Tilt tests with ASTAP

[Stuart1971]

So, I have decided to do some testing on my set up for tilt using ASTAP, and I do have some, but it does seem too bad, so here comes, what maybe a stupid question, will field curvature, due to not having my flattener fitted with the images I was using to test, screw up the tilt results, as the results clearly show some tilt and curvature…and wondered how much of the tilt result would be affected by the field curvature…
I have only just got the flattener, so it’s not been used yet…

Thanks for looking

Stuart

[dan_adi]

Not sure about field curvature, but a while ago I tested some subs of mine with ASTAP and it reported moderate tilt. All I did was to disassemble my imaging train and put it back together and the tilt was gone. With time and temperature variation connections get a bit loose. So before you panic make sure your connections are reasonably tight 

[Stuart1971]

1 hour ago, dan_adi said:

Not sure about field curvature, but a while ago I tested some subs of mine with ASTAP and it reported moderate tilt. All I did was to disassemble my imaging train and put it back together and the tilt was gone. With time and temperature variation connections get a bit loose. So before you panic make sure your connections are reasonably tight 

I personally did have tilt on the sensor, and all corrected now with  home built laser tilt jig….👍🏻

[tomato]

If you have zero tilt, i.e. all components in the optical train aligned, then I would have thought field curvature would show up as a uniform aberration, looking the same in all four corners.

[Stuart1971]

18 minutes ago, tomato said:

If you have zero tilt, i.e. all components in the optical train aligned, then I would have thought field curvature would show up as a uniform aberration, looking the same in all four corners.

Well in my case, the tilt has now been adjusted out, but not tried imaging since, so I have no idea how it will change the curvature due to not using a flattener….

Edited October 21, 2022 by Stuart1971

[scotty38]

Are you now testing tilt on the full rig? You only removed tilt from "part" of the rig didn't you? If you're using the full rig now isn't it possible the focusser has some tilt for example?

Either way I wouldn't worry until you have everything fitted together and you've taken some pictures. To be honest ASTAP numbers on mine seem worse than pictures themselves, well they do to me anyway 🙂

[Stuart1971]

9 minutes ago, scotty38 said:

Are you now testing tilt on the full rig? You only removed tilt from "part" of the rig didn't you? If you're using the full rig now isn't it possible the focusser has some tilt for example?

Either way I wouldn't worry until you have everything fitted together and you've taken some pictures. To be honest ASTAP numbers on mine seem worse than pictures themselves, well they do to me anyway 🙂

Hi 

The test is in all except the focuser, which as you say could introduce some tilt, but my tak  focuser is adjusted pretty well and firm, as I like it like that, also I have enough  spacers fitted so the focuser only moves out about 10mm when in focus, so am limiting this happening….but you are correct about ASTAP, as I tested 10 images from the same night, and the results ranged from No tilt 5%, to severe tilt 33% 🤔

But they did all show mild curvature, hence me getting the new flattener…

[Stuart1971]

The question i was  asking at the start, was whether the curvature which I know is present, would skew the tilt figures, and make it show worse that it actually was….but I guess imaging in real conditions will answer this ….👍🏻

[RolandKol]

On 29/09/2022 at 22:14, Stuart1971 said:

So, I have decided to do some testing on my set up for tilt using ASTAP, and I do have some, but it does seem too bad, so here comes, what maybe a stupid question, will field curvature, due to not having my flattener fitted with the images I was using to test, screw up the tilt results, as the results clearly show some tilt and curvature…and wondered how much of the tilt result would be affected by the field curvature…
I have only just got the flattener, so it’s not been used yet…

Thanks for looking

Stuart

Curious to test mine... And was not able to find this option on ASTAP...
Can you please advise how to do that?

[Stuart1971]

8 minutes ago, RolandKol said:

Curious to test mine... And was not able to find this option on ASTAP...
Can you please advise how to do that?

CCD inspector under the tools menu, you need a RAW image not debayered, and then click on the test button….👍🏻

[Stuart1971]

See here, and scroll down to CCD inspector section…

https://www.hnsky.org/astap.htm#inspector

[RolandKol]

Thanks!!!
Not even suspected I had almost no tilt ;)))

I am greatly in Doubt if the result is correct...  as the test image is from standard Skywatcher 130PDS focuser holding ASI1600+GPU CC+EFW...
(need to test more images and see the average)

 

#

[Stuart1971]

2 minutes ago, RolandKol said:

Thanks!!!
Not even suspected I had almost no tilt ;)))

I am greatly in Doubt if the result is correct...  as the test image is from standard Skywatcher 130PDS focuser holding ASI1600+GPU CC+EFW...
(need to test more images and see the average)

 

#

That’s a very good result….👍🏻

[RolandKol]

HFD....

not sure how to interpret...

[tomato]

12 hours ago, Stuart1971 said:

That’s a very good result….👍🏻

I agree, if I saw a result like that I would stop adjusting and start imaging.

[Stuart1971]

21 hours ago, RolandKol said:

HFD....

not sure how to interpret...

Hmmmm, now that is showing bad tilt…so not sure what is going on there….

[RolandKol]

2 minutes ago, Stuart1971 said:

Hmmmm, now that is showing bad tilt…so not sure what is going on there….

That's was my initial point  not very reliable to go by 1 image.... 
From my personal experience, I am almost sure, HFD measurement actually was closer to the reality and I am bit confused why Tilt measurement does not pick it up... 
I checked around 20 images from the  last session, - all quite constant results... and very different to the ones I had before my adjustments to the optical setup, so it is kinda does the job and maybe my interpretation is the issue...  problem with HFD measurement, it does not show the Min/Max or deviation %, just within 10% and something else, cannot clearly read... 

[Stuart1971]

5 minutes ago, RolandKol said:

That's was my initial point  not very reliable to go by 1 image.... 
From my personal experience, I am almost sure, HFD measurement actually was closer to the reality and I am bit confused why Tilt measurement does not pick it up... 
I checked around 20 images from the  last session, - all quite constant results... and very different to the ones I had before my adjustments to the optical setup, so it is kinda does the job and maybe my interpretation is the issue...  problem with HFD measurement, it does not show the Min/Max or deviation %, just within 10% and something else, cannot clearly read... 

well, from what I have read, the darkest area should be in the middle, and then the lighter areas usually will be concentric around that. gradually getting lighter towards the outside, but an ideal optical system should show the same uniform colour all across the image…

[Stuart1971]

8 minutes ago, RolandKol said:

That's was my initial point  not very reliable to go by 1 image.... 
From my personal experience, I am almost sure, HFD measurement actually was closer to the reality and I am bit confused why Tilt measurement does not pick it up... 
I checked around 20 images from the  last session, - all quite constant results... and very different to the ones I had before my adjustments to the optical setup, so it is kinda does the job and maybe my interpretation is the issue...  problem with HFD measurement, it does not show the Min/Max or deviation %, just within 10% and something else, cannot clearly read... 

there is also an aberration  inspector in pixinsight, it’s worth trying that too…👍🏻

[alacant]

On 20/10/2022 at 21:01, dan_adi said:

disassemble my imaging train and put it back together and the tilt was gone

+1

This is our observation too, except we'd substitute 'gone' for 'changed'.

Threaded or not, low end focusers on low end telescopes will introduce tilt. Simply re-seating the camera will change the tilt, as will moving the telescope to a different angle. Cure it at one angle, and it's gone for the next. 

Perhaps don't stress too much over numbers. rather look at the averaged out final images.

Just our hands on but HTH anyway.

Cheers and clear skies.

Edited October 22, 2022 by alacant

[Stuart1971]

2 minutes ago, alacant said:

+1

This is our observation too, except we'd substitute 'gone' for 'changed'.

Threaded or not, low end focusers on low end telescopes will introduce tilt. Simply re-seating the camera will change the tilt, as will moving the telescope to a different angle. Cure it at one angle, and it's gone for the next. 

Perhaps don't stress too much over numbers. rather look at the averaged out final images.

Just our hands on but HTH anyway.

Cheers and clear skies.

My camera alone was tested on my laser jig, and had quite a bit of tilt on the sensor, when rotating the camera 360 degrees, with a laser pointing at the sensor, the reflected dot moved in a 4mm circle, which shows a lot of tilt…all adjusted out now, but yes there still can be tilt from a poor focuser…👍🏻