Working in the observatory - general
This section is mainly to add more general notes relating to observatory work.
Reminders
- Take the phone so that the dome can be operated
- Connect the camera to use. Usually one of the two Starlight Xpress cameras according to whether I want a large or smaller field of view. For the moon I normally choose the ZWO. That is black and white and I prefer the black and white images of the moon. Rebalance the scope if moving from deep sky to lunar or vice versa.
- Set date and time on scope mount – Best was it to launch “Carte du Ciel” which is planetarium software. Use the interface to connect it to the scope. Then click on set-time and date. This passes the date and time information from the computer to the mount and is picked up by the mount handset.
- Use the Starlight Xpress software to check the filter wheel, Lodestar and camera are connected.
- Put on the Bahtinov mask.
- Use the handset to choose 2 star align. Although the mount is supposed to remember from one time to the next, there seems to be accurate “go to” function by doing an align each time. I centre the first star and then use the focuser to focus that. Then align on the second star. For each star alignment I also use “sync” on Carte du Ciel to synchronise that with the mount.
- Take off the Bahtinov mask. Now ready to start.
Resolving power and pixel size of cameras
- The resolving power of a 305mm aperture scope theoretically is wavelength/aperture.
- For the ODK12 this comes out to 1.8×10^-6 radians – taking a central wavelength of 550nm.
- When this is converted to degrees it comes to 0.4 arc seconds (“).
- With average seeing only at Coppice Farm the effective resolution is likely to be 2 or 3 times larger – say at best 0.8″.
- If we stick to radians the likely best resolution is 2×1.8.10^-6 radians. Multiplying this angle by the focal length gives the distance on the photographic sensor corresponding to this resolution. This distance is 2040 x 3.6 x 10^-6 mm = 7344 x 10^-6mm = 7.344 μm. More likely, taking the 3 figure for seeing, this is 11.8 μm.
This is the chart for the various cameras:
| Camera | Colour/Mono | Horz Px | Vert px | Px Sz (μm) | Horz Sz (mm) | Vert Sz (mm) | Resolution (“/px) | Horz fov( ‘) | Vert fov (‘) | Download time (s) |
| ZWO ASI 120 | Mono | 1280 | 960 | 3.75 | 4.80 | 3.60 | 0.38 | 8.10 | 6.10 | 0.03 |
| ZWO ASI 174 | Mono | 1936 | 1216 | 5.86 | 11.3 | 7.10 | 0.59 | 19.12 | 12.01 | 0.03 |
| Atik Infinity | Colour | 1392 | 1040 | 6.45 | 9.00 | 6.70 | 0.65 | 15.00 | 11.30 | 0.50 |
| Starlight Xpress H694 | Mono | 2750 | 2200 | 4.54 | 12.50 | 10.00 | 0.46 | 21.04 | 16.83 | 3.50 |
| Starlight Xpress Trius 35 | Mono | 4032 | 2688 | 9.00 | 36.30 | 24.20 | 0.91 | 61.00 | 41.00 | 7.00 |
| Starlight Xpress Lodestar | Mono | 752 | 580 | 8.50 | 6.47 | 4.81 | 0.83 | 10.39 | 8.01 | 0.10 |
The above figures for resolution and field of view are for the use with Orion Optics ODK 12 which has a focal length of 2040mm.
Fields of View
(a) Deep Sky
(b) Lunar
ASI 120 ASI 174
Best fov calculator https://www.skyatnightmagazine.com/astronomy-field-view-calculator/
Polar Alignment
- 12/12/20 Did a polar align and adjusted the RA and DEC. (use ALIGNMENT/POLAR ALIGNMENT). Repeated twice with two star align to get the errors small. Then did a three star align and did a check that it reset the cone error.
PEC
- 12/12/20 Tried to do a PEC using PHD to autoguide. (UTILITY FUNCTION/PEC Training). The documentation says this is OK with the EQ8. But PHD just refused to co-operate. Read later that Autoguiding should go for at least a minute before starting PEC. Will make sure to remember this and try again.
Dome and Rotation
- Battery charged 13/12/20
To establish remote PC access.
- Switch on and boot up Observatory computer.
- Switch on the motor for dome control.
- On the remote machine:
- Click in “type here to search” and select “remote desktop connection”
- From the dialog box select “connect”
- This gives remote access to the whole of the observatory machine.
To access the dome rotation from computer.
- With access to the observatory computer click in “type here to search” and select “bluetooth and other device settings”
- If HC-06_23 is NOT in the list click “add bluetooth or other device” and select “bluetooth” – wait
- Select HC-06-23 from the list and enter the pin “1234”
- Select “done” when it says your device is ready to go.
- To rotate in the star rotation direction type “1” and return. The motor starts
- To stop type “2” and return and to rotate the other direction type “3” and return.
To operate the dome motor from phone.
- Select “serial bluetooth terminal” and then devices”. Select HC-06-23. Best to give time to settle first, otherwise may need more than one go to connect.
- From the start menu select “bluetooth serial terminal” and then “connect”.
- To rotate in the star rotation direction type “1” and return. The motor starts
- To stop type “2” and return and to rotate the other direction type “3” and return.
General Wrinkles
To disable touch screen on Lenovo. Use remote access from Dell to get in and do the following
- Type “device manager” in search and select it
- Expand Human Interface Devices
- Right click on “HD compliant touch screen”
- Select disable device