I have a ZWO 2600mm, EAF, and Rokinon 135mm. As Ekos gets close to the perfect focus, it no longer detects any stars. It’s like the star it picked (auto star selected) focuses itself down to something too small to detect. I’ve tried changing (and tweaking but I don’t really know what I’m doing) the star detection algorithm to no avail. I think if I could force it to pick a bigger star (I’ve tried selecting “big stars”) it might work, but I have been unable to force it to do it. Any help is appreciated. Thanks. -Tim

Hi Tim,

It would be helpful if you could include some screenshots of your focus parameter setup as that might provide some clues as to why you're getting this issue.

You seem to be using a single star to focus on. Is there a reason for this? Have you tried multi-stars?

The star detection most people use is SEP With 1-Focus-Default. This generally works OK. If you use 5-BigSizedStars then the smaller stars are filtered out (which might be what you are seeing)?

The important parameters on the SEP profile are:
Min Size - should be 0 or just above 1 (to filter out hot pixels).
Cut Dimmest - shouldn't be above 10 or 20%

My suggestion would be:
1. Use SEP with 1-Focus-Default
2. Algorithm = Linear 1 Pass
3. CurveFit = Hyperbola
4. UseWeights = checked

5. Auto Select Star = checked
6. Full Field = checked
7. Annulus = 0% - 100% (at least initially)

If you still have problems post some screen shots and I'm sure we'll figure it out.

Problem solved! I get perfect focus in 7-ish frames. Thanks!