What is this happening….🤔🤔

[Stuart1971]

Hmmm, can anyone explain how I can take a set of 10 x 5 min images, one after another, autofocus at the start and runs continuously till the 10th sub, and I can go from this ….in the first sub, (first picture) to the awful results in the last one of the 10, (second picture) and the ones in between got progressively worse…

It makes no sense to me at all how things can change in the same set of subs, the one in between  were just progressively worse till the last one….

I think I must be doing something fundamentally wrong…abut for the life of me I can’t think what…No flexure, everything is rock solid…

This is the same in all my batches of subs, all different…And the stars in the images tell the same story.🤔🤔

Edited January 23, 2023 by Stuart1971

[tooth_dr]

One suggestion - temp changes. My APM105 is quite bad for temp changes to focus. One night I forgot to enable focus on temp change and over 30 minutes my images went completely out of focus.  This was at 2:30am too. 

[Stuart1971]

17 minutes ago, tooth_dr said:

One suggestion - temp changes. My APM105 is quite bad for temp changes to focus. One night I forgot to enable focus on temp change and over 30 minutes my images went completely out of focus.  This was at 2:30am too. 

Hmmm, I think I have the re focus on temp change enabled, and I always keep an eye on the HFR, it seems that the focus hasn’t changed but that tilt has appeared form nowhere…which I turn then causes mid shapen stars, I have days of images ruined…and about ready to throw this Tak FSQ85 scope through the window….😮😮

Edited January 23, 2023 by Stuart1971

[Stuart1971]

19 minutes ago, tooth_dr said:

One suggestion - temp changes. My APM105 is quite bad for temp changes to focus. One night I forgot to enable focus on temp change and over 30 minutes my images went completely out of focus.  This was at 2:30am too. 

It’s that dark area on the CCD inspector image, I assume that is the best focused part of the image, and that has shifted, which I assume is because of the tilt appearing in the bottom left corner….🤔🤔

[tooth_dr]

8 hours ago, Stuart1971 said:

It’s that dark area on the CCD inspector image, I assume that is the best focused part of the image, and that has shifted, which I assume is because of the tilt appearing in the bottom left corner….🤔🤔

Ok that makes sense. Can you post the subs too?

[CraigT82]

10 hours ago, Stuart1971 said:

No flexure, everything is rock solid…

Are you sure about this? Where was the scope pointing during this run? Rising or falling?  This looks like focuser sag to me, although quite severe for only 50 mins elapsed time .

[Stuart1971]

1 hour ago, CraigT82 said:

Are you sure about this? Where was the scope pointing during this run? Rising or falling?  This looks like focuser sag to me, although quite severe for only 50 mins elapsed time .

Why would the focuser take 50 mins to sag, and such a tiny amount..we are talking microns of sag here, over 50 mins of subs…if it was going to sag it would sag as soon as the weight was re distributed, after the slew to position and settle…wouldn’t it….

 

[tooth_dr]

52 minutes ago, Stuart1971 said:

Why would the focuser take 50 mins to sag, and such a tiny amount..we are talking microns of sag here, over 50 mins of subs…if it was going to sag it would sag as soon as the weight was re distributed, after the slew to position and settle…wouldn’t it….

 

No it sags relative to its position.  It’s quite feasible to sag differently through the session as the scope moves.  The fact it’s so small does point towards tilt 

[Stuart1971]

22 minutes ago, tooth_dr said:

No it sags relative to its position.  It’s quite feasible to sag differently through the session as the scope moves.  The fact it’s so small does point towards tilt 

Ok, I get that, but I have other sets of data where the tilt can be on the opposite side, when pointing in the same position in the sky as the above data…I am totally perplexed by this 🤔🤔

‘Just wondering if having the heat band around the outside of the tube directly where the front optics are, would cause any thermal expansion issues with the glass, that would show like this…something else to look at I guess

[CraigT82]

1 hour ago, Stuart1971 said:

Why would the focuser take 50 mins to sag, and such a tiny amount..we are talking microns of sag here, over 50 mins of subs…if it was going to sag it would sag as soon as the weight was re distributed, after the slew to position and settle…wouldn’t it….

 

No as Adam says it can change as the scope moves, gravity is acting on everything in the focuser which is in a constant direction and so the effect would change as the rig moves around the sky. Normally seen to change most after meridian flip though so probably not what you’re suffering from.
 

Something seems to be moving over time though and as it’s a frac this is most likely to be something in the focuser… Cable drag maybe? 

Or could it be dew slowly forming on the objective from one side to the other (or top to bottom?) 

[Stuart1971]

13 minutes ago, CraigT82 said:

No as Adam says it can change as the scope moves, gravity is acting on everything in the focuser which is in a constant direction and so the effect would change as the rig moves around the sky. Normally seen to change most after meridian flip though so probably not what you’re suffering from.
 

Something seems to be moving over time though and as it’s a frac this is most likely to be something in the focuser… Cable drag maybe? 

Or could it be dew slowly forming on the objective from one side to the other (or top to bottom?) 

Certainly not cable drag, as al the cables move with the scope, there is only 1 to the mount and that a power cable…so all good there

I have never seen any dew in the lens, and have checked a few times, but this is something I asked about, my dew band is around the outside directly above the front element, and wonder if it’s something to do with thermal issues as Adam said…maybe it should be further up the dew shield, and it’s heating the glass up too much and causing thermal shift of the glass, enough to give these results…as all my runs of subs show it, and the tilt can come from all directions, there is not pattern with that at all…?? Even when pointing on the same side of pier, to the same part of the sky…🤔🤔

[tooth_dr]

1 hour ago, Stuart1971 said:

Certainly not cable drag, as al the cables move with the scope, there is only 1 to the mount and that a power cable…so all good there

I have never seen any dew in the lens, and have checked a few times, but this is something I asked about, my dew band is around the outside directly above the front element, and wonder if it’s something to do with thermal issues as Adam said…maybe it should be further up the dew shield, and it’s heating the glass up too much and causing thermal shift of the glass, enough to give these results…as all my runs of subs show it, and the tilt can come from all directions, there is not pattern with that at all…?? Even when pointing on the same side of pier, to the same part of the sky…🤔🤔

Would be easy to rule out and worry trying but removing or moving the band. 

[tomato]

My rig is set up for a refocus if the FWHM numbers change by more than 10%, and this usually happens 15-20 subs in and thereafter for the entire session. The scopes are permanently set up in the dome so I don’t think it is temperature change, I put it down to focus sag as the scope changes orientation and/or change in atmospheric conditions as the altitude changes. It’s a real deterioration as the numbers are always much better after the refocus.

[Stuart1971]

15 minutes ago, tomato said:

My rig is set up for a refocus if the FWHM numbers change by more than 10%, and this usually happens 15-20 subs in and thereafter for the entire session. The scopes are permanently set up in the dome so I don’t think it is temperature change, I put it down to focus sag as the scope changes orientation and/or change in atmospheric conditions as the altitude changes. It’s a real deterioration as the numbers are always much better after the refocus.

Mine is set to change on 10% too….🤔

[tomato]

Do you get a massive range of quality values when you analyse the subs? I usually discard the worst 5% excluding any obvious outliers and then let APP weight the rest for contribution to the stack. I’m usually satisfied with the result given the improvements that can be made with BlurXterminator  etc but maybe I’ve got too much of a relaxed approach to this stuff.

[michael8554]

Hi Stuart

Please post an image of the setup.

"autofocus at the start and runs continuously"

Does that mean you refocus between each shot ?

Michael

 

[Stuart1971]

1 hour ago, michael8554 said:

Hi Stuart

Please post an image of the setup.

"autofocus at the start and runs continuously"

Does that mean you refocus between each shot ?

Michael

 

No, the autofocus runs at the start, then on HFR increase of 10% or more, and in temp change of 5 degrees, and also on filter change of course, but between the images above there was no autofocus

what set up are you referring to, to show a picture of…? My complete rig..?

[Stuart1971]

On 24/01/2023 at 06:59, tooth_dr said:

Ok that makes sense. Can you post the subs too?

Ok, here are two image stacks of 10 subs from the night in question, these are rough stacks with only darks, and just an EZ soft stretch in PI, no other processing at all, 

1st image completely as came from camera, 2nd has had BlurX run in the correct only setting, both are un-cropped from a QHY268m and Ha 6.5nm filter, I used BlurX to see how it would help the corner stars, so see what you think of both and do some pixel peeping assuming they have not been compressed too much on here..

 

Edited January 26, 2023 by Stuart1971

[Adam J]

On 23/01/2023 at 21:55, Stuart1971 said:

Hmmm, can anyone explain how I can take a set of 10 x 5 min images, one after another, autofocus at the start and runs continuously till the 10th sub, and I can go from this ….in the first sub, (first picture) to the awful results in the last one of the 10, (second picture) and the ones in between got progressively worse…

It makes no sense to me at all how things can change in the same set of subs, the one in between  were just progressively worse till the last one….

I think I must be doing something fundamentally wrong…abut for the life of me I can’t think what…No flexure, everything is rock solid…

This is the same in all my batches of subs, all different…And the stars in the images tell the same story.🤔🤔

So you focus, it gets gradually worse with each image, you refocus and then its back to being good again? Very odd as I would normally expect focus drift due to temperature change to have a more global effect on focus but the above is indicating tilt....

So tilt is changing over time....

Can yo notice any physical lateral movement in the focuser tube?

The images are not ruined BTW. You can create two stacks, one using all the date, the second using just the data with good stars, they you remove the stars from the stack with all the data and process the good stars in from the other stack...assuming your using starless processing anyway. Most do these days. 

 

Adam

Edited January 25, 2023 by Adam J

[Stuart1971]

11 minutes ago, Adam J said:

So you focus, it gets gradually worse with each image, you refocus and then its back to being good again? Very odd as I would normally expect focus drift due to temperature change to have a more global effect on focus but the above is indicating tilt....

So tilt is changing over time....

Can yo notice any physical lateral movement in the focuser tube?

The images are not ruined BTW. You can create two stacks, one using all the date, the second using just the data with good stars, they you remove the stars from the stack with all the data and process the good stars in from the other stack...assuming your using starless processing anyway. Most do these days. 

 

Adam

Hi,

No there is no movement on anything physical at all, and with other stacks pointing in the same area of sky, the tilt that appears comes from all different angles, it’s not at all consistent, sometimes from the bottom left corner, sometimes all across the top, and also from the left, BUT, the actual images done look any different…so I think it’s an anomaly with CCD inspector somehow, as the figures it churns out are just not right at all, I have some that show 40% curvature and 35% tilt, and yet the images look pretty much the same as above….and those about were all with approx 15-17% curvature, and between 1-9% tilt….really odd….

[Adam J]

Just now, Stuart1971 said:

Hi,

No there is no movement on anything physical at all, and with other stacks pointing in the same area of sky, the tilt that appears comes from all different angles, it’s not at all consistent, sometimes from the bottom left corner, sometimes all across the top, and also from the left, BUT, the actual images done look any different…so I think it’s an anomaly with CCD inspector somehow, as the figures it churns out are just not right at all, I have some that show 40% curvature and 35% tilt, and yet the images look pretty much the same as above….and those about were all with approx 15-17% curvature, and between 1-9% tilt….really odd….

Oh if its just CCD inspector and its not related to what you are actually seeing then I would chin CCD inspector off, I have always considered it to be inconstant at best. If you are using NINA then try the Hocusfocus plugin instead. 

Adam

[michael8554]

"show a picture of…? My complete rig..?"

Focuser, CC, FW, camera etc.

Tooth_dr wanted some subs, not cropped stacks.

Michael

[Stuart1971]

46 minutes ago, michael8554 said:

"show a picture of…? My complete rig..?"

Focuser, CC, FW, camera etc.

Tooth_dr wanted some subs, not cropped stacks.

Michael

They are not cropped at all, individual subs do not show enough with the noise…have no idea how a picture of my rig helps but this is the best I have ATM

Edited January 25, 2023 by Stuart1971

[michael8554]

"They are not cropped at all,"

You said "both are in cropped from a QHY268m and Ha 6.5nm filter,"

"have no idea how a picture of my rig helps "

So that we can look for points where the image train could be sagging.

Since you say everything is "rock solid", but it looks like something isn't.

"and also on filter change of course,"

Ah, didn't know you use filters.......

Is the filter wheel inside the FW housing loose enough to allow wobbling ?

Short exposure subs remove guiding and stacking errors from the equation.

Michael

 

[Stuart1971]

2 hours ago, michael8554 said:

"They are not cropped at all,"

You said "both are in cropped from a QHY268m and Ha 6.5nm filter,"

"have no idea how a picture of my rig helps "

So that we can look for points where the image train could be sagging.

Since you say everything is "rock solid", but it looks like something isn't.

"and also on filter change of course,"

Ah, didn't know you use filters.......

Is the filter wheel inside the FW housing loose enough to allow wobbling ?

Short exposure subs remove guiding and stacking errors from the equation.

Michael

 

They are both Un cropped…👍🏻