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frequentual pulsing GPUSB for tracking comets

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#1 Corne

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Posted 13 August 2014 - 02:47 PM

Hello all,

 

Since a while Im searching for a program to track comets when the head is too weak to follow with autoguiding.

I found that Maxim DL and metaguide has the options, but with both I have problem to connect with my guidecamera, a QHY5.

For some actual comets I have/can calculated the daily offsets in RA/DEC arcsec/hour.

I want to give by software for example each 2 or 5 seconds a sign to the GPUSB a small movement to follow the comets.

The focus length is 200mm (canon lens) and with an atik 314L+ mounted on a Vixen GPD2 I see no severe problem with trackerror (normally unguided 1 a 2 pixels error)

The reason for this program is that I want to create long subs without vague/blurred comets.

 

Greetings,

Corne



#2 freestar8n

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Posted 14 August 2014 - 04:32 PM

Hi-

 

I appreciate your interest in this feature because it does work well - especially for fast moving comets that have faint tails with fine detail in them.  People who just guide on a star will use long exposures to catch the faint regions - but they will be blurred in each subexposure if you don't move along with the comet.  High end mounts can self-guide and track comets and asteroids, but mid-range mounts need guiding, and you need a way to offset the motion from the guidestar.  I think Maxim can only accept a sequence of x,y guidestar moves rather than the actual RA/Dec rate of motion of the comet, which MetaGuide can work with.

 

Here is an example using a c11 and a comet moving fast enough that 2-minute exposures leave the stars trailed, but with shift-guiding the comet is sharp:  http://www.astrogeek.../Comet103P.html

 

I think some of the older QHY cameras now have video drivers that will work with MetaGuide - so you may be able to use it.  But I think some can and some can't.  If you really want to do this, MG will do it for you, but you may need a different guide camera.

 

Unfortunately unless you have a high end mount, you won't reliably be able just to pulse in dec. and have the mount respond as you want.  RA may work ok - but dec. motion is much less reliable and you need to guide relative to a guidestar.  In RA you also need very low periodic error if you aren't guiding.  But if you can use MG, you just find a guidestar, enter the RA/Dec rate of motion of the comet, turn on guiding, enable shift-guiding - and the comet will be very accurately tracked since the mount is locked onto a nearby star and moving relative to it at the exact specified rate.

 

Frank



#3 Corne

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Posted 15 August 2014 - 12:04 AM

Hi Frank.
With maxim dl and metaguide im not able to connect with the guide camera. And unfortunately both dont track the offset without calibration.
With a focus point of 200 mm i nearly dont have any errors unguided so thats not the problem.
Is it very difficult to program how to connect with gpusb?

#4 freestar8n

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Posted 15 August 2014 - 02:21 AM

Hi-

 

Please take a look at the driver downloads on the QHY site and see if the WDM driver for QHY5 will work for your camera.  MG may not work with your camera now - but there may now be a video driver that will let it work if you install it first.  I was surprised to learn that some of the QHY cameras I thought would not work with MG - in fact can if you install recent drivers.

 

Unfortunately I may be wrong because I'm not sure your exact camera - but it is worth a try.

 

As for pulsing GPUSB - that shouldn't be hard at all to pulse at the expected motion rate of the comet - but it probably won't work well in dec. because dec. motion is much more unpredictable.  It will stay still when you think it should move - and it may overshoot if there is stiction.  That's why dec. guiding is hard, and it benefits from guiding on an actual star - so you see the true motion of the mount.

 

If you want to try it out you can connect to GPUSB using ascom and pulse it occasionally with vbscript or something.  But the RA behavior will be limited by PE - and the dec. behavior will be limited by the dec. axis anomalies.  Plus - if you aren't guiding in the first place, you get less benefit from the improved clarity by trying to follow the comet.

 

Frank



#5 Corne

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Posted 18 August 2014 - 02:37 PM

Hi

 

Last 2 nights I found on the ascom site how to connect the ascom driver with visual basic. From that point I created an application with guidepulse depending on the own moving of the comet during 24 hours on august 18th.

Hereby a screenshot of Jacques 2014 E2

CometTracker.PNG

 

With a timer of 2000ms the offset for RA is -21 ms and for DEC +17ms. Hopefully I can test the program soon but it is cloudy for weeks here...


Edited by Corne, 18 August 2014 - 02:38 PM.







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