I see--I do not have experience with longer focal lengths. You may be right about that. Can you up your gain as well (of course, don't clip too many stars, though).
Here's a recent sub of mine (240s blue filter 1x1 binning gain 75 bortle 5 skies) uploaded to astrometry.net for the Sunflower Galaxy: nova.astrometry.net/user_images/3492359#original (hasn't finished yet, as I write this).
This is the full resolution from the ASI1600mm pro and my refractor, and the pixel scale should be about 1.34 arcsec/pixel
I understand your argument against 2x2, I thought the same, but honestly a friend recommended it and I found he was right, it worked for me. Try it!
I think it's important to get a reasonable exposure for focus, hence the gain 200 and binning 2x2 (of course, I could use longer exposures, but that increases the time for AF, and this tradeoff seemed to work for my setup).
I focus in Ha and it works fine for me. I really think the key is getting a lot of stars to average the HFR over. Even if you can't get 70 like I do for the wide field, if you can get 20, you may find an improvement.
I was tempted originally to try and write a better star-detector/hfr-calculator, but then I realized Jasem had put in a scheme (SEP) that had been worked on for years by the pros, so I figured that was something I wasn't going to improve upon.
If you are using the Scheduler, and you image an area which has no, nearly no or actually fake stars, you need to change your workflow.
Add a first target as observation, where you know you can run a reliable focus. Enable the focus step, and add a short dummy capture sequence (you will trash its result). This will be your focus stage.
Then add your object as second target. Make sure you do not tick focus, and make sure the associated capture sequence does not trigger a refocus. Configure it so its total duration is shorter than the delay you want to between each refocus.
Then arrange your observation session to have focus, observation, focus, observation, etc. This makes your focus workflow independent. Just make sure your focus target is always visible during observation
You can use the same idea when unable to align on an object because of the lack of stars. Use a dummy intermediate job to approach and sync your mount, and untick align from your observation job.
HEQ5-Pro - Atik 314E - Orion ED80T - DMK21 on Orion 50mm
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I had the same thoughts as you, I guess it might depend on your target, if you have a bright small galaxy at the centre of your field of view then it might cause star detection issues. So when dooing nebulous images I have been setting 0% - 75% for my focusing (although still manually focusing in and out and just using it as a tool rather than autofocus).
Yes, that's it, not absolutely necessary to avoid the center/typical target area, but if you can get plenty of stars elsewhere then why not. If you're starved for stars then see if it works fine including it. I guess removing the edges would be avoiding areas that can have more coma, which might adding noise to the hfr values.
I just images m95/m96 where the galaxies weren't centered but I didn't change the annulus, and had no issues, so it's just something to make things run more automatically, that I've adopted from others, and I've seen bad star detections, eg in the center of m31, but the averaging and outlier removal would likely have avoided issues.
As Hy says, use SEP. It's what sextractor uses. And I wonder if results would get better if you switch the camera to 8bit. PHD2 seems to perform (for me) substantially better in 8bit mode.
star field area
One other reason to use a ring is a (possible) field curvature. For 1-star focus a suggestion also is to use a star half or 2/3rd away from center, then both center and rim would still be in the depth-of-focus range...
openSUSE Tumbleweed KStars git INDI git
GPDX+EQMOD, CEM60EC, ASI2600/1600/290mini+EFW+EAF
So I am testing full field with SEP as star detection. One thing that happens here, is that the focuser moves a lot! The first move is 500 tics. BUT: I have set initial step size to 100 and Max Travel to 400... So how come it moves this much? I have those more conservative values so as not to land it too unfocused settings, increasing the risk for misidentification of stars.
Did I miss something?
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I may not have much time later today to look into it, but a quick initial look shows that:
Now I'm not sure if it's sortware or hardware.
it is asking the focuser to move to a certain position to start, and the focuser doesn't get there, and the Linear algorithm doesn't
reset to the new position that the focuser is insisting on.
For instance, in the first attempt.
Starts at 10760
Linear wants to start its sweep at 11160, but does this by planning to go out to 11660, then back in 500 to 11160 (It doesn't violate max position, but it is ignoring max travel)
So it requests that the moonlight go to 11660. Indi copies that. But the focuser reports getting to 10916.
*** Do you have some kind of backlash removal active or something like that that could be confusing it?
The Linear focus seems to ignore this discrepancy and then moves back in by 500 which gets it to 10416 (instead of 11660) and now things are messed up and Linear isn't recovering well.
2nd focus session:
Starts at 11000
Plans to go out to 11900 and back to 11400.
But only gets to 11134 and then goes back to 10634.
Same finish as above.
I'm not sure why your focuser is not going out to the position requested in the first outward movement.
It seems to work fine for the inward movements, but not the outward movements.
Does it all work well in polynomial?
Can you manually command it to move out to these positions and back in?