Meridian Flip - Flop & Flexure compensation factor


Joe Zeglinski
 

Hi,

I have been trying to improve the alignment of my AP-900 for the past couple of summers, using drift align, with no obvious improvement. Seems that if I achieve perfect alignment on one side, and repeat on the other side of the Meridian, there is never a perfect alignment – GOTO’s are always slightly out of the field, for targets on the flip side.

The mount is carrying a 175 lb RC-14.5 truss, and is “feather balanced”, so that Meridian Flips should not be affected by OTA imbalance. The mirror is fixed at the hub, though, with advice from Paul Jones the master optician for Star Instrument (RCOS) mirrors, I have been careful not to overstress the glass hub by tightening the baffle beyond just “finger tight” – though I was tempted to do so. Perhaps “mirror flop” still can’t be ruled out – maybe placing three “soft rubber wedges” around the mirror edge, might be an idea to try. Being a carbon fiber truss tube, the OTA should be structurally rigid. So, I am frustrated with this image shift on Meridian Flips. I’ll still pursue the problem with alignment software.

I would like to see some method of providing a “Compensation Factor” (plus/minus RA & DEC), every time there is a meridian flip. It would be simple to record the delta error in coordinates before a re-aligned RCAL is done on the same target on the flip side. Take a screen shot of the ASCOM control panel coordinate display, before & after adjusting for meridian flip, to record the change in target coordinates before doing the compensating RCAL.

The delta flip/flop correction could be entered as a new option in future Keypad firmware, or in an upcoming ASCOM driver revision. Barring that, maybe somebody can write a TSR program to monitor Ascom Meridian Flips, and the originating pier side, to add or subtract the flip/flop error.

I think this might be an easy alternative to fixing mirrors in their cells, or compensating for tube flexure, even providing for correcting for a slightly misaligned mount. We already have to do this manually, so a Meridian Flip adjustment factor might help automate this task. It certainly would lessen the need to RCAL every time there is a Meridian Flip.

Just a thought,
Joe Z.

[Non-text portions of this message have been removed]


Dean S
 

Hi Joe,

I was having a similar issue with my 1200. I finally tried a T-point model and it is now perfect after a flip. I am pretty sure it is more of an orthogonal issue in my case.

Dean

-----Original Message-----
From: Joseph Zeglinski
Sent: Tuesday, September 03, 2013 12:42 PM
To: ap-gto@...
Subject: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

Hi,

I have been trying to improve the alignment of my AP-900 for the past couple of summers, using drift align, with no obvious improvement. Seems that if I achieve perfect alignment on one side, and repeat on the other side of the Meridian, there is never a perfect alignment – GOTO’s are always slightly out of the field, for targets on the flip side.

The mount is carrying a 175 lb RC-14.5 truss, and is “feather balanced”, so that Meridian Flips should not be affected by OTA imbalance. The mirror is fixed at the hub, though, with advice from Paul Jones the master optician for Star Instrument (RCOS) mirrors, I have been careful not to overstress the glass hub by tightening the baffle beyond just “finger tight” – though I was tempted to do so. Perhaps “mirror flop” still can’t be ruled out – maybe placing three “soft rubber wedges” around the mirror edge, might be an idea to try. Being a carbon fiber truss tube, the OTA should be structurally rigid. So, I am frustrated with this image shift on Meridian Flips. I’ll still pursue the problem with alignment software.

I would like to see some method of providing a “Compensation Factor” (plus/minus RA & DEC), every time there is a meridian flip. It would be simple to record the delta error in coordinates before a re-aligned RCAL is done on the same target on the flip side. Take a screen shot of the ASCOM control panel coordinate display, before & after adjusting for meridian flip, to record the change in target coordinates before doing the compensating RCAL.

The delta flip/flop correction could be entered as a new option in future Keypad firmware, or in an upcoming ASCOM driver revision. Barring that, maybe somebody can write a TSR program to monitor Ascom Meridian Flips, and the originating pier side, to add or subtract the flip/flop error.

I think this might be an easy alternative to fixing mirrors in their cells, or compensating for tube flexure, even providing for correcting for a slightly misaligned mount. We already have to do this manually, so a Meridian Flip adjustment factor might help automate this task. It certainly would lessen the need to RCAL every time there is a Meridian Flip.

Just a thought,
Joe Z.





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observe_m13
 

Sounds to me like a classic case of the scope being slightly non-orthogonal to the mount. TheSkyX with TPoint or MaximDL with MaxPoint (and PinPoint) do what you are asking through the computer run software. APCC will be able to do it too.

The keypad won't. It is standalone and doesn't have modelling software in it.

--- In ap-gto@..., "Joseph Zeglinski" <J.Zeglinski@...> wrote:

Hi,

I have been trying to improve the alignment of my AP-900 for the past couple of summers, using drift align, with no obvious improvement. Seems that if I achieve perfect alignment on one side, and repeat on the other side of the Meridian, there is never a perfect alignment â€" GOTO’s are always slightly out of the field, for targets on the flip side.

The mount is carrying a 175 lb RC-14.5 truss, and is “feather balancedâ€�, so that Meridian Flips should not be affected by OTA imbalance. The mirror is fixed at the hub, though, with advice from Paul Jones the master optician for Star Instrument (RCOS) mirrors, I have been careful not to overstress the glass hub by tightening the baffle beyond just “finger tightâ€� â€" though I was tempted to do so. Perhaps “mirror flopâ€� still can’t be ruled out â€" maybe placing three “soft rubber wedgesâ€� around the mirror edge, might be an idea to try. Being a carbon fiber truss tube, the OTA should be structurally rigid. So, I am frustrated with this image shift on Meridian Flips. I’ll still pursue the problem with alignment software.

I would like to see some method of providing a “Compensation Factor� (plus/minus RA & DEC), every time there is a meridian flip. It would be simple to record the delta error in coordinates before a re-aligned RCAL is done on the same target on the flip side. Take a screen shot of the ASCOM control panel coordinate display, before & after adjusting for meridian flip, to record the change in target coordinates before doing the compensating RCAL.

The delta flip/flop correction could be entered as a new option in future Keypad firmware, or in an upcoming ASCOM driver revision. Barring that, maybe somebody can write a TSR program to monitor Ascom Meridian Flips, and the originating pier side, to add or subtract the flip/flop error.

I think this might be an easy alternative to fixing mirrors in their cells, or compensating for tube flexure, even providing for correcting for a slightly misaligned mount. We already have to do this manually, so a Meridian Flip adjustment factor might help automate this task. It certainly would lessen the need to RCAL every time there is a Meridian Flip.

Just a thought,
Joe Z.



Ram
 

Something that works great for me is a "Solve and Sync" with platesolve
after meridian flip. This takes care of a bunch of the orthogonality issues
as a result of flipping to the other side of the meridian. This typically
takes around 1 minute to execute with pinpoint.

--Ram


On Tue, Sep 3, 2013 at 9:42 AM, Joseph Zeglinski <J.Zeglinski@...>wrote:

**


Hi,

I have been trying to improve the alignment of my AP-900 for the past
couple of summers, using drift align, with no obvious improvement. Seems
that if I achieve perfect alignment on one side, and repeat on the other
side of the Meridian, there is never a perfect alignment GOTOs are
always slightly out of the field, for targets on the flip side.

The mount is carrying a 175 lb RC-14.5 truss, and is feather balanced,
so that Meridian Flips should not be affected by OTA imbalance. The mirror
is fixed at the hub, though, with advice from Paul Jones the master
optician for Star Instrument (RCOS) mirrors, I have been careful not to
overstress the glass hub by tightening the baffle beyond just finger
tight though I was tempted to do so. Perhaps mirror flop still cant
be ruled out maybe placing three soft rubber wedges around the mirror
edge, might be an idea to try. Being a carbon fiber truss tube, the OTA
should be structurally rigid. So, I am frustrated with this image shift on
Meridian Flips. Ill still pursue the problem with alignment software.

I would like to see some method of providing a Compensation Factor
(plus/minus RA & DEC), every time there is a meridian flip. It would be
simple to record the delta error in coordinates before a re-aligned RCAL is
done on the same target on the flip side. Take a screen shot of the ASCOM
control panel coordinate display, before & after adjusting for meridian
flip, to record the change in target coordinates before doing the
compensating RCAL.

The delta flip/flop correction could be entered as a new option in future
Keypad firmware, or in an upcoming ASCOM driver revision. Barring that,
maybe somebody can write a TSR program to monitor Ascom Meridian Flips, and
the originating pier side, to add or subtract the flip/flop error.

I think this might be an easy alternative to fixing mirrors in their
cells, or compensating for tube flexure, even providing for correcting for
a slightly misaligned mount. We already have to do this manually, so a
Meridian Flip adjustment factor might help automate this task. It certainly
would lessen the need to RCAL every time there is a Meridian Flip.

Just a thought,
Joe Z.

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Joe Zeglinski
 

Hi Ram,

Yes, that is basically what I do ... every time the mount changes sides.

Last night I just got tired of this exercise, and figured it would be much easier to have a compensation factor - which I have to apply anyway, with this problem. I was imaging M57 last night, right at the zenith, on both sides of the flip, and realized that with that same target directly overhead, there really shouldn't be a flexure or mirror flop problem, since the OTA and mirror start and end at exactly the same position - mirror resting flat, OTA straight up, neither is stressed or imbalanced. The only change is mount's pier side. Flexure and any mirror flop should have resettled themselves after the 180 degree contortion to get to the other side. If I re-flip, (without a doing a RCAL on the other side), the mount still centres , on the same target back at the original position on the original side of the pier. The reversed translation is perfect, so any mirror flop or flex, is repeatable, and if present, re-adjusts itself without any change.

The only remaining minor suspicion, at the back of my mind, is whether the new DOVELM162 saddle "twists around ever so slightly" around its four attachment screws, during the rotation of the meridian flip. But, I torqued them all tightly, short of stripping the threads in the mount head itself. I have also tightened all other locking bolts and clutches with a hex wrench, and the OTA is perfectly balanced fore & aft, so the mount should be rock solid. The only difference is that the heavy OTA is resting on the plate, then hanging from it on the flip side. But at a near-zenith target, the difference should be minimal.

I, as many others, am eager to finally see the arrival of the APCC.

Joe


Joe Zeglinski
 

Hi Dean,

Thanks for reminding me about a possible "Orthogonality" issue, which I had been discounting so far.
I had been confident in trusting the excellence in machining in all parts of the AP-900, saddle and plate, as well as the solidly built RCOS truss. Perhaps there is still something still out of kilter there. I haven't tried TheSky-X and T-Point yet, but maybe it is time to finally do that ... unless the APCC will soon be available.

Joe


Ray Gralak <groups2@...>
 

Joe,

Last night I just got tired of this exercise, and figured it would be
much easier to have a compensation factor - which I have to apply anyway,
That will likely work well only in a very localized part of the sky.

As others have pointed out, to fix your telescope/camera flexure and orthogonality issues you should consider using
pointing correction software. Again, as others have said, there are a couple of common programs that do this that have
been around for many years: TPoint, and MaxPoint. APCC Pro also does this and can also do tracking rate correction,
which will significantly increase the amount of time you can image an object unguided (or allow longer autoguider
exposure times to compensate for seeing).

Note that pointing correction software will only be as accurate as data input to it so if your scope has random mirror
flop incidents then the resulting pointing correction will not always be as good as it could if there were no mirror
flopping.

well as the solidly built RCOS truss.
That doesn't mean it doesn't flex. It does. I have seen several instances where flexure in a RCOS truss tube has turned
out to be one of major contributors to pointing errors.

-Ray Gralak
Author of Astro-Physics Command Center (APCC)
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma

-Ray Gralak
Author of Astro-Physics Command Center (APCC)
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...] On Behalf Of Joseph Zeglinski
Sent: Tuesday, September 03, 2013 10:56 AM
To: ap-gto@...
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor



Hi Ram,

Yes, that is basically what I do ... every time the mount changes sides.

Last night I just got tired of this exercise, and figured it would be
much easier to have a compensation factor - which I have to apply anyway,
with this problem. I was imaging M57 last night, right at the zenith, on
both sides of the flip, and realized that with that same target directly
overhead, there really shouldn't be a flexure or mirror flop problem, since
the OTA and mirror start and end at exactly the same position - mirror
resting flat, OTA straight up, neither is stressed or imbalanced. The only
change is mount's pier side. Flexure and any mirror flop should have
resettled themselves after the 180 degree contortion to get to the other
side. If I re-flip, (without a doing a RCAL on the other side), the mount
still centres , on the same target back at the original position on the
original side of the pier. The reversed translation is perfect, so any
mirror flop or flex, is repeatable, and if present, re-adjusts itself
without any change.

The only remaining minor suspicion, at the back of my mind, is whether
the new DOVELM162 saddle "twists around ever so slightly" around its four
attachment screws, during the rotation of the meridian flip. But, I torqued
them all tightly, short of stripping the threads in the mount head itself. I
have also tightened all other locking bolts and clutches with a hex wrench,
and the OTA is perfectly balanced fore & aft, so the mount should be rock
solid. The only difference is that the heavy OTA is resting on the plate,
then hanging from it on the flip side. But at a near-zenith target, the
difference should be minimal.

I, as many others, am eager to finally see the arrival of the APCC.

Joe




Joe Zeglinski
 

Hi Rick,

You may be quite right.

Perhaps I, like many, have been avoiding admitting the obvious. I haven't needed the more advanced tools like TSX, but I may have to take that option, if the APCC isn't available before the snow hits.

One thing about "modelling" however. I think it is more relevant for "fixed" position installations, to perfect sky pointing accuracy.
But, for those that have portable setups, having a predefined meridian flip correction factor, to compensate just the mirror flop and flexure errors, might be a good alternative for the additional step of recreating a new model after every setup, which adds orthogonally correction, to the overall solution. For portable systems, having a basic flop/flex correction just might be sufficient.

Thanks,
Joe

-----Original Message-----
From: observe_m13
Sent: Tuesday, September 03, 2013 1:17 PM
To: ap-gto@...
Subject: [ap-gto] Re: Meridian Flip - Flop & Flexure compensation factor

Sounds to me like a classic case of the scope being slightly non-orthogonal to the mount. TheSkyX with TPoint or MaximDL with MaxPoint (and PinPoint) do what you are asking through the computer run software. APCC will be able to do it too.

The keypad won't. It is standalone and doesn't have modelling software in it.


Joe Zeglinski
 

Thanks Ray,

That is interesting indeed. Based on your observations, have you seen as many cases of Truss tube flexure compared to flexure in "solid" carbon tube OTA's? Maybe I should have chosen a different OTA construction.

I had thought that the truss members were solidly fixed/epoxied in their truss joints. However, I do notice that each end of the carbon member is pinned with a tiny (maybe 2-56 thread) grub screw through its truss joints. Perhaps it isn't (also) glued in place, and thus the truss can stretch unequally, back & forth on that tiny pin/screw, inside those supposedly joints. I guess a truss OTA isn't as well fixed in place as a "riveted truss plate & beam" on a bridge construction. Scary !

I'm confident your APCC will easily solve the problem.

Joe

-----Original Message-----
From: Ray Gralak
Sent: Tuesday, September 03, 2013 2:39 PM
To: ap-gto@...
Subject: RE: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

Joe,

[SNIP]

well as the solidly built RCOS truss.
That doesn't mean it doesn't flex. It does. I have seen several instances where flexure in a RCOS truss tube has turned
out to be one of major contributors to pointing errors.


-Ray Gralak
Author of Astro-Physics Command Center (APCC)
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


Jim Jones
 

Joe

Are you really putting a 175 pounds on a AP900 or is that a typo? As I read the specs on the AP 900 it is good for 70 pound payload.

It sounds like you are operating portable. Does the tripod or whatever you are using have the capacity for that load?

Are you solving an image after you do the flip? If you can get a solution, all you have to do is to recal and reslew to the target. Should put you right on. If you are using automation software like ACP or CCDCommander it will do this for you. If you are so far off that you can't get a solution, then you need a model.

There are many sources for error during a meridian flip. That is why modeling software is the ultimate solution.....assuming you don't have a mechanical problem. That is also why a constant fudge factor probably won't work. The error sources will change for different points in the sky. But modeling software might be a bit of a pain if you have to build a new model every night.

Jim Jones

On 9/3/2013 9:42 AM, Joseph Zeglinski wrote:
Hi,

I have been trying to improve the alignment of my AP-900 for the past couple of summers, using drift align, with no obvious improvement. Seems that if I achieve perfect alignment on one side, and repeat on the other side of the Meridian, there is never a perfect alignment – GOTO’s are always slightly out of the field, for targets on the flip side.

The mount is carrying a 175 lb RC-14.5 truss, and is “feather balanced”, so that Meridian Flips should not be affected by OTA imbalance. The mirror is fixed at the hub, though, with advice from Paul Jones the master optician for Star Instrument (RCOS) mirrors, I have been careful not to overstress the glass hub by tightening the baffle beyond just “finger tight” – though I was tempted to do so. Perhaps “mirror flop” still can’t be ruled out – maybe placing three “soft rubber wedges” around the mirror edge, might be an idea to try. Being a carbon fiber truss tube, the OTA should be structurally rigid. So, I am frustrated with this image shift on Meridian Flips. I’ll still pursue the problem with alignment software.

I would like to see some method of providing a “Compensation Factor” (plus/minus RA & DEC), every time there is a meridian flip. It would be simple to record the delta error in coordinates before a re-aligned RCAL is done on the same target on the flip side. Take a screen shot of the ASCOM control panel coordinate display, before & after adjusting for meridian flip, to record the change in target coordinates before doing the compensating RCAL.

The delta flip/flop correction could be entered as a new option in future Keypad firmware, or in an upcoming ASCOM driver revision. Barring that, maybe somebody can write a TSR program to monitor Ascom Meridian Flips, and the originating pier side, to add or subtract the flip/flop error.

I think this might be an easy alternative to fixing mirrors in their cells, or compensating for tube flexure, even providing for correcting for a slightly misaligned mount. We already have to do this manually, so a Meridian Flip adjustment factor might help automate this task. It certainly would lessen the need to RCAL every time there is a Meridian Flip.

Just a thought,
Joe Z.




------------------------------------

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gtoYahoo! Groups Links





W Hilmo
 

Lesser mounts deal with this problem by using multiple alignment stars. For
example, my Celestron mount uses two stars on one side of the meridian to
build the sky model, and then it uses up to 4 stars on the other side of the
meridian to calculate orthogonality error, which it then uses to correct
goto slews. It works well enough that, when doing visual with my C14 and
CGE mount, it puts any target - anywhere in the sky - near the center of my
31 Nagler.



Honestly, though, I have not missed this on my AP mount. When setting up
the mount in a new location, I just use a bubble level with the clutches
released to get the mount into Park 1. Then, I power it up, polar align it,
use the hand controller to go to a bright star and sync.



Once that's done, each night I just turn on the mount, connect the ASCOM
driver and resume from last parked. My automation software slews to the
desired target, syncs and does a second slew. I've got a pretty small field
of view with an ST-10 at 2300mm focal length and I'm using an SCT with the
associated mirror flop. Still, it's never missed the first sync (it takes
about 30 seconds; 20 seconds of exposure and about 10 seconds to solve) and
my target typically ends up within several arc seconds of the center of the
field. It's not uncommon for me to start the software before evening
twilight, leave it unattended, and get my sub exposures the next day before
powering down until the next evening.



I will say that it makes a difference what software plate solve routine that
I use. TheSkyX Pro seems to handle plate solving when slightly off target
better than Pinpoint does. I've got the software configured to use TSX
which gets me the above reliability. If I use Pinpoint, it sometimes takes
several minutes unless I am very close, and I've seen an occasional
incorrect solution.



Like everyone else, though, I am eagerly awaiting APCC Pro.



-Wade







_____

From: ap-gto@... [mailto:ap-gto@...] On Behalf Of
Joseph Zeglinski
Sent: Tuesday, September 03, 2013 11:42 AM
To: ap-gto@...
Subject: [ap-gto] Re: Meridian Flip - Flop & Flexure compensation factor





Hi Rick,

You may be quite right.

Perhaps I, like many, have been avoiding admitting the obvious. I
haven't needed the more advanced tools like TSX, but I may have to take that

option, if the APCC isn't available before the snow hits.

One thing about "modelling" however. I think it is more relevant for
"fixed" position installations, to perfect sky pointing accuracy.
But, for those that have portable setups, having a predefined meridian flip
correction factor, to compensate just the mirror flop and flexure errors,
might be a good alternative for the additional step of recreating a new
model after every setup, which adds orthogonally correction, to the overall
solution. For portable systems, having a basic flop/flex correction just
might be sufficient.

Thanks,
Joe

-----Original Message-----
From: observe_m13
Sent: Tuesday, September 03, 2013 1:17 PM
To: ap-gto@... <mailto:ap-gto%40yahoogroups.com>
Subject: [ap-gto] Re: Meridian Flip - Flop & Flexure compensation factor

Sounds to me like a classic case of the scope being slightly non-orthogonal
to the mount. TheSkyX with TPoint or MaximDL with MaxPoint (and PinPoint) do

what you are asking through the computer run software. APCC will be able to
do it too.

The keypad won't. It is standalone and doesn't have modelling software in
it.


Richard Moore
 

Hi Joe,

When I first got my scope brand new from RCOS, I was surprised that my target was at the edge of the FOV
after a meridian flip. After ruling out mirror movement, I determined the amount of pixels that the target moved.
From knowing the amount of arc seconds per pixel of the camera, I calculated the total amount of arc seconds
that the target moved. Then it just took simple trigonometry to figure out the thickness of a shim to place between
one of the scope rings and the male dovetail plate that came with the scope.

If the target moves outside of the FOV, just start with the target off centered before the meridian flip. Just figure
out how many pixels the target moves using the meridian delay feature. In that way you do not have to wait for
the meridian crossing and trying to find a suitable star.

I too am portable a lot of the time to avoid the light pollution of San Jose, CA, and this solution works well for me.

----- Original Message -----
From: Joseph Zeglinski
To: ap-gto@...
Sent: 9/3/2013 12:04:32
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor



Thanks Ray,

That is interesting indeed. Based on your observations, have you seen as
many cases of Truss tube flexure compared to flexure in "solid" carbon tube
OTA's? Maybe I should have chosen a different OTA construction.

I had thought that the truss members were solidly fixed/epoxied in their
truss joints. However, I do notice that each end of the carbon member is
pinned with a tiny (maybe 2-56 thread) grub screw through its truss joints.
Perhaps it isn't (also) glued in place, and thus the truss can stretch
unequally, back & forth on that tiny pin/screw, inside those supposedly
joints. I guess a truss OTA isn't as well fixed in place as a "riveted truss
plate & beam" on a bridge construction. Scary !

I'm confident your APCC will easily solve the problem.

Joe

-----Original Message-----
From: Ray Gralak
Sent: Tuesday, September 03, 2013 2:39 PM
To: ap-gto@...
Subject: RE: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

Joe,

[SNIP]

well as the solidly built RCOS truss.
That doesn't mean it doesn't flex. It does. I have seen several instances
where flexure in a RCOS truss tube has turned
out to be one of major contributors to pointing errors.

-Ray Gralak
Author of Astro-Physics Command Center (APCC)
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma




[Non-text portions of this message have been removed]


Joe Zeglinski
 

Sorry for that typo Jim,

Yes, I meant 75 lbs., maybe a trifle more. AP mount load limits are always specified conservatively, and the AP-900 works like a charm. I'm using a Losmandy HD pier, for the AP-900 and RC-14, and it is rock solid. Doesn't shake, and the servo motors are response, even with 60 lbs of counterweights (2 x 21 lb. Cassady + AP 18 lb.), including the (added 6.53 lb.) AP 9" shaft add-on. Functions as a permanent pier - year round. I only mentioned "portable users", because they might benefit even more from my suggested "compensation factor" as a starting point on the pier flip side. Of course, further RCALs would be necessary to fine tune the centering to neighboring targets, but at least it would get the mount in the ball park with current target still in FOV.

Likewise, I do centre the target after slew with meridian flip, and issue a RCAL. I realize that it won't be perfect at all sky positions, but surely, if the mount could have a relatively decent position to resume, following the flip, the rest of the targets ( ... on THAT side of the pier), will require only a minimal adjustment and RCAL later. My concern is finding the target I was working on, after a flip. I hate hunting for it every time, since it is not in the field of view - a huge waste of scope time.

Joe


Joe Zeglinski
 

Hi Richard,

You are probably talking about shimming up a guide scope, to compensate for the flexure, on top of your RCOS OTA. I don't have one, yet. The main truss scope integrated D-Plate is bolted into the saddle, so no shim is possible. The target in main scope is outside the FOV after a flip. As Ray suggested, maybe all of the truss members flex during the transition. Don't see how to fix that mechanically. Modeling seems to be the only answer.

Joe


Roland Christen
 

What you have is classic non-orthogonality. The scope optics point slightly different direction from the scope mechanical axis. Although it always looks like a mount problem, it is really simply an inherent offset in the scope itself. You can try shimming the mounting plate, or you can use one of the software programs to compensate for this offset.
 
Rolando 


-----Original Message-----
From: Joseph Zeglinski
To: ap-gto
Sent: Tue, Sep 3, 2013 1:00 pm
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

Hi Ram,

    Yes, that is basically what I do ... every time the mount changes sides.

    Last night I just got tired of this exercise, and figured it would be
much easier to have a compensation factor - which I have to apply anyway,
with this problem. I was imaging M57 last night, right at the zenith, on
both sides of the flip, and realized that with that same target directly
overhead, there really shouldn't be a flexure or mirror flop problem, since
the OTA and mirror start and end at exactly the same position - mirror
resting flat, OTA straight up, neither is stressed or imbalanced. The only
change is mount's pier side. Flexure and any mirror flop should have
resettled themselves after the 180 degree contortion to get to the other
side.  If I re-flip, (without a doing a RCAL on the other side), the mount
still centres , on the same target back at the original position on the
original side of the pier. The reversed translation is perfect, so any
mirror flop or flex, is repeatable, and if present, re-adjusts itself
without any change.

    The only remaining minor suspicion, at the back of my mind, is whether
the new DOVELM162 saddle "twists around ever so slightly" around its four
attachment screws, during the rotation of the meridian flip. But, I torqued
them all tightly, short of stripping the threads in the mount head itself. I
have also tightened all other locking bolts and clutches with a hex wrench,
and the OTA is perfectly balanced fore & aft, so the mount should be rock
solid. The only difference is that the heavy OTA is resting on the plate,
then hanging from it on the flip side. But at a near-zenith target, the
difference should be minimal.

    I, as many others, am eager to finally see the arrival of the APCC.

Joe



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Joe Zeglinski
 

Thanks for the confirmation, Rolando.
 
    Spent all last night using Pempro-2 to adjust the alignment, but as it turned out -  much to my regret - there wasn’t much to tweak to what I had done initially with my original manual drift alignment. The alignment seemed to be pretty decent already. Sky testing clouded out tonight, to see if it made any difference, or if the target comes closer to FOV on both sides of the pier.
 
    As for shimming, I am a little dubious about trying to slip a thin piece of copper under that hefty 75 lb scope. Not much room under the D-plate, or even knowing which end – fore or aft. Are there procedures to determine which way the OTA is tilted in its saddle, and roughly how thick a shim might be needed, and where to place the brass shim? Sure would be a neat feature to add to Pempro, or any other alignment software
 
    The software modeling approach might be the easiest.
 
Joe
 

Sent: Wednesday, September 04, 2013 3:36 PM
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor
 


What you have is classic non-orthogonality. The scope optics point slightly different direction from the scope mechanical axis. Although it always looks like a mount problem, it is really simply an inherent offset in the scope itself. You can try shimming the mounting plate, or you can use one of the software programs to compensate for this offset.
 
Rolando


Richard Moore
 

Hi Joe,

If you decide to use a shim to solve your non-orthogonality, here is the trigonometric formula for the thickness of the shim:

(thickness of the shim) equals (distance between fore and aft connection to the male D plate) times
( cosine( arc seconds that the target moves after the meridian flip ))

The scientific calculator on my computer required me to convert the arc seconds to arc degrees by dividing by 3600.

I then went to the hardware store with my micrometer and measured their brass sheet stock until I found the right combination.

Sketch the geometry of the scope and camera on both sides of the meridian to find whether to shim fore or aft, (or just trial and error),

Good Luck

Richard

----- Original Message -----
From: Joseph Zeglinski
To: ap-gto@...
Sent: 9/4/2013 18:03:29
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor



Thanks for the confirmation, Rolando.

Spent all last night using Pempro-2 to adjust the alignment, but as it turned out - much to my regret - there wasn’t much to tweak to what I had done initially with my original manual drift alignment. The alignment seemed to be pretty decent already. Sky testing clouded out tonight, to see if it made any difference, or if the target comes closer to FOV on both sides of the pier.

As for shimming, I am a little dubious about trying to slip a thin piece of copper under that hefty 75 lb scope. Not much room under the D-plate, or even knowing which end – fore or aft. Are there procedures to determine which way the OTA is tilted in its saddle, and roughly how thick a shim might be needed, and where to place the brass shim? Sure would be a neat feature to add to Pempro, or any other alignment software

The software modeling approach might be the easiest.

Joe

From: chris1011@...
Sent: Wednesday, September 04, 2013 3:36 PM
To: ap-gto@...
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor




What you have is classic non-orthogonality. The scope optics point slightly different direction from the scope mechanical axis. Although it always looks like a mount problem, it is really simply an inherent offset in the scope itself. You can try shimming the mounting plate, or you can use one of the software programs to compensate for this offset.

Rolando




[Non-text portions of this message have been removed]


Roland Christen
 

Remember that 1 degree of orthogonal error in the scope produces two degrees of error on the sky. Example: if the mount is pointing dead straight up and the scope is pointing 1 degree to the east due to mechanical orthogonal error, when the mount flips sides, it will point dead straight up, but now the scope will point 1 degree due west. Total pointing error is 2 degrees (twice the scope mechanical offset).
 
Rolando


-----Original Message-----
From: Richard Moore
To: ap-gto Sent: Thu, Sep 5, 2013 1:47 am
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

Hi Joe,

If you decide to use a shim to solve your non-orthogonality, here is the
trigonometric formula for the thickness of the shim:

(thickness of the shim)  equals  (distance between fore and aft connection to
the male D plate)  times
   ( cosine( arc seconds that the target moves after the meridian flip ))

The scientific calculator on my computer required me to convert the arc seconds
to arc degrees by dividing by 3600.

I then went to the hardware store with my micrometer and measured their brass
sheet stock until I found the right combination.

Sketch the geometry of the scope and camera on both sides of the meridian to
find whether to shim fore or aft, (or just trial and error),

Good Luck

Richard


----- Original Message -----
From: Joseph Zeglinski
To: ap-gto@...
Sent: 9/4/2013 18:03:29
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor



Thanks for the confirmation, Rolando.

    Spent all last night using Pempro-2 to adjust the alignment, but as it
turned out -  much to my regret - there wasn’t much to tweak to what I had done
initially with my original manual drift alignment. The alignment seemed to be
pretty decent already. Sky testing clouded out tonight, to see if it made any
difference, or if the target comes closer to FOV on both sides of the pier.

    As for shimming, I am a little dubious about trying to slip a thin piece of
copper under that hefty 75 lb scope. Not much room under the D-plate, or even
knowing which end – fore or aft. Are there procedures to determine which way the
OTA is tilted in its saddle, and roughly how thick a shim might be needed, and
where to place the brass shim? Sure would be a neat feature to add to Pempro, or
any other alignment software

    The software modeling approach might be the easiest.

Joe

From: chris1011@...
Sent: Wednesday, September 04, 2013 3:36 PM
To: ap-gto@...
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor




What you have is classic non-orthogonality. The scope optics point slightly
different direction from the scope mechanical axis. Although it always looks
like a mount problem, it is really simply an inherent offset in the scope
itself. You can try shimming the mounting plate, or you can use one of the
software programs to compensate for this offset.

Rolando




[Non-text portions of this message have been removed]



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Joe Zeglinski
 

Thanks Richard and Roland,
 
    As I awoke this morning, I thought of a possibly  nifty way of “shimming the scope without using brass shims” – since otherwise, it might be a bit tricky sliding in a brass shim, or shifting it just right under the plate, for each change of OTA you might own.
 
    Seems to me, since it is already there to prevent the OTA from disastrously sliding down the saddle, we could put the typical D-Plate “dead man stop bolt”, to work as an adjustable “micrometer shim-screw”. Typically, this is just a narrow-headed standard 1/4-20 screw, but I use a wide brim one, taken from use on a photographic camera flash bracket, or camera bottom screw. It is just wide enough to fill the width of the “slide notch” machined into D-Plate  saddles – I will have to check the DOVEM16 design to verify. If one would use this type of wide-head bolt, and drill a ring of holes around the periphery, you could use it as a “captains-wheel” (capstan ?) adjuster.
 
    With the OTA specifically balanced over the top of the mount, on Park-2, marginally back off the forward (or aft) saddle clamp screw (depending on parallax error direction), insert a suitable awl or nail into one of the screw edge holes, and tighten or loosen it to raise up or lower one end of the D-Plate, up onto the screw. You need a long awl, since the screw could be somewhat deeper inside the saddle slide notch, depending on your OTA balance point, and thus be  otherwise inaccessible to finger adjustment. Then check the alignment through meridian flips. The target should shift away from the prior ideal alignment on one side, and come equally closer on the flip side. Measure the pixel shift on CCD on each flip. The shim adjustment should be quite precise, after a few just angular twists of the bolt, re-clamping the saddle plate, and rechecking the pointing error shift,  after each marginal change – no trigonometry involved. Finally, redo your mount polar alignment, to set things right, after the saddle plate tilt adjustment.
 
    Using the typical 1/4-20 dead-bolt, a full turn would shim up one end of the D-Plate by 1/20” – drill 8 adjustment holes in its head, each angular adjustment raises one end by 1/160" of an inch (or less) per notch. It might make  a useful AP accessory to the mount saddle product line, if it could have the individual hole positions stamped with numbers, to make it easy keeping track of turns. You might even add a compass circle (disk) as a reference,  double-sided taped under the saddle end area, where the awl/nail in the notch would line up to indicate fractional turns, to get even less than a 1/160 inch shimming height adjustment. Part of the compass disk would be under the saddle, and other half would hang over the forward end until adjustments are completed, then removed.
 
Does this make good sense?
Just a thought,
Joe Z.
 


Richard Moore
 

Hi Joe,

When I awoke this morning, I realized I had made an error in using the cosine function in the shim formula. OOOps!! It should have been the tangent
function. Trig classes too long ago with only occasional use since then. And when I read Rolando's reply about the pointing error being twice the
mechanical error, I realized that, long ago when I calculated my shim thickness, that I had divided the measured shift in arc seconds by two. So the formula should read:

(thickness of the shim) equals (distance between fore and aft connection to the male D plate) times
( tangent (( arc seconds that the target moves after the meridian flip ) divided by 2))

Your idea of using a 1/4-20 screw to raise one end of the male D plate sounds intriguing, especially if you change OTAs frequently.
However, you would have to be careful that there would still be enough of the male D plate for the clamps of the DOVELM162 to get
a firm grip.

Richard

----- Original Message -----
From: Joseph Zeglinski
To: ap-gto@...
Sent: 9/5/2013 07:51:00
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor



Thanks Richard and Roland,

As I awoke this morning, I thought of a possibly nifty way of “shimming the scope without using brass shims” – since otherwise, it might be a bit tricky sliding in a brass shim, or shifting it just right under the plate, for each change of OTA you might own.

Seems to me, since it is already there to prevent the OTA from disastrously sliding down the saddle, we could put the typical D-Plate “dead man stop bolt”, to work as an adjustable “micrometer shim-screw”. Typically, this is just a narrow-headed standard 1/4-20 screw, but I use a wide brim one, taken from use on a photographic camera flash bracket, or camera bottom screw. It is just wide enough to fill the width of the “slide notch” machined into D-Plate saddles – I will have to check the DOVEM16 design to verify. If one would use this type of wide-head bolt, and drill a ring of holes around the periphery, you could use it as a “captains-wheel” (capstan ?) adjuster.

With the OTA specifically balanced over the top of the mount, on Park-2, marginally back off the forward (or aft) saddle clamp screw (depending on parallax error direction), insert a suitable awl or nail into one of the screw edge holes, and tighten or loosen it to raise up or lower one end of the D-Plate, up onto the screw. You need a long awl, since the screw could be somewhat deeper inside the saddle slide notch, depending on your OTA balance point, and thus be otherwise inaccessible to finger adjustment. Then check the alignment through meridian flips. The target should shift away from the prior ideal alignment on one side, and come equally closer on the flip side. Measure the pixel shift on CCD on each flip. The shim adjustment should be quite precise, after a few just angular twists of the bolt, re-clamping the saddle plate, and rechecking the pointing error shift, after each marginal change – no trigonometry involved. Finally, redo your mount polar alignment, to set things right, after the saddle plate tilt adjustment.

Using the typical 1/4-20 dead-bolt, a full turn would shim up one end of the D-Plate by 1/20” – drill 8 adjustment holes in its head, each angular adjustment raises one end by 1/160" of an inch (or less) per notch. It might make a useful AP accessory to the mount saddle product line, if it could have the individual hole positions stamped with numbers, to make it easy keeping track of turns. You might even add a compass circle (disk) as a reference, double-sided taped under the saddle end area, where the awl/nail in the notch would line up to indicate fractional turns, to get even less than a 1/160 inch shimming height adjustment. Part of the compass disk would be under the saddle, and other half would hang over the forward end until adjustments are completed, then removed.

Does this make good sense?
Just a thought,
Joe Z.