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Blurry subrames coming from my 10" Newt

Optolong L-eXtreme Acquisition Deep Sky Help Needed Troubleshooting
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Dimitris Kavallieratos avatar
Dimitris Kavallieratos avatar
Hello everyone! Merry christmas and a happy new astro-year for 2023!

Last night had a session capturing the tadpoles nebula, and while focusing my 10" Newt the preview on NINA was very blurry (using ASI533 and L-Extreme filter).My collimaiton was spot on and all other parameters was the same when capturing with the same telescope and had sharp images previously...

Just to get the picture this is "good" 5min subframe from my last session and my 2secs frames for focusing was as blurry as this (stretched and debayered):



The maximum HFR with 0.77"/pixel scale that I observed yesterday was about 3.1-3.3. The frame above has a FWHM of about 2.55. My worst ones are about 5-6 FWHM and twice as bad as this...

I hope this has to do with atmospheric turbulance ,but the weather was quite calm yesterday...

Also,as another side effect of this-I imagine that loose stars are to blame- the integrated image cannot be plate solved in PI with image solver or WBPP through GAIA DR3 database.

Any ideas?

Thank you in advance.
Dimitris.
andrea tasselli avatar
andrea tasselli avatar
It does happen, from time to time, that the seeing is really bad, mostly when there is an inversion layer further up in the atmosphere. The night feels steady but in reality isn't. Clearly, if your FWHM varies during the session in random fashion then the issue is with the seeing and not with a systemic issue.
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Dimitris Kavallieratos avatar
Dimitris Kavallieratos avatar
andrea tasselli:
It does happen, from time to time, that the seeing is really bad, mostly when there is an inversion layer further up in the atmosphere. The night feels steady but in reality isn't. Clearly, if your FWHM varies during the session in random fashion then the issue is with the seeing and not with a systemic issue.


Thanks for the answer Andrea! I hope that this was the issue and not my setup's fault...

But how does this effect the PI PlateSolving capacity?? Because during the night also,ASTAP failed to plate solve many times.

Edit: Also guiding was a mess.
andrea tasselli avatar
andrea tasselli avatar
Thanks for the answer Andrea! I hope that this was the issue and not my setup's fault...

But how does this effect the PI PlateSolving capacity?? Because during the night also,ASTAP failed to plate solve many times.

Edit: Also guiding was a mess.

If it happens it is because your FWHM is really bad with a signficant defocus component (instead of random movement), then the issue is with difficulties finding the psf locations. Again, it does happen with REALLY bad seeing. I mean, really really BAD. Or, there is an issue with the motorfocus position/feedback loop (which is why I don't rely on autofocusing routine most of the times). Can you check that the motorfocus does change position whne you issue movement commands up/down. IOW, it doesn't slip.
Dimitris Kavallieratos avatar
Dimitris Kavallieratos avatar
andrea tasselli:
Thanks for the answer Andrea! I hope that this was the issue and not my setup's fault...

But how does this effect the PI PlateSolving capacity?? Because during the night also,ASTAP failed to plate solve many times.

Edit: Also guiding was a mess.

If it happens it is because your FWHM is really bad with a signficant defocus component (instead of random movement), then the issue is with difficulties finding the psf locations. Again, it does happen with REALLY bad seeing. I mean, really really BAD. Or, there is an issue with the motorfocus position/feedback loop (which is why I don't rely on autofocusing routine most of the times). Can you check that the motorfocus does change position whne you issue movement commands up/down. IOW, it doesn't slip.


I don’t have autofocus motor for my newt, I get by because the tube is carbon made and it loses minimum focus per time. Just started shooting again tonight and frames are sharp again
Brian Puhl avatar
Brian Puhl avatar
Looks to me like you just picked up your ONTC.  Congrats, I'm jealous.  It will likely be my next purchase smile

Welcome to newt land.  You are definitely seeing limited now.   Bad seeing is typically a downward spiral.       

Bad seeing not only increases your FWHM but also kills any chance at good guiding.    Your image scale is 0.77, and you should be guiding at roughly 70% of your image scale.  That means to keep your FWHM in check, you need 0.5 arc second guiding or better.  

So, in a nutshell:

Bad seeing = bad guiding = bad FWHM, it's pretty much a cascade effect.     You'll know when you have good seeing, everything will run smooth.   In my case, I have an image scale of 0.87, my images start suffering if my guiding is above 0.5 arc seconds.  I'll watch the star counts go down, my HFR's will go up.  If I'm guiding at 0.87 which is my image scale, my FWHM will double.


I recommend if you haven't already doing a full PEC train on your EQ6, make sure bearings aren't too tight and theres no backlash on your RA.     Also, ANY amount of wind is going to send you packing for the night, newts are like sails in the wind.         

If you are unable to keep things in check, consider bin 2 as an option.
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Dimitris Kavallieratos avatar
Dimitris Kavallieratos avatar
Looks to me like you just picked up your ONTC.  Congrats, I'm jealous.  It will likely be my next purchase

Welcome to newt land.  You are definitely seeing limited now.   Bad seeing is typically a downward spiral.       

Bad seeing not only increases your FWHM but also kills any chance at good guiding.    Your image scale is 0.77, and you should be guiding at roughly 70% of your image scale.  That means to keep your FWHM in check, you need 0.5 arc second guiding or better.  

So, in a nutshell:

Bad seeing = bad guiding = bad FWHM, it's pretty much a cascade effect.     You'll know when you have good seeing, everything will run smooth.   In my case, I have an image scale of 0.87, my images start suffering if my guiding is above 0.5 arc seconds.  I'll watch the star counts go down, my HFR's will go up.  If I'm guiding at 0.87 which is my image scale, my FWHM will double.


I recommend if you haven't already doing a full PEC train on your EQ6, make sure bearings aren't too tight and theres no backlash on your RA.     Also, ANY amount of wind is going to send you packing for the night, newts are like sails in the wind.         

If you are unable to keep things in check, consider bin 2 as an option.

Yeap just entered Newt land as you say and I love it,despite of all the difficulties.

I know that my sensor is limiting my frames' sharpness due to tracking limitations/image scale and I am going to take care of that with a new bigger mono camera in the future.

But, considering all the difficulties (image scale/LP) I feel that shooting with the little refractor of mine instead of the big newt, is astrophotography in easy mode and nearly not as rewarding and thrilling! I have already almost eliminated my backlash on my EQ6R ,but have not "trained" the GS server that is controlling it yet. Guiding usually on a good night sits around 0.5 arc seconds with an OAG and gives me 5 min subs that are OK, I try to weight out the bad ones in WBPP Also, if the wind is about 3 beaufort upwards, I do not use this telescope.

The issue was definitely a seeing one though thankfully, and the next night HFR was around 2.7 which is ok for 0.77 arc seconds per pixel,I think!
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Brian Puhl avatar
Brian Puhl avatar
Dimitris Kavallieratos:
Yeap just entered Newt land as you say and I love it,despite of all the difficulties.

I know that my sensor is limiting my frames' sharpness due to tracking limitations/image scale and I am going to take care of that with a new bigger mono camera in the future.

But, considering all the difficulties (image scale/LP) I feel that shooting with the little refractor of mine instead of the big newt, is astrophotography in easy mode and nearly not as rewarding and thrilling! I have already almost eliminated my backlash on my EQ6R ,but have not "trained" the GS server that is controlling it yet. Guiding usually on a good night sits around 0.5 arc seconds with an OAG and gives me 5 min subs that are OK, I try to weight out the bad ones in WBPP Also, if the wind is about 3 beaufort upwards, I do not use this telescope.

The issue was definitely a seeing one though thankfully, and the next night HFR was around 2.7 which is ok for 0.77 arc seconds per pixel,I think!

2.7 HFR sounds pretty reasonable.  You can probably do even better.    I sit around 2-2.3 HFR on good nights with 0.83 image scale.    Collimation, backfocus, and tilt have a fairly large affect on hfr/fwhm.     Before I had my backfocus dialed in, I was around 2.7 HFR.    0.4 arc second guiding keeps me in the 2.2 HFR's, yet 0.6 guiding will have me up around 2.5-2.7 pretty quickly.   Also watch your spikes on your guide graph...   preferably it should be smooth, but if the spikes are outside your image scale, that will be a detriment as well.
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