Addendum - EAF Focuser

EAF Backslash Compensation

updated: 2024-05-30

Definition

Backslash is a type of idling after a change of direction and occurs in most gearboxes. The backslash is caused, for example, by slight gaps between the teeth of the two gears. In the event of a change of direction, the dead angle must first be overcome within the gearbox before the change of direction becomes effective.

There is also a small gearbox in the EAF motor drive as well in the focuser, both generating a tolerance-related backslash. 

Procedure

Step

Action

1

Move the focuser from the innermost position outward e.g. to step position 1000, so that the focuser is fully engaged

2

Mark the fine focus knob with a little dot

3

on the ASIAIR App goto EAF Settings and set the coarse steps to 200 and the fine steps to 10

4

Now move and count the focuser backwards in fine steps of 10 steps until you feel or see a movement of the fine focus knob. 

Example: EAF on TS-Optics 2.5" Rack and Pinion Focuser  (TSFOCR25): it took 27 fine steps until the focuser knob started moving

5

Multiply the number of fine steps by the number of steps per fine step to get the backslash
Example: EAF on TS-Optics 2.5" Rack and Pinion Focuser  (TSFOCR25): 27 * 10 = 270 steps until the focuser knob started moving
WARNING: The measured backslash is extreme and beyond the maximum of 255, there seems to be a problem somewhere in the focuser. 

6

Enter the backslash result n(in this case limited to the max. value of 255)  in to the ASIAIR app and you are done.

7

To determine even more precise backslash values, you can reduce the Fine Step value to 5 or less, for example, and then use this value.


Tutorial:  Calculate and Adjust Backlash on a ZWO EAF with the ASIAir (youtube.com)


Optical Configuration

Measured EAF Backslash

EAF on TSO 2.5" Rack & Pinion Focuser

 ~270 (max. allowed input in ASIAIR App is 255!)

EAF on M90 TS600 Rack + Pinion (TSO APO 90/600)

20

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