Re: Other possibility for oblong stars
>>>PHD can¡¯t see the error that¡¯s below the resolution of the guider, and so will happily report low error numbers. I am not sure exactly what you mean by this, but PHD has sub-pixel accuracy. I've seen it guide down to 0.10 pixel and even lower
I think the more relevant spec is the image scale of the guider setup vs. the imaging. The general rule of thumb is 4:1 max image scale, where the guide camera image scale should not be more than 4x coarser than the imaging camera's image scale.
?
On Sun, Aug 8, 2021 at 3:28 PM Paul Kanevsky < yh@...> wrote: Not odd at all. Guider has to be able to detect guide star deflection from center. If the resolution/image scale of the guider is low, it will detect and correct errors too late, after they have become?already?sufficiently large to be visible on the main imager. PHD can¡¯t see the error that¡¯s below the resolution of the guider, and so will happily report low error numbers.
On Sun, Aug 8, 2021 at 06:01 PM, wa1vta01452 wrote:
Oddly, PHD2 showed nominal numbers but the images would still be smeared. I first started guiding with my ASI1600mm using my old ST4 autoguider in the ST80 400mm guider and had similar streaky results on stars till I realized I was guiding 3.8 micron pixel size with approx. 13 x 15 micron ST4 pixels. That's when I purchased an ASI120mm for guiding and all was fine.
Tom
-- Brian?
Brian Valente portfolio
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Re: Other possibility for oblong stars
My only point was a suspicion: the polar alignment at one particular pointing location may not hold well enough at a different object location.??
(The elevation is held by a short fork arm, and those metals expand and contract with temperature too.? So elevation may shift.? Remember Murphy's Law... )
In an SCT or even Newtonian,? the inherent mirror flop creates a problem.? Reflective optics must me held loosely to prevent optical surface pinch distortion.??
Piggyback autoguiding always has a question of "differential flexure."
The only solution that worked consistently for me was OAG guiding.? So I recommend Peter give this a try and if that works, give up on perfecting the mechanical elements that defy perfection.? Get your imaging done we th a practical way that works consistently.??
This is a single 500 sec sub, taken from a C14edgeHD and 0.7 FL reducer, and a QHY168C camera.? The mount was a G11T, with Celestron off axis guider, and PHD2.? I only processed in Affinity photo and that was not very good.? But the point is that the 500 sec image has no eccentric stars.? I know that M51 is near NCP, so not a hard test.? If the smoky skies and fog would clear up, I'd take more!
Very best of luck, Michael
On Sun, Aug 8, 2021, 3:01 PM wa1vta01452 < loeblt@...> wrote: Oddly, PHD2 showed nominal numbers but the images would still be smeared. I first started guiding with my ASI1600mm using my old ST4 autoguider in the ST80 400mm guider and had similar streaky results on stars till I realized I was guiding 3.8 micron pixel size with approx. 13 x 15 micron ST4 pixels. That's when I purchased an ASI120mm for guiding and all was fine.
Tom
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Re: Other possibility for oblong stars
Not odd at all. Guider has to be able to detect guide star deflection from center. If the resolution/image scale of the guider is low, it will detect and correct errors too late, after they have become?already?sufficiently large to be visible on the main imager. PHD can¡¯t see the error that¡¯s below the resolution of the guider, and so will happily report low error numbers.
On Sun, Aug 8, 2021 at 06:01 PM, wa1vta01452 wrote:
Oddly, PHD2 showed nominal numbers but the images would still be smeared. I first started guiding with my ASI1600mm using my old ST4 autoguider in the ST80 400mm guider and had similar streaky results on stars till I realized I was guiding 3.8 micron pixel size with approx. 13 x 15 micron ST4 pixels. That's when I purchased an ASI120mm for guiding and all was fine.
Tom
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Re: Other possibility for oblong stars
Given your focal length, you might what to consider a higher res camera like ASI 178mm. I would want my guide resolution to be under 1.25 x my image resolution, else who knows what your measuring in PHD2.?
Peter
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Re: Other possibility for oblong stars
Oddly, PHD2 showed nominal numbers but the images would still be smeared. I first started guiding with my ASI1600mm using my old ST4 autoguider in the ST80 400mm guider and had similar streaky results on stars till I realized I was guiding 3.8 micron pixel size with approx. 13 x 15 micron ST4 pixels. That's when I purchased an ASI120mm for guiding and all was fine.
Tom
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
Les and Paul,
That's what is strange about this. My guiding was better on the bad image. Is was only just about dark on the good image. Total rms was 0.71". On the second bad image it was about 1 hour later total rms was 0.56". So better guiding as target was higher in the sky and properly dark.
I showed the first bad image in total nights imaging that were all trash.
Boy this is a real hair puller!
Peter
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
The exact location of the guide star doesn¡¯t matter, as long as it¡¯s in or near the field of the main camera, then given that all the trails are about the same length, it can¡¯t be field rotation ¡ª that would show up as rotation around the guide star, so trails further away would be longer. ?
You may have mentioned this before ¡ª what does the guiding software report for guiding performance when there is trailing vs. when there is no trailing?
This really looks like something is loose between the guide scope/camera and main scope/camera. ?An OAG should fix it, though if the something loose is in the main scope, it still may adversely impact guiding performance since the guider will have to compensate for that in addition to compensate for mount, polar alignment, etc.
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On Sun, Aug 8, 2021 at 09:53 AM, Les Niles wrote:
One more question: Is the guide star somewhere in this field of view of the main camera?
?
Yes, but likely off center, not sure were. Like I said to Paul, first image is fine, slew to a southern target and return back and everything gone to pot. I think I know what you are thinking, I'm going to install my OAG. In all my experience I've not had this problem before. Peter
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
Hi Peter,
Hard to say. Maybe something shifted or loosened up after slewing to low altitudes? Differential flexure is often hard to find, as it can be unpredictable. It depends on the position relative to the ground and can change direction when crossing from one side of the mount to the other. Friction between parts, tightness of screw-in connections, mirror supports (if any), focusers, and even rings and dovetails can all play a role.
Regards,
? ? ? ?-Paul
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On Sun, Aug 8, 2021 at 02:08 PM, <pcboreland@...> wrote:
Paul thanks,
So why the sudden change? First image stars are great. Slew to a target at low altitude and 150 rotated, then come back to same target and suddenly the stars are drifting north.
Could my clutch be slipping?
Peter
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Re: Need your help: table of terms and abbreviations
Thank you, Paul. A very nice idea to save, not lose, the efforts being offered.??
On Sun, Aug 8, 2021, 10:08 AM Paul Kanevsky < yh@...> wrote: Hi Folks, I've created a new table for this group that is meant to contain short descriptions and definitions of obscure terms and abbreviations. The table is editable by all members, and I invite everybody to add to it. The table is located here (in the Databases section of this group):? /g/Losmandy_users/table?id=33190The goal is to help new users and those who may not be familiar with Losmandy mounts or related software to quickly decipher some of the messages being posted here. I started the list by copying some of the definitions from website, but would love to see others add and expand the list over time.?? Please contribute! Here are some examples from the table:
Regards, ? ? ? -Paul
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
On Sun, Aug 8, 2021 at 09:53 AM, Les Niles wrote:
One more question: Is the guide star somewhere in this field of view of the main camera?
?
Yes, but likely off center, not sure were. Like I said to Paul, first image is fine, slew to a southern target and return back and everything gone to pot. I think I know what you are thinking, I'm going to install my OAG. In all my experience I've not had this problem before. Peter
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
On Sun, Aug 8, 2021 at 08:25 AM, Paul Kanevsky wrote:
Why not, Peter? If your guide scope guiding is not showing any large errors and the main imager shows constant drift, this is most likely differential flexure. Other possibilities include differential refraction at low altitudes and image rotation due to polar misalignment. There aren¡¯t too many other possibilities.
Regards,
? -Paul
Paul thanks, So why the sudden change? First image stars are great. Slew to a target at low altitude and 150 rotated, then come back to same target and suddenly the stars are drifting north. Could my clutch be slipping? Peter
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Need your help: table of terms and abbreviations
Hi Folks, I've created a new table for this group that is meant to contain short descriptions and definitions of obscure terms and abbreviations. The table is editable by all members, and I invite everybody to add to it. The table is located here (in the Databases section of this group):? /g/Losmandy_users/table?id=33190The goal is to help new users and those who may not be familiar with Losmandy mounts or related software to quickly decipher some of the messages being posted here. I started the list by copying some of the definitions from gemini-2.com website, but would love to see others add and expand the list over time.?? Please contribute! Here are some examples from the table:
Regards, ? ? ? -Paul
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Re: Other possibility for oblong stars
Undersampled guiding can certainly result in worse tracking performance. Usually it will not result in a continuous star drift on the main imager but can result in bloated stars and sometimes, elongated ones. Another possible source of star drift is guiding on a hot pixel.
Regards,
? ? -Paul
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On Sun, Aug 8, 2021 at 11:52 AM, wa1vta01452 wrote:
I live in the northeastern US and am a G11 owner. ...I image with a 1000mm f/l scope and use 400mm for tracking, with a? ratio of 2.5, typically getting RMS values under 0.5 and with good seeing, under .45 in PHD2 .? Last fall I attempted to use a? 180mm? guide scope for tracking with a ratio over 5.5 and I consistently got oblong stars even on the most stable atmosphere nights. I switched back to the 400 and all is well again.
Tom
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
One more question: Is the guide star somewhere in this field of view of the main camera?
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On 8 Aug 2021, at 9:51, Les Niles < les@...> wrote:
Those are some serious star trails.
A couple more questions:? Are those star trails north-south, or east-west? ?That is, is it trailing in declination or in RA? How good is the DEC balance? ?With the clutch loose, and the counterweight bar ~horizontal, will the scope stay in whatever position you put? Not just horizontal, but vertical or at an angle ¡ª if not, can you rotate the tube so that it will stay put? ?If it is well balanced, then the mount won¡¯t know what declination you have it aimed at and the problem must be on the scope itself.
Here is a run down on the problem.
1. It occurred after changing out the Ra axis thrust bearings.
2. Polar alignment is via Sharpcap and was bang on at CDW. Just installed the NINA 3-point polar alignment plugin and at Michaels suggestion I will be able to double check polar alignment after slew to target to see if something has moved.
3. Target is 25 degrees altitude due south. Not a region of the shy I typically shoot, so problem could have existed before the Ra upgrade work and I would not know. My location is NJ.
4. As a test I decided to shoot the cave nebula which follows the typical trajectory of object I shoot. The first image shows the result of slewing to the target and taking a 400s image.
5. I slewed to the 2nd target due? south at 25 degrees lat and got terrible guiding results and could not get any data even at 60s exposure, so I slewed back to the cave nebula and resumed imaging. The second image shows what I got. I do not thing this is differential flexure??
6. I've taken the following steps to run down this problem. A. Cleaned the Ra clutch disc? with lacquer thinner. These are Michaels clutch disc not Losmandy.? At Michaels suggestion I will install my OAG setup and retest.
Peter
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
Those are some serious star trails.
A couple more questions:? Are those star trails north-south, or east-west? ?That is, is it trailing in declination or in RA? How good is the DEC balance? ?With the clutch loose, and the counterweight bar ~horizontal, will the scope stay in whatever position you put? Not just horizontal, but vertical or at an angle ¡ª if not, can you rotate the tube so that it will stay put? ?If it is well balanced, then the mount won¡¯t know what declination you have it aimed at and the problem must be on the scope itself.
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Show quoted text
Here is a run down on the problem.
1. It occurred after changing out the Ra axis thrust bearings.
2. Polar alignment is via Sharpcap and was bang on at CDW. Just installed the NINA 3-point polar alignment plugin and at Michaels suggestion I will be able to double check polar alignment after slew to target to see if something has moved.
3. Target is 25 degrees altitude due south. Not a region of the shy I typically shoot, so problem could have existed before the Ra upgrade work and I would not know. My location is NJ.
4. As a test I decided to shoot the cave nebula which follows the typical trajectory of object I shoot. The first image shows the result of slewing to the target and taking a 400s image.
5. I slewed to the 2nd target due? south at 25 degrees lat and got terrible guiding results and could not get any data even at 60s exposure, so I slewed back to the cave nebula and resumed imaging. The second image shows what I got. I do not thing this is differential flexure??
6. I've taken the following steps to run down this problem. A. Cleaned the Ra clutch disc? with lacquer thinner. These are Michaels clutch disc not Losmandy.? At Michaels suggestion I will install my OAG setup and retest.
Peter
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Other possibility for oblong stars
I live in the northeastern US and am a G11 owner. ...I image with a 1000mm f/l scope and use 400mm for tracking, with a? ratio of 2.5, typically getting RMS values under 0.5 and with good seeing, under .45 in PHD2 .? Last fall I attempted to use a? 180mm? guide scope for tracking with a ratio over 5.5 and I consistently got oblong stars even on the most stable atmosphere nights. I switched back to the 400 and all is well again.
Tom
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Re: Gemini-2 momentarily went haywire
Very good thinking, Les!
I will see if the PC DEC slew works properly.??
Best, Michael
On Sun, Aug 8, 2021, 7:52 AM Les Niles < les@...> wrote: The next obvious guess would be resoldering the hand controller socket. Then start tracing the HC signals to look for something gone wrong. This would be easiest if you have a good board to do an A/B comparison.?
The fact that a bright star slew works makes it seem like a controller input problem rather than a motor/encoder problem. What happens if you initiate a dec movement through the driver or web interface?
? Hi gang!
I received John's questionable G2 mini board, to test it out.??
Symptoms:
It boots up fine.
It slews to an Align Bright Star target fine.
If you press the RA diamond East West button it slews RA fine.
If you let it run Sidereal rate it tracks fine.
If you press the DEC diamond East West button, the DEC motor runs away!?
This is repeatable.
John got a new board from.the factory and his system is fixed...it is definitely a problem with this board, not the cables, motors or handset.??
I'm unsure what to do to try and repair this board...John did try to resolder his DEC socket.??
Any suggestions from the above clues?
Very best, Michael
Was the board repaired at Losmandy?? From experience a runaway flew is a bad motor socket solder join.?
The ICs used are mostly capable of ?minus 20C.? All ICs were chosen to suit this wide temp range spec. Very much doubt it¡¯s that.?
Is I¡¯d all good now ? Has it been repaired ¡if not¡.it¡¯ll come back to bite when you least expect?
--
Brendan
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
On Sun, Aug 8, 2021 at 09:17 AM, <pcboreland@...> wrote:
The second image shows what I got. I do not thing this is differential flexure??
Why not, Peter? If your guide scope guiding is not showing any large errors and the main imager shows constant drift, this is most likely differential flexure. Other possibilities include differential refraction at low altitudes and image rotation due to polar misalignment. There aren¡¯t too many other possibilities.
Regards,
? -Paul
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Re: Gemini-2 momentarily went haywire
Ooops this is a G2 ¨C in which case a burnt out motor control PIC. ?
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From: David C. Partridge <david.partridge@...>
Sent: 08 August 2021 16:23
To: '[email protected]' <[email protected]>
Subject: RE: [Losmandy_users_io] Gemini-2 momentarily went haywire? Most likely a burnt out PAL decoder for the Dec? channel ¨C you need to program it of course. ? From: [email protected] <[email protected]> On Behalf Of Michael Herman
Sent: 08 August 2021 15:24
To: [email protected]
Subject: Re: [Losmandy_users_io] Gemini-2 momentarily went haywire ? Hi gang! I received John's questionable G2 mini board, to test it out.?? It slews to an Align Bright Star target fine. If you press the RA diamond East West button it slews RA fine. If you let it run Sidereal rate it tracks fine. If you press the DEC diamond East West button, the DEC motor runs away!? John got a new board from.the factory and his system is fixed...it is definitely a problem with this board, not the cables, motors or handset.?? I'm unsure what to do to try and repair this board...John did try to resolder his DEC socket.?? Any suggestions from the above clues? ? Was the board repaired at Losmandy?? From experience a runaway flew is a bad motor socket solder join.?
The ICs used are mostly capable of ?minus 20C.? All ICs were chosen to suit this wide temp range spec. Very much doubt it¡¯s that.?
Is I¡¯d all good now ? Has it been repaired ¡if not¡.it¡¯ll come back to bite when you least expect?
--
Brendan
|
Re: Gemini-2 momentarily went haywire
Most likely a burnt out PAL decoder for the Dec? channel ¨C you need to program it of course. ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Michael Herman
Sent: 08 August 2021 15:24
To: [email protected]
Subject: Re: [Losmandy_users_io] Gemini-2 momentarily went haywire ? Hi gang! I received John's questionable G2 mini board, to test it out.?? It slews to an Align Bright Star target fine. If you press the RA diamond East West button it slews RA fine. If you let it run Sidereal rate it tracks fine. If you press the DEC diamond East West button, the DEC motor runs away!? John got a new board from.the factory and his system is fixed...it is definitely a problem with this board, not the cables, motors or handset.?? I'm unsure what to do to try and repair this board...John did try to resolder his DEC socket.?? Any suggestions from the above clues? ? Was the board repaired at Losmandy?? From experience a runaway flew is a bad motor socket solder join.?
The ICs used are mostly capable of ?minus 20C.? All ICs were chosen to suit this wide temp range spec. Very much doubt it¡¯s that.?
Is I¡¯d all good now ? Has it been repaired ¡if not¡.it¡¯ll come back to bite when you least expect?
--
Brendan
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Michael Herman
Paul Kanevsky
David C. Partridge