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Elongated Stars Following Merdian Flip

Bruce Donzanti
 

I recently replaced my Stellarvue with a Takahashi FSQ-85 EDX on top of my C11" EdgeHD.  The mount is an AP1100.  I've have used this setup the past 2 years with NINA with issues until I replaced the Stellarvue with the Tak.  Everything works fine except for the first 5-minute frame following meridian flip, which is showing elongated stars.  Then, things settle down for the rest of the session.  All screws are tight, scope is well-balanced, cables are managed through the mount with no snags, and I cannot find any loose parts. I use an Optec ThirdLynx auto-motor focuser on the Tak, similar to the one that I used on the Stellarvue.  I've heard stories in the past of the Tak focuser slipping but the Optec autofocuser has it locked in place.  I have not had time (weather-related) to test the C11 to see if it will start doing the same thing.  I do not think it is a mount issue but I am asking here just in case someone else has experienced this and what the potential causes could be.  I guess if the C11 now starts doing this, it could be a mount problem, but I find it suspicious that it only started happening when I swapped the scopes (along with the dovetail plate and support rings).  I've attached a couple of pics of the setup but they may not help much.  

Any thoughts would be appreciated.

Bruce

Cheng-Yang Tan
 

I'd suggest looking at the camera angle rotator CAA. My CAA on my FSQ106 was slipping even though I thought I had really tightened it down. I replaced the entire focuser mechanism with a NiteCrawler and have had no problems ever since.

cytan

On Friday, September 23, 2022 at 08:19:35 AM CDT, Bruce Donzanti <donza2735@...> wrote:


I recently replaced my Stellarvue with a Takahashi FSQ-85 EDX on top of my C11" EdgeHD.  The mount is an AP1100.  I've have used this setup the past 2 years with NINA with issues until I replaced the Stellarvue with the Tak.  Everything works fine except for the first 5-minute frame following meridian flip, which is showing elongated stars.  Then, things settle down for the rest of the session.  All screws are tight, scope is well-balanced, cables are managed through the mount with no snags, and I cannot find any loose parts. I use an Optec ThirdLynx auto-motor focuser on the Tak, similar to the one that I used on the Stellarvue.  I've heard stories in the past of the Tak focuser slipping but the Optec autofocuser has it locked in place.  I have not had time (weather-related) to test the C11 to see if it will start doing the same thing.  I do not think it is a mount issue but I am asking here just in case someone else has experienced this and what the potential causes could be.  I guess if the C11 now starts doing this, it could be a mount problem, but I find it suspicious that it only started happening when I swapped the scopes (along with the dovetail plate and support rings).  I've attached a couple of pics of the setup but they may not help much.  

Any thoughts would be appreciated.

Bruce

Bruce Donzanti
 

I would not have thought to check the CAA.

Thank you

Kent Kirkley
 

I doubt a mount problem. More than likely differential flexure. Are you using the Tak as a guidescope? Tak instruments are heavy and even if hardware attachment devices are seemingly beefy and secure, things can move. The felt inside rings can allow movement. 


On Sep 23, 2022, at 8:23 AM, Cheng-Yang Tan via groups.io <cytan299@...> wrote:


I'd suggest looking at the camera angle rotator CAA. My CAA on my FSQ106 was slipping even though I thought I had really tightened it down. I replaced the entire focuser mechanism with a NiteCrawler and have had no problems ever since.

cytan

On Friday, September 23, 2022 at 08:19:35 AM CDT, Bruce Donzanti <donza2735@...> wrote:


I recently replaced my Stellarvue with a Takahashi FSQ-85 EDX on top of my C11" EdgeHD.  The mount is an AP1100.  I've have used this setup the past 2 years with NINA with issues until I replaced the Stellarvue with the Tak.  Everything works fine except for the first 5-minute frame following meridian flip, which is showing elongated stars.  Then, things settle down for the rest of the session.  All screws are tight, scope is well-balanced, cables are managed through the mount with no snags, and I cannot find any loose parts. I use an Optec ThirdLynx auto-motor focuser on the Tak, similar to the one that I used on the Stellarvue.  I've heard stories in the past of the Tak focuser slipping but the Optec autofocuser has it locked in place.  I have not had time (weather-related) to test the C11 to see if it will start doing the same thing.  I do not think it is a mount issue but I am asking here just in case someone else has experienced this and what the potential causes could be.  I guess if the C11 now starts doing this, it could be a mount problem, but I find it suspicious that it only started happening when I swapped the scopes (along with the dovetail plate and support rings).  I've attached a couple of pics of the setup but they may not help much.  

Any thoughts would be appreciated.

Bruce

Bruce Donzanti
 

No- it is being used as an imaging scope.  I can guide using the guide scope attached to it or the OAG on the C11.  It is no heavier than the Stellarvue.  It could be some new flexure introduced by the Tak that I can't seem to identify yet. 

Thanks 

Kent Kirkley
 

Ok, I see people stacking all kinds of optical tubes on top of each other. This is just asking for flexure. I had an AP155 with a guidescope on top mounted in rings and kept having elongated stars. "Mr. AP" suggested using a lightweight guidescope attached directly to the 155's tube, not with plates or rings. I redid my guidescope arrangement to reflect this and elongated stars stopped happening.
Kent Kirkley


On Sep 23, 2022, at 8:46 AM, Bruce Donzanti <donza2735@...> wrote:

No- it is being used as an imaging scope.  I can guide using the guide scope attached to it or the OAG on the C11.  It is no heavier than the Stellarvue.  It could be some new flexure introduced by the Tak that I can't seem to identify yet. 

Thanks 

Bruce Donzanti
 

Then that argues going back to me using the OAG on the C11, which always worked well, even better than the guide scope on the Stellarvue.  Actually, the guide scope on the Tak is a backup in case the OAG does not play nice on certain nights.  This was only my second night testing it.  If the OAG on the C11 works as it has in the past, problem solved.

Kent Kirkley
 

Guiding the short focal length TAK with the very long focal length C11 can still be effected by flexure, it just may not show up. That might be OK, but, as you probably know finding a guide star with an OAG isn't always easy, although with the much wider field of the TAK there are more suitable stars available.
In my AP155 elongated star issue I got rid of the longish focal length guidscope and stated using a very lightweight, short focal length guidscope attached directly to the 155's rear tube.
With today's guide cameras long focal length guidscopes aren't necessary.
Kent

On Friday, September 23, 2022, 9:14:14 AM CDT, Bruce Donzanti <donza2735@...> wrote:


Then that argues going back to me using the OAG on the C11, which always worked well, even better than the guide scope on the Stellarvue.  Actually, the guide scope on the Tak is a backup in case the OAG does not play nice on certain nights.  This was only my second night testing it.  If the OAG on the C11 works as it has in the past, problem solved.

Bruce Donzanti
 

What guide scope did you use? 

Kent Kirkley
 

I use an SBIG STL-11000 full frame camera with the SBIG Remote Guide Head camera.
The actual 'guidescope' is a 100mm focal length optic that SBIG once sold, which name I can't remember at the moment. It screws into the Remote Guide Head. So this 100mm fl guidescope guides the AP155, 1000mm fl with no problem. Now the SBIG STL-11000 system in now old but
there are any number of short focal length optics that can be used, even old, manual focus 100mm camera lenses mounted to a guide camera, light weight and cheap. It's just a matter of figuring out how to put it together.
Kent

On Friday, September 23, 2022, 10:05:48 AM CDT, Bruce Donzanti <donza2735@...> wrote:


What guide scope did you use? 

Terry Martin
 

Hi Bruce,

Are you using the Smart Meridian Flip plug-in in NINA?  If not, you should.  I've seen the same issue in NINA when not using the plug-in as NINA will initiate the flip when it is time whether your in the middle of an exposure or not.  Using the plug in will eliminate the issue.  

Now, I'm not saying that differential flexure is not an issue as well, with that mountain of stuff on top of your C11, but if you're not seeing any issues beyond the time of the meridian flip, then try the plug-in.

~Terry

Roland Christen
 


Everything works fine except for the first 5-minute frame following meridian flip, which is showing elongated stars.  Then, things settle down for the rest of the session. 
If the guiding is normal then the mount is doing what the guide program is telling it to do. The mount cannot know what the imaging scope is doing. The imaging scope may be flexing when pointing straight up after the flip. As long as the guiding is correct and accurate, that's all that the mount can do - it cannot compensate for differential flexure between imaging scope and guide scope.

The most accurate way to guide is with an off-axis guider. That way any flexure in the imaging scope is automatically resolved by the guiding software. You can never expect that a separate guide scope will eliminate errors of flexure in an imaging scope, no matter how well you think that things are connected. And this is especially true when the guide scope is connected to the rings instead of hard fixed to the focuser of the imaging scope.

Roland Christen
Astro-Physics


-----Original Message-----
From: Bruce Donzanti <donza2735@...>
To: main@ap-gto.groups.io
Sent: Fri, Sep 23, 2022 8:19 am
Subject: [ap-gto] Elongated Stars Following Merdian Flip

I recently replaced my Stellarvue with a Takahashi FSQ-85 EDX on top of my C11" EdgeHD.  The mount is an AP1100.  I've have used this setup the past 2 years with NINA with issues until I replaced the Stellarvue with the Tak.  Everything works fine except for the first 5-minute frame following meridian flip, which is showing elongated stars.  Then, things settle down for the rest of the session.  All screws are tight, scope is well-balanced, cables are managed through the mount with no snags, and I cannot find any loose parts. I use an Optec ThirdLynx auto-motor focuser on the Tak, similar to the one that I used on the Stellarvue.  I've heard stories in the past of the Tak focuser slipping but the Optec autofocuser has it locked in place.  I have not had time (weather-related) to test the C11 to see if it will start doing the same thing.  I do not think it is a mount issue but I am asking here just in case someone else has experienced this and what the potential causes could be.  I guess if the C11 now starts doing this, it could be a mount problem, but I find it suspicious that it only started happening when I swapped the scopes (along with the dovetail plate and support rings).  I've attached a couple of pics of the setup but they may not help much.  

Any thoughts would be appreciated.

Bruce

--
Roland Christen
Astro-Physics

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