Backlash compensation at the start of my shot is missing my start point (or we are missing the end point)

Here's a revised version of your text with some proofreading and minor improvements for clarity:

Summary of the Issue:

You are most likely working at high magnification or with a probe lens where the front elements are far from the camera. In these types of shots, even minor backlash in the eMotimo ST4 can become more noticeable.

When you set a precise start point, where differences of 1/10th or even 1/100th of a degree matter, the issue arises when the rig returns to the start point and uses backlash compensation. Sometimes it aligns perfectly, but other times, it can be significantly off from where you initially set it.

The Quick Fix Technique to Achieve Precise Start and End Points:

To eliminate the impact of backlash when working with programmed shots, use the following technique.  First you need to understand and know the direction of your move from start to end.  If you are running a programmed shot where you start and then:

1. For pan-right and tilt-up shots:

   • Set your start point by moving your rig into position using pan-right and tilt-up.
   • Ensure that the last inputs from the remote, which move the rig, are pan-right and tilt-up.
   • If you overshoot your point, pan-left and tilt down slightly until you overshot your start point by a degree or two.
   • Slowly pan-right and tilt-up until you've precisely reached your start point, then lock it in.
   • Set the end point in the same manner.

2. For pan-left and tilt-up shots:

   • Set your start point by moving your rig into position using pan-left and tilt-up.
   • Ensure that the last inputs from the remote, which move the rig, are pan-left and tilt-up.
   • If you overshoot your point, pan-left and tilt down slightly until you overshot your start point by a degree or two.
   • Slowly pan-left and tilt-up until you've precisely reached your start point, then lock it in.
   • Set the end point in the same manner.

3. For pan-right and tilt-down shots:

   • Set your start point by moving your rig into position using pan-right and tilt-down.
   • Ensure that the last inputs from the remote, which move the rig, are pan-right and tilt-down.
   • If you overshoot your point, pan-left and tilt down slightly until you overshot your start point by a degree or two.
   • Slowly pan-right and tilt-down until you've precisely reached your start point, then lock it in.
   • Set the end point in the same manner.

4. For pan-left and tilt-down shots:

   • Set your start point by moving your rig into position using pan-left and tilt-down.
   • Ensure that the last inputs from the remote, which move the rig, are pan-left and tilt-down.
   • If you overshoot your point, pan-left and tilt down slightly until you overshot your start point by a degree or two.
   • Slowly pan-left and tilt-down until you've precisely reached your start point, then lock it in.
   • Set the end point in the same manner.

Explanation of what is happening:

eMotimo maintains positions and start points in internal registers as reported by the motor drivers. These registers store highly detailed information about where the rig should go.

In mechanical systems with gearing, such as ours, there is a small amount of backlash (space between gears) present. This backlash is designed and tested to be less than 0.3 degrees, usually even less, for both pan and tilt movements.

Backlash occurs when:

• The motors actually turn.
• The registers (stored values for position) change.
• However, the rig itself does not move.

During this backlash zone, which can be up to 0.3 degrees of pan input, there is a disconnect between where the rig is actually pointed and what the ST4 is storing in its internal registers.

By following the suggested technique and being mindful of how you set your points, you can effectively eliminate the effects of backlash, even when working with high focal length shots.