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A good night with the EXOS2 #EXOS2

Jim McKee
 

All,

After many months of absence, poor weather and figuring out new gear, I am happy to report that all the right things came together with my EXOS-2 PMC-8 last night.  As you all know, it can be quite a journey as a beginner with a lot of distracting side trips that don’t seem to get you where you want to go.

 

Highlights

1)    Remarkably clear seeing.  This may have been a key to the guiding.  More on this later.

2)    10 second unguided  times on M31, round stars.  Great PA with Sharpcap

3)     2-4 minute guide times on M31.  Round Stars

4)    10 Minute guide time on Triangulum Galaxy.  Round stars

5)    Throughout the night, PHD2 RMS performance was:

a.     RA     0.23 Px / 0.60”

b.     DEC  0.19 Px / 0.48”

c.     Total 0.33 px / 0.76”

What was new:

1)    Update of firmware to 13A version

2)    Integration of newly acquired Orion 115mm F7 with EXOS2

3)    Dedicated Dell lapton to run all ASCOM

4)    Remounting of 60mm Guidescope and camera to top of the 115mm OTA (ASI 120mm-s)

5)    Calibrate the entire rig to point in the same direction and be focused.

 

What had changed since my last good photo session (late April)

1)    Complete rebuild of software package on the new Dell.  I used all installed defaults for EXOS2 ASCCOM and PHD-2.   When you are first learning to use these programs, you can change so many settings trying to find your way, that it throws everything out of whack.  Just a thought, but maybe a clean start was helpful.

a.     ASCOM Platform (EXOS-2 ASCOM driver, with default settings.)

b.     ASCOMPAD

c.     PHD2 (Standard setttings, no adjustments, just a calibration run)

d.     SHARPCAP

e.     APT

f.      BACKYARD EOS

g.     Stellarium Scope and Stellarium

2)    Seeing was beautiful.  No haze and no visible lights from our small town. For the last 4 months, there had always been a yellow glow from town on the sky.

3)    Better focus and scope.  The 115 is a remarkably sharp APO for my first big scope.  I purchased a PrimaLuce Sesto Senso for remote focusing.  Using APT, I focused the two shots attached and they looked damn good.  But later In the night, I refocused on M13 and realized I really need to zoom in first and focus the little doughnut-looking stars into sharp points.  Unfortunately I needed to get some sleep and dew was starting to get the best of me (no heater for the 115 yet).   But it meant I still hadn’t gotten my focus down to its best.  So that will be worked on in the next session and we will see what that does for photo quality.

4)    Failure of Parallax USB-Serial Adapter.   While I don’t think this has anything to do with last night’s session success, I mention this to say I bought an AMAZON FTDI USB-Serial adapter (not Parallax) and it ran like a dream. I have a new Parallax as a backup.

 

5)    Polar Alignment.  I had really good polar alignment but not perfect alignment.  Some have said that this might make guiding a little more consistent by inducing some minor alignment error.  Still I got good 60 second unguided shots, so I am not sure if this was a factor.

 

That’s my report for now, I will update if I remember other details.  But for those who doubt the EXOS2 capabilities, 10 minute guiding is possible (to corroborate Bob H’s 10 minute guiding sessions also).

 

Thanks to all on the forum who keep us all on track and thanks to Jerry and ES for their support.

 

Shots for last night are attached.  Very rough processing with DSS and Photoshop.  I need to really work this also, but the scope work was the focus last night.  One thing at a time

 


--
Scope:        Orion EON 115mm APO
Mounts
:      ES EXOS2-GT w/ PMC-8
Cameras:   Canon 6D Astro Mod, Canon 7D2, 1D Mk 2, EOS 60D Asto Modified
Lens:
          Canon EF 100-400mm f/4.5-5.6L IS II
Misc:          TELRAD, ZWO ASI120MM Guide Camera, Astromania 60mm Guidescope, Senso Sesto Focus Motor
Software:   EXPLORESTARS IOS & WIN, Stellarium. Backyard EOS, StarTools, APT, DSS
Computer:  Dell Latitude E5450, Windows 10

Jim McKee
 

Having problem posting Triangulum photo.  Here is  link
https://mckeejh.smugmug.com/Astro/i-zNsK3gP/A

--
Scope:        Orion EON 115mm APO
Mounts
:      ES EXOS2-GT w/ PMC-8
Cameras:   Canon 6D Astro Mod, Canon 7D2, 1D Mk 2, EOS 60D Asto Modified
Lens:
          Canon EF 100-400mm f/4.5-5.6L IS II
Misc:          TELRAD, ZWO ASI120MM Guide Camera, Astromania 60mm Guidescope, Senso Sesto Focus Motor
Software:   EXPLORESTARS IOS & WIN, Stellarium. Backyard EOS, StarTools, APT, DSS
Computer:  Dell Latitude E5450, Windows 10

 

Jim,
 
Very nice!  
 
So... You had round stars at 600s with the mount carrying... perhaps 18lbs?, a scope/camera assembly that must be at least 1.0 meter long, and a FL of 805mm.
 
That's a longer, heavier load than mine, and a longer FL.  I wonder what the limit is?  Doesn't sound like we've hit it yet.  Happy dance!
 
 
- Bob
 
  
 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2-IMX224C
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64

Jim McKee
 

Hi Bob
Bob.  I just weighed the whole assembly at 22 Lbs.   Scope is 15, then add Canon 60D, 60mm Guidescope and Camera, focus motor and assorted Vixen dovetail bars and saddles, USB hubs and wires.
--
Scope:        Orion EON 115mm APO
Mounts
:      ES EXOS2-GT w/ PMC-8
Cameras:   Canon 6D Astro Mod, Canon 7D2, 1D Mk 2, EOS 60D Asto Modified
Lens:
          Canon EF 100-400mm f/4.5-5.6L IS II
Misc:          TELRAD, ZWO ASI120MM Guide Camera, Astromania 60mm Guidescope, Senso Sesto Focus Motor
Software:   EXPLORESTARS IOS & WIN, Stellarium. Backyard EOS, StarTools, APT, DSS
Computer:  Dell Latitude E5450, Windows 10

 

Jim,
 
There might be a pattern here...  
 
You were able to obtain surprisingly long exposures, and you did it while using a longer, heavier payload than I did.    
And then we have Chris T., who just for fun put an FCD-100 on a little iEXOS-100, and was able to do 180s exposures comfortably.  That was a surprise, too!
These mounts appear to be less sensitive to payload than conventional wisdom would suggest.

Perhaps available motor torque is a factor in all this?  Command authority, if you like.  Taken together with the PMC8, that may help explain why both of these mounts can do better than one might expect for their size and price point.  Yes, there are mechanical issues that we need to manage, and guiding need to be set up well but I'm wondering if what we have here, is the mount equivalent of a larger-than-usual engine in a small car.  Not a bad thing. :-)
 
[ Jerry - thoughts? ]
 
There's an interesting thread over at CloudyNights called "What limits the weight on a mount?".  Makes the point that the simple "weight limit" statement typically used by mfrs doesn't really say a lot about how well a given mount will do, when managing scopes that may vary greatly in shapes and sizes.  Gets into discussions about torque, inertia, etc.  It's an interesting read and may be relevant.

FWIW...
 
- Bob
   
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2-IMX224C
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64

Jim McKee
 
Edited

Bob,
Interesting hypothesis.   Could a long scope which has a larger moment of inertia provide a damping effect to guiding?  Maybe in DEC, but is RA affected by a longer, larger scope? 

Moment of inertia ( ), also called "angular mass" (kg. · m2), is the inertia of a rotating body with respect to its rotation. It is a rotating body's resistance to angular acceleration or deceleration, equal to the product of the mass and the square of its perpendicular distance from the axis of rotation.
--
Scope:        Orion EON 115mm APO
Mounts
:      ES EXOS2-GT w/ PMC-8
Cameras:   Canon 6D Astro Mod, Canon 7D2, 1D Mk 2, EOS 60D Asto Modified
Lens:
          Canon EF 100-400mm f/4.5-5.6L IS II
Misc:          TELRAD, ZWO ASI120MM Guide Camera, Astromania 60mm Guidescope, Senso Sesto Focus Motor
Software:   EXPLORESTARS IOS & WIN, Stellarium. Backyard EOS, StarTools, APT, DSS
Computer:  Dell Latitude E5450, Windows 10

Jerry Hubbell - Explore Scientific VP Engineering
 

On Sun, Sep 1, 2019 at 06:37 AM, Jim McKee wrote:
Moment of inertia ( ), also called "angular mass" (kg. · m2), is the inertia of a rotating body with respect to its rotation. It is a rotating body's resistance to angular acceleration or deceleration, equal to the product of the mass and the square of its perpendicular distance from the axis of rotation.
Hi Jim,

I have attached a calculation I did early on for the PMC-Eight system for the G11 and EXOS 2 mounts to size the motors back in January 2014. This was used to determine the maximum instantaneous rate that could be handled by the motors without skipping or losing lock with the stepper motor. This calculation does not include the frictional torque which would be added to the inertial torque (load). 


 
--
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!

 

Jim,
 
I wasn't looking at damping effect, I was looking at torque vs moment of inertia (good outline of that in post #14 of that CN link).  Thought it was interesting that these mounts seem not to be very sensitive to payload when guiding well, and that thread sheds some light.  
 
That appears to be exactly what Jerry's stepper motor attachment is about, and the input weights and distances he is using are not small.  So the motor torque started out generous, and then the last firmware upgrade bumped it up a bit.  And then he used the same motors in the iEXOS-100...  
 
[Thanks for the paper, Jerry!]
 
- Bob
 
 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2-IMX224C
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64

Jim McKee
 

Bob and Jerry,
Thank you for the paper and responses.   Very interesting perspective from both of you. I didn't give thought to the increased torque from the 13A firmware update.  Jerry, sounds like by your calculations I am pretty much running to design spec.   That never hurts. 
/Jim
--
Scope:        Orion EON 115mm APO
Mounts
:      ES EXOS2-GT w/ PMC-8
Cameras:   Canon 6D Astro Mod, Canon 7D2, 1D Mk 2, EOS 60D Asto Modified
Lens:
          Canon EF 100-400mm f/4.5-5.6L IS II
Misc:          TELRAD, ZWO ASI120MM Guide Camera, Astromania 60mm Guidescope, Senso Sesto Focus Motor
Software:   EXPLORESTARS IOS & WIN, Stellarium. Backyard EOS, StarTools, APT, DSS
Computer:  Dell Latitude E5450, Windows 10

Mark Christensen
 

Gents,

A longer scope is more likely (not certain) to have oscillation problems, not a dampening effect.
Plus it is more likely (not certain) to act as a sail in breezes. The cross section (diameter X length) matters a lot.
On really breezy nights I can see the difference with my 8 inch f/5.5 Newtonian vs my (equally massive) 8 inch f/4 on a G11.

And if it is outright windy I am always ready to fall back to short to moderate focal length lenses with my EXOS-2GT.

Everything is a trade off and being willing to be flexible helps.

Mark Christensen