Characterizing Filter Focus Points

[FarnhamMike]

@mmccomiskey

What does residual backlash look like on the AF curves?

A lop-eared appearance to the AF curve, see the screen-shot in this post, on the right-hand side.

Focusing problems

I increased the backlash as you advised and experiment with the step size. I went with 275. Everything worked well last night. Thank you. [IMG_9013]

@mmccomiskey

On these focus runs, I am continuously tracking a target, so don’t believe settle times factor into the equation?

You may be tracking but the movement of a heavy camera during the AF moves can cause a displacement which autoguiding (if running during AF) will endeavour to correct. But if you have a mount settle time specified this will be applied between AF exposures. You will see it in the SGP log.

@mmccomiskey

So, if I understand how things work correctly, returning to the proper focus position for a given filter at a given temperature should result in returning to the same step count, shouldn’t it?

No, If you have focus points defined in your filter definitions then if you change from say Lum to Red, SGP will calculate the relative movement between your Lum and Red definitions then move the focuser to the most recent Lum focus position plus/minus the delta. In my case I have the lowest deta (in my case Green) set at 0 then moving up to Ha at 46.