Autoguiders

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  • Member since
    April, 2013
Posted by mrakhoover on Friday, April 05, 2013 9:12 AM

Hi, I'd be interested to have your opinion on something as we have virtually the same equipment.

My eqpt. Celestron CPC925 on ALT/AZ mount, Orion Starshoot Autoguider, Orion Mini Guidescope, PHD Software, Mac OSX 10.8.x

First thing: The autoguider gives me a nice clean, focussed image and PHD can detect and lock onto (green box) a star with ease in loop mode, even with me moving the scope with the hand controller at centering speeds.

Second: PHD is talking to the mount. The manual controls in PHD move the scope in the correct sense.

Third: I have turned OFF backlash compensation.

After careful observation of what PHD is doing I found that whenever a pulse is sent to the scope, tracking ceases for the next 25 seconds on that axis before resuming. So, if a short pulse is sent to the RA axis, the star would then drift at sidereal rate (due to there being no tracking in RA anymore) PHD would attempt to re-aquire the star, but even with the autoguide speed set at maximum (sidereal rate) there was no way for PHD to catch up even with maximum pulse length set to say, 3000ms. Consequently an error flags up.

The same would happen in DEC.

In summary; any pulse sent to the mount rom PHD via the SSAG would cause the mount to cease tracking, in that axis, for the next 20-25 seconds, allowing the star to drift away.

The question is, why is it doing this?

Apart from that, everything works perfectly.

I don't know if this is an SSAG problem or a PHD software problem.

Any ideas anyone?

  • Member since
    November, 2009
Posted by Poppa Chris on Friday, April 05, 2013 10:25 AM

Neither one is the problem...  The mount's error is.  If you can "adjust" your error so that PHD is always sending the command in the same direction (against the error) then all of your corrections will be just intermittently speeding up th emount and not stopping its motion, which is where the delay is coming from.  Try turning your backlash correction back on also.  

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    April, 2013
Posted by mrakhoover on Friday, April 05, 2013 6:25 PM

Hmmm. I don't understand what you mean by "the mount's error".

Craig Stark recommends to have backlash comp. turned off.

I can't understand why the pulses from the autoguider should stop the telescope from tracking for 20-25 seconds. It does this when guiding "manually" through PHD and even when NOT guiding, just nudging the scope using the "manual buttons" with PHD in Loop mode.

  • Member since
    April, 2013
Posted by mrakhoover on Saturday, April 06, 2013 3:04 AM

Hi Poppa.

In the cold light of morning I now realise you mean the tracking gear's periodic error. I thought you were referring to some other error in the mount.

On that understanding then, I don't see how or why PHD can/will stop the tracking for 20-25 seconds (NB. whole seconds NOT milliseconds).

As you say, any guide commands from PHD (or from a human for that matter), will either speed up or retard the tracking motor momentarily to allow the star to come back to the cross hair. In the case of PHD the maximum pulse length is predetermined in the advanced settings (default 1000 milliseconds). Normal sidereal rate tracking should immediately resume until the next pulse is sent after the next exposure eg. 1.5 seconds.

The problem I am having is nothing to do with PE. The tracking motor simply stops for 20-25 whole seconds after a pulse regardless of that pulse's direction (speeding up or slowing down the tracking motor). If PHD is in guide mode with expoure duration of 2 seconds, the scenario would be thus;

An exposure is taken. PHD determines the star has drifted West. A short (say 150ms) pulse is sent to speed up the RA tracking motor. RA tracking then stops arbitrarily. 2 seconds later another exposure is taken. This time (with no tracking in RA since the first pulse was sent) the star has drifted much further west. PHD then sends a maximum duration pulse west. The next exposure reveals the star to be way off the cross hairs and PHD subsequently gives up and sounds the error. I press Stop. Approximately 20-25 seconds later, tracking resumes normally.

PHD does this even when it is not guiding. As soon as a pulse is sent to the tracking motor (via the PHD manual "nudge" controls), all further tracking motion arbitrarily ceases for the next 20-25 seconds.

When guiding manually, using the Nexstar hand controller, guide pulses are superimposed on top of the tracking motion either speeding it up or slowing it down and sidereal tracking resumes immediately the buttons are released.

I hope this makes the problem clearer.

Best regards and thanks for your input, much appreciated. Mark

  • Member since
    November, 2009
Posted by Poppa Chris on Saturday, April 06, 2013 8:30 AM

Actually I wasn't speaking of preriodic error.  I was thinking "backlash" since you had it turned off.  Wether done manually or by PHD, the speed adjustments should be the same.  That is why I suggested turning your backlash adjustment parameters back on.

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    April, 2013
Posted by mrakhoover on Saturday, April 06, 2013 11:07 AM

Hi

Unfortunately it makes no difference. I had backlash compenstion turned on and adjusted correctly for my mount from the start. I only switched it off when troubleshooting this issue.

Craig Stark's recommendation is to to have it switched off in order to save PHD from fighting it.

Thanks anyway.

  • Member since
    November, 2009
Posted by Poppa Chris on Saturday, April 06, 2013 3:42 PM

Hmm... How much polar alignment error are you trying to compensate for?  Maybe you should do a bit of drift alignment at the outset of the evening and see if that helps the issue.

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    April, 2013
Posted by mrakhoover on Sunday, April 07, 2013 4:39 AM

Hi. Thanks for your input, most appreciated.

The settings in PHD and the setup of the scope make absolutley no difference whatsoever to this issue I'm afraid. As the tracking is turned OFF for the arbitrary 20-25 seconds whenever a pulse command is sent (using the manual 'nudge' dialog). And this is in "Loop' mode, where no calculations are being made and no star is being tracked. The only setting that affects the 'nudge' dialog is the calibration pulse length.

The important thing to note here is that PHD is switching off the tracking in addition to the pulse commands. The normal, and proper pulse commands are being sent to the mount in accordance with the advanced settings in PHD. It's just that normal tracking doesn't resume again until 20-25 seconds after the last pulse is sent. This is completely abnormal, there is no setting and no scope setup thet can result in a 25 second cessation of normal tracking.

I am using the supplied ST-4 cable from the autoguider into the mount. I know the connections are fine because the manual 'nudge' controls in PHD operate the mount in the correct sense.

I have sent a bug report to Stark-Labs and posted on their Yahoo group and am awaiting a response. I'll post any developments here also.

I would love to hear from other Mac users as I suspect that it is a driver issue that does not affect the Windows version. The Mac driver is written by Stark-Labs (from my understanding) and built into PHD but the Windows driver is developed by Orion. The Mac driver for the Orion SSAG is a new development that only came out in the most recent version of PHD (v. 1.14.0).

If other Mac users have no issues (other than the "normal" hassles inherent with autoguiding) I would suspect the autoguider to be the device at fault and return it for exchange (I'll probably do that in the meantime anyway to be on the safe side). I hope it's not my mount though, that would be a right pain to send back :-(

Any Mac users out there?

  • Member since
    April, 2013
Posted by mrakhoover on Monday, April 08, 2013 3:00 AM

UPDATE.

I tested the set-up again en EQ mode and all behaves normally now (I was certain that the problem manifested itself in EQ mode from previous experiments but all seems ok now) and the problem only occurs in ALT/AZ mode.

Craig Stark contacted me following my bug report and tells me that PHD does not send a "stop" command to the mount in order to send pulse commands and suggests that the fault is probably in the way the mount is dealing with the commands sent from PHD when in ALT/AZ mode. He was very helpful, but did say that ALT/AZ can be hit or miss.

So my next step is to contact Celestron, as their knowlege base does say that the CPC can be autoguided in ALT/AZ mode (yes I know about the limitations of field rotation etc)

The reason I need it to work in ALT/AZ mode is down to a physical disability that makes setting the scope on a wedge every night very difficult for me.

Best regards, Mark

Anyone having success autoguiding a CPC in ALT/AZ mode?

  • Member since
    January, 2014
Posted by satha52 on Tuesday, January 07, 2014 3:23 AM

Hi,

This question is for Poppa Chris or anyone that can help.  I stumbled upon this thread recently and happen to have the same setup as Poppa Chris (CPC 1100, same wedge, tripod, etc).  I just scored an unused Celestron 94176 Radial Off-axis Guider like in your picture and explanation.  I was wondering if you are indeed using the Orion StarShoot AutoGuider with the Off-axis radial guider?  I wanted to make sure it works together before I purchase the autoguider cam and software.  I'd rather do it this way (great idea) so I can reserve where my autoguider would have been (mounted on the CPC 1100) for a 80mm or so refractor for wider field imaging (mostly nebula)

One other question, have you ever mounted a 2nd smaller telescope on your CPC 1100 and wedge?  How did it work, and did you switch the radial guider and autoguider cam to the smaller telescope when imaging through that or can you leave it on the CPC 1100 back?

Thanks for your help.  Looking forward to learning more from this community.

Shawn

 

  • Member since
    November, 2009
Posted by Poppa Chris on Tuesday, January 07, 2014 6:31 AM

Hi Shawn:

Yes I use the Orion autoguider with my OAG. By the way, I sold the 94176 and bought the newer model OAg Celestron just came out with to replace it.  Best new feature is a helical focuser on the auotguider camera pick-off tube.  Help with getting both cameras in focus simultaneously.  To Orion AG camera did need a short extension tube with it, same as with the 94176. 

Me mounting a second scope?  Well... Yes and no... A second scope in the traditional sense, no.  Mounting my DSLR "piggyback" with a 500mm mirror lens (basically a 500mm Maksutov-Cassegrain), yes.  When I do so, I don't need the OAG.  I use the full light of the main scope with the Orion camera for guiding.  One point to mention is focus - focus - focus.  After that focus some more.Big Smile       

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    January, 2014
Posted by satha52 on Tuesday, January 07, 2014 7:51 AM

Thanks Poppa Chris!  Appreciate your help.  Do you think if I use a small refractor piggybacked to the CPC 1100 (for imaging and visual only, not for autoguiding) that I would have to purchase another OAG and cam for the refractor?  Or could I essentially lock on the same object by adjusting the refractor similar to adjusting a finder scope? 

My main objective is to use both telescopes on the same CPC 1100 mount and wedge.  Without having to polar align each seperately upon use, or get seperate OAG's if possible.  Do you have any advice on doing this with medium to long exposure DSLR photography with this mount and wedge? 

I guess mounting your DSLR direct to the CPC 1100 would be similar.  Since you aren't using an autoguider for it, and you are utilizing the movement and autoguiding of the mount and wedge from your main telescope, are you able to do medium to long exposures with your DSLR while tracking objects with your CPC 1100 mount and wedge?

Thanks!

Shawn

 

  • Member since
    November, 2009
Posted by Poppa Chris on Tuesday, January 07, 2014 8:00 AM

With the small refractor you don't need the OAG at all.  When imaging through the main scope put the AG camera on the refractor.  When imagiang through the refractor put the AG camera on the main scope.  Guiding is all about controlling your mount.  It doesn't care one twit which scope is which as they are both only along for the ride.  And yes (within reason) you can guide on one object with one scope and image a different object with the other scope.  This in fact is typically the norm. FYI:  Polar alignment only concerns your mount.  Once again, the scopes are only along for the ride.

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    November, 2009
Posted by Poppa Chris on Tuesday, January 07, 2014 8:06 AM

Note:  I would consider the Orion Short tube 80 as the minimum guide scope/refractor for your CPC1100.  Celestron  also makes an 80mm longer F.L. guidescope that matches up well with the CPC1100.  Both may be used visually with 1-14" eyepieces.  Larger scopes are OK but the weight will become an issue possibly requiring a counterweight system to keep your setup in balance. (More $)  Even with the OAG + focal reducer + DLSR + AG camera my setup is a bit tail heavy.  I've been considering a Starizona counterweight system myself for a while.  Just haven't made up my mind to take the plunge.

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    January, 2014
Posted by satha52 on Tuesday, January 07, 2014 3:13 PM

Thanks for your reply.  I know about the Orion ST, but I've seen bad imaging through it.  I'm sure it is great for a guidescope though.  I was thinking more along the lines of the Orion EON 80mm but can't find it anymore.  Currently doing research on the normal Orion 80mm ED as well as the Explore Scientific 102mm F/7 refractor.  I think the latter is about 10 lbs if I remember correctly. 

I didn't know they made counterweight systems for fork mounted equatorials, that's awesome! They way the CPC 1100 hangs off the wedge is an incredible angle in th south... it's always amazed me it doesn't just fall over.

My CPC is tail heavy too since I added a microfocuser (crayford style).  I love having the extra fine focus on the SCT, but it is heavy.

If you or anyone else has any suggestions on a 3-4" refractor please feel free to chime in...

 

  • Member since
    November, 2009
Posted by Poppa Chris on Tuesday, January 07, 2014 3:20 PM

Really depends upon your budget.  A triplet APO refractor such as an Explore Scientific or Willaims Optics would be pretty darned good for AP. But that could be an investment of $2,000 to $4,000 just for the OTA.

I tried the Crayford style dual-speed focuser myself.  Added far too much tail weight for me.  So I put it up on Ebay and then spent the proceeds on a Starlight Microfocuser upgrade to the Celestron Focuser knob.  I chose it after rreading that it was used by NASA on a C925 that was sent to the ISS.  Good enough for Government work as they say.   Big Smile

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    January, 2014
Posted by satha52 on Tuesday, January 07, 2014 10:20 PM

The Explore Scientific 102mm f/7 I was looking at is the aluminum version.  I can get that OTA for just under $1k.  I see they have a carbon fiber version, the price has risen on that one to over $1700.  My CPC 1100 is the aluminum version, do you happen to have the CF version?

I'm impressed with the type of glass used in the above scope, which is usually only in higher priced scopes.  The only thing I would have to add is the piggyback mounting equipment and a focal reducer.  I would love to buy a Takahashi or Tele Vue, but I don't want to spend that much...  The quality from a good medium level scope should be good enough for me.

Unfortunately, I bought an OPT crayford focuser before learning that moonlite had one compatible with the f/6.3 focal reducer.  So I decided to mod my OPT to hold the focal reducer.  Then I learned about the replacement type you have.  I already have the JIT version of the motorized focuser for remote focusing on the celestron knob.  As you did, I will probably in the future have to sell off some equipment and just go with the 2 speed changeout for the knob.  I haven't hooked up the JIT version yet, but it is an older version that has a variable speed screw to allow very slow focusing. 

BTW, does that pic/prism on the OAG that comes into the field of view lower the quality of the image at all?

Thanks!

 

  • Member since
    November, 2009
Posted by Poppa Chris on Wednesday, January 08, 2014 7:46 AM

My CPC is also the aluminum tube version.  My Moonlight feather touch focuser replaces the original Celestron focuser knob and bearing.  As for the OAG the naswer is no  The prism image is actually outside what hit the camera senser so ther is no effect to your DSLR.  If you possibly got the paperwork with your used OAG, ther is a sketch of the light cone in it that explains things a bit better.

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

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