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Eqmod & mount limits & plate solving


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Although I use eqmod on each imaging night I have never really got to grips with the mount limits function. On reading the documentation (something I never usually do!) it says that I need to set a Meridian limits for the east and west side of my pier, how/what does this mean? I Thought the meridian was the point whenthe mount changes from north to south...... I think I am missing something very fundamental here! Can somebody explain ( in idiot terms) what I need to do to set mount limits with regards to where do I slew my scope to for each limit.

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The PDF manual for limits is here for anyone looking for it:

http://eq-mod.sourceforge.net/docs/EQASCOM_Limits.pdf

It's actually quite similar to the Horizon Mapping in TheSky

Meridian Limits

This is to stop the mount tracking too far over the Merdian. Obviously if you are on a target on the correct side of the Meridian and leave it running, it will keep going, even until the mount crashes into itself. Best to make a limit of a few minutes past each side. Just slew to the required position (one for east side, one for west) and hit "+"

I have the limits set in CCDC for it to do an auto-pier flip while imaging, but I'm going to set these limits just after that in case it fails for any reason

Horizontal Limits

As with most things in EQMOD this is genius. It uses the same file format as Cartes du Ciel, which I'm hoping is quite similar to the file in TheSky (see here: http://stargazerslounge.com/imaging-tips-tricks-techniques/100954-horizon-mapping-thesky-6-a.html). Even if not, it's probably quite easy to put the data in. Either that or go round each of the points on your horizon and hit "+" then it will give you a contour of your limits.

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Am I right in thinking with EQMOD that if you 'goto' past the meridian, the scope will execute a meridian flip along the way. If you track past the meridian it won't, so you need to set mount limits?

Correct, you need to set limits so your OTA or whatever will not hit your pier.

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Am I right in thinking with EQMOD that if you 'goto' past the meridian, the scope will execute a meridian flip along the way. If you track past the meridian it won't, so you need to set mount limits?

Not quite.... EQMOD has an option to enable automatic flip if enabled. If not, it will hit the limit (if configured) and stop tracking. Unsure if this option is enabled or disabled by default.

If left to track (and limits disabled), the mount will continue quite happily past the meridian without any issues, and plough into the mount legs a few hours later. If a goto command is received after you have tracked past the meridian, EQMOD will then issue a flip. This doesnt mean you will be absolutely 100% back on the same location! Close, but not good enough for imaging.

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This doesnt mean you will be absolutely 100% back on the same location! Close, but not good enough for imaging.

This is where Plate Solving becomes a necessity :mad:

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I've got the limits and auto flip setup. It's close, as in puts the target in the FOV, but nowhere near the same place on the chip... How do you use plate solving and as Craig said, how do you do that with an SLR ?

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I've got the limits and auto flip setup. It's close, as in puts the target in the FOV, but nowhere near the same place on the chip... How do you use plate solving and as Craig said, how do you do that with an SLR ?

I would have to try it to find out for sure

Craig, if we can try and find a clear-ish night at the weekend you could try it on my setup

Is the 350D all USB control or do you have to have a serial remote switch as well?

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Meridian Limits

This is to stop the mount tracking too far over the Merdian. Obviously if you are on a target on the correct side of the Meridian and leave it running, it will keep going, even until the mount crashes into itself. Best to make a limit of a few minutes past each side.

Most mount/scope combinations will allow you to happily track past the meridian for several hours (rather than minutes) before there's any danger of collision. In general folks really don't want to stop or flip if they can help it so my advice would be to set the limits as far round in RA that you can get without any collision for any reasonable DEC value.

Chris.

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I never used the limits before but I want to leave it imaging unattended now. I just cannot work out how to do it? Do I go as low down as possible in the east and mark it, then do the same for west?

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I've got the limits and auto flip setup. It's close, as in puts the target in the FOV, but nowhere near the same place on the chip... How do you use plate solving and as Craig said, how do you do that with an SLR ?

The accuracy of the flip will ultimately depend on your alignment data around the region of sky the flip is made to. A plate solve and subsequent sync will give you an accurate local alignment point such that a subsequent "corrective goto" should put the object back in the same position on chip (albeit inverted unless you have a rotator). Ideally you would issue the goto using a previously "bookmarked" position (EQASCOM can do this) taken before the flip (to take into account any movement away from the true coords of the object that may have occurred when framing the image).

I wrote a little client application for the free Elburus plate solver which will trigger a plate solve (assuming a fits image has been captured), issue sync and subsequent corrective goto all at the press of a single button (see EQMOD group).

Chris.

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I never used the limits before but I want to leave it imaging unattended now. I just cannot work out how to do it? Do I go as low down as possible in the east and mark it, then do the same for west?

For "meridian" limits yes you just set them to the furthest "safe" position that you feel you can move the RA axis to that will allow the scope to be positioned in DEC without collision. I know it seems a little odd to set two limits but EQASCOM can potentially track "backwards" (don't know if anyone ever has, perhaps when satelite tracking??)

When limits are enabled EQASCOM will track until it reaches a limit (either merdian or horizon). Once the limit is reached tracking will be stopped and you can leave it there or have the mount automatically park or perform an automatic flip and continue (but not recommended for unattended use!) EQASCOM will show an indication of the time to Limit (both meridan and horizon) should you wish to calculate how many subs you might get (or if you want to return to the mount just in time to see the limit bite).

Chris.

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How about Friday night if it's clear?

Sounds good, I will keep an eye on the weather and PM you if it's even half clear, it's says rain at the mo but it could all change in a few days

We can try out the mount limits as well, I've not tried it yet

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Ah, now wait a minute Euan. I forgot I have another astro event I am attending on Friday night in Perth so we will have to leave it this weekend as I am out on Saturday night as well - next week perhaps?

BTW I tried setting mount limits and failed miserably! Obviously did something wrong as I could not even GoTo Vega without it hitting the mount limit and parking!

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The accuracy of the flip will ultimately depend on your alignment data around the region of sky the flip is made to. A plate solve and subsequent sync will give you an accurate local alignment point such that a subsequent "corrective goto" should put the object back in the same position on chip (albeit inverted unless you have a rotator). Ideally you would issue the goto using a previously "bookmarked" position (EQASCOM can do this) taken before the flip (to take into account any movement away from the true coords of the object that may have occurred when framing the image).

I wrote a little client application for the free Elburus plate solver which will trigger a plate solve (assuming a fits image has been captured), issue sync and subsequent corrective goto all at the press of a single button (see EQMOD group).

Chris.

Chris,

Is there any way you could modify this app to allow it to use a JPG or TIFF (or better still a RAW from a Canon DSLR)?

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So in theory (assuming we mod the app to allow standard image formats). We could bookmark a location in eqmod (Chris, how do we do this?), do a pier flip, import a fresh image into elburus and have it plate solve then issue a fresh goto?

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Ah, now wait a minute Euan. I forgot I have another astro event I am attending on Friday night in Perth so we will have to leave it this weekend as I am out on Saturday night as well - next week perhaps?

That's fine we can just play it by ear, there will be a clear spot eventually, you never know it might even be before Xmas :mad:

Edited by Euan
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*

Is there any way you could modify this app to allow it to use a JPG or TIFF (or better still a RAW from a Canon DSLR)?

What I have written is a little app that uses the scripting interfaces of Elbrus and EQASCOM to provide a semi-automated pointing correction. I understand you can do the same by writing scripts in Maxim (and with Maxim you can script the image capture as well).

Elbrus is the application that takes the image and does the plate solving. I've had no part in the development of ELBRUS and whilst it is free, it isn't open source, so if you go that route you're with the image formats it supports (currently FITS, BMP or JPF).

Chris.

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