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Gemini Closed Loop tracks in DEC too?

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#26 DeanS

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Posted 28 June 2009 - 08:54 AM

And no, I don't think AP is perfect... None of these systems are perfect. It bugs the you know what out of me that a $10k mount doesn't have a bubble level built in... How lame is that!?


But these types of mounts do not need to be level to work perfectly well. Once you get the polar scope aligned it matters not what the base of the scope is. However if you are drift aligning it does make adjusting the AZ a bit quicker, but by no means a must.

Roland use to argue this on the AP lists all the time. But it looks like he gave in as there is a bubble level on the Mach1GTO now which I do find handy however I don't do much except get it close.

#27 Chris Curran

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Posted 28 June 2009 - 09:51 AM

Yes, yes, yes, I know. However, the closer you are to level, the fewer iterations you'll need to make when polar aligning with PEMPro v2 or similar software...

#28 David Pavlich

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Posted 28 June 2009 - 11:40 AM

Yes, yes, yes, I know. However, the closer you are to level, the fewer iterations you'll need to make when polar aligning with PEMPro v2 or similar software...


I agree, Chris, especially if setting up for imaging. Why make the job tougher?

David

#29 LLEEGE

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Posted 28 June 2009 - 11:45 AM

And no, to the best of my knowledge, no other mount provides a Meridian Delay type feature.

Actually, the new Celestron software does.

#30 rsbfoto

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Posted 28 June 2009 - 12:14 PM

Hi,

Meridian Delay type feature.



Would somebody please explain what does this feature do and how does it work ?

I tried to find a manual for the GoTo from AP but in theier site in the web I dod not find anything ¿?

Thanks in advance

#31 Chris Curran

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Posted 28 June 2009 - 12:34 PM

Rainer,

See the bottom of pg 65 in this document.

#32 Chris Curran

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Posted 28 June 2009 - 12:35 PM

Actually, the new Celestron software does.


cool...

#33 LLEEGE

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Posted 28 June 2009 - 01:28 PM

Hi,

Meridian Delay type feature.



Would somebody please explain what does this feature do and how does it work ?

I tried to find a manual for the GoTo from AP but in theier site in the web I dod not find anything ¿?

Thanks in advance

It allows a flip to be either delayed or done prior to the target crossing the meridian. Doing so allows one to image through the meridian. It is most useful for starting a session easto of the meridian with the OTA on the "wrong" side of the mount. It also allows a polar alignment to be done simulating a drift alignment. Very handy tool.

#34 lineman_16735

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Posted 28 June 2009 - 01:29 PM

Hi Dean,

I think you will find PulseGuide works very well. I have used it for comet tracking and it was quick and easy.

#35 DeanS

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Posted 28 June 2009 - 03:15 PM

I need to try the pulse guide but was waiting for the newest version to come out. My set up now does not allow me to connect to the mount with more than one cable. When I run Pempro I must dissconnect TheSKy. I just need another cable and find an open USB but everytime I mess with it I worry about screwing up something else.

And I also have not used the meridian delay but need to learn how it works. Sounds easy just need to do it. It would come in very handy when I want to start an object before the meridian for sure.

Another way I think it would help is with the centering feature of Maxim. I have often been on the 'wrong' side and asked it to center and object and off it goes. The delay should stop that right? And of course finding a focus star under the same situation would help too.

Seems like my imaging nights are so few and far between that I hate to waste good nights to learn new things. Then on the not so good nights when I should go out to try out these things, I stay in and sleep instead/

#36 rsbfoto

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Posted 28 June 2009 - 09:32 PM

Rainer,

See the bottom of pg 65 in this document.


Hi Dean,

Thanks. Well I read that part and I guess if I compare it to a Gemini then it comes down to the following.

AP does not allow to set a limit further the -90 or +90 degrees eg. the DEC axis can not move further down then horizontal.

Enabling the so called Meridian delay does allow it by defining an amount of time which has to be found by trial and error until one know does the camera or whatever hits the pier or the tripod ¿ correct ?

Then if I take my Gemini control I just slew to the safe position on each side and I set mi Safety limits on the EAST and WEST side and I have the meridian delay on my Gemini ¿ correct ?

For example I have a GM-8 here and the safety limits I set are EAST side 100° and WEST side 100° and my understanding then that If I would have set this on an AP mount I would have had to specify for each side a Meridian delay of 40 minutes eg. 10° ¿ correct ?

Gemini offers also a command named " Set GoTo "

See Instruction Manual page 68 point 5.2.10.2.6 "Set Safety Limit " and following pages ...

If I compare this, it is easier to define a forced meridian flip in Gemini as you just define when to do it. With an adjustment Set GoTo : 90 then that defines that any object beyond the meridian (90°) will force Gemini to locate the Telescope on the EAST side of the Mount ...

A practical case would be that if the meridian time is 12:00 and the object is at 12:15 and you have 40 minutes eg. 10° of reserve on the east side then Gemini will position the telescope on the east side. Should the object be further away then 10° to the West, seen from the meridian then, then Gemini will not move ¿? or will it move to the West side (if I have more then 10° on the West side) if there the limit is more then 10°¿? as the safety limit on the East side is only 10°. ¿ Is it ?

Will have to test this next time I am in the Observatory

#37 gnowellsct

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Posted 29 June 2009 - 12:52 AM

You don't have to "train it" or follow to set the Dec correction for polar misalignment. All you have to do is turn the option on.

The Gemini electronics will make the correction based on the pointing model.

So far, AP paddles do not make pointing models. So if AP paddles are going to have this function, they have to do it some other way.

This function is not related to PEC.

The Gemini pointing model is one of the most sophisticated out there at the amateur level. Software Bisque has an add on that does much the same thing. Argo Navis is unique among the dscs for also being able to make an accurate pointing model, but if you're using it with a G11 you can't use it to correct the tracking drift in Dec, because the nature of the dsc beast is not to "talk" to the drive. You're using stupid iron with dscs, which has its merits and demerits; inability to correct for dec drift is one of the demerits.

The Gemini, Argo Navis, and Software Bisque pointing models use a lot more variables than are typically employed in other go-to GEM systems. I think with Gemini the number of variables uses increases as you zap more stars; in Argo Navis, you have to choose the variables, and it will make you zap stars to the tune of N+1 alignments where N is the number of variables you are trying to correct.

Argo Navis has "zero issues" with flipping across the meridian. It seems to be a problem on go-to systems as a function of backlash settings which introduce some uncertainties into the positional measurements.

But yes, the G11 is very neat, Gemini is neat, and the Dec drift correction is under-appreciated. HOWEVER, you will still get some field rotation with the dec adjustment. It will however be very slight, most alignments with polar scopes are within ten to fifteen arc minutes of true N, so the field rotation is obviously much smaller than it would be in alt-az configurations where one axis of rotation is at zenith.

regards
Greg N

#38 gnowellsct

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Posted 29 June 2009 - 01:03 AM

You are correct, polar alignment with the polar scope is pretty much all one needs. However, when you are trying to keep everything to within a pixel or two you pay attention to details.

One of the reasons why the Dec drift correction is not so well known is that autoguiding performs a similar function.

using Argo Navis for several years I've been able to measure the accuracy of my polar scope alignments. I often get it "dead nuts on" (within the two arc minute resolution of my encoders) but 5 to 15 arc minutes off true N is fairly common. This introduces Dec drift and field rotation. Dec drift is the worse of the two. If you can correct for Dec drift you can do longer unguided exposures.

So it's a good utility to have, and makes it that much easier for folks with fast refractors etc. to get good results over long-ish exposures. However, it can't really eliminate the need for autoguiding and the better PE is controlled the better the photographic results will be.

But it removes a substantial source of tracking error from the system and that's a good thing. The only other way to "get at" this problem is be doing better polar alignment with the drift method etc. It can be done but it's hard to do really really well. Zapping ten to twelve stars and letting the computer figure it out is much better.

regards
Greg N

#39 DeanS

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Posted 29 June 2009 - 09:51 AM

Rainer,

One of the main reasons I switched to the AP mounts from the MI-250 was to be able to image well past the meridian. My limits where set at 95* on the MI so that was about 20 minutes before it started to beep and a few more before the mount would hit itself.

With the AP I don't know if we even have a limits on it for tracking like the Gemini. Probably do but I have not used it as depending on the DEC, and my scope and camera set up, I can go several hours past the meridian. This saves me a time from having to flip and reaquire, not that it is a big deal but it could take me 15+ or so minutes before I was back imaging. The meridian delay feature I believe is only for going to an object that is past or before the meridian in case you want to start imaging early to avoid a flip in the middle of a sequence.

#40 LLEEGE

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Posted 29 June 2009 - 10:13 AM

The AP limits are only "Slew" limits. They will not stop the mount from tracking. You can set pulse guide to stop the mount and a pre-set time to prevent the mount from crashing.
The new APCommander software will, I think, stop the mount from tracking into the limit zones. Now if they would just release it. :scratchhead:

#41 DeanS

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Posted 29 June 2009 - 10:16 AM

I understand the new AP commander will also have the object database in it. Wonder if it will be like a planetarium program and we can do away with TheSky?

#42 LLEEGE

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Posted 29 June 2009 - 10:48 AM

I don't think so.






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