Viewing Report 30th May 2020 – IMT3

5pm – 3:19am

I opened the dome at 5pm. I wanted to try tonight to sort guiding via PHD2 again on the 12″ this evening and then on Esprit120 if enough time allowed.

I changed the PHD2 Profile for 12″ from 6 calibration steps to 12. Performed calibration. Started test guiding in West at +47 Alt. Tried 300 seconds exposure x2 all good

I Slewed back to the East and to Pelican Nebula. Set the Reverse Dec Output After Meridian Flip tick box again ! It then re-calibrated for this side of the mount.

I have also changed the assume Dec orthogonal to the RA axis.

I reran the calibration a number of times until there was no longer an error at the end of the calibration. There was also trailing of stars. Some of the problem seems to have been an incorrect calibration, we need the RA and DEC rates to be very close indeed. Some of ours this evening were 1.5 arcsec difference. The good calibration we finally settled on was 0.5 arcsec difference. The other change was I went out and tightened up the grub screw holding the Lodestar guider on the prism tube that goes into the OAG body, this was loose and I could move the back end of the guider around. This was due to changing the OAG position recently and clearly not tightening the grub screw in enough.

Good calibration
Good guiding after good calibration

I then refocused on Lum and then switched to Ha. This is the image after 300s with a much better HFR of 5.21

Pelican 300s in focus with no trailed stars
Close up of stars from 300s image

When I had a bump in the seeing (assumed) the PHD2 graph looked like this

PHD2 graph bump in seeing

the resulting image of 300s I was in the middle of looked like this :

Image effected by seeing and bump in PHD2 graph

and zoomed in you can see the problem.

Trailed stars due to that seeing bump

Watching Chris Woodhouse’s excellent YouTube video on PHD2 guiding he has also set the min star size to stop it picking up a hot pixel, something we have seen this evening. He has also disabled Star Mass Detection, which stops PHD restarting if it if it thinks another star has been picked even though it may not have, both of these under the brain and guiding tab.

Settings before the change
Minimum star HFD and Star Mass Detection changes

It’s now 2:51am, the sky is brightening but the seeing has settled, the mount is behaving and I am taking 600s Ha images of the Pelican Nebula without any trailing of stars. The odd spike sees a jump up to 3 arcsecs occasionally.

600s Pelican in Ha with good guiding
Close up view of stars at 600s

The guiding graph below shows a really good small RMS below 1 which is key.

PHD good guiding below 1 RMS

So by 3:19am the sky is really getting bright and showing on the SQM as 18.6 and dropping fast. I have stopped guiding and imaging and will now head to bed. The final focus position for Ha was 59925 so I can grab flats tomorrow! I will then take a look at the Esprit120 tomorrow night.