"Star lost - low HFD"

[Fearless Leader]

I am asking for help for the problem I am having with using PHD2.

1) My log file has been uploaded :   https://openphdguiding.org/logs/dl/PHD2_logs_CoE4.zip

2) 23:12:21.872 00.002 7312 Throw from C:\cygwin\home\Andy\projects\phd2-build-20251209-235857\src\guider.cpp:1371->unable to update current position

3)At 23:12::21.874 I see "Star lost - low HFD"

4) For guiding I am using a William Optics SpaceCat and a ZWO ASI432mm.  I have also used a ZWO ASI1600mm camera.

5) I am using 5 second exposures.

6)  This seems to happen everytime I try guiding.

7) When I view the image using ASIImg the image looks very good.  However, when I look at the image via PHD2 it seems very dim no matter how I position the scroll bar.

Please Advise,

Tom Gehm

[Bruce Waddington]

I think you've assembled a guiding arrangement that doesn't make much sense.  Here's the way ZWO characterizes appropriate use for your guide camera:

The review in this case was done using a 14-inch PlaneWave scope as the imager, a system with a focal length of over 2500mm and an OAG for the guider.  In contrast, you've put the camera on a refractor that evidently has a focal length of only 160mm.  The unusual property of the guide camera is its very large pixels, over 9u.  That makes sense for a long focal length setup which isn't what you have.  Your guider image scale is over 11 arc-sec/pixel with your current setup, which is pretty much a non-starter.  This is also the reason you get lost-stars due to low-HFD.  Your configured Min-HFD value is 1.5 pixels so it's not surprising that many of your available stars fall below that level.  You could try reducing that number but you will then be vulnerable to finding sensor noise.  Dark libraries aren't perfect so I wouldn't recommend taking this approach.  

I think the real answer is to use this guide camera on a long focal length scope with an OAG.  If that isn't what you have, you should get a more appropriate guide camera, one that will get your guider image scale down below 5 arc-sec/pixel.

Regards,

Bruce

[Fearless Leader]

Let's first diagnose the problem.  Based upon the log file what do the errors mean?

[Bruce Waddington]

Sorry, I have diagnosed the problem, it's painfully obvious.  If you read the section in the User Guide that explains lost-star errors, perhaps it will become clear to you:

https://openphdguiding.org/man-dev/Trouble_shooting.htm#Problems-_Lost_stars

But you don't have to accept my analysis of it, you can seek guidance elsewhere.

Bruce

[Fearless Leader]

I'm not saying you aren't right.  But I would like some other opinions.  So, this posting is still open.  Primarily I was looking for somebody who could look at the PHD2 log file and tell me what the error means.

[Sonny Edmonds 2]

Have you tried the slider along the bottom of PHD that adjusts the image brightness?

I'm using an ASI290 Mini, which is a planetary camera. Or was, before ASI got so smart and decided the ASI220 was a replacement for the 290. (Which was about 1 week after I purchased mine.)

But I was looking for a finer camera (higher definition) at the time my original guide camera died on me. RIP, it worked itself to death.

Multi star guiding in PHD2 was a huge bonus over the long used single star. But before the Multi star guiding emerged, all we needed was for our guiding to catch a star and follow it over the night.

A pretty simple task for any guide camera. But since I was replacing my original guide camera anyway, I went for High Res (Resolution). My thought was to give the new and improved PHD2 lots of stars to pick from.

And it has worked fine for me. (My original guide camera was an Orion Star Shoot. So pretty outdated as this sport goes.)

Don't discount posible USB problems. USB was not intended for how we use it. It isn't weather resistant at all. I often "exercise" my USB connectors by unplugging and reinserting the connectors several times to wipe the contacting surfaces.

Not every problem lands in a log file. 😉

--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/4e882dc8-a89f-493a-9a97-834c90ff3faan%40googlegroups.com.

[Fearless Leader]

Pedmond:  Thanks for the input.  I understand that not every problem lands in the log file.  But I would like it if I could finds somebody who understands log files who would look at my log file and derive some additional insight other than just, it failed, good luck.

I have tried the slider along the bottom.  I moved it way over to the right.  And still the all of stars are really dim.  I find this very curious.  Because when I view the same setup using ZWO's ASIImg, it shows a really nice bright star field.  Why can't I see a similar star field viewing through phd2?

I own some other uncooled mono ZWO cameras and I have also tried both the ASI174MM and the ASI1600MM.  These have both exhibited the same problem, although ASI432MM seems to be worse.  Maybe So I do need the smaller pixel size camera, but which one?  

Tom

[Sonny Edmonds 2]

I had that happen once when I forgot to take my lens cap off....

You'll figure it out, I have confidence in you.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/dd248a15-2bb5-4fa8-a4a5-926b8a120ba0n%40googlegroups.com.

[Fearless Leader]

Actually, I think I have found the answer (with some help from Claude).  I just need to wait for a clear night (which I haven't got tonight) to prove it.  I was using the ASCOM driver.  And the ASCOM driver is not very good for tracking.  It defaults to a gain of 0, which is ridiculous for guiding, but apparently it does have some other use.  PHD2 works better with the ZWO ASI native driver because PHD2 is able to control the gain (and it can't with the ASCOM driver).  And this explains why the stars in the PHD2 display are always very dim.  I can see a good starfield in ASIImg because it uses the ASI native driver.  As far as the ASI432mm is concerned, because of the 9um pixel size, it is a poor camera for guiding.  But, the thing is, Star Lost is not the expected failure mode.  According to Claude, don't expect it to fail with an error and stop working, you just won't get good tracking results.  But, if you use the ASI432mm and you still get "Star Lost" there is probably another issue besides the pixel size mismatch.  So it was a good debug step.  And this is what I have found, I think.

Tom

[Bruce Waddington]

This is getting even more bizarre, now we've got rubbish from Claude about "expected failure modes":.  I have to ask now: I sent you a link to the PHD2 user guide that explains the various reasons that stars can be lost including the 'Min-HFD' error.  Did you actually read that material?  If you can't understand what was said, perhaps you can ask specific questions that will help clarify the explanation.  Part of that explanation is that guiding doesn't "just stop", lost star events can intermittently happen and PHD2 soldiers on and keeps trying unless your session manager app tells it to stop.  Are you familiar with the term half-flux-diameter (HFD) and do you understand how it applies to your situation?  Do you understand image scale and how it affects star sizes and why your guider image scale is over 11 arc-sec/px?  For example, if the optics of your guide scope optics can produce stars with sizes of 3 arc-sec, how many pixels will that star disk cover using your setup?   None of this is hard but it requires reading, thinking,  and learning about concepts that aren't part of normal daily life.  That's the nature of this hobby.

Bruce

[Fearless Leader]

I have ordered some new equipment.  I have already received an Askar 50mm F3.8 and am waiting for my new ZWO ASI220mm.  It should be here in a couple of days.  Pixel size is 4 Um.  In the meantime I want to find out why the stars in the PHD2 viewing screen are so dimm.  I can't believe that is normal.  Fortunately the polar alignment is really good on my setup so I am just going without tonight.  Maybe there is some SGP setting that I can set which will prevent Star Lost from ending the sequence.

Tom

[Bryan]

Tom

Changing the slider on the 'PHD viewing screen' has no impact on PHD2 guiding.  The slider is there for your convenience IF you choose to select a guide star manually, but moving it neither degrades nor improves performance.

PHD2's algorithms can find suitable guide stars even if you can't.  In fact, it selects stars that meet multiple criteria, rather than just star brightness on the screen.  That's why Auto-select is the preferred route.  It also allows the multi-star function to execute.  Manual selection is single star only.  See Exposure Time and Star Selection

Another advantage to multi-star guiding is that PHD2 can continue to guide even if some stars are lost.  See Multi-Star Guiding

In addition, the HFD window is a more useful means of focusing than using the screen.

Bryan

[Fearless Leader]

Bryan,

Maybe I was unclear, even if I thought I was.  I have understood since well before I posted this message, that the slider bar does not affect guiding.  But the gain of the Camera driver absolutely does affect guiding.  The ASI cameras have two options, as far as drivers.  There is the ASCOM driver, and there is the ASI native driver.  I was using the ASCOM driver and was seeing the "Star Lost" message and the stars were very dim no matter where I placed the slider.  When I changed to the native ASI driver the stars became as bright as they should be.  Same brightness as with ASIImage.  My usage of the ASI432mm was an experiment that I was trying.  I had the idea that with 9um pixels it won't have "Star Lost" failures, it will just be a crappy guider.  I tested that last night by running the guider without connecting it to the mount and it did not get the "Star Lost" errors after I started using the native driver.  Fortunately, my Losmandy G11 is very well polar aligned, and I can get pretty good 1 min exposures without guiding.  As soon as my ASI220MM comes (maybe today) I will try guiding with it.

Tom

[Brian Valente]

Tom

>>> There is the ASCOM driver, and there is the ASI native driver.  I was using the ASCOM driver and was seeing the "Star Lost" message and the stars were very dim

Are you familiar with setting up an ASCOM camera - specifically reviewing/adjusting the camera settings including gain in the ZWO ASCOM Driver?

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/2d4ee746-d886-4536-9e00-87f98ff404a9n%40googlegroups.com.

--

Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Don Waters]

TOM

If you want to use Claude, try this:

1. Open PhD2 manual in a tab on browser

2. Open PhD2 logfile 

3. Find the guiding session you want to analyze

4. Highlight 250 -300 lines of output of that session including header with equipment data

5. Copy the highlighted lines and paste into Claude

6. Ask Claude to analyze.

Claude will access the PhD2 manual and give you a report. It will look at data for your hardware and make suggestions. 

KEEP IN MIND THAT AI WILL MAKE ERRORS AND IS SIMPLE MINDED. But you can follow up with questions and pursue a lot of the things you are asking about.

I second Brian's comment that this is just the nature of the hobby. There are no shortcuts - one basically has to keep digging.

Don