SharpCap Forums

HI All
I installed a new EAF, been working with it for 3 nights now
with not a lot of success. I think I'm very close but need some
expert advice. Following is everything I can think of showing the SC folks.
Any feedback would really help.
Thanks Frank


SC Version 4.1.14254.0 - 4/20/2026
I haven't upgraded since everything I use has been working great.


Equipment:
ASI2600MC Pro
102ed Refractor with Reducer/FLattener
Zwo EAFn (just purchased so latest version)

SC Settings and Procedure

Focus Assistant / Multi-Star FWHM Measurement

Settings:

Suppress Hot Pixel checked on
Use Display Stretch checked on
Sensitivity 90
Mac Brightness 80
Noise Reduction 1.00

Options
Scan Step Size 100
Max step count 10
Samples to collect 3
Move to best focus position when scan complete checked on
Use smart scanning checked on
Prompt to update measurement area on refocus checked on

Exposure 4 seconds
Gain 300

Zwo focuser properties (right SC panel)
Step Size course 200 / fine 20
Start Position at 11060 after positioning tube using Coarse and Fine clicks.
This is where I had good focus and see plenty of stars in the display.

My process.
After getting a very good focus by eye, I clicked Course Negative 2 times, stepped back 400.
Next I Click Positive on Focus Scan to start the process.
I actually had a curve created 2 times, the first time it seemed to do some final processes
but I failed to catch if it actually repositioned the tube. (i believe this is what happens ?)
I tried a second time, this time it created a curve but just stopped.
I had the Smart Scanning off so maybe a mistake here ?

Hi,

the first thing to do is to check that you are moving far enough away from the initial rough focus point to get a robust focus curve. For instance suppose your rough focus gives an FWHM of 3 or so, you want to be moving far enough away to get an FWHM of 10 to 15 maybe before starting the scan, so that the curve is nice and deep and robust to a bit of fluctuation in the measurements. Exactly how far depends on the mechanics of your focuser, so maybe moving 400 is enough, or maybe it needs to be 800 or 1000 or whatever. You would then set up the step size/max step count so that

* the max step count is at least 9 or 10

* the result from multiplying together the step size and the max step count is a bit more than twice the distance you had to move to go from your rough focus (FWHM 3 in our example) to noticeably out of focus (FWHM 12) - this ensures the whole scan distance will be enough to go from out-of-focus through best focus and then out the other side a similar distance.

With these settings you should get a decent U shaped curve when you hit the 'Scan positive' button. Once you have about 3 or 4 points on each side of the minimum then SharpCap will highlight the bottom point of the 'U' as the point of best focus (those 3 or 4 points need to be noticeably worse focus than the bottom of the U to be sure that the difference isn't just randomness).

When the best focus position is highlighted and the scan is finished, you can press the 'Goto Best Focus' button to move the focuser to the calculated position (or you can tick the options checkbox to make this happen automatically when the scan succeeds).

The 'smart scanning' option makes two changes to how the scan works

* stops early if there is already enough data to work out a clear best focus position
* adds extra steps at the end if it looks like the scan is working but is still missing a few out-of-focus points on the end of the scan to give a good result

This can help speed up the process in the first case and sometimes rescue a scan that would otherwise stop too soon and fail in the second, but won't help if you start too close to best focus so that the 'U' curve isn't deep enough.

Hope this helps,

Robin

Thanks Robin.
I actually got it working last night. After some research and reading some SC posts, I made a few adjustments and it worked as expected. Since our summer temps drop rapidly here, I paused my livestack after about 2.5 hours and refocused, again, worked as expected. It actually adjusted focus about 10 steps from the original.
Thanks again for your response.
Frank