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Mach1GTO (July 2018 batch) PEMPro (PEC), PHD2 guide results`

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#1 cytan299

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Posted 04 August 2018 - 09:27 AM

Hi guys,

   I was finally able to take my Mach1GTO (Jul 2018 batch) outside to be tested. All the data was taken on the night of 03 Aug 2018. I will be using my FSQ106 (focal length: 530 mm) + SBIG guide camera kit (modified to give 200 mm focal length) for the measurements. Unlike my previous experience with my ZEQ25 (which I still own) and the CEM60 (which I sold) the Mach1GTO is so well made that the comparison of the build quality between it and the iOptron mounts is just unfair smile.gif The quality of the Mach1GTO in its DEC and RA adjustments, fit and finish, is really fantastic. For example, when I was setting up the CEM60, I always had the fear of damaging the worm. Not so with the Mach1GTO: the clutches on the Mach1GTO are really a life (or mechanical) saver! 

 

Anyhow, continuing. The parameters are:

  1. ST-i guide kit: 7.63 arcsec/pixel (confirmed with Astrometry.net where it measured 7.59 arcsec/pixel)
  2. STF8300C+FSQ106: 2.1 arcsec/pixel

Here's how my setup looks like in my living room:

small1.jpg

small2.jpg

 

The PE measurement with PEC OFF:

PEC_OFF.jpg

PEC_OFF_FFT.jpg

PEC_OFF_ANALYZED.jpg

Continued in next post ...


Edited by cytan299, 04 August 2018 - 10:19 AM.


#2 cytan299

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Posted 04 August 2018 - 09:31 AM

Here's with PE ON:

 

PEC_ON.jpg

PEC_ON_FFT.jpg

PEC_ON_ANALYZED.jpg

 

So I can see that the something that are 2x and 6x the worm period have been completely reduced, but the fundamental period remains. Is this supposed to be what PEC does? Or my loaded PE is already screwed up and I need to reload it with the new measurements?

 

Continued below ...


Edited by cytan299, 04 August 2018 - 10:20 AM.


#3 cytan299

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Posted 04 August 2018 - 09:44 AM

Here's where I transition back to using my ST-i guide kit with PHD2 for the measurements of guide quality.

 

The results from Guide assistant:

guide_assistant.jpg

 

Here's the DEC backlash results:

backlash.jpg

 

which I think, is actually very good and very similar to the CEM60 with magnetic clutches.

 

Here's PHD2 guiding using the Guide assistant parameters *except* that I disabled the DEC backlash and so did not load the backlash value.

 

guiding.jpg

 

I am happy with the guide results which are < 1 arc sec rms since my resolution of the main camera is 2.1 arcsec/pixel. IMO, seeing wasn't the best when I did this, as you can see from the many corrections in both RA and DEC. Plus I did not do any optimization of the PHD parameters. I'll have to try Rolando's method of setting the MinMov settings on another night. Guide assistant's MinMov value may be too aggressive.

 

Any comments as to how to improve guiding?

 

 

Continued in next post ...


Edited by cytan299, 04 August 2018 - 09:46 AM.


#4 cytan299

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Posted 04 August 2018 - 09:53 AM

Finally, an interesting observation: I can make both RA and DEC spike by just walking up to the mount and sitting next to it. The setup is on a concrete pavement.  I've never seen this before with my cem60 mounted on the same Tri-pier. 

 

Here's the picture:

bump.jpg

 

My hypothesis is the configuration of the counterweights. I have 3 counterweights (29 lbs) snugged up high on the counterweight bar with one counterweight (9 lb) right at the end of the bar. (see photos at the start of this post) I think in this configuration, the bar shakes like a pendulum when there is any vibration. This is clearly not good. Is the solution more counterweights so as to move the 9lb weight higher towards the top end of the bar?

 

 

Anyway, comments are welcome!

 

cytan

 



#5 james7ca

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Posted 04 August 2018 - 10:06 AM

Were these curves generated with your main scope at 2.1 arc seconds per pixel? If so there seems to be something odd about your data, showing a range of about +/-3 pixels or at least +/- 6 arc seconds of periodic error. I think A-P says that a new Mach1GTO should be equal to or better than +/- 3.5 arc seconds (prior to any error correction).

 

In any case, I think your PEC could do better. It seems that you went from about +/- 6 arc seconds to about +/- 4 arc seconds with PEC enabled (very roughly). With a good curve you should be able to get down to at least +/- 1.5 arc seconds.

 

As for walking on concrete, yes, that will really affect your tracking. I see the same thing with my Mach1GTO with a Losmandy HD tripod.


Edited by james7ca, 04 August 2018 - 10:08 AM.


#6 cytan299

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Posted 04 August 2018 - 10:24 AM

Were these curves generated with your main scope at 2.1 arc seconds per pixel? If so there seems to be something odd about your data, showing a range of about +/-3 pixels or at least +/- 6 arc seconds of periodic error. I think A-P says that a new Mach1GTO should be equal to or better than +/- 3.5 arc seconds (prior to any error correction).

 

In any case, I think your PEC could do better. It seems that you went from about +/- 6 arc seconds to about +/- 4 arc seconds with PEC enabled (very roughly). With a good curve you should be able to get down to at least +/- 1.5 arc seconds.

 

As for walking on concrete, yes, that will really affect your tracking. I see the same thing with my Mach1GTO with a Losmandy HD tripod.

Yes, it's with the main scope with 2.1 arc seconds/pixel. If what you say is true about the specs for the PE, then yes, something is definitely wrong :(

 

I guess I'll have to send my measurements to AP to see what they say ...

 

cytan



#7 james7ca

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Posted 04 August 2018 - 10:42 AM

Generating a good PEC curve is NOT easy. I'd check everything you did before you assume that the Mach1GTO is running a little high on its periodic error. IMO, you need a night with good seeing and some careful setup to make certain that you are measuring correctly.

 

In any case, when I said you should be able to get down to about +/-1.5 arc seconds of error with PEC enabled that assumes a very good curve used under good conditions. Most likely, in day-to-day operation you won't get that good of a result (but, YMMV).


Edited by james7ca, 04 August 2018 - 10:50 AM.


#8 cytan299

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Posted 04 August 2018 - 11:02 AM

Generating a good PEC curve is NOT easy. I'd check everything you did before you assume that the Mach1GTO is running a little high on its periodic error. IMO, you need a night with good seeing and some careful setup to make certain that you are measuring correctly.

 

In any case, when I said you should be able to get down to about +/-1.5 arc seconds of error with PEC enabled that assumes a very good curve used under good conditions. Most likely, in day-to-day operation you won't get that good of a result (but, YMMV).

Yes, I agree with your assessment because this is the first time that I'm using PEMPro and I'm sure there are idiosyncrasies that I have to watch out for. But I've sent the data off to AP to see what they have to say.

 

Also since PEMPro only supports SBIG cameras via PHD, I'm also wondering whether pixels is actually arc-seconds ... but that's another story.

 

cytan



#9 james7ca

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Posted 04 August 2018 - 11:09 AM

...Also since PEMPro only supports SBIG cameras via PHD, I'm also wondering whether pixels is actually arc-seconds ... but that's another story.

 

cytan

I don't know, when I uses PEMPro I allow PEMPro to control the camera and generate the tracking results.



#10 CharlesW

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Posted 04 August 2018 - 11:14 AM

If I may offer a little advice, and I don’t want to appear to be an a$$ but the older I get the blunter I get. You don’t have a picture of what your mount looked like when you actually captured the data for PEC, but as long as you have dangling cables, PEC and guiding are going to be affected.  I wouldn’t spend two seconds thinking about that until you get your cable management sorted out. 

 

You’ve got your largest, heaviest, most expensive, counterweight first on the shaft where it is, I imagine, the least effective. You might try making it the last so you might bring everything in closer. 

 

It’s very cool to have an automated B-mask and an automated flat panel but those things add unnecessary weight and bring me back to paragraph one, they require a lot of extra cables. I would remove them and only put them on when they are actually needed. 

 

You’ve got some very nice equipment but the B-mask tells me that you don’t have software commensurate to its quality. Maybe I’m wrong and you are only using the mask to get the first focus of the night. But, I would strongly suggest getting TheSkyX Pro to run your stuff. It will take care of camera and mount control, it has two great focusing apps. It has a very easy to use PA app. Finally, it provides for extremely precise framing of your targets and has very fast, offline, plate solving. You’ll also be able to ditch the finder scope, which is again, unnecessary weight. You’ve got about $10k wrapped up in your mount, scope, and camera. Don’t go cheap on the software. 



#11 Stelios

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Posted 04 August 2018 - 12:13 PM

You’ve got about $10k wrapped up in your mount, scope, and camera. 

I think closer to $15K. 

 

The proper CW placement is: All but the *lightest* CW go on top of the CW bar, in order of weight (heaviest closest to top). The lightest (6lb) is used to balance. If the lightest can't balance, then it's time for another CW. 

 

I think your PhD2 settings (especially for poor seeing) can be improved. With the Mach1 I've found that 3-4" exposures work better. The DEC MinMo should almost certainly be raised, and the RA aggression probably lowered (I don't say certainly because you have a larger PE than normal after PEC. Still, the largest component of any move you are correcting would likely be the seeing).

 

I also think you have way too many things hanging on your scope, although they may be necessary for remote operation. One of the things I love about my (mobile) setup with OAG, is that there's *nothing* on the scope (after polar alignment): No finderscope or guidescope. Just the load on the rear with camera + EFW + OAG, cables routed through mount. 



#12 cytan299

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Posted 04 August 2018 - 01:21 PM

If I may offer a little advice, and I don’t want to appear to be an a$$ but the older I get the blunter I get. You don’t have a picture of what your mount looked like when you actually captured the data for PEC, but as long as you have dangling cables, PEC and guiding are going to be affected.  I wouldn’t spend two seconds thinking about that until you get your cable management sorted out. 

 

You’ve got your largest, heaviest, most expensive, counterweight first on the shaft where it is, I imagine, the least effective. You might try making it the last so you might bring everything in closer. 

 

It’s very cool to have an automated B-mask and an automated flat panel but those things add unnecessary weight and bring me back to paragraph one, they require a lot of extra cables. I would remove them and only put them on when they are actually needed. 

 

You’ve got some very nice equipment but the B-mask tells me that you don’t have software commensurate to its quality. Maybe I’m wrong and you are only using the mask to get the first focus of the night. But, I would strongly suggest getting TheSkyX Pro to run your stuff. It will take care of camera and mount control, it has two great focusing apps. It has a very easy to use PA app. Finally, it provides for extremely precise framing of your targets and has very fast, offline, plate solving. You’ll also be able to ditch the finder scope, which is again, unnecessary weight. You’ve got about $10k wrapped up in your mount, scope, and camera. Don’t go cheap on the software. 

Hi Steve,

   You don't need your disclaimer because it does not do you any service: you still sound like an a$$.

 

   The reason why the largest and heaviest CW is on top is because the goal is to minimize the moment of inertia (which scales as m*r^2 where m is the mass of the CW and r is the distance from the fulcrum. OTOH moments to balance the mount scales as m*r). See page 23 of the Mach1GTO_GTOCP4 manual, point 3 in the section "Precision Balancing":

 

"It is best to add counterweights and slide them to the top of the shaft with the heaviest at the top and then use the smallest weight to perform the precision balancing." (Emphasis is mine)

 

Yes, I agree there are dangling cables that I should take care of --  1 arc second is a gnat's eye. The only cable that is not routed to my USB hub is the Polemaster cable which can be easily taken off when I do the PE curve. Everything, including power goes through the USB hub. A power cable, and USB cable (+ mount motor control cable) goes through the mount. See photo:

 

365a17f9-7d1b-4629-b4c9-dc5d4cd3a0bd.jpg

 

I'm ignoring your comments after the paragraph "It's very cool ..."

 

cytan


Edited by cytan299, 04 August 2018 - 01:32 PM.


#13 cytan299

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Posted 04 August 2018 - 01:24 PM

I think closer to $15K. 

 

The proper CW placement is: All but the *lightest* CW go on top of the CW bar, in order of weight (heaviest closest to top). The lightest (6lb) is used to balance. If the lightest can't balance, then it's time for another CW. 

 

I think your PhD2 settings (especially for poor seeing) can be improved. With the Mach1 I've found that 3-4" exposures work better. The DEC MinMo should almost certainly be raised, and the RA aggression probably lowered (I don't say certainly because you have a larger PE than normal after PEC. Still, the largest component of any move you are correcting would likely be the seeing).

 

I also think you have way too many things hanging on your scope, although they may be necessary for remote operation. One of the things I love about my (mobile) setup with OAG, is that there's *nothing* on the scope (after polar alignment): No finderscope or guidescope. Just the load on the rear with camera + EFW + OAG, cables routed through mount. 

Thanks for the input. I try to do things remotely as much as possible. Once I set the scope up, it's in the house I go until it's time to tear things down again.

 

Although I use plate solving, I still find it useful to have a finder scope. Like last night when I "lost" the star smile.gif  when I was monkeying around with the software, I used the finder scope to find it again with my home built hand controller.

cytan


Edited by cytan299, 04 August 2018 - 01:29 PM.


#14 rockstarbill

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Posted 04 August 2018 - 02:05 PM

Hi Cytan,

 

You have 19 arc-minutes of Polar Alignment error according to the screenshots you showed. Not sure if that is real, or some other problem, but you will want to dial that in a bit better in order to do a PEMPro run. Luckily PEMPro can assist you in doing this, and should allow you to correct the alignment quite well. Similarly, you will want to remove things that are not necessary for the run itself to avoid having a cable drag/snag skew the results. Roland did comment on your post, with a post of his own on the AP-GTO group (since he does not post on CN):

 

https://groups.yahoo...ns/topics/63155

 

He brings up a good point that the factory curves are generated unloaded, and that loaded runs may show different results. If the factory curve is not giving you the results you want, you can export it and save it, then generate a new one and upload it to the mount and test it. Roland gives some good guidance on how to generate the curve in his reply as well.



#15 cytan299

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Posted 04 August 2018 - 02:36 PM

Hi Cytan,

 

You have 19 arc-minutes of Polar Alignment error according to the screenshots you showed. Not sure if that is real, or some other problem, but you will want to dial that in a bit better in order to do a PEMPro run. Luckily PEMPro can assist you in doing this, and should allow you to correct the alignment quite well. Similarly, you will want to remove things that are not necessary for the run itself to avoid having a cable drag/snag skew the results. Roland did comment on your post, with a post of his own on the AP-GTO group (since he does not post on CN):

 

https://groups.yahoo...ns/topics/63155

 

He brings up a good point that the factory curves are generated unloaded, and that loaded runs may show different results. If the factory curve is not giving you the results you want, you can export it and save it, then generate a new one and upload it to the mount and test it. Roland gives some good guidance on how to generate the curve in his reply as well.

Thanks for pointing out that Roland answered. I had emailed AP directly. 

 

It's good to know I screwed up the measurement. Like I had posted earlier, this the first time that I am measuring PE and I'm not surprised that I didn't do it right. Also I didn't notice the problem with PA until you pointed it out above because usually, at least on my previous cem60, the PA is usually spot on . Perhaps there's some flexure with the Polemaster mounted at the end of the saddle -- I did notice that the star chosen during the Polemaster alignment process did not quite trace the computed circle. I'll do drift align the next time.

 

Of course, that's together with cleaning up the cabling as well.

 

Cytan

 

P.S. it's weird that I haven't seen Rolando's post in my email feed yet ...

P.P.S. It had landed up in my email's spam folder smile.gif


Edited by cytan299, 04 August 2018 - 03:05 PM.


#16 Ron in Michigan

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Posted 10 August 2018 - 02:23 PM

Anyway, comments are welcome!

 

cytan

 

 

When I was a new Mach1 owner I did the same - I wasted a lot of time with Pempro looking for a fix. It wasn't until I gave up on the pe and solved the issues.

 

1. your scope looks like a pack mule.  I own a bmask but have never used it once, because SGP takes care of that.

 

2. Eliminate non essentials and tack down any and all cords or things that might move.  It doesn't take much for 1 micron of shift.  

3. place your flat panel manually when needed. (that's pretty rare). so why hang it on the the scope.

 

4. forget pempro - your issue is likely something else you're doing. 

 

5. Feel with the touch of a surgeon if you have ANY play in ra and dec axis. I found both mine had some very slight play and using the manual/instructions I loosened the set screw and with thumb pressure, I removed ALL SLOP out of both axis - which I have read can occur from shipping. 

6. If possible use a OAG.

 

7. Align, do guiding and then turn off guiding and watch your Ra and Dec paths. Make sure Dec stays in line.

 

8. I find that reset switch is better for quality mounts and hysteresis. 

9 IMPORTANT as I don't see it in your graphs.  REDUCE the time - so that graph is spread out - then turn on corrections. You need to see each correction and what is produces. (enough or not enough?) so that you can tweak your aggression. (mine is much lower than yours). 

10) if the corrections are not happening fast enough - reduce min move. (mine is lower than yours). 

11. make sure no wind. I left my dome fan on the other night (I was remote in the house) and that fan caused + .20 RMS error increase. (shocked me) I powered it off and guiding dropped from a poor  .55 to .35 instantly.

 

Some things that helped me. It took me 6 months to get my mach1 guiding well. But the one thing I learned was not to look at the Pec as the problem.  Now that things are working well for me, I may see if I can improve it with Pempro.  I average around .35  My worst at times is .45 I on occasion see .25    (total rms arc sec).

 

I run a side by side 80mm and 152mm scopes - but moved my guide scope into the AOG.  Lodestar X2 (which also was one of the changes I made for the better as I removed a ASI 290 camera from this duty.

12. Make sure there is NO MOVEMENT in the camera train.  SCREW connections only, no pressure screws.

13. Try to set up your focuser to be less extended outside the OTA. Move inside, less possible sag. We can do this by adding more extension tubes to extend the camera outward - while drawing the focuser more inside the ota.

 

14. I lost my Pec from factory messing with Pempro.  To regain a decent pec curve I simply recorded one in ASCOM ... it recorded a full worm read (about 6 minutes) and then started playing it back.  Not as accurate as a pempro curve, but less prone to user error.  It removed all apparent PE from my guiding graphs.

 

Worked for me. I didn't make any real head way until I stopped messing with pempro and dealt with the real issues.
With the rig - Cleanliness is next to Godliness...  Strip all but essentials.

 

 


 

 

 

 

 

 

Attached Thumbnails

  • mydomelive.JPG
  • clean.JPG
  • guiding-well.JPG
  • newscope.JPG


#17 orlyandico

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Posted 10 August 2018 - 09:30 PM

Unrelated question, cytan: I like that USB hub. Care to share a link?

 

I think measuring PE with a short guide scope and such huge pixel scale is not worth doing.

 

When I trained my Mach1's PE I used the main scope (600+ mm focal length) and a barlow, and stuck the guider on it.

 

At 2.1"/pixel you would be undersampling since a Mach1 with PEM trained properly is sub-1" p-p or should be.



#18 StephenW

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Posted 10 August 2018 - 10:07 PM

Cytan: can you confirm which scope you measured your PE with? I assume it was the main scope (PemPro shows an image scale of 2.1 arc/s).

And were you using PemPro connected through PHD2, or PemPro direct to the camera?

I train PEC with PemPro using PHD2 with a guide image scale of 2.9 arc/s and I am able to see significant improvement in PE.

PHD2 is capable of sub-pixel centroid tracking so if using it, a scale of 2.1 arc/s should be fine.

#19 wz5mm

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Posted 10 August 2018 - 11:27 PM

I remember reading somewhere that 1"/px or less was the desired threshold.  The following from the CCDWare/PEMPro web site seems to state the same or similar:

==============================

 

I am going to start out this section with something that I think we all learned early on with CCD Imaging and focusing. You cant focus at a 2x2 bin and then image at 1x1 binning. You can, although, focus at 1x1 binning and image at 2x2 binning. If you are going to image at 2x2 binning only, then you can focus at 2x2 binning. The rule is you must focus at the highest binning mode you plan on using.

 

I have found that PEMPro follows the same rule. Think of it as focusing the periodic error of your mount. If you only image at a 3.5 arc seconds per pixel for wide field work, then you can use that image scale to program your mount with PEMPro. But don't expect to throw on your 12 inch Meade at .55 arc second per pixel on your mount and still expect the same level of performance.

 

Use the smallest image scale you will use with your mount to program your mount. The better then sampling rate (i.e. smaller the image scale) the better PEMPro can analyze and correct your mount. Remember, ideal sampling is the seeing in your local area divided by 3.3. If your local seeing conditions averages 2.0 arc seconds, then you should aim for a image scale of ~.60 arc seconds per pixel. Anything more than that wont achieve much better performance.

 

Now, if you only image at 1.75 arc seconds per pixel, then use that to program your mount. I have programmed my mount with PEMPro at 3.5 arc seconds per pixel and it worked great with my wide field set-up. But when I measured my PE with a C9.25 SCT, I found the error to be to large for that image scale. So I re-programmed my mount with the C9.25 and decreased my PE error by 4X! Now the next time I do wide field imaging, my mount will be 'super-tuned' for the job, and that's just what we want.



#20 james7ca

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Posted 11 August 2018 - 12:34 AM

Measuring your PE at an image scale of 2.1 arc seconds per pixel should be okay. Remember, to get a good PE curve you need to average several full cycles of your PE and given that centroid calculation can be accurate to about 1/10 pixel that means your averaged results should easily be within 0.2 arc seconds. Given that, you are likely to see a lot more error in your tracking from things like differential flexure and the atmosphere than you will from a PEC calibration that is measured to an accuracy of "only" 0.2 arc seconds.

 

Also, any tracking errors caused by a less than perfect PEC are likely to be completely swamped by things like atmospheric refraction (and the latter will prevent you from going unguided for more than a few minutes anyway, no matter how good your mount or your PEC). Thus, once you have a good PEC that can correct to better than say +/- 1.5 arc seconds you're going to have to rely on guiding to do the rest. In fact, I've been told by Astro-Physics that you have to guide if you want to image with any of their mounts.

 

My Mach1GTO has an uncorrected PE of around +/- 6 arc seconds (I know, I got a "bad" one) but with a good PEC calibration I can get that down to a measured +/- 1 arc second. However, my unguided imaging is NEVER even close to that kind of accuracy given atmospheric refraction, flexure in my system, and non-periodic errors in the mount. However, under good seeing conditions and when everything is well behaved I can record total RMS errors while guiding with PhD to below 0.5 arc seconds (over several worm periods, meaning twenty or thirty minutes, combined or total error in both R.A. and Dec.).

 

Given that kind of RMS error you might assume that I could then use exposures of almost an indefinite length (or at least similar to those twenty or thirty minutes). However, since I'm typically imaging at a scale of 0.75 arc seconds per pixel with a guide scope and not an OAG I've found that I routinely get small drifts in both axes that could limit my maximum exposures to something between five and ten minutes, most likely from differential flexure between my guide and main scopes. However, that's not much of a concern for me since I'm imaging under red/orange zone light pollution with a CMOS camera so my exposures, even in the narrow band, are almost always less than ten minutes.

 

I guess what I'm saying here is that measuring your PEC to 0.2 arc seconds is certainly good enough (IMO). Also, if you want the absolute best guiding performance you need to be using an OAG (but the latter depends upon your image scale).


Edited by james7ca, 11 August 2018 - 03:04 AM.


#21 cytan299

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Posted 11 August 2018 - 02:35 PM

Hi Ron,

 

   Thanks for the comments!

 

   I did a second run with PemPro last night (in fact, the 2nd time I've used the mount) and I have come to the conclusion that using my FSQ106 setup is not the right way to measure the PE of my Mach1GTO. Here's the graph:

 

PEC_OFF_10Aug2018.jpg

 

Clear DEC drift. See comment 2 below.

 

I don't believe there is anything wrong with my new mount. It's pilot error smile.gif

 

Here's some of my observations and comments.

  1. I agree there's just too much stuff in this setup. Even with me cleaning up cabling etc. I think it's really not the right scope+camera to do the PE measurement because
    1. PemPro does not directly support my STF8300 but uses PHD2. I cannot zoom into PHD2 to see the star except for 1 pixel and subframing doesn't seem to work either.
    2. Also, with the FSQ106, I get 2.1 arcsec/pixel while it is recommended to use 1 arcsec/pixel. 
    3. I think the solution, at least for me, is to get a guidescope + a 2 um pixel sized guide camera to get 1 arcsec/pixel. This will also be a lot lighter and without extra cables. Plus if the guide camera is natively supported in PemPro, I think it'll be easier to use. Right now all my cameras are from SBIG.
  2. I checked the play on both axes and they feel fine to me. *BUT* one problem that I found (learning curve here) is that I did not have the DEC lever tightened completely and there was DEC drift during my PEMPRO measurement. I think this came from slewing from North to South for the measurement. The polar alignment was done with PoleMaster.
  3. I have an OAG (OAG8300) that I have on my LX200 setup. But I really don't like OAGs for guiding. Finding a guide star is a pain in the rear.
  4. I'll try the reset switch algorithm later tonight.
  5. Everything has been tightened down. My camera is on an extension tube. The focuser is only out by less than 1/2".
  6. My guide scope is the SBIG guide kit + ST-i. I added a lens to increase its focal length from 100 mm to 200 mm. The resolution is 7.63 arcsec/pixel. I think, this is really quite large. In principle, if the best PHD can guide is 0.1 pixels, then the best rms I can get is about 0.7 arcsec. So I think  about 1 arcsec is probably the best I can do. But note that my main camera's resolution is 2.1 arcsec/pixel and so it is still ok. I'm thinking of replacing the ST-i with an QHY5P-II which has 2.2 um pixels which is more than 3 times smaller than the ST-i. Perhaps, with this new camera I can have be more sensitive to guide errors. What do you think? P.S. looking at my PHD2 rms error box, I see that I'm guiding to ~0.1 pixels => 0.7 arcsec, while you are at 0.15 pixels => 0.22 arcsec. My guide sensitivity is 3x worse than yours!
  7. I turned off the guide pulses to see what the "seeing" looked like. The peaks that I see are around 2 to 3 arcsec. Not the best seeing last night.

I think for any new equipment, there's a learning curve. And I agree with you that it might take 6 months to get proficient in using this mount. Unfortunately, the weather and work prevents me using the Mach1GTO every day, so I'm not at all surprised that it will take this long.

 

More comments are welcome!

 

cytan

 

 

Anyway, comments are welcome!

 

cytan

 

 

When I was a new Mach1 owner I did the same - I wasted a lot of time with Pempro looking for a fix. It wasn't until I gave up on the pe and solved the issues.

 

1. your scope looks like a pack mule.  I own a bmask but have never used it once, because SGP takes care of that.

 

2. Eliminate non essentials and tack down any and all cords or things that might move.  It doesn't take much for 1 micron of shift.  

3. place your flat panel manually when needed. (that's pretty rare). so why hang it on the the scope.

 

4. forget pempro - your issue is likely something else you're doing. 

 

5. Feel with the touch of a surgeon if you have ANY play in ra and dec axis. I found both mine had some very slight play and using the manual/instructions I loosened the set screw and with thumb pressure, I removed ALL SLOP out of both axis - which I have read can occur from shipping. 

6. If possible use a OAG.

 

7. Align, do guiding and then turn off guiding and watch your Ra and Dec paths. Make sure Dec stays in line.

 

8. I find that reset switch is better for quality mounts and hysteresis. 

9 IMPORTANT as I don't see it in your graphs.  REDUCE the time - so that graph is spread out - then turn on corrections. You need to see each correction and what is produces. (enough or not enough?) so that you can tweak your aggression. (mine is much lower than yours). 

10) if the corrections are not happening fast enough - reduce min move. (mine is lower than yours). 

11. make sure no wind. I left my dome fan on the other night (I was remote in the house) and that fan caused + .20 RMS error increase. (shocked me) I powered it off and guiding dropped from a poor  .55 to .35 instantly.

 

Some things that helped me. It took me 6 months to get my mach1 guiding well. But the one thing I learned was not to look at the Pec as the problem.  Now that things are working well for me, I may see if I can improve it with Pempro.  I average around .35  My worst at times is .45 I on occasion see .25    (total rms arc sec).

 

I run a side by side 80mm and 152mm scopes - but moved my guide scope into the AOG.  Lodestar X2 (which also was one of the changes I made for the better as I removed a ASI 290 camera from this duty.

12. Make sure there is NO MOVEMENT in the camera train.  SCREW connections only, no pressure screws.

13. Try to set up your focuser to be less extended outside the OTA. Move inside, less possible sag. We can do this by adding more extension tubes to extend the camera outward - while drawing the focuser more inside the ota.

 

14. I lost my Pec from factory messing with Pempro.  To regain a decent pec curve I simply recorded one in ASCOM ... it recorded a full worm read (about 6 minutes) and then started playing it back.  Not as accurate as a pempro curve, but less prone to user error.  It removed all apparent PE from my guiding graphs.

 

Worked for me. I didn't make any real head way until I stopped messing with pempro and dealt with the real issues.
With the rig - Cleanliness is next to Godliness...  Strip all but essentials.

 

 

 

 



#22 cytan299

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Posted 11 August 2018 - 02:44 PM

Unrelated question, cytan: I like that USB hub. Care to share a link?

 

I think measuring PE with a short guide scope and such huge pixel scale is not worth doing.

 

When I trained my Mach1's PE I used the main scope (600+ mm focal length) and a barlow, and stuck the guider on it.

 

At 2.1"/pixel you would be undersampling since a Mach1 with PEM trained properly is sub-1" p-p or should be.

The USB hub that I'm using is a modified GEARMO industrial usb3 hub. I chose this hub because there is space between the USB sockets to install power sockets. See here:

 

https://www.amazon.c... Rail Mountable

 

I had my friend who is a tech drill holes for the 2.1mm sockets. I had him do it because he's much more precise than I am :) plus the odd U-shape requires the use of a drill press. And the case is make from steel, so it's a little bit more difficult to drill compared to aluminum.

 

Here's a photo of the inside:

 

IMG_2695.jpg

 

 

I'm going to get another guidescope (maybe an ORION) with a small pixel camera QHY5P-II (2.2 um) to get the 1 arcsec/pixel. This will be much lighter and no cable mess to do a good measurement. What do you think?

 

cytan



#23 StephenW

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Posted 11 August 2018 - 03:18 PM

Hi Cytan,

 

>I did a second run with PemPro last night (in fact, the 2nd time I've used the mount)

 

What did you final PE end up as?  It looks really small! - in fact it almost looks like PEC may have been enabled during this capture?

 

>*BUT* one problem that I found (learning curve here) is that I did not have the DEC lever tightened completely and there was DEC drift during my PEMPRO measurement.

 

The tightness of the DEC leaver might affect backlash but should not cause drift.  Drift is generally due to polar misalignment.

 

>I cannot zoom into PHD2 to see the star except for 1 pixel and subframing doesn't seem to work either.

 

Did you open the "Star Profile" (View -> DIaplsy STar Profile) - it basically shows a magnified view of the star, as well as it's FWHM.

 

Again - once you adjust for drift - your measured PE looks really good - I'd guess around 1 arc-s.

 

Steve



#24 cytan299

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Posted 11 August 2018 - 04:08 PM

Hi Cytan,

 

>I did a second run with PemPro last night (in fact, the 2nd time I've used the mount)

 

What did you final PE end up as?  It looks really small! - in fact it almost looks like PEC may have been enabled during this capture?

 

>*BUT* one problem that I found (learning curve here) is that I did not have the DEC lever tightened completely and there was DEC drift during my PEMPRO measurement.

 

The tightness of the DEC leaver might affect backlash but should not cause drift.  Drift is generally due to polar misalignment.

 

>I cannot zoom into PHD2 to see the star except for 1 pixel and subframing doesn't seem to work either.

 

Did you open the "Star Profile" (View -> DIaplsy STar Profile) - it basically shows a magnified view of the star, as well as it's FWHM.

 

Again - once you adjust for drift - your measured PE looks really good - I'd guess around 1 arc-s.

 

Steve

Hi Steve,

  You know I'm a newbie when I get the terms wrong smile.gif When I say "DEC lever" I meant the ALT lever. My mind was filled with "DEC drift".

 

Here's a picture with the vertical scale in arcseconds:

PEC_OFF_ARCSEC_10Aug2018.jpg

 

Looks like even if I don't compensate for drift, my PE is +/- 2.5 arcsec. But I don't want to be too optimistic :)

 

and here's the analysis results which says for some reason +/-5 (units? arcseconds or pixels).

 

PEC_OFF_Analyzed.jpg

 

Yes, the PEC was off. I double checked the contents of the file that was generated.

 

I've sent the data to Howard for him to have a look as well since he asked for it :)

 

With regards to PHD. Yes, I opened up the star profile to have a look. The large format really bothers me though ...

 

cytan



#25 StephenW

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Posted 11 August 2018 - 04:28 PM

>You know I'm a newbie when I get the terms wrong smile.gif When I say "DEC lever" I meant the ALT lever. My mind was filled with "DEC drift".

Been there done that :).  Yeah, once you're close to the right altitude, you can lock it down and still adjust via the DEC adjustment knob.  When I got my Mach-1 first I also made the mistake of not locking down the lever before adjusting altitude during polar alignment - once I thought I was aligned I locked down the lever and threw my alignment completely off :).

 

And ok - missed that the original graph was in pixels nor arc-s!

 

If you click on the Adjust X and Adjust Y options it should overlay all the lines on top of each other, but even without doing that it does appear to cover about 9 or 10 arc-s pk-to-ps (e.g. the first blue line goes form 0 down to -10), so that matches the +/-5 arc-s reported after generating the curve.

 

Did you try applying your curve from your second run and measuring PE after?  How much was it reduced?




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