John replied to the topic 'Auto Focus failures' in the forum. 2 months ago

The software handles the backlash compensation. The exposure of backlash on the Mechanics tab is a convenience to avoid having to use the indi tab (both are kept in sync).

For L1P it works as follows:

Backlash: All mechanical devices with gears suffer from backlash. In a typical focuser there will be a dead zone where changing direction (e.g. from “in” to “out”) results in movement of the focuser by a few ticks, but no actual movement of the optical train.

The Linear 1 Pass algorithm (like the Linear algorithm) provides backlash compensation in the 2 places during an auto focus run when the focuser moves outwards:

The initial outward movement of Initial Step Size * Out Step Multiple at the start of the run.

When the inward pass is complete and Ekos has determined the best focus position and moves outward to it.

Linear 1 Pass will extend (by x ticks) the outward movement, and then, as a separate movement it will move inward by x ticks. So it always approaches the desired position in an inward direction.

There are 2 schemes that can be used:

Set Backlash to 0. Ekos will use a value of 5 * Initial Step Size.

Set Backlash > 0. EKOS will use this value in its backlash calculations. There will probably be instructions with your focuser for determining the value of Backlash. It is not necessary to set an exact value for either Linear or Linear 1 Pass to work correctly; all that is required is that the value set in Backlash is >= the actual backlash value. For example, if you measure backlash and get a value around 100, any value >=100 will work equally well. For example, set Backlash = 200.

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