Hi Frank,

I am sorry for not getting you more information sooner. I think my will-power to fight these battles has sagged, but I will do my best to get fired up again. I will redo my test with the new update, and will be sure to record a log.

Thanks for looking at it,

Scott

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Though I promised to record one, I forgot. Fortunately, this behavior is highly repeatable, so I will redo the measurements this weekend, and record a log.

Thanks for your support,

Scott

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5) As measurement 4 made me suspicious of my OTA offset, I include a picture of measuring it. It looks close to 14.5 to 15 inches, or 0.38 m, to me. See picture below. However, INDI seems to work better if I use 0.5 m. Then the dome rotates far enough in the E and W positions to not occlude the scope. Unfortunately, I have not been able to find and E-W offset that will center it. It seems to want a very big number, like 1m, that makes no sense, and only works on one side of the dome.

So what am I doing wrong?

As always, my sincere thanks,

Scott



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4) Next, I repeated this test in the west. Note I changed the meridian setting in ICP to West. In this position, the scope was not occluded, but only just barely. The spreadsheet thought the angle should be -2.6°, INDI called for 341.8°, and I would estimate that it actually needed to be ~339°. Pictures, and spreadsheet below.

I interpret this to suggest that the the length of the OTA offset needs to be bigger, and the pier offset E-W larger as well.

File Attachment:

File Name: DomeSlitWest.xlsx.tar.gz
File Size: 9 KB


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Continued from above:

3) Next, I decided to test the dome positioning at two positions that I think simplify the issues. I first put the scope on the East side of the mount dead flat, looking due north (see figure and picture). I believe this will remove any issues of offsets in pier position in the N-S direction. Thus, the only measurement problems I can have are E-W offsets, Up-Down offsets, and OTA length offsets.

In this position, the spreadsheet says the dome should be at 0.2°, INDI places the dome should be at 10°, and I estimate the dome actually needs to be at about 16° to be centered. About 1/2 of my scope view is occluded by the dome in this position.

The software settings are shown in the attached image. Sorry for the crazy moire patterns.



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Hello all,

First, to fcasarra: Thanks for the spreadsheet! That I could do easily, and the results were interesting.

Here are the new tests from last night. The high level summary: The values calculated in the spreadsheet are different than those from INDI (Server, ICP, AT, etc), and appear to be even less correct than INDI.

Here is a detailed description:

1) I polar aligned the scope as an absolute positional reference.

2) I shown a flashlight through the polar scope port of my CGEM DX. It's wide illumination filled the port, and illuminated a point on the dome that is presumably within 1 degree of north. No amount of flashlight tipping would move the spot (it isn't a laser, it is a broad; see the attached picture named DefiningNorth). I defined the positioning of the dome to be at 0 degrees when the spot was centered on the shutter.

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This looks straightforward! Thanks! I will get going on it this afternoon!

Scott

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Dear Wildi - I think I will start by getting some numbers from the debug side of INDI - if I am still confused, I will go to the work of installing the code you mentioned!

My sincere thanks,

Scott

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Thanks Wildi, it is great to have your help!

I looked up RTS2 - I didn't know about it, and it looks pretty neat. I see that it wants Ubuntu to compile. I am running a late model OS X on a Jurassic era Mac Mini (2010). Is that going to be a problem, or do you think it will work out of the box?

Thanks,

Scott

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Hi Ferran,

Thanks for taking a look. In my previous experiments, all measures were in meters, yet that didn't end up working very well. I am working on redoing the test I described with debugging turned on, so I can send you a more detailed log.

Sincerely,

Scott

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A few more comments:

1) The dome seems centered on the scope when it is vertical and pointing north. So I don't think I have a rotational error exceeding 1 degree or so.

2) I understand that in theory, this calculation is usually unit-less. I am creating hypotheses for the results I am seeing. Looking at the code for the calculation, it looks reasonable, but I can't be sure without working a detailed example.

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Hello Jasem and INDI guru's,

Peter Polakovic got a new version of the INDI Server to me tonight, and indeed, the dome now frequently rotates! Solved - thank you!

However, telescope pointing is off everywhere but the South East quadrant. I suspect something may be wrong with the units in the Dome Parameters. My carefully measured values are here:

Inches Meters
Radius 45 1.14
Width 25 0.64
N -2.75 -0.07
E -0.75 -0.02
Up - 3.75 -0.10
OTA 15 0.38

To test the parameters, I set the scope to pointing due north, and rotated it so the GEM weight bar was flat, with the weights in the East, then later in the West. I set the meridian appropriately for each case. With the scope in the East, the scope optical axis was aligned with the east-side dome slot edge, partially occluding it's view (it looked like my 11" scope could move at least 7" to the West to get it closer to centered). With the scope in the West, the scope top was aligned with the west edge, enabling a view, but was still very close to the dome slot (it looked like it should move 3" towards the East).

This suggested to me that OTA offset was too small (even though it was carefully and easily measured from the intersection of RA and DEC to the optical axis), as well as there being an E-W offset, in the W direction, of about 4". I increased the OTA offset to 0.5m, which resulted in the western side scope being nearly centered in the dome slot, and the eastern side scope position being just inside the east edge of the dome. I don't understand how this could be the case though, as the size of the offset is clearly smaller than 0.5m.

Next I tried offsetting the E-W dome parameters 4" to the east (-0.13m total). The dome didn't move at all with this change. I then tried -0.5m. This led to a small positional change, but not enough to center the scope in the slot. Finally, I tried a -1m change. The dome moved noticeably, but still not far enough. This doesn't make much sense, as a 1m move of the pier in a small 8' dome is huge!

Is it possible that the units are not all in meters? For example, these observations make sense if the Radius and width are in meters, but the N, E, and Up are in centimeters. I don't yet understand the OTA offset value, unless it is from the DEC-RA to the far side/top of the scope. 0.38 to 0.5 made a noticeable difference in dome position, in the right direction, and I think adding a little more would help. It is almost like it needs to be 1.5X to 2X the distance between the RA-DEC intersection and the optical axis.

Does any of this sound like a known issue?

As always, big thanks,

Scott

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