10 replies to this topic

[gadac]

Hi everyone,

 

I have been imaging with my freshly acquired skywatcher 150i strain wave mount and experimenting with guiding, which is all very new to me.

 

I managed to get some good numbers on average, I think, at about  0.4-0.6" in both RA and DEC but when I look at the guide graph in the log viewer I do see a lot of spikes that go above 1, 2 or even 3". I wondered if that is par for the course for this kind of mount and usual to see or if this is something that I should (could?) fix one way or another? Here are some examples (between the dithering phases):

 

 

 

My PHD2 parameters are the following:

 

0.5s exposure

RA/DEC Agr: 60

Hysteresis: 10

RA/DEC MnMo: 0.1

RA/DEC Max impulsion length: 300ms

Calibration step: 2080ms

 

I have left the default guiding algorithms (hysteresis and resist switch) and did not enable backlash compensation either, I'm not sure if I should with this kind of mount ?

Harwdare is a Svbony SV165 30mm guidescope (120 mm focal length) and an ASI220MM. These guiding sessions where in a rather large light polluted city so seeing is not the best.

 

My set up for now is only a light set up consisting of a samyang 135mm and an ASI2600MC. I know that at such focal length it does not matter much but I want to be sure my mount is future proof. Is this guiding acceptable? What I really want to know is if these spikes matter in the grand scheme of things or is it fine as the average values are pretty low and I'm worrying for nothing? I will probably push up to 1000mm focal length in the long term but more likely 400-600mm in the short term.

 

I have also attached a guide log if anyone wants to take a look a it. I'd be glad for any inputs as I'm a complete beginner.

 

Cheers and thanks

 

[daveco2]

I see pretty much the same thing with PHD2 on an asiAirPlus, guiding an Ioptron CEM40 mount with scopes from 180 mm to 2000 mm focal length.

 

I think the bottom line is star shape.  I get pinpoints with the 180 mm fl and small, round fuzzies at 2000 mm.  I think that makes sense as the guide spike durations are

much shorter than exposure times.  I have tried different guide settings, rebalanced the payload, and recalibrated guiding many times; but with the same result more or

less.  I sent the mount back to Ioptron for a checkup, and they gave me a list of adjustments they made; but that made no difference either.

 

Although I can live with the spikes as they don't seem to affect the image, it still bugs me.  I was thinking a strain wave mount would be the solution.  Maybe not.

[gadac]

I see pretty much the same thing with PHD2 on an asiAirPlus, guiding an Ioptron CEM40 mount with scopes from 180 mm to 2000 mm focal length.

 

I think the bottom line is star shape.  I get pinpoints with the 180 mm fl and small, round fuzzies at 2000 mm.  I think that makes sense as the guide spike durations are

much shorter than exposure times.  I have tried different guide settings, rebalanced the payload, and recalibrated guiding many times; but with the same result more or

less.  I sent the mount back to Ioptron for a checkup, and they gave me a list of adjustments they made; but that made no difference either.

 

Although I can live with the spikes as they don't seem to affect the image, it still bugs me.  I was thinking a strain wave mount would be the solution.  Maybe not.

 

Thank you for sharing your experience. Would you say that the fuzzies you see at 2000mm are problematic to your final image quality? Do you also see them in the 1000mm range? 

 

I do wonder these spikes are found in all strain wave mount, maybe someone with an am3/am5 can weigh in

Edited by gadac, 23 April 2025 - 12:09 PM.

[Sacred Heart]

The bottom line is the image, streaks / footballs / round dots.  Seeing plays a huge roll in guiding.  Three things, to me that helps guiding.  Polar alignment, focus and seeing conditions.  With a wide FOV, 135mm & a 2600, just get it as close as you can, focus as best you can - again with a small FOV stars are tiny. Seeing conditions, not every night is an imaging night.  Though with a 5 or 6 arc second image scale it is very forgiving.   At 500mm to 600mm you will see a difference in detail, polar alignment can get better. with an 800mm to 1000mm focal length and an OAG, focus is similar to the 500mm focus and focusing an OAG is quite easy once spacing is worked out.That narrower FOV gives you bigger stars, easier to see and focus.

 

When you get to the 500mm and up focal length mounting of the guide scope is critical / important.  Needs to always be rock solid. No play anywhere.   Always try to guide at a 1:1 ratio with your imaging camera, as close as you can anyway.

 

Joe

[gadac]

The bottom line is the image, streaks / footballs / round dots.  Seeing plays a huge roll in guiding.  Three things, to me that helps guiding.  Polar alignment, focus and seeing conditions.  With a wide FOV, 135mm & a 2600, just get it as close as you can, focus as best you can - again with a small FOV stars are tiny. Seeing conditions, not every night is an imaging night.  Though with a 5 or 6 arc second image scale it is very forgiving.   At 500mm to 600mm you will see a difference in detail, polar alignment can get better. with an 800mm to 1000mm focal length and an OAG, focus is similar to the 500mm focus and focusing an OAG is quite easy once spacing is worked out.That narrower FOV gives you bigger stars, easier to see and focus.

 

When you get to the 500mm and up focal length mounting of the guide scope is critical / important.  Needs to always be rock solid. No play anywhere.   Always try to guide at a 1:1 ratio with your imaging camera, as close as you can anyway.

 

Joe

 

My polar alignment should be allright, I use Nina's TPPA process and aim for <3" error which I get quite well. I do use the guide scope for polar alignment as the asi2600mc output images so large nina has a hard time giving frequent update for the alignment error. Using the guide scope and camera makes the value update almost in real time.

 

I do image from a large city (Paris suburbs) so my seing is probably not great. Could that be the reason for the spikes? I'm waiting for clear skies to drive out to the country in darker skies. 

Edited by gadac, 23 April 2025 - 12:52 PM.

[Infomastr]

I have an Esprit120ED on top of a Wave150i and definitely struggled with guiding performance the first few nights.  The guide scope is svbony 40mm and guide camera is ZWO ASI120mm-mini.  It's much better now -

 

 

Seeing has a large impact on guiding with shorter exposures.  I have been using 1s exposures over 0.5s to reduce the possibility of chasing seeing.  You may want to tinker with this (the 220 is much more sensitive and has a larger sensor than the 120, so you may also need to reduce gain to avoid saturation of optimal guide stars). 

 

Strainwaves benefit from having real, mounted weight.  It sounds like your setup is very light - this could impact your results.  What tripod are you using?  Are all your cables well secured?  How is the guide scope mounted (is there any flexure possible between the guide scope+camera and main lens)?

 

You may want to check the firmware of your mount.  Mine shipped with 3.58, which I updated to 3.59.

[gadac]

I have an Esprit120ED on top of a Wave150i and definitely struggled with guiding performance the first few nights.  The guide scope is svbony 40mm and guide camera is ZWO ASI120mm-mini.  It's much better now -

 

 

Seeing has a large impact on guiding with shorter exposures.  I have been using 1s exposures over 0.5s to reduce the possibility of chasing seeing.  You may want to tinker with this (the 220 is much more sensitive and has a larger sensor than the 120, so you may also need to reduce gain to avoid saturation of optimal guide stars). 

 

Strainwaves benefit from having real, mounted weight.  It sounds like your setup is very light - this could impact your results.  What tripod are you using?  Are all your cables well secured?  How is the guide scope mounted (is there any flexure possible between the guide scope+camera and main lens)?

 

You may want to check the firmware of your mount.  Mine shipped with 3.58, which I updated to 3.59.

Your guiding resuts are impressive! Could you share your settings? Were your initial guiding trouble also similar spikes?

 

I will try with longer exposure maybe that will help, I might have a clear window tommorow evening. I'm using the default skywatcher carbon tripod and its pier extension. Maybe the steel tripod may help but I really want to keep the set up light to go to dark sites. My cabling should be good, I bought short cables and it all goes through the saddle so cable snag should not happen.

 

I'm using the redcat ring+hotshoe to mount the guidescope on the samyang, it seems solid enough but since the load is on one unique ring it may not be ideal. I will soon probably buy an Askar FRA400 so maybe the assembly will be more rigid as it is purposely made for the scope.

 

My scope is indeed at the latest firmware.

Edited by gadac, 23 April 2025 - 01:10 PM.

[Infomastr]

Your guiding resuts are impressive! Could you share your settings? Were your initial guiding trouble also similar spikes?

 

I will try with longer exposure maybe that will help, I might have a clear window tommorow evening. I'm using the default skywatcher carbon tripod and its pier extension. Maybe the steel tripod may help but I really want to keep the set up light to go to dark sites. My cabling should be good, I bought short cables and it all goes through the saddle so cable snag should not happen.

 

I'm using the redcat ring+hotshoe to mount the guidescope on the samyang, it seems solid enough but since the load is on one unique ring it may not be ideal. I will soon probably buy an Askar FRA400 so maybe the assembly will be more rigid as it is purposely made for the scope.

 

My scope is indeed at the latest firmware.

300ms ra/dec pulses, 1800ms calibration step (this could get bumped up a bit), 40% ra/dec aggression, 1s guide exposures at 48 gain (for the 120mm-mini, this is the "high" setting, but for better cameras like yours, it may need a lower gain setting), dark library enabled.

 

My initial guiding (two separate nights) was problematic -

 

 

 

In particular, the peak to peak excursions were much worse than now.  I've observed 2.5 hours of guiding at <2.5" peak to peak since making various tweaks to the setup noted above.

 

 

I've shot 5-6 hours over 3 nights with similar performance.  None of the subs have needed to be tossed.

 

I would also add, and should have mentioned in my initial post, to make sure that your RA and DEC locking knobs are really, really tight.  I used a wrench and rubber strap to tighten both beyond what I could do by hand.

[Zambiadarkskies]

I see pretty much the same thing with PHD2 on an asiAirPlus, guiding an Ioptron CEM40 mount with scopes from 180 mm to 2000 mm focal length.

 

I think the bottom line is star shape.  I get pinpoints with the 180 mm fl and small, round fuzzies at 2000 mm.  I think that makes sense as the guide spike durations are

much shorter than exposure times.  I have tried different guide settings, rebalanced the payload, and recalibrated guiding many times; but with the same result more or

less.  I sent the mount back to Ioptron for a checkup, and they gave me a list of adjustments they made; but that made no difference either.

 

Although I can live with the spikes as they don't seem to affect the image, it still bugs me.  I was thinking a strain wave mount would be the solution.  Maybe not.

You are bang on!  Ultimately star shapes are the real metric.  I am down a rabbit hole right now chasing guiding improvements and have been here many times as we all have....   Tonight my star shapes were very poor but guiding numbers were good.  I have been tweaking settings for two hours now and some subs were okay and others very poor.  I re-ran calibration and everything tightened right up...  And I calibrated on my target and not where I should be!  Worry about stars and not graphs is the mantra that I keep telling myself and it is true.  If you don't like spikes a strainwave mount is absolutely not going to help IMHO.  The really exceptional guiding numbers (and graphs) are from high end conventional mounts and more exotic stuff even.  I can screen shot my AM5 looking amazing with numbers,  but with stars that look like noodles... 

 

My guiding was so bad two nights ago I re-ran polar alignment (even though I am on a permanent pier.  It was not PA!  

[gadac]

You are bang on!  Ultimately star shapes are the real metric.  I am down a rabbit hole right now chasing guiding improvements and have been here many times as we all have....   Tonight my star shapes were very poor but guiding numbers were good.  I have been tweaking settings for two hours now and some subs were okay and others very poor.  I re-ran calibration and everything tightened right up...  And I calibrated on my target and not where I should be!  Worry about stars and not graphs is the mantra that I keep telling myself and it is true.  If you don't like spikes a strainwave mount is absolutely not going to help IMHO.  The really exceptional guiding numbers (and graphs) are from high end conventional mounts and more exotic stuff even.  I can screen shot my AM5 looking amazing with numbers,  but with stars that look like noodles... 

 

My guiding was so bad two nights ago I re-ran polar alignment (even though I am on a permanent pier.  It was not PA!  

I completely agree with you and the mantra, star shapes are what matters! It is just that since I'm very new to it and image at a very short focal length for now, so I can't really say what my stars will look like later when I purchase a larger scope. In essence I want to be sure that my mount is adequate and that I will not run into trouble later on. If even with these spikes my stars look fine I will be more than happy.

[gadac]

300ms ra/dec pulses, 1800ms calibration step (this could get bumped up a bit), 40% ra/dec aggression, 1s guide exposures at 48 gain (for the 120mm-mini, this is the "high" setting, but for better cameras like yours, it may need a lower gain setting), dark library enabled.

 

My initial guiding (two separate nights) was problematic -

 

 

 

In particular, the peak to peak excursions were much worse than now.  I've observed 2.5 hours of guiding at <2.5" peak to peak since making various tweaks to the setup noted above.

 

 

I've shot 5-6 hours over 3 nights with similar performance.  None of the subs have needed to be tossed.

 

I would also add, and should have mentioned in my initial post, to make sure that your RA and DEC locking knobs are really, really tight.  I used a wrench and rubber strap to tighten both beyond what I could do by hand.

Thanks for sharing, I will try tommorow night with that I mind. I think I might get away with lower MinMo and lower agression too. Will also check the tightening of the locking knobs !