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INDI Library v1.9.7 Released (29 Jul 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

For those with focus issues

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Eric,

I'll let Hy respond to the more technical aspects of your suggestions. However, I'm not sure that number of stars is a reliable measure of quality. My experience is that it is more a function of seeing as opposed to focus... but just my opinion.

After all of this helpful discussion, I'm thinking that my issues may be solved by adjusting the various settings (step size, star selection, etc.) and improving collimation.

Thanks!

Ron
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Celestron Focus Motor, Meade 80mm APO Triplet Refractor w/ZWO EAF
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
6 months 3 weeks ago #79850

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Replied by Jim on topic For those with focus issues

It was mentioned a few times about having a nebula in the frame possibly throwing things off a bit. Between that and edge of field optical distortions, I settled on an annulus configuration of 15% / 55%. This gives me a nice donut that avoids the center of the field where a nebula might be, and the corners of the field, but still has plenty of star quantity inside the large donut. I have full field checked with this configuration, and it seems to work quite well for my needs with the linear algorithm.
12" pier with HDX110 using EQMod
ASI 1600 mono/color mains with ASI290MM in off-axis
ASI filter wheel
Moonlite focusers for the sharpening
AT115EDT w/.8x for the light
Fedora Linux, 100% INDI
6 months 3 weeks ago #79857

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Yes, that works best for me as well when doing something that has a nebula or galaxy in the center. Works best having those settings.

Plus my Mak-Newts are optimized for APS-C sensors, when I use a larger sensor, I have to cut out the edges so the focus procedure works best. 
 
Last edit: 6 months 3 weeks ago by Sonny Cavazos.
6 months 3 weeks ago #79860

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Okay... more testing tonight and success!

I first checked my collimation and it is pretty good. I can probably improve a little... but I'll leave that for another night.

I tried changing several parameters (step size, image settings, etc), but they made things worse... bad focus, poor/non curve, etc. I finally tried one of Giles' suggestions and changed bin to 2x2... immediately got a perfect curve and a great focus!

It seems that on my SCT that the in-focus range is pretty small... approximately 20,480 to 20,500. Outside of that range I start to get halos or donuts, and EKOS doesn't correctly measure HFR with donuts. It seems that when I bin, it reduces the halo effect and EKOS correctly measures the HFR... and is able to get me to the minimum HFR.

So, I changed binning to 2x2, tightened the focus range and all seems well.

Thanks for everyone's help!

Ron
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Celestron Focus Motor, Meade 80mm APO Triplet Refractor w/ZWO EAF
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
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6 months 3 weeks ago #79870

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Hey Ron,

that's great to hear! And makes me wonder: Do you use a color camera?
I did have comparable issues (with star detection) when using a color camera as guider, and everything started working when switching to LUMA mode, or bin 2x2.....

And a short remark again to that different-stars issue: On first hand, seeing and defocus determine the point spread function for the image, and in theory this PSF is the same everywhere. So the shape (and thus things like FWHM etc.) are the same for all stars, and it doesn't really matter which of them you use.
In praxis, especially for short exposures, seeing will vary over the FOV, and averaging over many stars will give you a much better estimate of the seeing than a single star. The same is the case for the instrumental PSF, that can vary across the image: Collimation errors, as mentioned already, curvature of the focal plane (mainly for refractors) etc. Also there you usually want to get the best field-averaged focus. And again, the errors there do not depend on the star, only on position in FOV, and as long as your star ensemble is spread uniformly across the FOV it doesn't matter which ones are used....
openSUSE Tumbleweed KStars git INDI git
GPDX+EQMOD, CEM60EC, ASI2600/1600/290mini+EFW+EAF
6 months 2 weeks ago #79878

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Peter,

I use an ASI290mm for guiding, which is mono.

Yes, I am learning a lot more about focusing from all of the comments on this forum. Additionally, from my testing, I see that sub-frame focusing doesn't work well on a SCT. Due to its design, the stars move slightly when you change the focus... meaning that it is difficult to hold a particular star within a frame. While I don't understand it all, there is some genius behind must-star focusing.

When I've collected a few more pennies, I would love to replace the SCT with a larger reflector... but that may be a ways down the road.

I'm really thankful for everyone's assistance!

Ron
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Celestron Focus Motor, Meade 80mm APO Triplet Refractor w/ZWO EAF
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
6 months 2 weeks ago #79887

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Hi!
I am also an SCT owner and know what you mean with image shift when shifting focus orientation. However, if you use Linear mode, the risk for this is minimized, as the focuser does not shift direction (it does when moving back for the second go, but then moves forward again). Maybe more importantly: I use a Crayfoord focuser on my SCT, which removes all such issues. Much cheaper than a new scope, and you can keep the nice optical performance in the C8 Edge :)

Magnus

Celestron C11, Skywatcher 100 ED Pro
Losmandy G11
Atik 383L+, ASI294
6 months 2 weeks ago #79888

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Magnus,

Yes, I use linear focusing. It takes a bit longer than polynomial, but I get better results. I'm using the Celestron electronic focuser, which is "okay". It has some backlash... but doesn't really matter with the linear process.

Ron
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Celestron Focus Motor, Meade 80mm APO Triplet Refractor w/ZWO EAF
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
6 months 2 weeks ago #79891

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It gives me a hard time tonight.... Askar400, Antlia 5nm, Omegon 533, crystal clear sky.
Starts with the recognition of more than 30-40 stars and then I can see with every single step - even with just step 5 - gradually goes down to 10 or less with a bad distribution across the field. The HFR calculation is bad and I am not really confident that this is good for the algorithm. 

Any idea is more than welcome. I find myself to spend more time to this than before with just a bahtinov mask :-/ 

 
 
6 months 1 week ago #80317
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@Euripides,

The V-curves in your screenshots look reasonable to me. At least that's about what I get and I think the focusing works well for me.

If you're hoping for more stars, you can play with the StellarSolver parameters (e.g. perhaps your minimum star size is filtering out stars once they get small and focused), but honestly, it may be working fine.
Why not try a Bahtinov mask and see if you're get about the same focus position as autofocus?

Hy 
 
AP1100 & Orion Atlas Pro, WO/ZS105 w/Moonlight V2 focus, GSO RC10 w/RSF focus
ZWO ASI1600, Astronomik Filters, ST80, QHY 5L-IIm.
KStars/Ekos/Indi on NUC10 & RPi4 w/SSD -- Ubuntu
Projects: Greedy Scheduler, Terrain, Polar Align, Analyze, Linear Focuser, SEP MultiStar & GPG Guide, FITS autostretch.
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6 months 1 week ago #80326

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Great idea about the minimum star size, I will definitely check it!

Thank you Hy
6 months 6 days ago #80368

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You get exactly the same curve response I get, only I get fewer iterations. The cause for the tail off is related to my optics and the algorithm. When your example goes to (2) my optics are far out of focus there is a brighter spot in the middle of the star. The algorithm looks only at the smaller dot and responds with a smaller reading.

I haven't bothered too much as I can blaming my optics and working around it. The way I work around is starting lower than my expected focal point.
Malcolm
Telskop Service TS80 480mm APO FL53 Glass
Canon 450D DSLR
ASI120MM Guide camera.
HEQ5 Pro
TIC Focuser NG
Raspberry Pi 4 8GB with Astroberry
6 months 6 days ago #80371

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