I know that some people have had good results with the use of the planetary imaging focus measurement tools, including getting autofocus to work reliably. However, that hasn't been the case for everyone, and I have struggled myself at times to get a working autofocus for planetary (or solar/lunar) imaging. I've been slowly trying to chip away at this problem recently, making improvements here and there to try to make things more reliable, with some success.
The last time we had some clear sky, since the seeing was only mediocre, I took the opportunity to capture some videos of Jupiter at various focuser positions - basically the sort of frames that would be analysed during an autofocus scan, but 500 frames at each position saved to SER file. With those SER files saved, I was able to go back and analyze them in lots of different ways - different focus tools, different settings, varying the number of frames to average from each file, etc, to see which gave a reliably strong focus curve and which gave noisy, unreliable ones.
To cut a long experiment short, these were the settings that worked best (in order, from most important to least)
* Use 'Contrast (Edge) Detection' focus measurements
* Set Image Processing to 'Bin 4x4'
* Set black level to between 10 and 25% (enough to ensure that all the black background round the planet is excluded)
* Ensure that 50+ frames are being measured at each position - use the 'Average Over' option at 1s or 2s for this (depends on frame rate)
* Set the 'Show' option in averaging to 'Average of best 25%'
* Set noise reduction to 1.0
That combination of settings was very successful in producing a good focus graph with a clear peak and minimal noise - so much so that I have now changed the defaults for the 'Contrast (Edge) Detection' tool to set the values given above, meaning that new users should automatically see the benefits of these optimized settings.
If you are an existing SharpCap user, but have never adjusted the settings in the 'Contrast (Edge) Detection' focus tool then you will also pick up these new defaults when you update to the latest version of SharpCap (4.1.13041 - uploading as I write this). If you *have* changed these settings then your preference changes will have been saved and SharpCap will keep using them - you would need to manually apply the settings shown above.
Here's a pair of graphs of the focus scores that would come out from my 'Jupiter Focus Scan' data - the left graph is the old defaults for this measurement tool and the right is the new defaults. You can see that while both give a best fit curve that is believeable, the 'new' options give a much smoother result with less deviation from the curve and also a much stronger signal.
- Screenshot 2025-01-20 152016.jpg (45.39 KiB) Viewed 4803 times
Robin