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silios

HEQ5Pro stars trailing in one direction!

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Hello stargazers!

after fixing the ED80 focuser tilt and FFR spacing issues (http://stargazerslounge.com/topic/249588-sw-ed80-reducer-elongated-stars-problem/)
I have some trail (i think) in all exposures i take but it takes a lot of time to really build up and manifests in the images even in the center of the field!
It becomes slightly visible in 10mins, worse in 20mins and in my opinion unusable in 30mins exposures.

Gear used :

Heq5 Pro

Modified finderscope with QHY5 bolted firmly (although on 3 screw baader rings on single shoe on one of the rings not on a plate) on top of the ED80

Pulse guiding through ascom + pec trained and applied corrections while imaging

One shot of 1800secs from last night
post-39392-0-49388500-1442327555_thumb.j

Here is the plate solve of the image if that is of any help.
Image Plate Solver script version 3.5.1
===============================================================================
Referentiation Matrix (Gnomonic projection = Matrix * Coords[x,y]):
            +0.00059136       -3.35323e-005           -0.948749
          +3.35667e-005        +0.000591379           -0.805052
                     +0                  +0                  +1
Projection origin.. [1676.147757 1266.175055]pix -> [RA:+02 54 45.62 Dec:+60 26 33.75]
Resolution ........ 2.132 arcsec/pix
Rotation .......... 176.752 deg
Focal ............. 522.35 mm
Pixel size ........ 5.40 um
Field of view ..... 1d 59' 7.6" x 1d 29' 59.1"
Image center ...... RA: 02 54 45.583  Dec: +60 26 33.36
Image bounds:
   top-left ....... RA: 02 47 15.353  Dec: +59 37 27.51
   top-right ...... RA: 03 02 57.738  Dec: +59 44 03.24
   bottom-left .... RA: 02 46 12.014  Dec: +61 07 05.13
   bottom-right ... RA: 03 02 38.669  Dec: +61 13 59.48
===============================================================================

200% crop of the centre of the image shows the problem clearly.
post-39392-0-09993400-1442327571_thumb.j

And here is PhDLabs last night's analysis log.
post-39392-0-22278000-1442327578_thumb.j

Second run does not look much different than the first one (to my untrained eyes at least).

post-39392-0-21357400-1442327584_thumb.j

The phd graph did look at its best (flatline like)

What do ladies and gents think? bad polar alignment, backlash on gears, differential flexure?

If anyone has suggestions of the nature of the problem might be, I would be grateful.
 

Edited by silios

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Just a few clarifications from me please.  What was the orientation of your chip compared to North, South East West?  On the first screen shot your polar alignment error is nearly 3x that of your second screen shot.  Did you drift align in PHD?

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Just a few clarifications from me please.  What was the orientation of your chip compared to North, South East West?  On the first screen shot your polar alignment error is nearly 3x that of your second screen shot.  Did you drift align in PHD?

Not sure, i always get confused on that, but the cameras cabling was looking upwards as in the image

post-39392-0-32493300-1442329152_thumb.j

the second graph is after the meridian flip. I did the drift alignment in PHD before starting the imaging session.

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Now Ive seen your set up as well I would put some money on flexure somewhere particularly in the guidescope connection.  Lets see what others decide.  I don't think its field rotation looking at the 'ovality'.

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its not that high anymore (this an older image) but still os mounted on a single point. will get an image up as soon im at home

Sent from my Nexus 5 using Tapatalk

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  On the first screen shot your polar alignment error is nearly 3x that of your second screen shot.

Is this really the case? I find that I can't trust the phd lab calculations at the best of times. My PA can vary by several arc minutes between guides and I'm on a concrete post.

I suspect that the dithering doesn't get filtered out of the calcs.

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seems to be struggling in RA judging by those scatter plots.  What RA aggressiveness and Hysteresis settings are you using, what was your RA Osc if you remember.  Guide step size in the mount, exposure time for PHD ?  Maybe it'll help if you can give some screen grabs of your phd settings too

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its not that high anymore (this an older image) but still os mounted on a single point. will get an image up as soon im at home

Sent from my Nexus 5 using Tapatalk

Are you sure it's pointed at roughly the same patch of sky as your scope?

I've had the same issue and it was differential flexure - I had inadvertently knocked the guidescope out of alignment.

Had to drop a diagonal on both scopes in the daytime and aligned them with a crosshaired EP.

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Ok i'm near the setup (well.. five floors above with no elevator, but exercise is good i guess :D )

Here are photos of the current setup (the other one was just for the camera orientation, my bad)

post-39392-0-92130000-1442334415_thumb.jpost-39392-0-96233000-1442334422_thumb.jpost-39392-0-60743800-1442334426_thumb.jpost-39392-0-89911900-1442334432_thumb.jpost-39392-0-76936600-1442334436_thumb.j

and the PHD settings

post-39392-0-30846400-1442334440_thumb.jpost-39392-0-51726400-1442334443_thumb.j

i was dithering last night so i dont know if that affects the phdlabs software as previously suggested.

Apart from the min motion setting on both RA and DEC in PHD everything else was populated by the equipment wizard.

I have calculated the min motion to 0.019 for my setup (6.66 arc/px guider and 2.18arc/px imager)

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Hi

You could try running the PHD2 Guiding Assistant Tool and see if anything shows up. Are any cables dragging?

Louise

I have them attached to the dec portion with velcro , not sure if that could cause drag.

Are you sure it's pointed at roughly the same patch of sky as your scope?

I've had the same issue and it was differential flexure - I had inadvertently knocked the guidescope out of alignment.

Had to drop a diagonal on both scopes in the daytime and aligned them with a crosshaired EP.

Last night before starting to image i made sure that both pointed roughly at the same spot (a distant antenna on a mountain some 5-6 khm away).

roughly because the finderguider is modded (by me) and there is no easy way to disassemble the camera.

Going to realign them as we speak, while there is still light and can be sure at what im looking at. Will place also a proper dovetail underneath attached to both the ED80 rings and get ready for night testing!

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After firmly bolting down the guiding rings on a dovetail i started the PHD assistant (thanks Thalestris never used that one before!).

Some mixed - weird results occurred :

Initially without changing anything from last night (apart from the guider mounting) and using pulse guiding i got the following output

post-39392-0-91611500-1442345529_thumb.j

BUT, after changing to ST4 guiding (after a full restart of equipment and PC as well) i get the following

post-39392-0-07555800-1442345536_thumb.j

in the meantime i haven't been anywhere near the mount, let alone move it or something!

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It may make no difference, but good practice would be to mount the guidescope with its centre of gravity over the RA axis.

Mounting on the rear ring would be close enough.

Michael

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Ok i'm near the setup (well.. five floors above with no elevator, but exercise is good i guess :D )

Here are photos of the current setup (the other one was just for the camera orientation, my bad)

attachicon.gifIMG_20150915_185525.jpgattachicon.gifIMG_20150915_185532.jpgattachicon.gifIMG_20150915_185541.jpgattachicon.gifIMG_20150915_185554.jpgattachicon.gifIMG_20150915_185658.jpg

and the PHD settings

attachicon.gifIMG_20150915_190900.jpgattachicon.gifIMG_20150915_190914.jpg

i was dithering last night so i dont know if that affects the phdlabs software as previously suggested.

Apart from the min motion setting on both RA and DEC in PHD everything else was populated by the equipment wizard.

I have calculated the min motion to 0.019 for my setup (6.66 arc/px guider and 2.18arc/px imager)

What's the red stuff in your top guiderscope ring? Is it rubber or something similar? If this expands or contract either due to temperature change or different loads at different orientations, it would be a source of flexure.

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It may make no difference, but good practice would be to mount the guidescope with its centre of gravity over the RA axis.

Mounting on the rear ring would be close enough.

Michael

I have now secured the guidescope firmly on a dovetail, on top of the custom made( really sturdy) ED80 rings , and it feels quite solid.

post-39392-0-96612800-1442412794_thumb.j

What's the red stuff in your top guiderscope ring? Is it rubber or something similar? If this expands or contract either due to temperature change or different loads at different orientations, it would be a source of flexure.

Its PVC, i plan to exchange it for some aluminium today or even better solid rings without screws.

Good news is that after :

getting the guider lower - dovetail

PA carefully

use suggestions from PHD guiding assistant

and using ST4 instead of pulse guide (due to being a programmer i am not entirely convinced that the problem wasn't some malfunction in my setup - pulse guide - pec method although the graph and number looked better while using this method)

i was able to shoot consistently 30mins subs without trail (i think) despite the wind that blew sometimes aggressively throughout the night.

post-39392-0-60030400-1442412796_thumb.j

Scatter graph looks quite nice and i hope that the problem is now fixed.

post-39392-0-04982200-1442412798_thumb.j

I wonder, are there any people guiding with a HEQ5 more than 30 mins up to 1000-1500mm ??

Thank you all for the help :)

Edited by silios

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Always align your chip with RA and Dec when the image allows it, either in landscape or portrait format. This is easy. Take a 5 second sub and while it is exposing just slew the mount slowly in one axis. You'll get star trails which will be horizontal or vertical when the camera is aligned along RA and Dec. This has two advantages.You can easily see which axis is causing a problem in guiding and, maybe a year or two later, you can come back and add more data to an image without spending an hour finding the right camera angle!

A guiding error will be in the same direction for all stars in all parts of the image.

A polar alignment error will not look like this. It will look like rotation when you look into all the corners. Don't expect perfect symmetry when looking for this because...  life isn't like that!

Olly

Edited by ollypenrice
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Are you sure it's pointed at roughly the same patch of sky as your scope?

I've had the same issue and it was differential flexure - I had inadvertently knocked the guidescope out of alignment.

Had to drop a diagonal on both scopes in the daytime and aligned them with a crosshaired EP.

Does the guide scope need to be pointing at the same patch of sky as the telescope? I just have my ST80 bolted on top of my ED80 and they are not aligned with each other. I didn't think this mattered. Is this another thing I've got wrong?

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Always align your chip with RA and Dec when the image allows it, either in landscape or portrait format. This is easy. Take a 5 second sub and while it is exposing just slew the mount slowly in one axis. You'll get star trails which will be horizontal or vertical when the camera is aligned along RA and Dec. This has two advantages.You can easily see which axis is causing a problem in guiding and, maybe a year or two later, you can come back and add more data to an image without spending an hour finding the right camera angle!

A guiding error will be in the same direction for all stars in all parts of the image.

A polar alignment error will not look like this. It will look like rotation when you look into all the corners. Don't expect perfect symmetry when looking for this because...  life isn't like that!

Olly

Good to know Olly, i always mess the orientation up :) Luckily i just did the mini drift slewing west and the trail was horizontal so i guess im good to go!

Does the guide scope need to be pointing at the same patch of sky as the telescope? I just have my ST80 bolted on top of my ED80 and they are not aligned with each other. I didn't think this mattered. Is this another thing I've got wrong?

It certainly did seem to help in my case to have it 1:1 with the imager. Maybe someone more knowledgeable can chime in and explain the theory behind it.

I am gathering data for the past hour and the scatter graph is a beauty :)

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Does the guide scope need to be pointing at the same patch of sky as the telescope? I just have my ST80 bolted on top of my ED80 and they are not aligned with each other. I didn't think this mattered. Is this another thing I've got wrong?

Yes roughly it does otherwise you can experience poor subs.  It depends on how long your subs are and how much difference in scope alignment there is as to when you will see any signs in your exposures.

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