NEQ6 Mount Using EQMod

[Armsoft]

Hello All,

I`m using the titled setup and was wondering what level of accuracy I should expect when setting allignment points.

I`ve set several but when slewing to them again I don`t get them central in the eyepiece, and they don`t all show as being off in the same direction ie; some off to the right, others off to the left.

Any thoughts/Help appreciated

Thanks

Mark

[chrisshillito]

Hi Mark,

One thing you must consider is that the alignment point and alignment star only coincide in position at the instant the point is added. Going back to an alignment star does not take you back to the alignment point and that goto may well fall within (or even outside of) an area being modelled by a different set of points that what your are expecting (particularly if a three point transformation is active).

When it comes to alignment try to use a high power reticule eyepiece. If gotos are not as accurate as you would like then try switching to a 'nearest point' model. If this improves things then it is likely there is an innacurate point within model. Also if you are going for an all sky model make use of the point filter to only consider points within the same quadrant or on the same side of the meridian as your target.

Chris.

[Armsoft]

Hi Chris,

Thanks for the advice.

Being a mere novice with EQMod I was expecting the points to stay aligned ie; I set alignment points on 5 stars on Leo which was in the East quadrent last night, I then set a further 4 alignment points on stars in the Western quadrent, I just assumed that if I then slewed back to one of the stars in Leo it would still be central (I had tracking set to sidereal), but by the sounds of it that's not how it works?

My aim was to set as many points as I can across all 4 quadrents, to then be able to just start up and slew to various objects etc without the need to do any alignment..

Interestingly, when I slewed to Venus after setting a few points it was about 1 3/4 degrees out (according to Carte du Ciel).

Any further help/advice that you could give would be really appreciated.

Thanks again

Mark

[Skylook123]

Chris' comment regarding reticle eyepiece is very appropriate. Even with a high power non-reticle eyepiece, we all have physical "biases" in how we center a target in the eypiece. I have a problem where my eye is too close to my nose, so my 9mm Nagler width has me thinking I'm centering, but really I've got parallax error.

If you have an offset in your measurement of the center, then it might be a constant value but it rotates around the sky with the stars you use. As a result, you can warp the sky model. One alignment star with error is pretty much a static offset, depending a bit on the quality of your polar alignment. Two stars with errors, even though small, start to make the sky a bit wavy. Three stars and beyond, and you might just have modeled an amusement park fun house mirror. Errors may sometimes cancel, most often they twist and turn the model in local effects.

When my best friend and spouse for 44 years bought me a reticle eyepiece four years ago, the difference in alignment quality was striking. I tried an experiment where I had the star as a pinpoint focused, and no reticle lines visible, and guessed where the center of the eyepiece was. Then I turned on the reticle, and my error was disturbing. So I measured the reticle lines, and they were perfect; my processing the signal was not. So, back to Chris' comment, a reticle eyepiece can take out the natural human variances. Or, you could have some extreme cone error involved, and the left-right sides of the meridian could be causing some conflict.

I wouldn't worry as much about planetary precision; those locations are determined using your time, and remember that your time setting is constant across 15 degrees of longitude, more or less; that can cause planets to need fine tuning to get them in the field of view, depending on your physical location.

Good luck with your adventure!

[Armsoft]

Hi Jim,

Thanks for that.

I did use a Cross Hairs to do the alignments last night and got every one as spot on as I could.

It could be that I`m expecting too much, or maybe have not done enough alignment points yet (9 so far) or that the difference of around 1 3/4 degrees is the best that I should expect?

Thanks so far

Mark

Chris' comment regarding reticle eyepiece is very appropriate. Even with a high power non-reticle eyepiece, we all have physical "biases" in how we center a target in the eypiece. I have a problem where my eye is too close to my nose, so my 9mm Nagler width has me thinking I'm centering, but really I've got parallax error.

If you have an offset in your measurement of the center, then it might be a constant value but it rotates around the sky with the stars you use. As a result, you can warp the sky model. One alignment star with error is pretty much a static offset, depending a bit on the quality of your polar alignment. Two stars with errors, even though small, start to make the sky a bit wavy. Three stars and beyond, and you might just have modeled an amusement park fun house mirror. Errors may sometimes cancel, most often they twist and turn the model in local effects.

When my best friend and spouse for 44 years bought me a reticle eyepiece four years ago, the difference in alignment quality was striking. I tried an experiment where I had the star as a pinpoint focused, and no reticle lines visible, and guessed where the center of the eyepiece was. Then I turned on the reticle, and my error was disturbing. So I measured the reticle lines, and they were perfect; my processing the signal was not. So, back to Chris' comment, a reticle eyepiece can take out the natural human variances. Or, you could have some extreme cone error involved, and the left-right sides of the meridian could be causing some conflict.

I wouldn't worry as much about planetary precision; those locations are determined using your time, and remember that your time setting is constant across 15 degrees of longitude, more or less; that can cause planets to need fine tuning to get them in the field of view, depending on your physical location.

Good luck with your adventure!

[Merlin66]

It should be much closer than that.

I park my mount after a session - having selected a few synch's along the way and the next evening just fire the mount up and GOTO the new selected target - no 2-3 star alignment...nothing...

[Armsoft]

Hi

That`s what I was expecting to be able to do, but I`m out trying again this evening and loaded up the points I saved from Last night, but they are all out of alignment again (so frustrating) and all needed further movement of the scope to get them centered again.

I`m wondering if my Polar Alignment is not accurate enough? and maybe this is the cause?

I`ve done the alignment points on Stars, and then tonight slewed to M42 and it was way off so I realigned the scope to M42 so that it was centered (or as centered as you can withM42).

I then slewed to Venus (and went through the same process with this too).

But when I slewed to M42 again, whilst it was in view it had moved upwards in the fov and was not centered.

I`m getting more confused by the minute:confused:

Mark

It should be much closer than that.

I park my mount after a session - having selected a few synch's along the way and the next evening just fire the mount up and GOTO the new selected target - no 2-3 star alignment...nothing...

[Merlin66]

When you do finally get an object into the centre of the field of view, does it stay there for a while, say 5 mins?

It certainly could be that your polar alignment isn't exact enough.

Is this a permanent installation ie the mount remains in the same position night after night, or do you set it up each time?

[chrisshillito]

Being a mere novice with EQMod I was expecting the points to stay aligned ie; I set alignment points on 5 stars on Leo which was in the East quadrent last night, I then set a further 4 alignment points on stars in the Western quadrent, I just assumed that if I then slewed back to one of the stars in Leo it would still be central (I had tracking set to sidereal), but by the sounds of it that's not how it works?

No, that is not how it works. The purpose of alignment is to measure the pointing errors (optical and mechanical) and these errors are essentially Alt/Az in nature and do not change with the rotation of the sky. So if when pointing due south at an elevation of 20 degrees you measure a certain pointing error then whenever the mount subseqently moves to a position due south, 20 degrees elevation a correction based upon your original alignment will be applied. EQMOD does not align on stars, you simply use stars as a handy way to fix a known position in space, at a given time, with a known position of the mount's stepper motors. So you could use the same star to add multiple alignment points to the pointing model as the star move across the nights sky.

If you want to go for an all sky model then first clear out you current model and then add three points in each quadrent forming a triangle that covers as much of the quadrant as possible. The alignment editor will show you the current mount position within the quadrant to assist in point placement. Once you are happy you have the quadrants covered make sure the alignment filter is set to local quadrant.

Polar alignment should affect your gotos as it is just a contributary factor to the overall pointing error that alignment aims to correct. Thay said reducing polar alignment, cone and home position errors will reduce the complexity of the pointing model and if you have a permanently located mount its well worth doing.

One thing that will mess with the accuracy of the pointing model is excessive backlash - make sure there is no play in either axis and if there is adjust the gear meshing.

Chris

[Gina]

I'm beginning to get my pointing a little bit better. At least M42 now appears in the frame when slewed to with CdC. No sign of M51, M101 or other "M"s though. I'll do a drift alignment tonight weather permitting.

Got PHP guiding last night but the result was dogleg star tracks More fiddling required. I'll get there one day! At least I think I've go some reasonable subs of M42 before it disappears into the western ground (or trees).

[Armsoft]

Thanks Chris/Merlin

It is a fixed mount (pier in Observatory)

I'll get the polar alignment checked to see if that makes a difference.

I'll have a go at 3 alignment points in each quadrent too see what that results in.

While viewing M42 last night having centred it, it stayed in fov for a good time (in excess of 5mins) but it did end up near the top of the fov after about 15mins

Help/advice appreciated

Mark

[Merlin66]

Mark,

Obviously if the polar alignment was spot on, there would be no movement of the object (in Dec) over an extended period.

Start with the PA.

[chrisshillito]

Mark,

Obviously if the polar alignment was spot on, there would be no movement of the object (in Dec) over an extended period.

...or indeed persistant drift in RA (i.e. in addition to the periodic error) as polar alignment error affects both RA and DEC tracking. The direction and magnitude of the drifts in each direction varying depending where you happen to point.

[chrisshillito]

To rule out any mechanical problems such as backlash or a slipping clutch you could try centering a reticule on a terrestial target (if that is at all possible from wihin your observatory) and defining that as a park position. Then slew the mount off to positions either side (with respect to RA/DEC movement) and check that parking returns the reticule onto the target. Alignment models play no part in parking so this is a good test of the basic repeatability of mount movement.

Chris.

[Gina]

That's a good thought Chris - thank you I'll give that a try.

I've been having problems with finding objects, even the moon last night. I'd manually put my scope/mount back in the Park position as accurately as I could then slewed to the moon in CdC. It was way off. I then unlocked the mount, manually pointed it at the moon and locked the mount. Then I slewed to M42 and it was in the frame (though not dead centre). I took a hundred subs of M42 at 20s and M42 hadn't noticeably moved in the frame by the end of the run. So I tried slewing to M51 and M101 and found only individuate stars even with 10m exposure. I guess the galaxies were around there somewhere, others have found M51

[ncjunk]

That's a good thought Chris - thank you I'll give that a try.

I've been having problems with finding objects, even the moon last night. I'd manually put my scope/mount back in the Park position as accurately as I could then slewed to the moon in CdC. It was way off. I then unlocked the mount, manually pointed it at the moon and locked the mount. Then I slewed to M42 and it was in the frame (though not dead centre). I took a hundred subs of M42 at 20s and M42 hadn't noticeably moved in the frame by the end of the run. So I tried slewing to M51 and M101 and found only individuate stars even with 10m exposure. I guess the galaxies were around there somewhere, others have found M51

Gina,

I have to use astrometry.net for my initial pointing corrections, it saves no end of pain.

Do a 3x binned 45 sec pic and send it to them and find your actual position.

Then i bring up cdc and find where i should be and calculate the difference.

Then i bring up eqmod and right click on the dec which brings up a "move to" box. Set the new values by correcting for the error hit move to and it should then be centered.

I have even used 3/4 x binning with 20sec subs.

Also good to use astrometry if your completely lost.

Enviado desde mi GT-I9003 usando Tapatalk

[dark knight]

hmmm, lots of food for thought here. Just a quick question, which software are you using as the planetarium software. I use The Sky6, with EQMod, I select star star in planetarium software and slew to it, using a ccd I then use EQMod to center the star on the ccd, go back into Sky6 and hit "Sync", this automatically adds the star to the EQmod sky map.

My EQMod is set to save the pointing list and sky map when I park the mount and reload them whenever I restart, I also have EQMod set to automatically add the stars to the list upon "Syncing" from my planetarium software. I have found no problems using everything in this way, I can pick up wherever I left off from just fine, usually placing any target on the camera chip fairly centrally. I know my polar alignment is not perfect, yet it all just works for me, similarly as it does for Merlin. Add as many points to the list as possible as this can only make things more accurate in my opinion. I tend to map as many triangular points as possible, starting at the quadrant periphery and then map the points working inwards including whole constellations. It took a while for me to suss out some of the settings in EQMod, but now I have a reasonable system up and running.

Don't give up, Eqmod is brilliant and once worked out does what it is mean't to.

[Gina]

Gina,

I have to use astrometry.net for my initial pointing corrections, it saves no end of pain.

Do a 3x binned 45 sec pic and send it to them and find your actual position.

Then i bring up cdc and find where i should be and calculate the difference.

Then i bring up eqmod and right click on the dec which brings up a "move to" box. Set the new values by correcting for the error hit move to and it should then be centered.

I have even used 3/4 x binning with 20sec subs.

Also good to use astrometry if your completely lost.

Enviado desde mi GT-I9003 usando Tapatalk

Thanks I'll try that

[Gina]

hmmm, lots of food for thought here. Just a quick question, which software are you using as the planetarium software.

CdC.

I use The Sky6, with EQMod, I select star star in planetarium software and slew to it, using a ccd I then use EQMod to center the star on the ccd, go back into Sky6 and hit "Sync", this automatically adds the star to the EQmod sky map.

Ah, I see - I havn't tried Sync yet - must have a read

My EQMod is set to save the pointing list and sky map when I park the mount and reload them whenever I restart, I also have EQMod set to automatically add the stars to the list upon "Syncing" from my planetarium software. I have found no problems using everything in this way, I can pick up wherever I left off from just fine, usually placing any target on the camera chip fairly centrally.

Now that sounds good

I know my polar alignment is not perfect, yet it all just works for me, similarly as it does for Merlin. Add as many points to the list as possible as this can only make things more accurate in my opinion. I tend to map as many triangular points as possible, starting at the quadrant periphery and then map the points working inwards including whole constellations. It took a while for me to suss out some of the settings in EQMod, but now I have a reasonable system up and running.

I have a lot to learn but I think I get what you're saying

Don't give up, Eqmod is brilliant and once worked out does what it is mean't to.

I don't tend to give up easily! Yes, I like EQMOD - it seems very good. Thank you

[Gina]

To rule out any mechanical problems such as backlash or a slipping clutch you could try centering a reticule on a terrestial target (if that is at all possible from wihin your observatory) and defining that as a park position. Then slew the mount off to positions either side (with respect to RA/DEC movement) and check that parking returns the reticule onto the target. Alignment models play no part in parking so this is a good test of the basic repeatability of mount movement.

Chris.

Just checked this and with fairly small movements the mount returns to pretty well exact position. However if I move 180 degrees away and then Park there is an error of about quarter of a frame. That's with 1100D at prime focus and SW Evostar 80 ED DS Pro scope.

This is not too bad and at least an object would be in the frame. I haven't checked if the error is cumulative though.

[Armsoft]

To rule out any mechanical problems such as backlash or a slipping clutch you could try centering a reticule on a terrestial target (if that is at all possible from wihin your observatory) and defining that as a park position. Then slew the mount off to positions either side (with respect to RA/DEC movement) and check that parking returns the reticule onto the target. Alignment models play no part in parking so this is a good test of the basic repeatability of mount movement.

Chris.

Chris,

Just tried your suggestion on a distant chimney pot and set a Parked Mode point, then slewed very far away from the point in both directions (to reverse quartiles infact)

When then selecting to Park, it goes straight back to the chimney pot with it centered.

Should Polar Alignment be my next step?

Thanks for the help/advice so far

Mark