Elongated stars.

[SteveBz]

Hi Guys,

What has happened here?  This is my first attempt at guiding with PHD2 and a QHY5 legacy camera.  Here is the Messier 36 open cluster from Auriga last night.  As you see it's drifting off to the top left!  That's NGC 1907, centre left.

This photo comprises 7 subs of two minutes each, shot between the clouds.  With flats and biases but no darks processed in DSS, followed by cleaning up in GIMP.

For focusing I used a FWHM utility on my computer (inside the house) with remote but manual focusing (ie not automated). The focus is not perfect, but there is some strangeness around the stars on the RHS of the photo.  That is to say the stars on the RHS seem more oval than the stars on the left.

Does it mean my focuser is not straight or am I just out of collimation?

What are your thoughts?

Regards,

Steve.
 

[alacant]

Hi. Did you run the guiding assistant to get the correct values? Did you drift/polar drift/static polar align (all available in PHD2)? Without the PHD2 guide log it's not easy to say. There's coma. Evidence in the snap is that the cc needs to be 1mm further from the sensor and the camera is tilted along its long axis. Collimate using a Cheshire with cross-hairs and perfect using a defocused star by adjusting primary only.

But hey, your first attempt was fine. HTH.

[Demonperformer]

It isn't just top left (although it is clear in the cluster). I would say it is your guiding is out, but I am no expert. If it is, PHD2 produces a log file, which may help to sort why.

 

[SteveBz]

20 minutes ago, alacant said:

Did you run the guiding assistant to get the correct values?

No, is it too late now?  Can I retrieve the guidelog for the period?

20 minutes ago, alacant said:

Did you drift/polar drift/static polar align (all available in PHD2)?

No, I thought guiding would avoid having to do that.  I will do.

21 minutes ago, alacant said:

There's coma. Evidence in the snap is that the cc needs to be 1mm further from the sensor

How can you tell it's 1 mm?  Is it just that it's also out of focus by that amount?  If I fix the focus, will that fix the coma?

21 minutes ago, alacant said:

the camera is tilted along its long axis.

Is it?  Is that the focuser?  Do I need to fix the focuser?

And you think my primary collimation is off.  That's the easiest thing to look at.

Thanks for you analysis.

Steve. 

[SteveBz]

24 minutes ago, Demonperformer said:

It isn't just top left (although it is clear in the cluster). I would say it is your guiding is out, but I am no expert. If it is, PHD2 produces a log file, which may help to sort why.

 

I'll look.  Is the log still there from Tuesday?

Regards,

Steve.

[alacant]

49 minutes ago, SteveBz said:

No, is it too late now?

Yes

49 minutes ago, SteveBz said:

Can I retrieve the guidelog for the period?

Yes. try:

c:\users\you\Documents\PHD2

51 minutes ago, SteveBz said:

I thought guiding would avoid having to do that

Get it close. 5´is fine unless you're at a high declination. PHD2 will do the rest.

52 minutes ago, SteveBz said:

How can you tell it's 1 mm?

The stars are pointing toward the centre. Knowing the Baader cc, I'm guessing...

53 minutes ago, SteveBz said:

If I fix the focus, will that fix the coma?

It will look better because the stars will not be as fat but the coma will still be there. The focus doesn't change the sensor to cc distance. There are some other ricks too like focusing on 1/3rds to try.

55 minutes ago, SteveBz said:

Do I need to fix the focuser?

No. If you've collimated accurately and left the focus tube at the focus position it should be fine. Just make sure the camera is square in the focuser.

56 minutes ago, SteveBz said:

you think my primary collimation is off.

Probably. If you want to improve the image (there's nothing wrong with what you have if it's OK for you remember) you have to be systematic. Everything has to be perfect. One step at a time.

Probably just re-seating the camera will bring you some improvement.

HTH and good luck.

[SteveBz]

10 minutes ago, alacant said:

c:\users\you\Documents\PHD2

Here are the logs.  Not sure that it says much, except I have extreme periodic error.  Which I knew and I have PEC switched on.

[SteveBz]

13 minutes ago, alacant said:

Yes

Yes. try:

c:\users\you\Documents\PHD2

Get it close. 5´is fine unless you're at a high declination. PHD2 will do the rest.

The stars are pointing toward the centre. Knowing the Baader cc, I'm guessing...

It will look better because the stars will not be as fat but the coma will still be there. The focus doesn't change the sensor to cc distance. There are some other ricks too like focusing on 1/3rds to try.

No. If you've collimated accurately and left the focus tube at the focus position it should be fine. Just make sure the camera is square in the focuser.

Probably. If you want to improve the image (there's nothing wrong with what you have if it's OK for you remember) you have to be systematic. Everything has to be perfect. One step at a time.

Probably just re-seating the camera will bring you some improvement.

HTH and good luck.

So, the quick things to do are check the primary collimation and reset the camera carefully afterwards. And maybe put a narrow washer in the MPCCIII.

[SteveBz]

1 hour ago, alacant said:

Just make sure the camera is square in the focuser.

Hmm..  It wasn't.  It had slipped on one side by a mm or even less.

[alacant]

7 minutes ago, SteveBz said:

slipped on one side by a mm

That's very good news. You should be fixed:)

[SteveBz]

2 minutes ago, alacant said:

That's very good news. You should be fixed:)

Do you think the RA correction is a bit to severe?

[alacant]

3 minutes ago, SteveBz said:

RA correction is a bit to severe?

Without the guide log, difficult to say. I'd create a new profile (default settings), run the guiding assistant for 10 minutes, accept what it suggests and see what needs doing then. The seeing counts for a lot though. I think you should be able to guide at under 1.5 RMS though which would be good for your setup. It's probably best to pull the mount apart, clean and re-grease it and adjust gear mesh before you start with the software. Or just leave it if you're satisfied otherwise it can take up valuable time spent sleeping, socialising and working;) HTH.

 

[SteveBz]

2 minutes ago, alacant said:

mount apart, clean and re-grease it and adjust gear mesh

I did that last summer.  I bought it second-hand and everything was seized solid.  It was quite hard, but I suspect that's what caused the irregularities.  I had to grind it down with very fine sandpaper (1200 grade) for about two weeks.

[SteveBz]

15 minutes ago, SteveBz said:

Do you think the RA correction is a bit too severe?

The other thing I wanted to do was use 16x speed because I navigate on the same handset as guiding.  Will the calibration account for that, do you think?

[Rodd]

I see the elongation left to right, except in the lower right where it does tend toward the center.  I think it IS a guiding issue, though the camera slipping out of orthogonality was definitely part of it.  You can always notch don the RA aggressiveness (or increase it perhaps).  Good luck!

Rodd

[SteveBz]

7 minutes ago, Rodd said:

I see the elongation left to right, except in the lower right where it does tend toward the center.  I think it IS a guiding issue, though the camera slipping out of orthogonality was definitely part of it.  You can always notch don the RA aggressiveness (or increase it perhaps).  Good luck!

Rodd

Ok, so at least I see how you guys are using "Orthogonal" now.  That helps!

I'm going to try the guiding assistant.

As I' steering and guiding on the same mechanism it would help the steering and navigation of stars if I could use guide with it set to the highest value, x16, do you think I could guide at that rate too?  Maybe I can use the electronics to do both speeds and ramp down while guiding.

What do you think?

Thanks

Steve.

[Rodd]

1 minute ago, SteveBz said:

Ok, so at least I see how you guys are using "Orthogonal" now.  That helps!

I'm going to try the guiding assistant.

As I' steering and guiding on the same mechanism it would help the steering and navigation of stars if I could use guide with it set to the highest value, x16, do you think I could guide at that rate too?  Maybe I can use the electronics to do both speeds and ramp down while guiding.

What do you think?

Thanks

Steve.

Not sure I understand.  Normally, when I slew manually I choose my rate  in multiples of sidereal (1x, 12x, 64x etc), but the mount always guides in sidereal (unless I switch to lunar or cometary etc).  You should be able to have a different manual slew speed than your guide speed.  If that was your question?

Rodd

[SteveBz]

2 minutes ago, Rodd said:

Not sure I understand.  Normally, when I slew manually I choose my rate  in multiples of sidereal (1x, 12x, 64x etc), but the mount always guides in sidereal (unless I switch to lunar or cometary etc).  You should be able to have a different manual slew speed than your guide speed.  If that was your question?

Rodd

Mine only has one port and I have to go outside to change the speed.  It's not a goto scope.  If I stay inside I can only guide (or slew) at a single rate.  The preferred guide rate seems to be x.5, but I prefer to slew short distances at x16.  (I still go outside and manually move it for larger distances).  What I want to do is leave it on x16 all the time so I can slew at that rate, but either guide at x16, or create an electronic switch to change the speeds electronically.

[Rodd]

3 minutes ago, SteveBz said:

Mine only has one port and I have to go outside to change the speed.  It's not a goto scope.  If I stay inside I can only guide (or slew) at a single rate.  The preferred guide rate seems to be x.5, but I prefer to slew short distances at x16.  (I still go outside and manually move it for larger distances).  What I want to do is leave it on x16 all the time so I can slew at that rate, but either guide at x16, or create an electronic switch to change the speeds electronically.

Ahh....I would think if you have the know how to create an electronic switch, it would work, as the mount would not know about the switch--it would guide at the rate it was told to guide at, whether it was set by hand or by switch.  But the waters just overflowed the gunnels I'm afraid...way beyond my ability.  You'll crack it.

Rodd

[SteveBz]

1 minute ago, Rodd said:

Ahh....I would think if you have the know how to create an electronic switch, it would work, as the mount would not know about the switch--it would guide at the rate it was told to guide at, whether it was set by hand or by switch.  But the waters just overflowed the gunnels I'm afraid...way beyond my ability.  You'll crack it.

Rodd

But you don't think I can guide at x16?

[Rodd]

Just now, SteveBz said:

But you don't think I can guide at x16?

That does not make sense to me.  The stars move across the sky at a known rate.  You must guide at that rate (or slightly more or less if your mount has trouble maintaining that rate).  But 16x that rate?  I may be missing something (not unusual).

Rodd

[SteveBz]

deleted.

[SteveBz]

7 minutes ago, Rodd said:

That does not make sense to me.  The stars move across the sky at a known rate.  You must guide at that rate (or slightly more or less if your mount has trouble maintaining that rate).  But 16x that rate?  I may be missing something (not unusual).

Rodd

Ok, well maybe I'm missing something, I thought guiding was making small corrections to the tracking.  Tracking is at sidereal rate, but I thought until I saw the PHD2 advice, that guiding could be done at any speed, and I imagined, the faster the better.  But maybe it creates wobble, if it's too fast and then the wobble has to be allowed to die down.  So I don't really know either.

[Rodd]

2 minutes ago, SteveBz said:

Ok, well maybe I'm missing something, I thought guiding was making small corrections to the tracking.  Tracking is at sidereal rate, but I thought until I saw the PHD2 advice, that guiding could be done at any speed, and I imagined, the faster the better.  But maybe it creates wobble, if it's too fast and then the wobble has to be allowed to die down.  So I don't really know either.

I think you refer to aggressiveness perhaps?  that is the strength of a correction.  The mount guides at sidereal rate and makes corrections as necessary to put eth star back in the box, or in the crosshairs, or what ever.  I think the aggressiveness relates to the response rate, as the mount will move the amount it thinks is necessary to make a correction

[SteveBz]

1 minute ago, Rodd said:

I think you refer to aggressiveness perhaps?  that is the strength of a correction.  The mount guides at sidereal rate and makes corrections as necessary to put eth star back in the box, or in the crosshairs, or what ever.  I think the aggressiveness relates to the response rate, as the mount will move the amount it thinks is necessary to make a correction

Ah, maybe.  Maybe I'll just try it and see if it works.