Topics

EXOS 2 GT Payload Capacity


Jeff Snell
 

Folks,
I mounted my Celestron Evolution Edge HD 8" on the EXOS 2 GT/PMC this weekend. It balanced out nicely with the weight which included cameras (T5i and Orion Starshoot Autoguider), a focal reducer and the 14 pound optical tube (around 18 pounds total).  After set up and balance, I took it out on a clear and essentially windless night for some test photos.

After PA with polemaster and sync with CDC, I slewed to a target and started taking shots using PHD.  Immediately I noticed that the Ra and Dec correction parameters started jumping around wildly.  Total moving well towards 4 plus.  I did not have that issue with the ES ED 80 APO (decidedly less weight).  All of my test shots had trailing stars.

My question: Does the payload capacity of 28 pounds also include the counterweights?  If not, then I am at a loss to understand why I was getting so much movement/jitter in the corrections.  I thought maybe flexing due to the counter weight positioning???  If counterweights included, I believe I am over the weight limit...

Thoughts?

Jeff
Jeff

PMC-Eight w/Explore Stars
ES ED80mm APO
Celestron 8" Edge HD
Canon Ti-5 w/ Spencer Camera Astro-mod


Jerry Hubbell - Explore Scientific VP Engineering
 

On Mon, May 11, 2020 at 03:39 PM, Jeff Snell wrote:
My question: Does the payload capacity of 28 pounds also include the counterweights?  If not, then I am at a loss to understand why I was getting so much movement/jitter in the corrections.  I thought maybe flexing due to the counter weight positioning???  If counterweights included, I believe I am over the weight limit...

Hi Jeff,

The payload capacity specified for the EXOS 2 mount is 28 lbs. for visual use. Typically you reduce this to 70% for astrophotography, some reduce it to 50%. This would mean around 20 lbs. for astrophotography so if you have 18 lbs. then that should be fine. You have to realize that the inertial load with your new setup has increased a lot so if you have not changed any of the tuned parameters in PHD2 for your lighter setup then it would need to be retuned. Any further analysis would need a look at the guide log.
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jeff Snell
 

Thanks Jerry.  I will look at the PHD parameters tonight.  Next clear night about a week away, I'll test it out and get some screen shots of the tracking.
 
Jeff

PMC-Eight w/Explore Stars
ES ED80mm APO
Celestron 8" Edge HD
Canon Ti-5 w/ Spencer Camera Astro-mod


On Mon, May 11, 2020 at 2:01 PM Jerry Hubbell - Explore Scientific VP Engineering <jrh@...> wrote:
On Mon, May 11, 2020 at 03:39 PM, Jeff Snell wrote:
My question: Does the payload capacity of 28 pounds also include the counterweights?  If not, then I am at a loss to understand why I was getting so much movement/jitter in the corrections.  I thought maybe flexing due to the counter weight positioning???  If counterweights included, I believe I am over the weight limit...

Hi Jeff,

The payload capacity specified for the EXOS 2 mount is 28 lbs. for visual use. Typically you reduce this to 70% for astrophotography, some reduce it to 50%. This would mean around 20 lbs. for astrophotography so if you have 18 lbs. then that should be fine. You have to realize that the inertial load with your new setup has increased a lot so if you have not changed any of the tuned parameters in PHD2 for your lighter setup then it would need to be retuned. Any further analysis would need a look at the guide log.
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jeff Snell
 

Hi Jerry,
OK, I'm lost.  Is there obvious drop down or button in PHD2 that allows some way to "retune" for the heavier gear?  I looked at every drop down in PHD2 and I don't see anything obvious.  I see a reference to review calibration data and modify calibration under the tools drop down.  That's it though...

Am I on the right trail?

Jeff

PMC-Eight w/Explore Stars
ES ED80mm APO
Celestron 8" Edge HD
Canon Ti-5 w/ Spencer Camera Astro-mod


On Mon, May 11, 2020 at 2:01 PM Jerry Hubbell - Explore Scientific VP Engineering <jrh@...> wrote:
On Mon, May 11, 2020 at 03:39 PM, Jeff Snell wrote:
My question: Does the payload capacity of 28 pounds also include the counterweights?  If not, then I am at a loss to understand why I was getting so much movement/jitter in the corrections.  I thought maybe flexing due to the counter weight positioning???  If counterweights included, I believe I am over the weight limit...

Hi Jeff,

The payload capacity specified for the EXOS 2 mount is 28 lbs. for visual use. Typically you reduce this to 70% for astrophotography, some reduce it to 50%. This would mean around 20 lbs. for astrophotography so if you have 18 lbs. then that should be fine. You have to realize that the inertial load with your new setup has increased a lot so if you have not changed any of the tuned parameters in PHD2 for your lighter setup then it would need to be retuned. Any further analysis would need a look at the guide log.
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jerry Hubbell - Explore Scientific VP Engineering
 

On Mon, May 11, 2020 at 08:25 PM, Jeff Snell wrote:
Is there obvious drop down or button in PHD2 that allows some way to "retune" for the heavier gear? 
Hi Jeff,

The adjustments or "tuning" I was talking about involve various parameters in PHD2 that are adjustable. I assumed, perhaps wrongly, that you were familiar with these. Here is an excerpt from the PHD Guiding 2 help file. This is just a small sampling of the information about how to get the best performance out of your EXOS 2 mount using PHD2.

Although my comments involve PHD2 and not the PMC-Eight system directly, it is important to understand that the PMC-Eight EXOS 2 mount (and the iEXOS 100) is an inexpensive mount that can be as capable as a more expensive mount only through the application of skills and knowledge of the user. It does not perform at its peak unless the user has learned enough about the mount and its behavior under load. YMMV. 

Guide Algorithm Parameters

In PHD2, the various guide algorithms can be applied to either the right ascension or declination axes.  Most of these algorithms include a minimum move parameter.  This is used to avoid making guide corrections that are overly small, are unlikely to have any effect on star shape, and are mostly due to transient seeing effects.  These values are entered in units of pixels, so you need to think about them in the context of how large your star images are.  The default values work well for short-to-medium focal length systems, but you may need to increase them if you are working at long focal lengths and expect stars to have larger diameters.

The hysteresis algorithms keep a history of the guiding corrections that have been made in the recent past, and these are used to help compute the next guide correction.  The hysteresis parameter, expressed as a percentage, specifies the "weight" that should be given to this history as opposed to  looking only at the star deflection in the current guide frame.  Consider an example where the hysteresis parameter is 10%.  In that case, the next guiding correction will be 90% influenced by the star movement seen in the current guide frame and 10% by the corrections that have been made in the recent past.  Increasing the hysteresis value will smooth out the corrections at the risk of being too slow to react to a legitimate change in direction.  The hysteresis algorithms also include an aggressiveness parameter, again expressed as a percentage,  that is used to reduce over-correcting.   On each frame, PHD2 computes how far it thinks the mount should move and in what direction(s) it should move. The aggressivness parameter scales this. For example, take a case where the star deflection has been evaluated and a corrective move of 0.5 pixels is warranted.  If the aggressiveness is set to 100%, a guider command will be issued to move the mount the full 0.5 pixels.  But if the aggressiveness is set to 60%, the mount will be asked to move only 60% of that amount, or 0.3 pixels. If you find your mount is always overshooting the star, decrease this value slightly (say, by 10% steps). If you find PHD2 always seems to be lagging behind the star's motion, increase this by a little bit. A little can go a long way here. 
 
The ResistSwitch algorithm behaves much as its name implies.  Like the hysteresis algorithms, it also maintains a history of past guide corrections, and any change of direction must be "compelling" in order to issue a reversing guide command.  This is appropriate for declination guiding, where reversals in direction are both suspect and likely to trigger backlash in the gears.  For that reason, ResistSwitch is the default algorithm for declination but not for right ascension, where valid direction reversals are expected.  Starting with Release 2.4.1, two additional parameters are available for fine-tuning the ResistSwitch algorithm.  The first is "aggression", a percentage amount that controls how much of the computed guide correction will be issued.  Reducing this parameter can help to avoid over-shooting with mounts that have little or no backlash. The second parameter is a checkbox labeled "Fast switch for large deflections."  If this is checked, PHD2 will react immediately to a large change of direction rather than waiting for three consecutive deflections in the new direction, which is the normal behavior.  This can help to more quickly recover from large excursions in Dec, perhaps caused by wind, cable snags, or other mechanical shifts  The definition of a "large deflection" is 3x the minimum-move value.  So if PHD2 is over-reacting to direction changes, you can tune the behavior with the min-move parameter or disable the "fast switch" option altogether.  It is worth remembering that "less is usually better" when it comes to Dec guiding, so don't try to over-tune these parameters.

The LowPass algorithms also employ a history of recent guiding corrections in order to compute the next correction.  The starting point for the computed move is the median value of the guide star deflections that have occurred in recent history.  This means that the star deflection seen in the current guide frame has relatively little impact on calculating the next move and the algorithm is very resistant to quick changes.  But the history accumulation also includes a calculation to determine if deflections are trending in a consistent direction.  The slope weight parameter, expressed as a percentage, determines how much influence this should have in calculating the actual guider movement - it is there to keep the algorithm from being overly sluggish.  If you set a slope weight of zero, the guide pulse will always be just the median value of the recent history.  If you set a non-zero slope weight, that median value will be adjusted either upward or downward based on the recent trend of guide star movements.  Because the low-pass algorithm is so resistant to quick changes, it is probably most applicable to declination guiding.

The LowPass2 algorithm is a variation of the original LowPass algorithm with somewhat different behavior.  It also maintains a history of guiding corrections, but the next correction is simply a linear extension of the commands that have come before it (i.e. a slope calculation).  This continues until a significant change in direction is seen, at which point the history is cleared.  The algorithm has two adjustable properties: minimum-move and aggressiveness.  Minimum-move has the same effect as it does in the other guide algorithms, and aggressiveness (percentage) is a way of further dampening the size of the guide corrections. LowPass2 is a very conservative, high-impedance algorithm that may be a good choice for users with good seeing conditions and well-behaved mounts with little or no declination backlash.
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Chris Tardif
 

Shift click on the green icon button and it will recalibrate.  That took me hours to figure out the first time.


--
Mounts: Explore Scientific IEXOS-100 w Celestron CG5 tripod, iOptron CEM 40
Scopes: Explore Scientific FCD-100 ED-102CF, Various Canon lenses, ZWO mini-guidescope, StarField 60mm guide-scope.
CameraASI120MM Mini (mono), Altair GPCAM 130
Control PC: Intel NUC
Loc: 44 -79


Steve Siedentop
 

Jeff -

The PHD2 Guiding Assistant will calculate appropriate values for the parameters Jerry enumerated and it’s probably the quickest route from point A to point B.

However, it’s important to understand what goes on under the hood so you can get yourself out of a hole when things don’t operate as they should.

I imaged with a C8 on a Celestron CG5 many moons ago.  With some TLC, your EXOS 2 will image with the Edge HD.  However, you’ll likely find that doing so will challenge your current level of expertise.

I’m looking forward to seeing what you can get out of this combination!

-Steve
--
Mounts: ES PMC-8 G11 with Ruland Couplers and One Piece Worm Blocks, Skywatcher NEQ-6
Scopes: ES ED127CF FCD100, Orion 6” Mak, Stellarvue SV80EDT, Coronado Solarmax 40
Cameras:  CentralDS CDS-600, CentralDS Astro 60D, Orion Starshoot SSAG
Msc: Moonlite Focusers, Astrozap Dew Straps, Pegasus Ultimate PowerBox
Software: PixInsight, Cartes du Ciel, BackyardEOS, SkySafari


Vince White
 

FYI, as a data-point, on a clear, calm night and when I do my part, I can get from 0.6 - 0.8 arc-sec total RMS error (10 minute exposures) with about 25lbs (heavy newt + camera + guide scope & camera + cables) on my PMC8 Exos2-GT.  It's also been a long journey to get to this point and even then, I can have a bad night with 2+ arc-sec RMS error.

Regards,
Vince
--
Mount: ES PMC-8 EXOS2-GT
Scopes: BRESSER 208mm f/3.9 Newt + ES HR Coma Corrector, Celestron C90 Mak, generic 50/191mm guide scope
Cameras:  Canon EOS RP, T7C (ZWO ASI120MC clone)
Misc: 2" Optolong UHC & L-eNhance filter, Raspberry PI 4
Software: INDI + Kstars + EKOS, DeepSkyStacker, GIMP, Lightroom, Photoshop, Sirl


 

Jeff,
 
When I first got my EXOS2, I expected to take it out of the box, do the necessary software and communications integration, and then everything would 'just work'.  Took me a while to recalibrate, because things are NOT that simple and yes, to Vince's point, it can be a long journey that requires a number of steps.
 
Some things to think about:
 
> Jerry mentioned PHD2 logs, and you mentioned screen shots afterwards.  Two different things.  PHD2 creates a log directory (on my Win7, it's under My Documents, not sure where if you're on win10).  while a screen shot is an interesting point-in-time look, logs carry more data, so they're more useful. When you do a session that you want looked at, don't start and stop every couple of minutes - let it run for a while - 10, 20 minutes at a minimum - long enough to for any regular behaviors to start showing up.  Just zip up the relevant log(s) and attach to a post.
 
> Check to make sure that your mount head, with its additional payload, cannot shift or wobble against the tripod head while in use.  All that holds it secure is the downward pull from the chrome rod.   Section 5 in my tuning doc covers this, but basically, make sure that chrome rod is screwed securely into the mount head's base and that the spacer ring is installed. Make sure that the aluminum nut is snugged *tight*, that the eyepiece tray tightens down horizontal and not tipped, and that the aluminum nut does not loosen as your session progresses.  
 
> Consider your balance.  Some members here get along ok with even balancing, but my (13lb) setup does not. It tracks better biased East-heavy (tracking always lifting weight, never lowering), and camera-heavy.  Something to try.
 
Hope this helps, and don't give up. :-)
 
- Bob
 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Jeff Snell
 

Jerry/Bob/Chris/Steve,
Thanks so much for the info (and the encouragement).  Wow.  I will dive in and start seeing what sense I can make of your great advice and technical prowess.  I have to admit that the enjoyment slips a bit when you have to break into things that you don't understand.  I've really only been doing the astro-photography since last fall and the visual since Jan '19.  My greatest fear is that I'll irreparably break something (mechanical, setting or code).  I am not an engineer, and I did not stay at a Holiday Inn last night.  I do however work everyday with about 15 engineers of all flavors and they all have the same thing in common...they love to tinker and they are perfectionists.  Whether it's tuning a mount, adjusting settings in programs or trying to understand the basics of Photoshop, I am an unarmed man.  I'm getting better but still unarmed.

However, the rewards I've reaped thus far from seeing the result of my work with the smaller ES ED 80 APO has kept me going and I do not intend to give up.  I understand to get good at this requires a lot of work.  I am under no illusion regarding the intricacies and technical aspects of this hobby as well as the need to keep at it.  One must immerse.  I just need to find the energy to immerse after a long day at work, three kids to keep up with, up late at night with a telescope and camera, and back at it again the next day.

In short, I will "endeavor to persevere" (name that movie).  I'll take a look at some of the things you point out and report back ASAP.  Thanks for being willing to help out as I work to get the most out of the mount and the PMC-Eight.

Jeff

PMC-Eight w/Explore Stars
EXOS 2 GT
ES ED80mm APO
Celestron 8" Edge HD
Canon Ti-5 w/ Spencer Camera Astro-mod


On Tue, May 12, 2020 at 7:40 AM Robert Hoskin <devonshire@...> wrote:
Jeff,
 
When I first got my EXOS2, I expected to take it out of the box, do the necessary software and communications integration, and then everything would 'just work'.  Took me a while to recalibrate, because things are NOT that simple and yes, to Vince's point, it can be a long journey that requires a number of steps.
 
Some things to think about:
 
> Jerry mentioned PHD2 logs, and you mentioned screen shots afterwards.  Two different things.  PHD2 creates a log directory (on my Win7, it's under My Documents, not sure where if you're on win10).  while a screen shot is an interesting point-in-time look, logs carry more data, so they're more useful. When you do a session that you want looked at, don't start and stop every couple of minutes - let it run for a while - 10, 20 minutes at a minimum - long enough to for any regular behaviors to start showing up.  Just zip up the relevant log(s) and attach to a post.
 
> Check to make sure that your mount head, with its additional payload, cannot shift or wobble against the tripod head while in use.  All that holds it secure is the downward pull from the chrome rod.   Section 5 in my tuning doc covers this, but basically, make sure that chrome rod is screwed securely into the mount head's base and that the spacer ring is installed. Make sure that the aluminum nut is snugged *tight*, that the eyepiece tray tightens down horizontal and not tipped, and that the aluminum nut does not loosen as your session progresses.  
 
> Consider your balance.  Some members here get along ok with even balancing, but my (13lb) setup does not. It tracks better biased East-heavy (tracking always lifting weight, never lowering), and camera-heavy.  Something to try.
 
Hope this helps, and don't give up. :-)
 
- Bob
 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Tony
 

I dont mean to sidetrack the OP's concerns, but I was just curious why the discrepancy on payload capacity depending on who or even where you read it from.  I've seen ES rate it at 40 lbs visual and 28 lbs AP (70% rule).  And I've also seen it rated at 28 lbs visual and 20 lbs AP (71.42857% rule doesn't have the same ring).  What is ES's official stance since I've seen them state it both ways?

I dont think anyone actually expects the mount to function well with 40 lbs even for visual.  I also dont think any of these limits are hard and fast rules, but more of a sliding scale.  The further you try to push it, the more error you will introduce.  Personally, I'm pushing my luck and am awaiting delivery of a nearly identical setup as Mr. Vince White.  I dont expect to get anywhere near his accuracy without both an exceptional amount of work (which I can do), and an exceptional amount of luck (which I don't have).  I calculate my weight will be 25.15 lbs, which is either well within, or well outside the generally accepted payload capacity, depending on the source.  Still I feel there are just too many variables in play to say this will either work or wont work.  So much will come down to proper setup, balancing, lubrication, gear mesh, perhaps bearing preload, or any of a couple dozen other minor tweaks.  And that's to say nothing of the weather.

Good luck to you Jeff, I hope its something as simple as recalibrating PHD2.  If not, maybe just start checking the obvious mechanicals, unwanted play or sticky points.  I'm sure youll get it dialed in soon enough.   


Chris Tardif
 

You're absolutely right.  Another thing that doesn't get much air play is the height of the OTA.  The higher the OTA (further it is from the fulcrum because really this is just a lever) the more "weight" and less capacity.  

The guy on Ben's Astrophotography exceeds the weight limit of his mount and still gets great results.  So as Jerry said, your mileage may vary and I also like what Kent said a while back on another thread..."I can't advise you to drive above the speed limit" or something to that effect.

Chris

--
Mounts: Explore Scientific IEXOS-100 w Celestron CG5 tripod, iOptron CEM 40
Scopes: Explore Scientific FCD-100 ED-102CF, Various Canon lenses, ZWO mini-guidescope, StarField 60mm guide-scope.
CameraASI120MM Mini (mono), Altair GPCAM 130
Control PC: Intel NUC
Loc: 44 -79


 

Hi Jeff,

I hope this message finds you well. While reading your post, I felt pretty identified with almost everything you wrote (even with that long day at work, kids (and wife) management, etc, part). I'm very interested in this because I happen to have the exact same rig as you (EdgeHD8 + EXOS2GT PMC8) and have had problems with the weight and balance which is pretty lame since it's a very basic task... I even noticed that the triangular markers on the Mount match for the DEC piece but not for the RA as if was sort of misaligned when assembled at the factory... I don't know if that's causing my balancing issues (I actually doubt it) but I started thinking maybe our OTA is too heavy for the mount even if it's stated to be theoretically ok on the specs.... I'd like to have the answer to your issue (and mine as well) but I just can hope you find it soon. I even asked an online ES technical support agent and wasn't able to answer my questions... I guess it's gonna take some time for us to figure this out, If I get to know something worthy of sharing with you, I'll let you know. Good luck!


Jerry Hubbell - Explore Scientific VP Engineering
 

On Tue, May 12, 2020 at 11:21 AM, Jeff Snell wrote:
In short, I will "endeavor to persevere" (name that movie).  I'll take a look at some of the things you point out and report back ASAP.  Thanks for being willing to help out as I work to get the most out of the mount and the PMC-Eight.
 
Hi Jeff,

Yes, it takes a lot of work to get good at this hobby.  I started down this path 12 years ago and it took me 4 years of nearly full-time work to get to where I thought I knew something. Then I wrote the book that I wish I had had when I first started out. I am amazed that even people that cannot and would not devote the time I did 10-12 years ago progress to the point where after only 1 or 2 years are at the same level I was at 4 years. That is how much the equipment and the information has improved. Most people that have only started this hobby over the past couple of years do not yet understand how it used to be, and how things are still getting better. 

The biggest thing I learned about this hobby over the years is that it is the journey, not the destination. There will always be something new to learn and do, which is why it is one of the top hobbies available, along with flying which I also do.

Thanks
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jerry Hubbell - Explore Scientific VP Engineering
 

On Tue, May 12, 2020 at 02:49 PM, <guitsboy@...> wrote:
I dont mean to sidetrack the OP's concerns, but I was just curious why the discrepancy on payload capacity depending on who or even where you read it from.  I've seen ES rate it at 40 lbs visual and 28 lbs AP (70% rule).  And I've also seen it rated at 28 lbs visual and 20 lbs AP (71.42857% rule doesn't have the same ring).  What is ES's official stance since I've seen them state it both ways?
Hi,  I think the increased capacity number past the normal 28/20 lbs. is related to the testing the Scott Roberts and Alex Sanchez did to demonstrate what the PMC-Eight and motor drive system could do. The way I would rate the mount is that there is a much wider spread between visual and AP with AP sticking to around 20-22 lbs probably and visual could be double that, or 40-45 lbs. As always YMMV.  So for our mounts, they perform at a very high capacity for visual use if you want to give it a try, but I would stick to the AP recommendations and cut it to 50% of the uprated visual number.  That's how I would look at it.  But as always, if you are handy at identifying issues and tuning these things and fully understand what is going on with your mount while guiding, you could maybe push things even further. Our recommendations are meant for the average, knowledgeable user.

That's my take on it.

Thanks
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Bill Black
 

Hi All,
I have a data point to share in this thread.
I use an older Celestron 8" SCT (NexStar 8SE orange tube) modified with an electric crayford focuser and flocking in the tube.
I have my 80mm APO piggyback mounted on top of the SCT, so I have both wide angle and tight field going at the same time.
I'm using a Losmandy D-style rail on the SCT with Farpoint clamps to keep the whole thing sturdy on the EXOS II puck.

The set-up is about 27 lbs and I have 27 lbs of counterweight on the mount as well. Similar to Vince, I get a total RMS error in the 0.6 to 0.8 arcsec range on an average night reported by PHDII.
On a night of good seeing, I can get a total RMS error of about 0.5 arcsec and on a bad night I've seen it climb as high 1.3 arcsec.
In PHD II shift clicking the guide button to force a recalibration is a must anytime I change something with the set-up. Then a little trial and error to go through fine-tuning the guiding algorithms.

Here's a pic of my current set up and some results.
The image of M51 is a stack of 4 5-minute exposures shot through the SCT+0.63 reducer/flattener using a ZWO ASI294MCPro camera.


--

Bill
Location: Dallas, GA
Scopes:
 Celestron C8, AstroTech 80mm APO

Mounts: EXOS II PMC-Eight, LXD75

Cameras: ZWO ASI294MCPro, ASI385


Mark Christensen
 

Roy,

 

It isn’t just weight  - it is the moment of inertia and focal length. With your EdgeHD the moment of inertia (short tube) should not be an issue. For you the issue is focal length – imaging at 2000mm focal length is very demanding of everything and is a very painful way to get introduced to astro-imaging. Not only is the focal length long, making guiding performance critical, but the large f/-ratio, f/10, means your exposures for things like galaxies and nebulae (extended objects) must be long, like 6 times what they would be for an f/4 optic or nearly 3 times longer than at f/6. Add in LRGB filters and you are in for a lot of learning and misery.

 

The moment of inertia of the rig, if excessive relative to the capacity of the mount, can cause jerky guiding. The moment of inertia is roughly the product of the weight and the length of the tube. So just focusing on the raw weight only tells part of the story. Again, for you, I don’t that is the problem with your rig – it is the focal length and the resulting sensitivity to guiding errors. And small chips with small pixels make it even more obvious if you have guiding (or focusing, or optical alignment) issues.

 

My own experience (over the past 15 years – the prior 25 are irrelevant) is…

 

I have a G11 (non-PMC, bought used in 2006) which tracks and guides very well after I spent the first few months with it adjusting it (and replacing a few parts the prior owner had distorted by grossly over-tightening fasteners). I can routinely image with a heavy 8 inch Newt at 1100mm throwing no images away. The Newt has a long tube so the cross section to wind and the moment of inertia are large. But the G11 can handle it  nicely. But if I stick a Barlow on it and image at (nominally-the Barlow to focal plane spacing increases it) 2300mm I have to have: 1. No breeze, as the tube makes a nice sail. 2. Stable atmosphere. 3. Perfect adjustment (so that the mount isn’t constantly responding in DEC). Failing anyone of those I might throw away 20 to 50% of the frames.

 

On nights of very stable atmosphere I can keep 100% at 2300mm with my 8 inch f/5.5 plus Barlow:

 

https://www.flickr.com/photos/76076778@N07/27367226762/in/photostream/

 

Also a test shot with a 8” f/8 RC I re-aligned for a friend (another example of why this is not a buy-and-shoot activity):

https://www.flickr.com/photos/76076778@N07/48272510521/in/photostream/

 

So something like the G11 can easily handle a scope like your EdgeHD. With a mount of the class of the EXOS-2GT, to be honest, it will be a hard slog.

 

I have also put a 12 inch f/5 (1500mm) that I built on the G11 – with a weight (full kit) of 60lb and a huge (wind) cross section and moment of inertia. With that I usually was stuck with 200sec or less frames and might have to pull in my horns to 60 second subs on a bad night. And if there was any wind gusts I had to fall back to visual. It was converted to a Dob a few years ago as lifting that rig up onto the G11 became life threatening. I called it the Blue Beast.

 

I have a (Bresser) EXOS-2gt. I use it for shorter focal length work with lenses and my 4.25 inch f/4 and 6 inch f/2.8 Newts for imaging and with a 120mm f/8 refractor for visual. Nice mount for the weight class and money.

 

Why two mounts? Because the G11 is the imaging workhorse, while the EXOS-2gt can be carried out of the garage, assembled without counterweight, with one hand into the yard or easily set up for shorter focal length imaging in the field without a lot of fuss.

 

Regards,

 

Mark Christensen

 

Losmandy G11

ES (Bresser) EXOS-2gt

Various Newtonians: 8 inch f/5.5, 8 inch f/4, 4.25 inch f/4, 6 inch f/2.8

Starshooter Pro V1 Single Shot Color CCD (APS-C format chip)

Pentax K50 and Q10

 

From: MAIN@ESPMC-Eight.groups.io [mailto:MAIN@ESPMC-Eight.groups.io] On Behalf Of Roy
Sent: Tuesday, May 19, 2020 4:13 PM
To: MAIN@ESPMC-Eight.groups.io
Subject: Re: [ESPMC-Eight] EXOS 2 GT Payload Capacity

 

Hi Jeff,

I hope this message finds you well. While reading your post, I felt pretty identified with almost everything you wrote (even with that long day at work, kids (and wife) management, etc, part). I'm very interested in this because I happen to have the exact same rig as you (EdgeHD8 + EXOS2GT PMC8) and have had problems with the weight and balance which is pretty lame since it's a very basic task... I even noticed that the triangular markers on the Mount match for the DEC piece but not for the RA as if was sort of misaligned when assembled at the factory... I don't know if that's causing my balancing issues (I actually doubt it) but I started thinking maybe our OTA is too heavy for the mount even if it's stated to be theoretically ok on the specs.... I'd like to have the answer to your issue (and mine as well) but I just can hope you find it soon. I even asked an online ES technical support agent and wasn't able to answer my questions... I guess it's gonna take some time for us to figure this out, If I get to know something worthy of sharing with you, I'll let you know. Good luck!


Jeny@
 

All EdgeHD optical tubes are Fastar-compatible, allowing the secondary mirror to be removed and replaced with a third party lens accessory for ultra-fast f/2 wide field imaging
I'm wandering if changing to dedicated astro-camera in Fastar setup will solve the issue...
--
EXOS2-GT PMC8
Orion150 Mak, Polemaster, ZWO ASI178MM


Kent Marts- Explore Scientific Customer Service
 

Whenever I'm faced with a difference like this, I ALWAYS refer to the manufacturer's information rather than a dealer or vendor. Why? Because there are fewer links in the information chain to get messed up. Sort of like the old Telephone Game, where you whisper a phrase in someone's ear, then they pass it to the next person, and the final person says it out loud.

About a year ago, after testing the payload capacity of the EXOS2 with PMC-Eight was raised from a broad statement of 28-pound capacity (and leaving it to the customer to learn about the 60% rule, or 50% rule for astrophotography) to a much more transparent statement -- this much for AP, this much for visual. The capacity went to 28 pounds of equipment (not including counterweights) for astrophotography.

--
Kent Marts
Customer Service
Explore Scientific

Gear: Anything in the store!


Jeff Snell
 

Aaaaah, flying.  Now that's something I can relate to Jerry.  I'm former USAF (now retired) with over 3000 hours in 6 different a/c.  Boy, do I miss that.  I was way more suited to that world than this.  But being a Type A fighter pilot, I don't give up that easy :-)

So weather has sucked by Utah standards for the last couple of weeks so I was unable to get "fresh logs."  I went ahead and pulled the old log from PHD2 from my first attempt at guiding with the higher weight.  It is attached.  I'm sure it will reveal other rookie mistakes and may even be akin to going to confession but I'm willing and able to take all criticism and correction to make this work.

Standing by for any analysis anyone can provide.

Jeff

PMC-Eight w/Explore Stars
ES ED80mm APO
Celestron 8" Edge HD
Canon Ti-5 w/ Spencer Camera Astro-mod


On Tue, May 19, 2020 at 4:14 PM Jerry Hubbell - Explore Scientific VP Engineering <jrh@...> wrote:
On Tue, May 12, 2020 at 11:21 AM, Jeff Snell wrote:
In short, I will "endeavor to persevere" (name that movie).  I'll take a look at some of the things you point out and report back ASAP.  Thanks for being willing to help out as I work to get the most out of the mount and the PMC-Eight.
 
Hi Jeff,

Yes, it takes a lot of work to get good at this hobby.  I started down this path 12 years ago and it took me 4 years of nearly full-time work to get to where I thought I knew something. Then I wrote the book that I wish I had had when I first started out. I am amazed that even people that cannot and would not devote the time I did 10-12 years ago progress to the point where after only 1 or 2 years are at the same level I was at 4 years. That is how much the equipment and the information has improved. Most people that have only started this hobby over the past couple of years do not yet understand how it used to be, and how things are still getting better. 

The biggest thing I learned about this hobby over the years is that it is the journey, not the destination. There will always be something new to learn and do, which is why it is one of the top hobbies available, along with flying which I also do.

Thanks
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!