Starsense still not accurate after calibration

[RicRob65]

First an apology... Being a bit new to SGL I wasn't sure which was the best forum to put this question on - there seems nothing specific to Starsense or alignment.

Twice last night after using Starsense Auto align using APT to ensure the star I selected (Sirius) was in the centre of my cameras view. I then used Menu->Starsense->Calibrate using the procedures to coarse then fine align to centre the star (finishing up with up and right as per the instructions). Starsense 'solved' the new postion and then asked for it's alignment procedure to be done again.

After doing this, I asked Starsense to go back to Sirius. It was quite a way off the target not even in the sensors view. I am using a small sensor (ZWOASI178MC) on a C11 - so a very narrow field of view. Has anyone else had this problem and solved it or am I asking too much of it?

Thanks

[Starwatcher2001]

I usually get somewhere in the middle third in a 25mm eyepiece (94x - 0.56 degrees) on my scope.  If you're working in a particular area of the sky, add another alignment point in that area and that should improve local accuracy.

 

Edited March 17, 2021 by Starwatcher2001
Added FOV

[Shimrod]

5 hours ago, RicRob65 said:

First an apology... Being a bit new to SGL I wasn't sure which was the best forum to put this question on - there seems nothing specific to Starsense or alignment.

Twice last night after using Starsense Auto align using APT to ensure the star I selected (Sirius) was in the centre of my cameras view. I then used Menu->Starsense->Calibrate using the procedures to coarse then fine align to centre the star (finishing up with up and right as per the instructions). Starsense 'solved' the new postion and then asked for it's alignment procedure to be done again.

After doing this, I asked Starsense to go back to Sirius. It was quite a way off the target not even in the sensors view. I am using a small sensor (ZWOASI178MC) on a C11 - so a very narrow field of view. Has anyone else had this problem and solved it or am I asking too much of it?

Thanks

I'm not sure I follow what you are doing. Are you using both APT and the handcontroller (for Starsense) when doing the alignment - I don't se APT so I'm not clear whether you are doing all these actions from APT  or not.

I haven't had the issues you are describing - I use the (free) Celestron CPWI software to control my AVX mount and have found Starsense to be pretty accurate.  You do the Starsense calibration first then do the alignment - as you are using a PC already it might be worth trying CPWI as it is much easier to use than the hand controller - see if you get a different result.

[RicRob65]

Thank you for the replies.

If I understand correctly what is being said, then an accuracy of about 11 minutes of arc is what has been experienced. My sensor (ZWO ASI178MC) seems to give me a field of view of little more than 9 minutes which suggests I was hoping for greater accuracy than Starwatcher2001 is experirencing.

To answer Shimrod's question, I tried the calibration twice. 1st using ASCOM to move the star in the centre (I only used APT to view the image), then because the star wasn't on target after re-runnng the alignment procedure, I tried again using the hand controller but got the same result. Haven't tried using CPWI yet.

I guess my expectations were a bit too high.

Thanks again

[Shimrod]

13 hours ago, RicRob65 said:

Thank you for the replies.

If I understand correctly what is being said, then an accuracy of about 11 minutes of arc is what has been experienced. My sensor (ZWO ASI178MC) seems to give me a field of view of little more than 9 minutes which suggests I was hoping for greater accuracy than Starwatcher2001 is experirencing.

To answer Shimrod's question, I tried the calibration twice. 1st using ASCOM to move the star in the centre (I only used APT to view the image), then because the star wasn't on target after re-runnng the alignment procedure, I tried again using the hand controller but got the same result. Haven't tried using CPWI yet.

I guess my expectations were a bit too high.

Thanks again

I've got a slightly bigger sensor (ASI533), but after aligment I find that I can get the target in the field of view of the camera on a EdgeHD 8". Assuming you are using an EQ mount, I did find that I was less accurate when I did an ASPA than when I just took the polar alignment as given by my ipolar.

[RicRob65]

12 hours ago, Shimrod said:

I've got a slightly bigger sensor (ASI533), but after aligment I find that I can get the target in the field of view of the camera on a EdgeHD 8". Assuming you are using an EQ mount, I did find that I was less accurate when I did an ASPA than when I just took the polar alignment as given by my ipolar.

Well, I use Polemaster so I think I'm alright there? I'm pretty sure it's just that my expectations were too high for the Starsense accuracy. I assumed that if you calibrate on a particular star then it would go back to exactly the position of that star next time you select it.

[bottletopburly]

If you are connected via ascom can you platesolve ,especially in APT using Goto ++ ,so get good PA and platesolve using Astap option in APT (once configured first you can do that in the daytime using an old image you have taken ).

[RicRob65]

On 19/03/2021 at 11:29, bottletopburly said:

If you are connected via ascom can you platesolve ,especially in APT using Goto ++ ,so get good PA and platesolve using Astap option in APT (once configured first you can do that in the daytime using an old image you have taken ).

Thanks. I've been looking at platesolve in APT as an alternative. Not managed to get it working yet though.

[bottletopburly]

51 minutes ago, RicRob65 said:

Thanks. I've been looking at platesolve in APT as an alternative. Not managed to get it working yet though.

Follow davids guide and use Astap option details further into thread

.

 

 

Edited March 21, 2021 by bottletopburly

[newbie alert]

Why even bother with starsense, just use platesolve within APT.. accurate within pixels

[RicRob65]

After much time spent on looking at why platesolving wasn't working, I discovered that by directly loading the image into Platesolve2, it did get solved - it was when I got APT to use Platesolve2 that it did not work. It appeared as if APT passed values to Platesolve2 that where different to what is in the FITS file header (focal length/field of view?). The image was taken using a focal length of 2800mm and my ZWO camera which gave a field of view of about 9' x 6'. The last OTA/camera I used on APT had a focal length of 227mm (a finderscope) and this is what appeared in the Camera tab on APT. When I changed it to 2800 plate solving working via APT. It is almost as if APT passed the focal length of the last camera it used to Platesolve2 rather than what is in the FITS file header. Has anyone else had this issue?

Edited April 22, 2021 by RicRob65

[newbie alert]

On 22/04/2021 at 13:29, RicRob65 said:

After much time spent on looking at why platesolving wasn't working, I discovered that by directly loading the image into Platesolve2, it did get solved - it was when I got APT to use Platesolve2 that it did not work. It appeared as if APT passed values to Platesolve2 that where different to what is in the FITS file header (focal length/field of view?). The image was taken using a focal length of 2800mm and my ZWO camera which gave a field of view of about 9' x 6'. The last OTA/camera I used on APT had a focal length of 227mm (a finderscope) and this is what appeared in the Camera tab on APT. When I changed it to 2800 plate solving working via APT. It is almost as if APT passed the focal length of the last camera it used to Platesolve2 rather than what is in the FITS file header. Has anyone else had this issue?

Yes, if you chop and change scopes, or camera's you need to update the file otherwise it will keep what you was using, and then fail.. At least now you can use it rather than faffing with starsense..