Guiding inconsistent

[ninjageezer]

Ok so this may be normal i'm not sure as im learning .

i have found that my total guing RMS error can sit at anywhere from .46 and then it will go up to 1 or just over ,this is on a hypertuned HEQ5 pro mount .

i watched it last night sat as low as .46 and then a few mins later it would creep up stay about .90/1 for a while and then go back down.is this normal behaviour ?

the mount is super smooth as i have just done a full rebuild with all new bearings and it has a rowan belt kit fitted ,it is better than it was but i can't understand the fluctuations.

i was using a WO zenithstar 73 and ZWO 50mm guidescope coupled to a ZWO 120 mm mini guide camera.

sharpcap was used for the polar alignment and it said excellent.

i was imaging M81 at the time .

Edited April 14, 2022 by ninjageezer

[Stuart1971]

Yes, what you are seeing is normal, as it depends on many factors, including, balance of the scope for any given point in the sky, the seeing conditions, side of the pier…and a few more. in a typical night mine will be between 0.3 and 0.8 and will fluctuate between theses figures, sometimes if you alter certain PHD settings on the fly, you can control it a bit to some extent….buts it’s not worth it…

‘My imaging scale is 1.72”/pixel, so as long as my guiding is around half of this then the starts will be perfectly fine, really in theory anything below your imaging scale should be good, but half you imaging scale will be perfect….as seeing limits it to around 2.0 RMS here in the UK anyway….so don’t worry about it…..👍🏼

[ninjageezer]

53 minutes ago, Stuart1971 said:

Yes, what you are seeing is normal, as it depends on many factors, including, balance of the scope for any given point in the sky, the seeing conditions, side of the pier…and a few more. in a typical night mine will be between 0.3 and 0.8 and will fluctuate between theses figures, sometimes if you alter certain PHD settings on the fly, you can control it a bit to some extent….buts it’s not worth it…

‘My imaging scale is 1.72”/pixel, so as long as my guiding is around half of this then the starts will be perfectly fine, really in theory anything below your imaging scale should be good, but half you imaging scale will be perfect….as seeing limits it to around 2.0 RMS here in the UK anyway….so don’t worry about it…..👍🏼

ok brilliant thank you ,maybe a daft question but how do i get my imaging scale number,i am using a canon 60DA.

[Stuart1971]

3 minutes ago, ninjageezer said:

ok brilliant thank you ,maybe a daft question but how do i get my imaging scale number,i am using a canon 60DA.

So in your case

206 x (your camera pixel size) 4.29 divided by (your focal length) 430mm = 2.05”/pixel

so anything under 1.0 RMS is perfect 👍🏼

[michael8554]

Possibly the RA guiding is worst at the peak of the Periodic Error ?

Michael

[ninjageezer]

1 hour ago, Stuart1971 said:

So in your case

206 x (your camera pixel size) 4.29 divided by (your focal length) 430mm = 2.05”/pixel

so anything under 1.0 RMS is perfect 👍🏼

many thanks ....😉

[The Lazy Astronomer]

Just to add to this: you should also consider your RA and DEC RMS separately as well, and not just focus on the total figure. You want both axes to have similar RMS values (ideally, the same) whilst also aiming for a total RMS of 0.5x image scale 

[Stuart1971]

12 minutes ago, The Lazy Astronomer said:

Just to add to this: you should also consider your RA and DEC RMS separately as well, and not just focus on the total figure. You want both axes to have similar RMS values (ideally, the same) whilst also aiming for a total RMS of 0.5x image scale 

Yes, I get what you mean, but as long as they are both well under the imaging scale, so say 50%,  it will make no odds to the final image, but if your image scale is much lower, then yes this does come into play….but not in the case of the OP….👍🏼

[Stuart1971]

1 hour ago, michael8554 said:

Possibly the RA guiding is worst at the peak of the Periodic Error ?

Michael

Yes good point, PE correction is a good idea, it does make a difference….also I’d you use EQMOD, think about trying GS Server instead, it’s much more modern and has some great new features, including simple PE correction, and DEC goto guiding to help mounts with large DEC backlash….

https://greenswamp.org

 

[ninjageezer]

this my calibration graph from last night, seems to be a lot of steps have i got something set incorrect ?

 

[Stuart1971]

5 hours ago, ninjageezer said:

this my calibration graph from last night, seems to be a lot of steps have i got something set incorrect ?

 

To reduce the amount of steps, you need to increase  the step size, you should have around 8-12 steps, also your backlash is very high and a bit all over the place, especially for a hyper tuned mount, but then if it was done by dark frame optics, I am not surprised it’s worse than they are normally….

I would either be sending it back or asking for a refund, as those jumps back and fourth in DEC are not good, a bit of backlash is normal, but that is very inconsistent….51 steps in RA to 20 in DEC is also not good, your expected RA and DEC rate should be approx the same and around 7.5 a-s/sec, for a guide rate set at 0.5 x sidereal….which is the default for these mounts….but you have it set in 0.2….why…?? That seems far to low, and might explain a few things….

[woldsman]

11 hours ago, Stuart1971 said:

So in your case

206 x (your camera pixel size) 4.29 divided by (your focal length) 430mm = 2.05”/pixel

so anything under 1.0 RMS is perfect 👍🏼

If you are feeling lazy, Astrometry.net generates the pixel scale value in results when you plate solve online. Then divide it. 

[Stuart1971]

2 minutes ago, woldsman said:

If you are feeling lazy, Astrometry.net generates the pixel scale value in results when you plate solve online. Then divide it. 

Not exactly easier or quicker than my method above, especially if you need to take an image first to solve it and use astrometry online….surely it’s easier just to open the calculator on your phone and do the sum….takes 15 seconds max….

206 x your pixel size divided by your focal length……Simple’s….👍🏼

[michael8554]

The Review Calibration image shows that the RA and Dec Guide Speeds are set too low - 0.20x.

So set the Guide Speed in the mount to at least 0.80x (or 8arcsec/sec or 80% depending on the mount).

Then the number of steps in the Cal should be more like the expected 12 or so, instead of 51.

Also you were Calibrating at Dec = 72.6, it's best to Cal near Dec = 0 and near south.

A read of the PHD2 Instructions would help ?

Michael

[Stuart1971]

32 minutes ago, michael8554 said:

The Review Calibration image shows that the RA and Dec Guide Speeds are set too low - 0.20x.

So set the Guide Speed in the mount to at least 0.80x (or 8arcsec/sec or 80% depending on the mount).

Then the number of steps in the Cal should be more like the expected 12 or so, instead of 51.

Also you were Calibrating at Dec = 72.6, it's best to Cal near Dec = 0 and near south.

A read of the PHD2 Instructions would help ?

Michael

Sorry to disagree, but 0.8 is too high, and far too aggressive for this mount,  0.5x is the norm

also 0.8x does not equate to 8 arc seconds per second, the guide rate is a fraction of sidereal rate, and sidereal is 15 arc second per second

Edited April 15, 2022 by Stuart1971

[michael8554]

Not familiar with the mount, all I know is 0.20x is too low, based on the number of Cal Steps.

Yes, 0.80x is actually 12arcsec/sec, my bad.

Sidereal is 15arcsec/sec, not 1arcsec/sec, I expect that you made a typo.

Michael

[Stuart1971]

When you guide in RA the mount is moving a sidereal rate 1 arc second per second, if your guide rate is set at 0.5 then when you need to pulse in the west direction, it means you actually speed the mount up by the guide rate amount, so your pulse will be at 1.5x sidereal, when you guide east it will slow it down by the amount of your guide rate, so the pulse will be 0.5x, the RA is moving all the time, and alters with guide pulse's but never stops or goes in the other direction….

[Stuart1971]

5 minutes ago, michael8554 said:

Not familiar with the mount, all I know is 0.20x is too low, based on the number of Cal Steps.

Yes, 0.80x is actually 12arcsec/sec, my bad.

Sidereal is 15arcsec/sec, not 1arcsec/sec, I expect that you made a typo.

Michael

Yes my mistake….👍🏼

[Stuart1971]

5 minutes ago, michael8554 said:

Not familiar with the mount, all I know is 0.20x is too low, based on the number of Cal Steps.

Yes, 0.80x is actually 12arcsec/sec, my bad.

Sidereal is 15arcsec/sec, not 1arcsec/sec, I expect that you made a typo.

Michael

Well the amount of calibration steps, is due to the low step size too, he maybe could just up that as well as up the guide rate…

[Stuart1971]

18 hours ago, ninjageezer said:

this my calibration graph from last night, seems to be a lot of steps have i got something set incorrect ?

 

This concerns me, especially on a mount that has supposed to have been hyper tuned….these yellow circled steps that are out of line, this could be slippage, or something loose somewhere….this red line should be perfectly straight, after the direction change at the top, where it shows the backlash, the line coming down should then be again straight….

 

[Stuart1971]

This is mine, yes a lot of backlash as it’s an old EQ8 mount, (it’s been adjusted out since this calibration some time ago) but before and after the change of direction at the top, the red lines are perfectly straight as they should be, as the gears are engaged and going in the same direction…I think I would check yours out….

 

[ninjageezer]

ok first of all thank you all for the help and comments ,just catching up as been bedbound for the last couple of days.

As for the hypertuning ,i changed all of the bearings for high quality SKF /Timken and fitted the rowen belt kit myself ,,I am from and engineering background and it was a simple job tbh....i will go back and check it again .it seems nice and free now an no real tight spots that it had before.(it was bad ) i really dont know how the guide speed dropped to .20 i never changed it but with put it to .50 as i did before when setting up.

are there any other settings other than guide speed i should be changing in PHD2 ..

[newbie alert]

13 hours ago, ninjageezer said:

ok first of all thank you all for the help and comments ,just catching up as been bedbound for the last couple of days.

As for the hypertuning ,i changed all of the bearings for high quality SKF /Timken and fitted the rowen belt kit myself ,,I am from and engineering background and it was a simple job tbh....i will go back and check it again .it seems nice and free now an no real tight spots that it had before.(it was bad ) i really dont know how the guide speed dropped to .20 i never changed it but with put it to .50 as i did before when setting up.

are there any other settings other than guide speed i should be changing in PHD2 ..

.5 is the default setting... I assume your RMS figures are in pixels as a heq5 aren't really capable of.4 arc secs, is a common misconception .. problem is everyone's setup is slightly different in pixel scale, so if using a small guidescope with a big pixel camera the RMS will be smaller in pixels where it's the same with arc secs, as a arc sec is a arc sec of measurement... Remember also using a separate guidescope as you are the values you see are the pixel scale of you guidecam.. 

I see you hypertuned your mount yourself, hypertune is a loose term... Some say it when they've just changed the grease and the bearings, to my mind it goes deeper than that..

Suggestions I could make are.. check your pulleys are running true.. I see lots of people on you tube showing off there newly belt mods with visible isolations on the pulley.. that will show on a PhD graph, on your backlash chart you have visible outliners and your Dec drifts south.. this could be mechanical ( various things that can cause this)or your PA, as again this shows on your guide assistant as 4.5 arc secs of error.. 

[ninjageezer]

3 hours ago, newbie alert said:

.5 is the default setting... I assume your RMS figures are in pixels as a heq5 aren't really capable of.4 arc secs, is a common misconception .. problem is everyone's setup is slightly different in pixel scale, so if using a small guidescope with a big pixel camera the RMS will be smaller in pixels where it's the same with arc secs, as a arc sec is a arc sec of measurement... Remember also using a separate guidescope as you are the values you see are the pixel scale of you guidecam.. 

I see you hypertuned your mount yourself, hypertune is a loose term... Some say it when they've just changed the grease and the bearings, to my mind it goes deeper than that..

Suggestions I could make are.. check your pulleys are running true.. I see lots of people on you tube showing off there newly belt mods with visible isolations on the pulley.. that will show on a PhD graph, on your backlash chart you have visible outliners and your Dec drifts south.. this could be mechanical ( various things that can cause this)or your PA, as again this shows on your guide assistant as 4.5 arc secs of error.. 

Many thanks for the suggestions ,yes i also saw the wobbly pulleys on some youtube videos .i am super keen on tolerances' with belt line ups ect . (engineering background)

i did the manual backlash adjustment at the using the belt cog with not belts on as you really can feel any binding ,i have just rechecked and re adjusted everything .i did find the the collar locking rings if you just tighten them more than just nipped slightly, causes some binding of the worm drive ,so i readjusted those ,and marked them in case of movement.

double checked the belts are the correct tension and the is no drift or wobble of anything ,just need clear skies weds as they currently promise here in the north east.

i will make sure the guide setting is put back to .5 as well ,its something i never changed ,the only other thing i noticed last time out when doing a phd2 calibration it took forever 51 steps.... its set it 12 but there is also a step adjustment.

i will reset the profile and start again me thinks.

one more thing is it worth still balancing east heavy or not ? ive tried to balance exactly.

oh ive just checked from a snap i took you was spot on it was on pixels nor arc .. doh

as for polar alignment i used sharp cap pro and it was steady on excellent so not sure it said 4.5 arc secs of error...

cheers

 

paul.

 

 

 

 

 

 

 

 

 

[Stuart1971]

2 hours ago, ninjageezer said:

Many thanks for the suggestions ,yes i also saw the wobbly pulleys on some youtube videos .i am super keen on tolerances' with belt line ups ect . (engineering background)

i did the manual backlash adjustment at the using the belt cog with not belts on as you really can feel any binding ,i have just rechecked and re adjusted everything .i did find the the collar locking rings if you just tighten them more than just nipped slightly, causes some binding of the worm drive ,so i readjusted those ,and marked them in case of movement.

double checked the belts are the correct tension and the is no drift or wobble of anything ,just need clear skies weds as they currently promise here in the north east.

i will make sure the guide setting is put back to .5 as well ,its something i never changed ,the only other thing i noticed last time out when doing a phd2 calibration it took forever 51 steps.... its set it 12 but there is also a step adjustment.

i will reset the profile and start again me thinks.

one more thing is it worth still balancing east heavy or not ? ive tried to balance exactly.

oh ive just checked from a snap i took you was spot on it was on pixels nor arc .. doh

as for polar alignment i used sharp cap pro and it was steady on excellent so not sure it said 4.5 arc secs of error...

cheers

 

paul.

 

 

 

 

 

 

 

 

 

After you change the guide rate back to 0.5, you have to re calibrate anyway, don’t try and guide without doing that, also when entering your pixel size and focal length into PHD, it should work out the step size needed for calibration, also set where in the sky you will do the calibration, should be just due south at 30 degrees is best…👍🏼
you should not have anywhere near 51 steps, that’s the highest I have seen….Should be set at 12, and it should take between 8 and 12 normally…