1. I haven't got my NexDome yet (anticipation is killing me) but I'm looking at how things are dimensioned relative to each other. I saw a PDF schematic off the website that shows the dome centerline apparently where the center of the GEM OTA is pointing to vertical (the meridian) and dimension offset of the pier of like 12". Yet the Installation and User Manual essentially gives the impression that the pier and dome C/L can be identical (no offset for GEM mounts) and you have to have the Center of Rotation of RA and Dec axis dimensioned off the dome C/L.I have a friend who has ordered a NexDome and he insists the schematic diagram is correct.
2. Another question is I have a GEM mount and determining a north/south line is easy using a laser level since the mount is polar aligned and pointing true due North. How do you determine East/West?
If you use a tripod you can indeed move the mount to center the Ra/Dec on all axis.. the issue is more for people who put a permanent pier.. put it dead center in X/Y.
I do all my measurement in mm (I grew up in a metric system country). If you use TheSkyX, you can use any units.. as long as all numbers are in the same units (mm, cm, inch, feet, Angstrom, ..).
Rodolphe, thanks for jumping in. My point was if you have a fixed mounting platform and the RA/DEC is at the sphere center offsets become easy. However doing the math to make that happen is beyond my patiences ability.
I had my CGEM DX Hypertuned and plan on keeping it awhile. However since I’m placing my tripod so the centerline intersects the sphere center my offsets should all be positive and measurable. If in the future I change my mount it would be CEM and the RA/DEC axis would align with the center line. I could theoretically match the RA/DEC axis at the sphere center giving me zero offsets in all directs except for the OTA offset.
Do you measure your offsets in mm or inches?
All offset are in relation to the center of the sphere.
If your dome wall intersect the sphere exactly at its equator and your Ra/Dec axis intersection is on the line then the Z offset is 0. X and Y are also 0 if the Ra/Dec intersection is the center of the equator circle (which would mean your pier is already offset from the center to bring the mount's Ra/Dec intersection to that center).
In my own dome I put the pier dead center and entered the proper offsets in TheSkyX. Offsetting the pier to put your Ra/Dec intersection at the center only works if you never ever ...ever plan to change your mount.
The measurements are somewhat critical as the math using them does a lot of transformations and errors get amplified and result in the slit not properly lining up with the telescope optical axis.
I have a few questions too in narrative form:
1. If the dome center axis in space of the X and Y axis is known and the RA/DEC axis of the GEM mount is positioned there than the N/S E/W offset would be zero, correct? N/S E/W offsets are required in the dome setup of the ASCOM HUB, I believe.
2. Now let's say the Z axis is at the dome wall height (53") and the RA/DEC axis center line up with that, there is no offset?
3. If these are true, then the only other offsets that needs to be determined is the OTA offset from the RA/DEC axis?
I think the NexDome drawing is trying to illustrate placing the centerline of the pier or tripod off the centerline of the dome, so you can place the RA/DEC axis in the dome centerline.
TheSky6 !!! ...
This plugin (and all X2 plugin for any hardware) are only for TheSkyX Pro as there was no plugin system in TheSky6 .. and TheSky6 has been out of development and support for over a decade and was Windows only.
If you haven't check what X2 Plugin are : https://www.bisque.com/wp-content/x2standard/index.html
Rodolphe I have one other question. Is the X2 Plugin compatible with TheSky6 Pro?
So the East/West numbers aren't needed.My intention is to center the NexDome on the pier. I've already measured some of the dimensions. The one I'm missing is the mount center of rotation relative to the dome/pier centerline. I don't have TheSkyX, I have TheSky6, but Maxim DL has observatory control also. I was contemplating using that. I don't know what I'm going to use until I get it built. Thank you...this has been a big help, especially the diagram.
Assuming you mount is properly aligned pointing due nother... What these instructions in the manual means is :
- If the pier is not dead center, what are the offsets in all 4 direction of the mount RA/DEX intersection in relation with the dome center.
- If the pier is centered, you will only need to find a few of the values.
As I use TheSkyX I can show what some of these represent :
So in the above ,the pier is centered in the dome on the horizontal plane but the RA/DEC intersection is above. All positions gave been exaggerated on purpose to show what the values represent.
So Zm represents the offset from the center of the sphere and the plane of the RA/DEC.
If the pier is center, the offset on the X axis (Xm) is zero, and the one on the Y axis (Ym) is positive.
You also need to Xt value which is the distance between the RA/DEC intersection and the optical axis of the telescope.
As said the above is using TheSkyX conventions, but it gives an idea of what values are needed. The side view doesn't show the OTA.. just the RA and DEC part of a GEM mount.
The Installation and User Manual states that the cardinal points need to be located in order to determine how much the mount intersection points are offset from the dome center of rotation and needs to be as accurate as possible. I'm somewhat new to GEMS and have been using a roll off roof for years not a dome. Just trying to find what I have to do to get the dome working with the mount.All this is new to me.
Ok, so .. why are you trying to "locate" east and west ? What re you trying to find out .. I'm not sure I understand the east/est question and how it relates to the pier position (and therefore the OTA) ?
When I aligned things in my dome I too used a laser level to mark north (and then put the home sensor there). This allowed me to do a rough alignement of the mount, then later I did a proper polar alignement.
The pier centrer location is one point I was trying to make to my friend rather than the schematic drawing from the web site that showed the OTA center line aligned with the centerline of the done. My mount is an Orion HDX110 so the OTA height is at or near the height of the walls. My old roll off roof walls are 53" tall. I'll determine true north with the laser mounted on the OTA since the mount is polar aligned.
The question about East/West wasn't about right or left but how to determine if I can locate East and West with the laser level. Should the laser be vertical with the dome center line and be lined up with the mount Center of Rotation?
I put my pier smack in the center and the RA/DEC intersection is about at the level of the dome opening.
I have a Paramoutn MX+ with 2 refractor on top. What's important is to enter the geometry data properly in the software you'll use (I use TheSkyX on Linux in the observatory). So you just enter the 2 offsets (center to RA/DEC intersection and horizontal to RA/DEC intersection) as well as what other data is needed by the software (usually it needs the distance between the RA axis and optical axis of your system to line up the OTA(s) in the slit).
North. South ... if you're in the dome and looking North and you are in the northern hemisphere .. east is on you right and west on your left ... opposite if you are in the southern hemisphere.
Twenty views and no one will answer?