Auto Focus vs Bahtinov Mask

I finally have autofocus settings for my newt astrograph that gives the desired V curve. But it’s a different position than where the mask says the focus is. Repeatably.

Notice the focuser position.

Now the autofocus.

I was running a sequence last night and want to see if my scope held it’s focus after a 5c temp drop. It hit that point at 4 am and the focus was the same. @29980

So who do I believe? Could there be a problem with my mask? Orion 8" astrograph. f3.9. ZWO EAF.


Auto focus is waaaaaaayyyyyyyy better than Bahtinov mask. No questions ask. Bahtinov mask is not as repeatable or accurate.

I used to think Bahitnov mask was the best thing until I tried auto focusing with SGP.

Your V-Curve looks fantastic. Are you getting bad looking stars using auto focus with SGP?


Thanks Peter.

What I’m getting is lower HFR with the mask setting. And when I cross check the autofocus back to the mask, the axis is not as aligned. It’s hard to see the size difference visually. The HFR for autofocus tends to be .2 to .3 higher. I’ll post the image of the mask cross check later when I get home.

I had originally thought that I was having this problem because I didn’t get a good curve. It was more of a J shape, not a V. But now I get repeatable V curve with the same results every time. The discrepancy has me curious.

If they’re not getting the same result this would tend to point to some backlash in your focuser. Essentially you’re pushing through it with the mask but auto focus will do a reverse move to get into position leaving the backlash intact. I’d try to add some backlash adjustment and see what the result is.


DING! DING! We have a winner.

Thank you Jared. I added some backlash comp and it’s hitting it solid now. Mask and autofocus agree with each other.


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