Wonky Stars after 5 years

[Startrek (Martin)]

I’ve been successfully imaging with my little 6” f6 Bintel GSO newt for nearly 5 years now and the last 2 nights ( which have been pristine conditions in Sydney ) I’ve been trying to resolve wonky stars (Star shape is a mixture between trefoil and rectangular , not really bad but noticeable across the field , all stars big and small are affected ) Sorry no images
I’ve had coma in all my newts so I know the signs , this is not coma or tilt
Achieved good focus as Ive done a thousand times before using a mag 2 star ( Alnair ) focus star is zoomed in 5x with diffraction spikes like sharp swords and centroid nice and round. Nice tight Focus Star
Both nights pristine conditions and my PHD2 Multistar guiding has been 0.50 arc sec total rms ( Dec and Ra even stevens )
My PA is around an arc min. Took an 80 sec exposure on my focus Star Alnair and zoomed in 5x . Alnair still had good shape , no eggy or odd shape
Using a Baader MPCC coma corrector like I’ve used a thousand times before
Tried some 0.5mm Shims , added one then two. Star shape still wonky so went back to my normal spacing

Remove mirrors and clean
Check primary mirror rubber clamps for possible pinched optics, they were nice and loose but not too loose
Collimate scope using laser and Cheshire like I’ve done a thousand times before. I always check to see if focus tube is clear of collimated view
Collimation spot on
Took a 90 sec image with camera way out of focus. You could see the collimated view of the scope in each of the stars. Then re focused nice and tight
Goto, focus , framing , guiding , capture all working fine as it’s done a thousand times before
EAF focuser working ok
Tried moving the primary mirror forward by 3 to 4 mm using some fibre washers but that just introduced more vignetting, so put the primary mirror back to its normal position
Checked focuser for slop, couldn’t feel any noticeable movement laterally, Focuser is pretty solid
Tried imaging with and without my L Extreme filter , no difference still wonky stars
Checked camera front plate for tilt with feeler gauges , same thickness all the way around as always, hasn’t moved
Insert camera into focuser with care to ensure it is flush and square as I’ve done a thousand times before
Used M83 and NGC5128 as test objects
Took 90 sec , 120 sec , 180 sec and 300 sec exposures on both , still wonky stars on all images
Also tried different gain settings on camera , stars still wonky

What has got me stumped I was imaging NGC 5128 3 nights earlier under crappy conditions ( heavy dew ) captured 50 x 90 sec subs , guiding was around 1.00 to 1.50 arc sec and stars were round , bloated due to seeing but at least round

3 nights later , same set up , same procedures and stars look crap , sort of blocky or triangular shaped ( not bad but noticeable)

Also another thing that’s got me stumped is that my focus Star looks perfect zoomed in 5x

But looking at a complete sub in APT plus using Astap , stars are crap across the field

Sorry for the long winded explanations but I’ve run out of puff trying to resolve the issue

It’s has to be Optics or in optical train but I’ve run out of ideas

Maybe the primary mirror is stuffed ?? It looked visually ok after I cleaned it

Comments, ideas , suggestions all welcome

Thanks

[glend (Glen)]

Martin, could it simply be the camera? Have you tried another camera? Given all that you have tried, there is no mention of the camera. I would look there, through every optical surface, right down to the sensor chamber.
Your focus star brightness may be over coming the diffraction. Is it a cooled camera, with the temperature set below 0C, humidity in the chamber could produce ice crystals. Have you serviced the dessicant? Etc. An examination of the camera at room temperature would tell you nothing.
The scary thing is that you may not find anything, until you duplicate the exact conditions again.
My money is on the camera.

[mura_gadi (Steve)]

If I read that right, after the heavy dew you have issues? I'd second the camera and sensor covers etc.

[RyanJones]

Hi Martin,

Images would help..... a lot.....

Is it possible that you’ve accidentally turned on heavy binning ?

That would explain when you’re doing a focus routine the settings are different for a live view vs when you’re imaging ?

Although that would explain the blockiness but not eggy...

[Startrek (Martin)]

Originally Posted by glend

Martin, could it simply be the camera? Have you tried another camera? Given all that you have tried, there is no mention of the camera. I would look there, through every optical surface, right down to the sensor chamber.
Your focus star brightness may be over coming the diffraction. Is it a cooled camera, with the temperature set below 0C, humidity in the chamber could produce ice crystals. Have you serviced the dessicant? Etc. An examination of the camera at room temperature would tell you nothing.
The scary thing is that you may not find anything, until you duplicate the exact conditions again.
My money is on the camera.

Glen
Thanks for your advice
I use a 2600MC cooled to -10C and leave my Anti dew setting in Ascom ticked or on ( as recommended by ZWO ) these cameras have an anti dew heater between the sensor and the UV/IR cut protective cover
Looking at my sensor with a bright light in a dark room it looks pristine
Desiccant was changed last year
I’ll try my DSLR next clear night and replicate procedures

Thanks
Martin

[Startrek (Martin)]

Originally Posted by mura_gadi

If I read that right, after the heavy dew you have issues? I'd second the camera and sensor covers etc.

Heavy dew 3 nights before but images were fine during that night
3 nights later clear pristine nights and issues with stars both nights
Camera is a 2600MC and cooled to -10C with in built anti dew heater to prevent frosting and dew issues , I always leave it switched on as recommended by ZWO
Camera sensor looks ok but I probably should clean and change desiccant
Going to try my DSLR next clear night and repeat sequence and capture

Thanks

[Startrek (Martin)]

Originally Posted by RyanJones

Hi Martin,

Images would help..... a lot.....

Is it possible that you’ve accidentally turned on heavy binning ?

That would explain when you’re doing a focus routine the settings are different for a live view vs when you’re imaging ?

Although that would explain the blockiness but not eggy...

Thanks Ryan
I only use live view for Goto ( centering) and framing which is bin 4x4 ( I don’t use live view for focusing
Focus and Capture I use bin 1x1 in the capture plan
I’m 100% sure I saw a 1 in the binning window, it’s a default setting and I have no reason to change it
Good point though
Thanks
Martin

[mura_gadi (Steve)]

Is there a way to display/retrieve the boot sequence from the camera(logs), that would contain a boot file for failed to load/detect errors on the BIOS/POST boot?

they may have failed after nearly five years, an indicator light is sometimes just part of the current, not a function is working per say...

[Startrek (Martin)]

Originally Posted by mura_gadi

Is there a way to display/retrieve the boot sequence from the camera, that would contain a boot file for failed to load/detect errors on the BIOS/POST boot?

they may have failed after nearly five years, an indicator light is sometimes just part of the current, not a function is working per say...

My 6” scope is 5 years old
My 2600MC camera is only 18 months old ( these entered the market in late 2019 early 2020 )
The reason for the title of the post was that I prematurely thought the cause was the scope ( didn’t even think of the camera as it gets cleaned every 12 months and new desiccant fitted )
I’m going to clean the sensor and protective window today and fit a new set of desiccant tablets
Then next clear night going try my DSLR , if the issue repeats itself it’s definitely the scope
If the stars are ok then it was the 2600MC camera. I can then swap over my DSLR for the 2600MC and take some images with fingers crossed

Thanks

Boot files and Bios is over my head , I’ll handball that my 38 year old Son whose an IT manager if needed in the future

[gregbradley]

The desiccant may need to be dried out. We have had a lot of rain and heavy humidity so I would not be surprised if you are getting frost on your sensor.

Frost disappears when you turn the camera off so when you are looking at it during the day you won't see any.

But frost appears in images like weird noisy area in the image that usually grows as it forms and disappears gradually if you turn the cooling off.

It may not be it but its a possibility.

Is it possible your camera has had a knock so the sensor's orthogonality has changed? So it might be tilt?

Wonky stars don't have many causes:

1. Poor collimation.
2. Coma. stars elongate towards the corners.
3. Tilt.
4. Out of focus.
5. Bad tracking (eggy).
6. Pinched optics.
7. Too great a thermal difference between the primary mirror and ambient air temps.

Do you get wonky stars when you do test exposures after focusing?

Try manually focusing as perhaps your autofocuser is not actually getting it to exact focus. I have some scopes that give triangular stars when a bit out of focus but perfectly round when tightly focused.

I wonder if the fact we've had so much rain in the last 9 months has had a deleterious effect on your mirrors. Do these glasses absorb some moisture over time if continually subjected to extremely moist air?

Could a lens in your corrector be loose?

Greg.

[AdamJL]

Hi Martin

+1, can you upload a sub? I know you said "no images", but it'd be good to inspect this "in person"

Cheers
Adam

[Shiraz (Ray)]

could it possibly be boundary layer/tube currents? nice clear nights are ideal for thermal effects in a Newt, as suggested by Greg.
cheers ray

[Startrek (Martin)]

Originally Posted by gregbradley

The desiccant may need to be dried out. We have had a lot of rain and heavy humidity so I would not be surprised if you are getting frost on your sensor.

Frost disappears when you turn the camera off so when you are looking at it during the day you won't see any.

But frost appears in images like weird noisy area in the image that usually grows as it forms and disappears gradually if you turn the cooling off.

It may not be it but its a possibility.

Is it possible your camera has had a knock so the sensor's orthogonality has changed? So it might be tilt?

Wonky stars don't have many causes:

1. Poor collimation.
2. Coma. stars elongate towards the corners.
3. Tilt.
4. Out of focus.
5. Bad tracking (eggy).
6. Pinched optics.
7. Too great a thermal difference between the primary mirror and ambient air temps.

Do you get wonky stars when you do test exposures after focusing?

Try manually focusing as perhaps your autofocuser is not actually getting it to exact focus. I have some scopes that give triangular stars when a bit out of focus but perfectly round when tightly focused.

I wonder if the fact we've had so much rain in the last 9 months has had a deleterious effect on your mirrors. Do these glasses absorb some moisture over time if continually subjected to extremely moist air?

Could a lens in your corrector be loose?

Greg.

Thanks Greg
All valid points and checks which I have looked at
My camera now has been cleaned and re desiccated
Friday night looks like an opportunity to test again
Martin

[Startrek (Martin)]

Originally Posted by AdamJL

Hi Martin

+1, can you upload a sub? I know you said "no images", but it'd be good to inspect this "in person"

Cheers
Adam

Thanks Adam
Hope to do further testing Friday night
Martin

[Startrek (Martin)]

Originally Posted by Shiraz

could it possibly be boundary layer/tube currents? nice clear nights are ideal for thermal effects in a Newt, as suggested by Greg.
cheers ray

Thanks
Good point , but why now after years and years using this scope ??

[Startrek (Martin)]

Problem resolved tonight
Re collimated scope
Cleaned 2600MC sensor and protective window plus installed new desiccant tabs
Tried my DSLR in the scope , round stars with 60 sec unguided subs
Installed the 2600MC , still wonky stars
Hmm.... penny dropped, must be my spacing on the coma corrector as the scope is an f6 whereas my bigger scope down south is an f5
Reduced my spacers up and down by 0.5mm and took test subs for review
Ended up with no spacers at all ( so 55mm neat to sensor ) and stars round to almost edge of field , just a bit of coma on the left hand side edges and corners only, right side perfect to edge and corners
Why this has happened now , and not a year or two ago , I have no idea
The camera sensor could have been a bit dirty or some moisture around but I doubt it
Ran a 300 sec sub and checked Star shape, all good

So now my 6” f6 newt requires no spacers
My 8” f5 newt requires 4 x 0.5mm spacers
I just received and built my 10” f5 Carbon fibre Newt today but no EQ8-R mount yet , it 3 to 4 weeks away , so another round of testing for Star shape when I build the new rig down south
Thanks for all your advice and assistance
Much appreciated !!

[AdamJL]

Glad you got it sorted, Martin

[Nikolas (Nik)]

Good outcome in the end

[RyanJones]

Glad you got it sorted Martin

I’m a little confused. I thought your wonky stars were right across the whole field ? This might have been where an image to look at would have helped. You were over corrected then ? So forming a star shape with the cross forming a concentric circle around the whole image as opposed to blocks? You mentioned that you added more shims so this would have made the problem worse and would have made the stars more cross shaped ? Again not on axis but getting worse further from the center of the image ?

Please don’t think I’m being antagonizing, it’s not my intention. I’m breaking this down for anyone else that might be reading it to understand what they might be looking at with over corrected coma.

It’s also important for others reading to note the issue that you came across and understand what is happening here. So the faster the optics, the greater the curve in the primary mirror. Consequently the more correction required to return the image to a flat plane for the sensor. At f/6 the distance required for that correction to occur is shorter than at f/5 hence the lower spacing. There is also a limit to how fast an optic a given corrector is capable of correcting. This is why really fast optics have specific correctors made for them as opposed to multi purpose correctors. It is also worth noting that the manufacturers specifications ie. 55mm is a starting point and will likely require adjustments to properly achieve correction of each individuals optics.

I hope this has broken things down for others to understand

Cheers

Ryan

[Startrek (Martin)]

Originally Posted by RyanJones

Glad you got it sorted Martin

I’m a little confused. I thought your wonky stars were right across the whole field ? This might have been where an image to look at would have helped. You were over corrected then ? So forming a star shape with the cross forming a concentric circle around the whole image as opposed to blocks? You mentioned that you added more shims so this would have made the problem worse and would have made the stars more cross shaped ? Again not on axis but getting worse further from the center of the image ?

Please don’t think I’m being antagonizing, it’s not my intention. I’m breaking this down for anyone else that might be reading it to understand what they might be looking at with over corrected coma.

It’s also important for others reading to note the issue that you came across and understand what is happening here. So the faster the optics, the greater the curve in the primary mirror. Consequently the more correction required to return the image to a flat plane for the sensor. At f/6 the distance required for that correction to occur is shorter than at f/5 hence the lower spacing. There is also a limit to how fast an optic a given corrector is capable of correcting. This is why really fast optics have specific correctors made for them as opposed to multi purpose correctors. It is also worth noting that the manufacturers specifications ie. 55mm is a starting point and will likely require adjustments to properly achieve correction of each individuals optics.

I hope this has broken things down for others to understand

Cheers

Ryan

Ryan
I think this maybe overcomplicating things by trying to analyse my issues to deeply, it’s an issue which has multiple fronts and I’ve tackled each one by trial and error with some success
And yes I did remove all my spacers last night to leave the distance at 55mm which has helped a lot , whereas a week before , I had spacers of 1.5mm and my stars were fine ( no answer at all for that scenario )
My stars are better now but still slightly off shaped on the far left hand side
Could be the coma corrector
Could be the primary mirror ( there is a slight chip on one side on the edge )
Could be the primary mirror cell holder or adjusting screws
Could be the focuser
Could be the camera
Could be ...... many things

What I can’t resolve is that a week ago my stars were fine and somehow they changed without me touching anything on the rig and it’s equipment

I don’t think my experience is of any use to others as there are so many variables and you have to work through them one at a time

No one shoe fits all with optical problems ( only the blatantly obvious)

Thanks as always for enquiring

Cheers
Martin