Max. backlash value for EAF

dark energy

Dear ZWO team,

my RASA 11" has this special type of "backlash", also known as mirror shift.
I haven't found out yet how exactly the autofocus routine works. I think the focus mechanics is moved in one direction, several shots are taken and a curve is calculated, where the min value represents the focus point.
To compensate the influence of the mirror shift it would be necessary to define a preferred "focus direction" because the mirror of the SCTs should always be "pushed" to the focus point (that means moved in direction of the sky).
As well a EAF backlash setting of at least 1,000 steps would be necessary (in my case) because it takes over 800 steps until the mirror shift stops. Could you please consider a solution for this?

Thank you

Markus

sebriviere

The AF sequence is always a jump up 150 steps, then it goes back down by steps of 30, calculating HFD on a center area of the capture (exposure set prior to AF sequence) then it compute the focus curve.
Once the focus point is estimated, a finer sequence is done, jumping back up about 70 so steps above estimated focus, then down by steps of 15, to fine tuned final focus.

This sequence is always in the same direction, and do not compute or use backlash value from focuser settings tab.
Backlash only used for manual touch focus tool.
So it should cover minor shifting, but for the range you are mentioning, might be worth moving on a belt/pulley to introduce a gear ratio, so your 800 steps fall below the 150 of the AF sequence...

But for your manual focus backlash, better set it with a bahtinov, when focus shift after direction change on EAF.

Be aware that AF sequence temperature trigger is only using full integer variation. If set for 1 deg, let's say EAF is @12.67, it will have to reach 11, and then goes below 11 (@10.99) to trigger the AF sequence.

See below log, you can find after an Autorun.

2020/11/05 21:56:55: Find Focus Star: detect and calculate star HFD 2.6 , EAF position 1258
2020/11/05 21:56:55: Find Focus Star: finding an appropriate star(1082,693) HFD 2.6 Brightness 454
2020/11/05 21:57:09: Find Focus Star: detect and calculate star HFD 7.7 , EAF position 1408
2020/11/05 21:57:09: Calculate V-Curve
2020/11/05 21:57:18: Calculate V-Curve: detect and calculate star HFD 8.7 , EAF position 1408
2020/11/05 21:57:27: Calculate V-Curve: detect and calculate star HFD 7.2 , EAF position 1378
2020/11/05 21:57:36: Calculate V-Curve: detect and calculate star HFD 5.8 , EAF position 1348
2020/11/05 21:57:46: Calculate V-Curve: detect and calculate star HFD 4.4 , EAF position 1318
2020/11/05 21:57:55: Calculate V-Curve: detect and calculate star HFD 2.9 , EAF position 1288
2020/11/05 21:58:05: Calculate V-Curve: detect and calculate star HFD 2.6 , EAF position 1258
2020/11/05 21:58:14: Calculate V-Curve: detect and calculate star HFD 3.3 , EAF position 1228
2020/11/05 21:58:23: Calculate V-Curve: detect and calculate star HFD 5.2 , EAF position 1198
2020/11/05 21:58:33: Calculate V-Curve: detect and calculate star HFD 6.9 , EAF position 1168
2020/11/05 21:58:42: Calculate V-Curve: detect and calculate star HFD 7.5 , EAF position 1138
2020/11/05 21:58:48: Find Focus Point
2020/11/05 21:58:56: Find Focus Point: detect and calculate star HFD 4.5 , EAF position 1326
2020/11/05 21:59:06: Find Focus Point: detect and calculate star HFD 4.4 , EAF position 1311
2020/11/05 21:59:15: Find Focus Point: detect and calculate star HFD 3.4 , EAF position 1296
2020/11/05 21:59:25: Find Focus Point: detect and calculate star HFD 2.9 , EAF position 1281
2020/11/05 21:59:25 [AutoFocus|End]: Auto focus succeeded