Flexure or tracking? (Another "cold night" from northern Indiana)


Joel Short
 

Like Roland experienced, last night was a very cold night in northern Indiana but the first clear night in a while.  Thankfully I operate everything remotely from the comfort of my living room.  

I have a new to me AGO 12.5" iDK riding on my AP1100GTO, and last night was the first true imaging test - 10min narrowband images of NGC2371 (ASI6200MM).  I noticed that more often than not the stars were slightly elongated in the same direction all across the image.  Interestingly, after the meridian flip, the elongation looked like is was rotated 90deg.  Prior to the flip the stars pointed toward the upper right corner; after the flip the stars pointed to the upper left corner.  I checked polar alignment and it is good.  Guiding was quite good.  I saw an average RMS RA of 0.4", Dec of 0.3".  Also, I use an OAG for guiding.

To me the star elongation, then rotated after the meridian flip, would indicate some kind of flexure issue.  Does that sound right?
I'm not sure where any flexure would come from since I'm using an OAG.  Any thoughts?
joel


Roland Christen
 

Sometimes the scope itself has problems in the cold. Things like pinched optics caused by metal cells contracting and pressing on the optics. You can also have heat plumes from the cameras and electronics that cause elongation of stars from the thermals inside focuser tubes. Last night, because of the intense cold, my camera fan vibrated the entire telescope tube to the point that it filled the observatory with a loud buzz. The tube acted like a drum skin and I could actually feel the vibration on the tube. I could see the effect on the star images when i turned the fan on and off.

One other thing i noticed is when imaging in Luminance below 45 degrees, the stars will be slightly oval simply because atmospheric refraction actually stretches the stars out into a short spectrum. I first noticed that with my 10"F14 Mak-Cass, but I can also see it when using the 160EDF refractor. The individual RGB images will be perfectly round, but the Luminance will be slightly oval. The effect was especially so last night because of the cold air and high pressure which increases the refractive effect of the atmosphere.

Finally, I feel that people make far too much out of stars being round or not, and lose sight of the beauty of the images that they can capture. On Cloudy Nights it seems that people obsess about round stars and how long they can image unguided, without realizing that nature throws lots of boulders in their way to the mountain top.

Rolando



-----Original Message-----
From: Joel Short <buckeyestargazer@...>
To: main@ap-gto.groups.io
Sent: Sat, Jan 23, 2021 10:29 am
Subject: [ap-gto] Flexure or tracking? (Another "cold night" from northern Indiana)

Like Roland experienced, last night was a very cold night in northern Indiana but the first clear night in a while.  Thankfully I operate everything remotely from the comfort of my living room.  

I have a new to me AGO 12.5" iDK riding on my AP1100GTO, and last night was the first true imaging test - 10min narrowband images of NGC2371 (ASI6200MM).  I noticed that more often than not the stars were slightly elongated in the same direction all across the image.  Interestingly, after the meridian flip, the elongation looked like is was rotated 90deg.  Prior to the flip the stars pointed toward the upper right corner; after the flip the stars pointed to the upper left corner.  I checked polar alignment and it is good.  Guiding was quite good.  I saw an average RMS RA of 0.4", Dec of 0.3".  Also, I use an OAG for guiding.

To me the star elongation, then rotated after the meridian flip, would indicate some kind of flexure issue.  Does that sound right?
I'm not sure where any flexure would come from since I'm using an OAG.  Any thoughts?
joel

--
Roland Christen
Astro-Physics


Joel Short
 

Well, I'm guilty as charged...I do obsess over round stars LOL.
This doesn't look like pinching optics to me.  I tried to do some experiments with the scope fans on and off, and I didn't see a difference.  I had the camera temperature set to -10C and the cooler/fan was hardly ever on. But I have read other reports of the fan on this camera causing something like this.  It's just hard to imagine a tiny, quiet fan affecting a 45lb scope. I suspect thermal issues here, but I'm not sure what to do about it, if anything. 

Your comment about the LUM stars being slightly oval because of atmospheric refraction is an interesting one.  The object was above 45deg most of the night.  Would narrowband filters show this same effect?  About every 4th image gave me nearly perfect round stars, but I can't correlate anything with those images.  

I appreciate your thoughts Roland.
joel


On Sat, Jan 23, 2021 at 11:04 AM Roland Christen via groups.io <chris1011=aol.com@groups.io> wrote:
Sometimes the scope itself has problems in the cold. Things like pinched optics caused by metal cells contracting and pressing on the optics. You can also have heat plumes from the cameras and electronics that cause elongation of stars from the thermals inside focuser tubes. Last night, because of the intense cold, my camera fan vibrated the entire telescope tube to the point that it filled the observatory with a loud buzz. The tube acted like a drum skin and I could actually feel the vibration on the tube. I could see the effect on the star images when i turned the fan on and off.

One other thing i noticed is when imaging in Luminance below 45 degrees, the stars will be slightly oval simply because atmospheric refraction actually stretches the stars out into a short spectrum. I first noticed that with my 10"F14 Mak-Cass, but I can also see it when using the 160EDF refractor. The individual RGB images will be perfectly round, but the Luminance will be slightly oval. The effect was especially so last night because of the cold air and high pressure which increases the refractive effect of the atmosphere.

Finally, I feel that people make far too much out of stars being round or not, and lose sight of the beauty of the images that they can capture. On Cloudy Nights it seems that people obsess about round stars and how long they can image unguided, without realizing that nature throws lots of boulders in their way to the mountain top.

Rolando


Roland Christen
 

At our Chile observatory we had to remove the fans from the FLI camera and replace them with low vibration fans. The original fans caused 2:1 oblong stars, which totally freaked me out at first until I realized the cause. The scope itself is very robust, but that's not what was moving around. The imaging train after the focuser included a large and heavy 10 position filter wheel, an off-axis guider and the camera itself. All of that equipment was vibrating, the scope itself was not.

Rolando

-----Original Message-----
From: Joel Short <buckeyestargazer@...>
To: main@ap-gto.groups.io
Sent: Sat, Jan 23, 2021 11:26 am
Subject: Re: [ap-gto] Flexure or tracking? (Another "cold night" from northern Indiana)

Well, I'm guilty as charged...I do obsess over round stars LOL.
This doesn't look like pinching optics to me.  I tried to do some experiments with the scope fans on and off, and I didn't see a difference.  I had the camera temperature set to -10C and the cooler/fan was hardly ever on. But I have read other reports of the fan on this camera causing something like this.  It's just hard to imagine a tiny, quiet fan affecting a 45lb scope. I suspect thermal issues here, but I'm not sure what to do about it, if anything. 

Your comment about the LUM stars being slightly oval because of atmospheric refraction is an interesting one.  The object was above 45deg most of the night.  Would narrowband filters show this same effect?  About every 4th image gave me nearly perfect round stars, but I can't correlate anything with those images.  

I appreciate your thoughts Roland.
joel

On Sat, Jan 23, 2021 at 11:04 AM Roland Christen via groups.io <chris1011=aol.com@groups.io> wrote:
Sometimes the scope itself has problems in the cold. Things like pinched optics caused by metal cells contracting and pressing on the optics. You can also have heat plumes from the cameras and electronics that cause elongation of stars from the thermals inside focuser tubes. Last night, because of the intense cold, my camera fan vibrated the entire telescope tube to the point that it filled the observatory with a loud buzz. The tube acted like a drum skin and I could actually feel the vibration on the tube. I could see the effect on the star images when i turned the fan on and off.

One other thing i noticed is when imaging in Luminance below 45 degrees, the stars will be slightly oval simply because atmospheric refraction actually stretches the stars out into a short spectrum. I first noticed that with my 10"F14 Mak-Cass, but I can also see it when using the 160EDF refractor. The individual RGB images will be perfectly round, but the Luminance will be slightly oval. The effect was especially so last night because of the cold air and high pressure which increases the refractive effect of the atmosphere.

Finally, I feel that people make far too much out of stars being round or not, and lose sight of the beauty of the images that they can capture. On Cloudy Nights it seems that people obsess about round stars and how long they can image unguided, without realizing that nature throws lots of boulders in their way to the mountain top.

Rolando

--
Roland Christen
Astro-Physics


Ray Gralak
 

Hi Joel,

Guiding was quite good. I saw an average RMS RA of 0.4", Dec of 0.3".
Also, I use an OAG for guiding.
Since auto-guiding looked good, that eliminates mount tracking as the problem. You need to look elsewhere.

My first thought was tilted/moving optics, a sagging focuser, or a non-orthogonal camera sensor. Or some mixture of these.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Joel Short
Sent: Saturday, January 23, 2021 9:27 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Flexure or tracking? (Another "cold night" from northern Indiana)

Well, I'm guilty as charged...I do obsess over round stars LOL.
This doesn't look like pinching optics to me. I tried to do some experiments with the scope fans on and off, and I
didn't see a difference. I had the camera temperature set to -10C and the cooler/fan was hardly ever on. But I
have read other reports of the fan on this camera causing something like this. It's just hard to imagine a tiny,
quiet fan affecting a 45lb scope. I suspect thermal issues here, but I'm not sure what to do about it, if anything.

Your comment about the LUM stars being slightly oval because of atmospheric refraction is an interesting one.
The object was above 45deg most of the night. Would narrowband filters show this same effect? About every
4th image gave me nearly perfect round stars, but I can't correlate anything with those images.

I appreciate your thoughts Roland.
joel

On Sat, Jan 23, 2021 at 11:04 AM Roland Christen via groups.io <chris1011=aol.com@groups.io> wrote:


Sometimes the scope itself has problems in the cold. Things like pinched optics caused by metal cells
contracting and pressing on the optics. You can also have heat plumes from the cameras and electronics that
cause elongation of stars from the thermals inside focuser tubes. Last night, because of the intense cold, my
camera fan vibrated the entire telescope tube to the point that it filled the observatory with a loud buzz. The tube
acted like a drum skin and I could actually feel the vibration on the tube. I could see the effect on the star images
when i turned the fan on and off.



One other thing i noticed is when imaging in Luminance below 45 degrees, the stars will be slightly oval
simply because atmospheric refraction actually stretches the stars out into a short spectrum. I first noticed that
with my 10"F14 Mak-Cass, but I can also see it when using the 160EDF refractor. The individual RGB images will
be perfectly round, but the Luminance will be slightly oval. The effect was especially so last night because of the
cold air and high pressure which increases the refractive effect of the atmosphere.



Finally, I feel that people make far too much out of stars being round or not, and lose sight of the beauty of
the images that they can capture. On Cloudy Nights it seems that people obsess about round stars and how long
they can image unguided, without realizing that nature throws lots of boulders in their way to the mountain top.


Rolando






Joel Short
 

Ray, 
I use this same focuser (Feathertouch) on another scope with the same camera setup and I don't see this same effect so I doubt it's focuser sag.  
However I now wonder about tilted optics. My collimation tests look good with round stars in the corners across a full frame sensor.  However I have noticed that the diffraction spike on very bright stars has one spike (of 4) that is much longer than the other 3.  If I remember, next time I'm out I'll save an image of this.  Any idea if that indicates a mirror tilt issue?  Again, collimation tests look good.  

Rolando, I might look around for a replacement low vibration fan for the camera.  That's an inexpensive and easy thing to do so it can't hurt.
joel


On Sat, Jan 23, 2021 at 11:39 AM Ray Gralak <groups3@...> wrote:
Hi Joel,

> Guiding was quite good.  I saw an average RMS RA of 0.4", Dec of 0.3". 
> Also, I use an OAG for guiding.

Since auto-guiding looked good, that eliminates mount tracking as the problem. You need to look elsewhere.

My first thought was tilted/moving optics, a sagging focuser, or a non-orthogonal camera sensor. Or some mixture of these.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


Ray Gralak
 

Joel,

However I now wonder about tilted optics. My collimation tests look good with round stars in the corners across a
full frame sensor.
You might want to verify that collimation holds throughout the sky by taking short images in different parts of the sky and checking the images for star roundness.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Joel Short
Sent: Saturday, January 23, 2021 9:48 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Flexure or tracking? (Another "cold night" from northern Indiana)

Ray,
I use this same focuser (Feathertouch) on another scope with the same camera setup and I don't see this same
effect so I doubt it's focuser sag.
However I now wonder about tilted optics. My collimation tests look good with round stars in the corners across a
full frame sensor. However I have noticed that the diffraction spike on very bright stars has one spike (of 4) that
is much longer than the other 3. If I remember, next time I'm out I'll save an image of this. Any idea if that
indicates a mirror tilt issue? Again, collimation tests look good.

Rolando, I might look around for a replacement low vibration fan for the camera. That's an inexpensive and easy
thing to do so it can't hurt.
joel

On Sat, Jan 23, 2021 at 11:39 AM Ray Gralak <groups3@gralak.com> wrote:


Hi Joel,

> Guiding was quite good. I saw an average RMS RA of 0.4", Dec of 0.3".
> Also, I use an OAG for guiding.

Since auto-guiding looked good, that eliminates mount tracking as the problem. You need to look
elsewhere.

My first thought was tilted/moving optics, a sagging focuser, or a non-orthogonal camera sensor. Or some
mixture of these.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver



Joel Short
 

That's a good idea Ray.  I'll check collimation throughout the sky next time I'm out.
joel


On Sat, Jan 23, 2021 at 12:02 PM Ray Gralak <groups3@...> wrote:
Joel,

> However I now wonder about tilted optics. My collimation tests look good with round stars in the corners across a
> full frame sensor.

You might want to verify that collimation holds throughout the sky by taking short images in different parts of the sky and checking the images for star roundness.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


Joel Short
 

"At our Chile observatory we had to remove the fans from the FLI camera and replace them with low vibration fans. The original fans caused 2:1 oblong stars, which totally freaked me out at first until I realized the cause. The scope itself is very robust, but that's not what was moving around. The imaging train after the focuser included a large and heavy 10 position filter wheel, an off-axis guider and the camera itself. All of that equipment was vibrating, the scope itself was not.
 
Rolando"

Following up with this, I decided to go ahead and replace my camera fans, but I'm having trouble finding a good low vibration fan.  Noctua is regarded as the best but they don't make the size I need (50mmx50mm).  Any other small case fan brand  recommendations?
joel


Roland Christen
 

I don't remember what was picked for our camera down there. Dave Jurasevich picked the fans.

Roland



-----Original Message-----
From: Joel Short <buckeyestargazer@...>
To: main@ap-gto.groups.io
Sent: Wed, Jan 27, 2021 3:26 pm
Subject: Re: [ap-gto] Flexure or tracking? (Another "cold night" from northern Indiana)

"At our Chile observatory we had to remove the fans from the FLI camera and replace them with low vibration fans. The original fans caused 2:1 oblong stars, which totally freaked me out at first until I realized the cause. The scope itself is very robust, but that's not what was moving around. The imaging train after the focuser included a large and heavy 10 position filter wheel, an off-axis guider and the camera itself. All of that equipment was vibrating, the scope itself was not.
 
Rolando"

Following up with this, I decided to go ahead and replace my camera fans, but I'm having trouble finding a good low vibration fan.  Noctua is regarded as the best but they don't make the size I need (50mmx50mm).  Any other small case fan brand  recommendations?
joel

--
Roland Christen
Astro-Physics


Mike Dodd
 

Following up with this, I decided to go ahead and replace my camera
fans, but I'm having trouble finding a good low vibration fan. Noctua
is regarded as the best but they don't make the size I need
(50mmx50mm). Any other small case fan brand recommendations?
I have used Sunon Maglev fans for many years with good results: <https://www.mouser.com/Sunon/Thermal-Management/Fans-Blowers/Fans/DC-Fans/MagLev/_/N-dwatb?P=1y9c0j0Z1y97tnr>

--- Mike


Joel Short
 

Mike,
The current fans in my cameras are actually Sunon Maglevs.  I know at least one other person has documented vibration induced oblong stars with these fans in the same camera I'm using (ASI6200MM).  
joel


On Wed, Jan 27, 2021 at 3:47 PM Mike Dodd <mike@...> wrote:

> Following up with this, I decided to go ahead and replace my camera
> fans, but I'm having trouble finding a good low vibration fan.  Noctua
> is regarded as the best but they don't make the size I need
> (50mmx50mm).  Any other small case fan brand  recommendations?

I have used Sunon Maglev fans for many years with good results:
<https://www.mouser.com/Sunon/Thermal-Management/Fans-Blowers/Fans/DC-Fans/MagLev/_/N-dwatb?P=1y9c0j0Z1y97tnr>

--- Mike


Don Anderson
 

If the OEM fans are causing these kinds of problems, wouldn't FLI replace them? For the kind of money those puppies cost, I can't believe they are not there for you.

Don Anderson


On Wednesday, January 27, 2021, 02:47:46 p.m. MST, Mike Dodd <mike@...> wrote:



> Following up with this, I decided to go ahead and replace my camera
> fans, but I'm having trouble finding a good low vibration fan.  Noctua
> is regarded as the best but they don't make the size I need
> (50mmx50mm).  Any other small case fan brand  recommendations?

I have used Sunon Maglev fans for many years with good results:
<https://www.mouser.com/Sunon/Thermal-Management/Fans-Blowers/Fans/DC-Fans/MagLev/_/N-dwatb?P=1y9c0j0Z1y97tnr>

--- Mike









Joel Short
 

An update to this...last night I had about 4hrs of clear sky and in order to test the theory about the fans causing the elongated stars I unplugged the fan from the camera.  It was still plenty cold enough to reach my -10C set point without issue.  Long story short, every single sub that came in had perfectly round stars.  The difference seems obvious to me.  With the fan operating as normal about 3/5 subs came in with elongated stars.  With the fan disconnected every sub was perfect.  

The problem is that I'm not exactly sure what to do about it.  Noctua is generally regarded as the best brand for silent and vibration free fans, but they do not make the size I need (50mm).  I did buy some fans that look better than the stock ones I have, and I'm going to try some Noctua silicone rubber mounting things that are supposed to help isolate the fan from the case (if they fit on the camera). We'll see how that goes. 

In any event, this is no longer an Astro-Physics related discussion so I'll look elsewhere.  
joel


Roland Christen
 

When we had the problem in Chile I improvised by using a frame with the fans mounted with 4 rubber bands for each fan. That solved the problem and allowed us to do some imaging before new fans were installed.

Rolando


-----Original Message-----
From: Joel Short <buckeyestargazer@...>
To: main@ap-gto.groups.io
Sent: Fri, Jan 29, 2021 4:15 pm
Subject: Re: [ap-gto] Flexure or tracking? (Another "cold night" from northern Indiana)

An update to this...last night I had about 4hrs of clear sky and in order to test the theory about the fans causing the elongated stars I unplugged the fan from the camera.  It was still plenty cold enough to reach my -10C set point without issue.  Long story short, every single sub that came in had perfectly round stars.  The difference seems obvious to me.  With the fan operating as normal about 3/5 subs came in with elongated stars.  With the fan disconnected every sub was perfect.  

The problem is that I'm not exactly sure what to do about it.  Noctua is generally regarded as the best brand for silent and vibration free fans, but they do not make the size I need (50mm).  I did buy some fans that look better than the stock ones I have, and I'm going to try some Noctua silicone rubber mounting things that are supposed to help isolate the fan from the case (if they fit on the camera). We'll see how that goes. 

In any event, this is no longer an Astro-Physics related discussion so I'll look elsewhere.  
joel

--
Roland Christen
Astro-Physics