I am having an odd problem with my Robofocus set up to do with the recorded position of the focuser. The autofocus function is working fine but what I am finding is that the step count position of the focuser does not return to its previous position from one imaging session to the next. For example, I may start an imaging session for the night with the focuser at a position count of 2100 at a temp of 600 (robo focus funky units). During the night the step count may drop to 2025 at a temp of 580 funky units. Now, you would expect that the next time out the position would return to 2100 if the temp is back to 600 but it doesn’t. It always starts off at the same position that it was in the previous night.(2025 in my example here). Every night I go out then the position count gets lower and lower until I have to reset the zero position. The physical focus point on the OTA is not changing much however (I drew a line on the draw tube so that I can see where it was changing).
Why are you expecting it to automatically go back to 2100? Are you using temperature compensation on your focuser (as this would be the only way I would expect it to automatically move based on temp).
SGP won’t move your focuser based on temp. We only use temp as a focus trigger and don’t store focus positions as a function as temperature.
Thanks Jared. I’m not using temperature compensation. I refocus every 30 or 60 minutes depending on conditions and always refocus on filter change. The issue that I see is difficult to explain so I will come at from another angle.
I would expect, for example, that the reading for the position of the focuser displayed by SGP would be consistent for a specific physical position of the focuser draw tube bit it isn’t. A reading of 2500 for example I would have thought would always correspond to the same physical position of the focuser draw tube. It doesn’t seem to though as each night the starting position count is smaller than the previous night even though the focuser draw tube is more or less in the same position. Over time the starting position noted in SGP at the commencement of the imaging session gets smaller and smaller.
I suspect that this may be an issue with the way that Robofocus is reporting the step count so I will be exploring that angle as well.
Ah I see what you’re after now. And yes, that makes sense that you should be close to the same focus point at the same template. Since it’s always getting smaller, the first place I would look would be slippage. This could be happening on the draw tube, drive gears, or even missed steps on the motor itself.
If you have a dial gauge you can setup your focuser to move in and out by a few hundred steps and see if it gets to the same locations on the dial gauge repeatedly. Also probably a good idea to test this with the gear moving against gravity. Like it would normally be on a mount.