Pulse width, Expopsure time, and Strain Wave Mounts

[mshe...@gmail.com]

Hello! I recently set up a Ioptron HEM44 with my 8"LX200 OTA at Starfront. I've gotten most of the bugs worked out, so now I'm looking closer at guiding with my Kowa 100mm f2.8 lens and QHY5III568 with 2 micron pixels. I use the recommended pulse width of about 1100 milliseconds and exposures of 2.5 seconds

    I generally get good results with guiding between 1.1 and 1.4 arc seconds.

    Should I use a lower pulse width and lower exposure times with this strain wave mount? I've read recommendations to such, though to keep exposures longer than the pulse width. Should I lower pulse width below that recommended by PHD2? Thanks.

Mike

    

[mshe...@gmail.com]

Any observer experiences that can provide real world guidance?

Mike

[Michael Yasko]

Hi Mike

If you are asking me,  Should I use a lower pulse width and lower exposure times with this strain wave mount? I've read recommendations to such, though to keep exposures longer than the pulse width. Should I lower pulse width below that recommended by PHD2? you are definitely asking the wrong person,lol   I can't even get my camera to be recognized by phd2 yet alone what roadblocks lie after that. 

Sorry

Mike

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[Brian Valente]

Mike

if you want feedback, please upload your logs via the log uploader.

https://openphdguiding.org/getting-help/

By "pulse width" i assume you mean step size?

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Brian 

Brian Valente

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[mshe...@gmail.com]

My apologies. I think I did not reply to the thread. Attached is the log.

    I think I misconstrued calibration step size under the advanced tab of guiding with the pulse width that has been referenced in other posts. I do not believe that the HEM44 has a pulse width adjustment.

    I ran my setup with a shorter exposure - 2.5 seconds on the attached log of 30-January, and 1 second on the attached log of 31-January. The most recent log shows better guiding with a number of sub-one arcsec regions. I'm curious if folks have other suggestions for strain wave mount in addition to shorter exposure time. Best regards.

Mike

[Brian Valente]

Mike

I'm not sure if you received my prior message (apparently it went directly to your email), but based on your last logs, it's still completely relevant and you still have the same issues. Please take a look at my suggestions below

Brian 

>>>but rather a setting inquiry. I've attached the most recent log.

The only way to really give you meaningful feedback on settings is to see how you're current settings are performing doing, right?

>>>I use the recommended pulse width of about 1100 milliseconds and exposures of 2.5 seconds/

I'm still not sure exactly are you referring to when you say pulse width? That's not a common term. It sounds like you're talking about the calibration step size? But maybe the duration of the guide pulse and the related aggression setting for the axis? 

If you're referring to the calibration step size, there's no need to guess at this value or (erroneously) get it from others: use the New Profile Wizard, enter your details accurately (focal length, pixel size, etc.) and it will calculate it for you. 

FYI all your guiding sessions in your log show an exposure of 1 second, not 2.5. not sure where is the disconnect or what you intended. Generally strainwave mounts need to be guided with shorter exposure times, so 1 second (or shorter) is probably a better approach

 Things that immediately jump out from your guidelog:

- poor polar alignment. All of your dec guide pulses are uniformly in one direction (pulses are the top vertical bars) and note the dec axis never returns to baseline position, always slightly off (higher or lower depending on the pier side). A guiding assistant run would have pointed this out to you. 

It's possible to still have reasonable guiding, but your mount has an issue getting settled to this point, The first 5-15 minutes shows a lot of thrashing on the dec axis. Here's a good example from the start of your 7+ hour run,  noted in the green box:

this happens in all your runs, except in the shorter runs, it never gets past this point, so your dec is in the 2" rms range - far too high

On your RA axis, it's just taking multiple guide pulses to reverse direction, as shown in the example below from your 7 hour run (arrows point out examples of multiple guide pulses, but it's everywhere):

Guiding is working well, it's just not doing it quickly enough. I would increase your aggressiveness and/or shortern your exposure time until your guidepulses and reversals are improved. 

if you post updated results, please make sure to include a calibration (via the calibration assistant) and a guiding assistant run (i.e., unguided output) so we can see additional diagnostic information.and offer further feedback if you want

Brian

On Sat, Jan 31, 2026 at 1:05 PM mshe...@gmail.com <mshe...@gmail.com> wrote:

Sorry. I mistakenly did not upload one since there was no specific problem I was addressing but rather a setting inquiry. I've attached the most recent log. Also, I was looking at the calibration step size under the Advanced tab in Guiding, so I don't think that has anything to do with the discussion, and my question about pulse width was likely an error from reading about other scopes. Best regards.

Mike

On Friday, January 30, 2026 at 11:38:13 AM UTC-5 bval...@gmail.com wrote:

Mike

if you want feedback, please upload your logs via the log uploader.

https://openphdguiding.org/getting-help/

By "pulse width" i assume you mean step size?

On Fri, Jan 30, 2026 at 4:31 AM mshe...@gmail.com <mshe...@gmail.com> wrote:

Any observer experiences that can provide real world guidance?

Mike

On Friday, January 23, 2026 at 9:05:50 AM UTC-5 mshe...@gmail.com wrote:

Hello! I recently set up a Ioptron HEM44 with my 8"LX200 OTA at Starfront. I've gotten most of the bugs worked out, so now I'm looking closer at guiding with my Kowa 100mm f2.8 lens and QHY5III568 with 2 micron pixels. I use the recommended pulse width of about 1100 milliseconds and exposures of 2.5 seconds

    I generally get good results with guiding between 1.1 and 1.4 arc seconds.

    Should I use a lower pulse width and lower exposure times with this strain wave mount? I've read recommendations to such, though to keep exposures longer than the pulse width. Should I lower pulse width below that recommended by PHD2? Thanks.

Mike

    

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Brian 

Brian Valente

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[mshe...@gmail.com]

Thank you for the input. Hopefully, Starfront will be open in the early evening so that I can run Guiding Assistant and update the Calibration assistant. I'll attach the logs when done.

    Of note, running with integrations of 1 sec rather than 2.5 seconds did improve things, from an average of between 1.1 and 1.5 arc-seconds (with occasional poor guiding), to often sub 1 arc-second guiding. I really appreciate the guidance confirming the shorter guider integration time for strain wave mounts.

    I am concerned about polar alignment. I have always had star trailing when guiding is off since the system was installed 2 months ago. Hopefully, with Guiding Assistant, if polar alignment is an issue, I can provide guidance to the folks at Starfront. I am encouraged, however, that even if polar alignment is an issue now, most images are usable for photometry, so PHD2 is able to guide that out.

    If there is still trouble with mount settling, then I may need to add the counterbalance. The weight is about 18 pounds, well under the nominal 44 pounds of the HEM44, so I may need to explore additional causes of settling problems, if it persists.

    Thank you again.

Mike

[mshe...@gmail.com]

Goodness! I just ran Calibration Assistant and Guiding Assistant. Some suggestions for guiding, but the major problem was an error of 120 arc-minutes in polar alignment. I did not realize it was that bad yet PHD2 was able to guide through it as you noted. I've had the scope at Starfront for 3 months. I've asked them to check the polar alignment.

    I'll upload the logs tomorrow after tonight's run. I've been paying attention to other things to get the system up and running and had not been overly concerned about guiding since it seemed fairly good. I appreciate your help with the Guiding Assistant. Thank you for your help. Best regards.

Mike

[Brian Valente]

glad you were able to see that. 2 degrees is a lot of misalignment ;)

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[Bruce Waddington]

That does seem like a large alignment error considering that StarFront has probably polar aligned hundreds of scopes.  So you should keep in mind that the PHD2 GA estimates polar alignment error based on declination drift.  So it can't distinguish between drift caused by polar alignment error and drift caused by some other mechanical misbehavior in the mount payload.  To pick an overly simplistic example, the combination of a Dec imbalance and a loose Dec clutch could also produce a large amount of drift that the GA would report as polar alignment error.  Similarly, if the altitude/azimuth adjustment controls on the mount aren't fully tightened, things can move around as you slew the scope.  So the real question here is what is causing the large drift rate in declination.

Hope you can track it down quickly,

Bruce

[mshe...@gmail.com]

Thanks! The folks at Starfront will have a look at it in the next day or two and, hopefully, will be able to shed more light on it. I've attached the two logs from last night's run. Not much to add from what I described. Best regards.

Mike

[mshe...@gmail.com]

Hello! It looks like Starfront over-corrected the polkar alignment error. Now 95 arc-min with dec corrections in the other directions. I've sent a note to them. They use Sharpcap, and I've read that Sharpcap and PHD2 sometimes give different results. I'll see what they say. Best regards.

Mike

[Brian Valente]

Mike

It's common for alternative approaches to polar alignment differ in their reported alignment accuracy, but i have only seen differences in maybe low arcminutes or arcseconds. A reported 95 arcminutes (or >1.5 degrees) is grossly out of alignment.

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