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EQMOD and the flipping meridian


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I have not had my GEM mount very long and am working my way up the learning curve with EQMOD. When I do a GOTO that results in the scope crossing the meridian instead of taking the obvious short path, both the RA and DEC axis rotate through 180 moving the scope to the other side of the tripod but leaving it upside down. Last night this was happening whenever I did a GOTO between Betelgeuse and Aldebaran.

After a bit of research I find out this is called a meridian flip and is done to prevent the back of the scope from hitting the tripod or pier. However, I am using a short SCT and there seems to be no need for action. Also when the scope is upside down the finderscope in too awkward a position to be of any use.

I have been through all the EQASCOM menus and disabled all the 'Allow Auto Meridian Flip' options I could find, but the unwanted flip action still persists.

So is this operation expected and can I disable it?

Thanks,

Chris

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The auto meridian flip only applies during tracking, when your telescope crosses the meridian limit the mount will perform a flip and continue tracking...

the meridian flip is always applies to slews that cross the meridian regardless of "auto meridian flip"

To get your mount tracking past the meridian you need to change the meridian limits. in order to do this you expand the EQASCOM window to show the settings, in the middle right is a box for limit settings, disable the limits then click the little spanner button, this will pop up the limits editor, now slew the mount to the eastern limit, then click the +. This will have set the eastern limit, repeat for the western limit. It is always a good idea to slew your scope in DEC to the position where it is going to collide with the legs earliest, before you set the limits, and leave yourself an inch or two clearance just to be safe.

Now your meridian limits will be just before the scope is about to crash in to the legs.

I dont know if you have read the EQmod Wiki or watched the tutorial videos, but it is definitely worth it, they are very useful, the wiki covers all features of the EQmod software including the clients such as eqmosaic and eqtour.

Edited by RyanParle
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Thanks for the help, I have now set up my meridian limits. I have actually spent quite a bit of time reading all the information I could find and watching the video tutorials, a consequence of cloudy nights... I had read about the limits but since I had limits disabled I was not bothered about them.

As you say both though, the GOTO always goes to the correct side of the meridian that the target is in leaving the telescope upside down on the western side. What I want is an option that says "DO NOT EVER TURN THE TELESCOPE UPSIDE DOWN AND RISK DUMPING MY EXPENSIVE EYE PIECES ONTO THE GROUND". As I said before I cannot use the finderscope when the telescope is upside down so I would really like to disable this feature.

Thanks,

Chris

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Thanks for the help, I have now set up my meridian limits. I have actually spent quite a bit of time reading all the information I could find and watching the video tutorials, a consequence of cloudy nights... I had read about the limits but since I had limits disabled I was not bothered about them.

As you say both though, the GOTO always goes to the correct side of the meridian that the target is in leaving the telescope upside down on the western side. What I want is an option that says "DO NOT EVER TURN THE TELESCOPE UPSIDE DOWN AND RISK DUMPING MY EXPENSIVE EYE PIECES ONTO THE GROUND". As I said before I cannot use the finderscope when the telescope is upside down so I would really like to disable this feature.

Thanks,

Chris

You cannot disable pier flip on a automated GOTO.

Only way it can be done is a manual GOTO with the OTA in the position you want.

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You cannot disable pier flip on a automated GOTO.

Only way it can be done is a manual GOTO with the OTA in the position you want.

That is a shame. Thanks for confirming that, it is good to know the limitations of the system. Though the software is open source so if I find time I may have to have a play with it.

Chris

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Thanks for the help, I have now set up my meridian limits. I have actually spent quite a bit of time reading all the information I could find and watching the video tutorials, a consequence of cloudy nights... I had read about the limits but since I had limits disabled I was not bothered about them.

As you say both though, the GOTO always goes to the correct side of the meridian that the target is in leaving the telescope upside down on the western side. What I want is an option that says "DO NOT EVER TURN THE TELESCOPE UPSIDE DOWN AND RISK DUMPING MY EXPENSIVE EYE PIECES ONTO THE GROUND". As I said before I cannot use the finderscope when the telescope is upside down so I would really like to disable this feature.

Thanks,

Chris

If your eyepieces are at risk of falling out then you need to think about why they are at risk of falling out. when I image I have both my cameras hanging from the underside of my newtonian (in line with the dovetail bar) they have never even moved!

in regards to the finderscope, you shouldn't ever need to use it once you have alignment sorted out, the mount should have the object in the field of view of a fairly mid powered eyepiece, I have a telrad which I use to get the first alignment star in the FOV of my camera, a 25mm or 33mm eyepiece, from then on I just use eyepieces or the camera to centre the alignment points.

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If your eyepieces are at risk of falling out then you need to think about why they are at risk of falling out. when I image I have both my cameras hanging from the underside of my newtonian (in line with the dovetail bar) they have never even moved!

in regards to the finderscope, you shouldn't ever need to use it once you have alignment sorted out, the mount should have the object in the field of view of a fairly mid powered eyepiece, I have a telrad which I use to get the first alignment star in the FOV of my camera, a 25mm or 33mm eyepiece, from then on I just use eyepieces or the camera to centre the alignment points.

I would say the EPs are at risk of falling out because because I find myself constantly fiddling with the thumb screws on the diagonal to allow the EP to face upwards after the scope has been turned upside down and back again. Forgetting to tighten a thumb screw fully seems an easy mistake to make on a cold night.

However, my experiences were probably due to me experimenting with the system going to here there and everywhere rather than observing in a normal manner. Also coming from an alt-az GOTO mount my expectations of how an equatorial GOTO mount operates were probably incorrect. The idea of the scope being upside down in normal operation was unthinkable! I still don't see why that is necessary, but if that is the way it works then that is the way it works.

Normally in going through the alignment procedure I would the finderscope to get the position into the EP FOV and a 12mm illuminated reticle EP to centre exactly. Swapping to an EP with a wider field of view to get the rough position instead does seem to be the way to go, but also seems a shame as I thought that is what the finderscope was there for and more swapping of EPs means more opportunities for leaving a thumb screw untightened.

Anyway, now I have a better understanding of how an equatorial GOTO mount operates I shall have another attempt, this time using the system how it was designed rather than fighting with it trying to make it work in line with my incorrect expecations.

Thanks again,

Chris

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Also coming from an alt-az GOTO mount my expectations of how an equatorial GOTO mount operates were probably incorrect. The idea of the scope being upside down in normal operation was unthinkable! I still don't see why that is necessary, but if that is the way it works then that is the way it works.

If your doing just visual with I presume a SCT alt-az was indeed the correct mount for your needs, equatorial will offer you no benefits unless your imaging, if your imaging it counters any field rotation.

Imagers don't worry what orientation their cameras are hanging at :)

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If your doing just visual with I presume a SCT alt-az was indeed the correct mount for your needs, equatorial will offer you no benefits unless your imaging, if your imaging it counters any field rotation.

Imagers don't worry what orientation their cameras are hanging at :)

Eaxctly so! After the SGL Beginner's Imaging day I decided that I would like to join the dark side and do some imaging. Hence my purchase of the EQ6 mount and my efforts in getting to grips with it.

The main thing that I have learnt so far is that clouds seem to prefer obscuring Polaris more than any other star.

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That is a shame. Thanks for confirming that, it is good to know the limitations of the system. Though the software is open source so if I find time I may have to have a play with it.

Chris

Good luck with that, let us know how you get on if you do have a go. Just remember that allowing the mount to move to the "wrong side" will have wise ranging consequences for the N-point alignment model algorithms. Also if you allow counterweights up slews you will need to implement a new and sophisticated limit protection mechanism such that movements are guaranteed not to result in collisions with the pier/tripod.

I have looked into this before but the scale of changes required, their complexity and associated risks to equipment associated with getting it wrong put me off.

Chris.

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Good luck with that, let us know how you get on if you do have a go. Just remember that allowing the mount to move to the "wrong side" will have wise ranging consequences for the N-point alignment model algorithms. Also if you allow counterweights up slews you will need to implement a new and sophisticated limit protection mechanism such that movements are guaranteed not to result in collisions with the pier/tripod.

I have looked into this before but the scale of changes required, their complexity and associated risks to equipment associated with getting it wrong put me off.

Chris.

Okay, it seems the scale of the work may be a little outside of the amount of spare time I am likely to have available! I would like to give something back to the EQMOD project at some point, but I guess attempting these changes would not be a great way forward.

Chris

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  • 2 years later...

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