Auto Focus Issues

[Enigma_RL]

Hey everyone!

I'm really just getting started with this hobby and was outside testing some aspects of my setup last night. One of the issues I ran into was with my auto focuser. I'm using a William Optics GT81 IV APO telescope, ASI ZWO 2600MM-Pro camera, an electronic filter wheel and a ZWO EAF focuser all connected to N.I.N.A.

I tried to run a simple auto focus sequence last night and oh my did my curve look interesting:

Does anyone have even the slightest idea of what I am looking at and where I can begin to troubleshoot? I know I'm supposed to get somewhat of a nice hyperbolic or parabolic curve rather than a graph from a well performing stock exchange. Thanks in advance for helping out!

[scotty38]

I am not in front of mine at the minute but I had similar issues until I changed a few of the focusser settings in NINA, now I get a nice curve. I used settings I found in a post either on here or CN but I've not been able to find it since. I'll dig them out later if you want to share your settings in the meantime.

[Skipper Billy]

Try doubling or even tripling your step size setting and reduce the number of steps to 11.

[bottletopburly]

Try using a bahtinov mask so your close to focus as possible.

[Adam J]

25 minutes ago, Enigma_RL said:

Hey everyone!

I'm really just getting started with this hobby and was outside testing some aspects of my setup last night. One of the issues I ran into was with my auto focuser. I'm using a William Optics GT81 IV APO telescope, ASI ZWO 2600MM-Pro camera, an electronic filter wheel and a ZWO EAF focuser all connected to N.I.N.A.

I tried to run a simple auto focus sequence last night and oh my did my curve look interesting:

Does anyone have even the slightest idea of what I am looking at and where I can begin to troubleshoot? I know I'm supposed to get somewhat of a nice hyperbolic or parabolic curve rather than a graph from a well performing stock exchange. Thanks in advance for helping out!

Cant see the image on my PC, maybe try posting it as a JPG. Got some experience in this area if you can. 

[Enigma_RL]

18 minutes ago, scotty38 said:

I am not in front of mine at the minute but I had similar issues until I changed a few of the focusser settings in NINA, now I get a nice curve. I used settings I found in a post either on here or CN but I've not been able to find it since. I'll dig them out later if you want to share your settings in the meantime.

Thanks! Here are my settings:

17 minutes ago, Skipper Billy said:

Try doubling or even tripling your step size setting and reduce the number of steps to 11.

Thank you, will try that on my next attempt.

1 minute ago, Adam J said:

Cant see the image on my PC, maybe try posting it as a JPG. Got some experience in this area if you can. 

Uploaded

[scotty38]

and here is mine. I am not saying this is what it should be but after changing things it all works fine for me at least.

 

[Enigma_RL]

2 minutes ago, scotty38 said:

and here is mine. I am not saying this is what it should be but after changing things it all works fine for me at least.

 

Thanks a ton! I'll definitely give it a go next run

[scotty38]

Just now, Enigma_RL said:

Thanks a ton! I'll definitely give it a go next run

I hope it works for you. My graph was pretty much like yours so I was massively sceptical a few changes would make such a drastic difference but they did. Even now every time I focus I am on edge expecting to see a crappy "curve" but so far so good 🙂

[Clarkey]

It will depends on the focuser and the scope but start with a largish step size (mine are 50 - 100) and also consider starting with a larger offset of maybe 6 steps. Once you get a better idea of the curve you should be able to see a clear pattern and fine tune it. If you have backlash in the focuser you may need to compensate for this.

[Enigma_RL]

Just now, scotty38 said:

I hope it works for you. My graph was pretty much like yours so I was massively sceptical a few changes would make such a drastic difference but they did. Even now every time I focus I am on edge expecting to see a crappy "curve" but so far so good 🙂

Hahaha at this point I am running into so many issues that I'm willing to give everything a go. Most of the people on here went through the same [removed word] as I currently am already so hearing all of your experiences definitely helps!

[Clarkey]

Just to add, for consistency and to make it a bit quicker I have set the brightest n stars to 50. This will avoid measuring hot pixels or noise.

[Laurin Dave]

Looks to me as if your step size is too small and that you have backlash (the cause of the flat bit on the right) , as @Skipper Billy says increase step size so that when the autofocus routine is at the extremes the FWHM or HFR or whatever NINA measure is 3 times larger than when it is in focus ie about 10, to start with i'd set your backlash to 200 or so and see if it removes the flat bit if not increase till it does...  

Also check all connections are tight

Dave

[Enigma_RL]

2 minutes ago, Laurin Dave said:

Looks to me as if your step size is too small and that you have backlash (the cause of the flat bit on the right) , as @Skipper Billy says increase step size so that when the autofocus routine is at the extremes the FWHM or HFR or whatever NINA measure is 3 times larger than when it is in focus ie about 10, to start with i'd set your backlash to 200 or so and see if it removes the flat bit if not increase till it does...  

Also check all connections are tight

Dave

NINA uses HFR to focus, and I will definitely experiment with the step size next session. When setting the backlash, I can set values for IN and OUT. Do I set both of them to 200 or how can I interpret those values? Thanks for the tips, I really appreciate it!

[StevieDvd]

There was a similar fous issue with NINA a few weeks back which was resolved. The issues were a loose grub screw and a decent value in the backlash.

The backlash values you had at zero implies the focuser instantly moves in both directions, whereas it probably has a movement of 10 to 30 steps of the motor before the cogs engage. The NINA settings need not be the actual values you will have on your motor, but are used to work out the actual backlash.

The IN/OUT directions can be reversed so unless you know which yours is set at put the NINA values as the same. Or you can try one at a time and set the one which works.

Your focus motor may have a note about backlas values to give you an idea of its value.

I found this and more with this NINA Backlash video on YT

[Laurin Dave]

21 minutes ago, Enigma_RL said:

NINA uses HFR to focus, and I will definitely experiment with the step size next session. When setting the backlash, I can set values for IN and OUT. Do I set both of them to 200 or how can I interpret those values? Thanks for the tips, I really appreciate it!

You can only set it for one I believe, on my GT71 its set to IN.

[Enigma_RL]

11 minutes ago, StevieDvd said:

There was a similar fous issue with NINA a few weeks back which was resolved. The issues were a loose grub screw and a decent value in the backlash.

The backlash values you had at zero implies the focuser instantly moves in both directions, whereas it probably has a movement of 10 to 30 steps of the motor before the cogs engage. The NINA settings need not be the actual values you will have on your motor, but are used to work out the actual backlash.

The IN/OUT directions can be reversed so unless you know which yours is set at put the NINA values as the same. Or you can try one at a time and set the one which works.

Your focus motor may have a note about backlas values to give you an idea of its value.

I found this and more with this NINA Backlash video on YT

Thanks for the explanation, I'll make sure to give it a watch!

6 minutes ago, Laurin Dave said:

You can only set it for one I believe, on my GT71 its set to IN.

All right I'll do some experimenting next clear night. Thanks again for the tips!

[Adam J]

1 hour ago, Enigma_RL said:

Thanks! Here are my settings:

Thank you, will try that on my next attempt.

Uploaded

Ok so the fist issue is that your backlash setting is way too low. 

The second issue is that your initial step size needs increasing by at least a factor of 3x  (maybe even more) what you are using here. 

The final issue is that you are using a linear fit to solve the focus position and I would recommend hyperbolic only. 

 

Adam

 

 

[Enigma_RL]

3 minutes ago, Adam J said:

Ok so the fist issue is that your backlash setting is way too low. 

The second issue is that your initial step size needs increasing by at least a factor of 3x  (maybe even more) what you are using here. 

The final issue is that you are using a linear fit to solve the focus position and I would recommend hyperbolic only. 

 

Adam

All right I've added this to my list. Thanks!