Anyone got an idea of why it is moving out so incredibly far - and more importantly how to tell it to stop this behaviour!

[g__day]

I may have been able to solve my own problem - will share for all - and not sure how presumably switching focuser triggered this.

I found in Settings -> Scope and Focuser -> Final Move Inwards Steps was set to a mind boggling 1500 (wonder if this was the side effect of adjusting back focus when I added a missing 22mm extension tube that was required to have a industry standard 55mm seperation from Imaging CCD to field flattener. I had used the Moonlights focuser manually two button controller to move the focuser a long way to its default position - but this focuser is normally connected to SGP with the colour camera - not APT.

When I changed over cameras and focuser I wonder if APT saw the massive focus adjustment and somehow recorded this in the Final move stepp - as it seems and very high value and was likely hitting the end of the focus run on the ZWO focuser!

So anyway I set this value down to 150 and applied it - disconnected and reconnected the focuser and with no imaging plan running just told the filter wheel to move through all its filters one at a time. Each time the focuser position changed correctly for the filter offset - with no more wild trips out to the end of the focus position!

So doing a final check now - and it seems to be good so far!

[Drac0]

Hi Matthew,

Yes, you found the cause with the final inwards move, though it seems you have "reverse direction" selected in the driver - the focuser tube will actually be further out on the red than the lum? But I recommend putting the inward move back on to a large setting as it eliminates any backlash issues you may have when switching between filters, which can cause focus to be well off. Note that this setting ONLY has an effect with an outward move of the focuser tube, inwards move will only be the specified number of steps.

EDIT: How many steps is your focuser capable of from the calibration? Saying 5997 must be "near its limit" seems a bit low to me. My focuser only has a very small travel distance, 48mm I think, and the focuser tops out at 17,000 steps. My friends ED80 has much longer travel and tops out at 35,000!

Cheers,
Mark

[g__day]

The manual only says 5760 steps for the ZWO electronic focuser. I wonder what I will have to do when I remove some tube extensions to set correct back focus?

What focuser are you using Mark?

[Drac0]

I'm using a ZWO EAF. Did you calibrate it fully when you installed it? When the focuser connects to APT check the log window where it will tell you the max steps reported by the EAF. If it is a very low number try calibrating it again & see what you get.

Cheers,
Mark

[g__day]

Hi Mark,


I new you can calibrate ZWO filter wheels - I never knew you could calibrate focusers too - will look this up! I purchased this second hand as a whole unit from IIS - so I never researched the focuser itself.

Learning more and more every day!

Matthew

[oska]

That's steps per per revolution, not the total steps. Total will be some big number. Eg with an SCT and 25 turns of the focus knob x 5760 = 144000 steps total

[g__day]

That makes a lot more sense. I was playing with the back focus between the field flattener and imaging camera - I went out as far as 120mm then back in to 55mm (much better). The camera went in to about 500 - scope about 4mm extended from the OTA out to around 17,400. So it certainly has excellent range.

I have had APT fail on one or two times during a change from Luminance to red filter - that triggered a small offset change - and the motor makes a whirring sound but nothing moved. I presume as the didn't reach its prescribed offset the imaging plan just halted with camera saying it's busy - but not saying hey I have been blocked for 20 minutes waiting for the focuser move to finish! I went out to the astro lab to check it when I noticed this - a turning he motor off and on in APT sorted it. I then did a series of filter changes and the focuser got th eoffset right each time.

So no idea what went wrong there - it had a bit of weight to lift as the OTA was pointing almost straight up. But when I disconnect and restarted the imaging run it then ran fine for hours.

Reckon APT should have a check and a loud / visible warning for a focuser failing to change position which then blocks a run - and or an option to select an automated disconnect focuser, wait 5 seconds and reconnect and see if the issue clears!

[xelasnave]

Things only start to go right Matthew after you have pulled all your hair out.

Each week I find I start with an insurmountable problem but after a week I solve it but a new one appears.

But do you learn patience as it seems to be key to solving all problems.

Great to see you hanging in there.

Alex