Weird "reverse direction" focus behaviour


#1

Hi,

So I have an SCT. When using autofocus, I want it to test the focus pushing against gravity, that means in the direction of increasing steps. The normal behaviour of the auto focus is to move increment the focus to (data_points/2 x step_size), and decrement back (data_points x step_size). Trouble is this is moving the mirror in the wrong direction for optimal results.

So - I checked the “reverse focuser direction” box, but this has a bizarre effect. My focus positions range from 0 to 57600. When the reverse option is used, SGP no longer reads the correct position from the focuser. To be specific, it achieves a reverse direction by manipulating the numbers. Eg when I tell SGP to set position 0, it actually commands the focuser to set 57600 (which is the max position). If I tell it to set 57600, it sets the position to zero. A position of 28800 works just fine !

Looking at this another way. If I’m at position 5000 and I tell it to increment the position by 10, it doesn’t set 5010 as I believe a reasonable person would expect, it sets the position to 4990.

What I believe the “reverse direction” control should do is change the effect of the In/Out buttons and the autofocus direction, not fake the positions of the focuser so that the positions no longer match the autofocuser display, and all other software I’ve tried.

So, the “reverse focus” direction control is useless to me, and unless there is a work-around, so is the SGP autofocus and by extension SGP. I have seen some old complaints about this in the forum, but apparently there has been no fix.

What would be more useful is if I could make the auto focus step size negative or just have a control to make autofocus work in the opposite direction… This would seem like a simple solution.

Rgds
Steve


#2

I have the same using a Seletek Armadillo focus controller.
The numbers in SGP are the opposite from the Seletek controller.
Not a big problem, as long as you are aware of it . . . . .
At least they both send the focuser in the same direction.
(I did have to reverse direction in the settings, but that depends of course how you have mounted the stepper motor. Left or right)


#3

Steve,

if your focuser driver (the ASCOM driver) also has a setting to “reverse focuser direction” you should activate that instead of the option in SGP. This would give you the behaviour you want.

If this is not possible, you should just ignore the display on the focuser handbox. It plays no role in the autofocus or in the workings of SGP.

Kind regards,
Horia


#4

Hi arie,
I can’t easily change the way the motor is mounted. My focuser is actually the MyFocuserPro2.
Cheers


#5

Hi Horia,
I’ll look into that option, but I don’t think I have it.
I guess if I only used SGP and didn’t have a display it wouldn’t be such a problem, but neither is the case. The SGP “reverse direction” looks like a cludge, and a much better option would be to allow auto focusing in each direction.
Thanks
Steve


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