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More Collimation Work, Cloud Shorten Session

Posted: 23 May 2016

Open: Sunday, 22 May 2016, 1826 MST
Temperature: 88°F
Session: 966
Conditions: Mostly clear, breezy

Equipment Used:
12" f/8 LX600 w/StarLock
Wireless AutoStar II handset
2" 24mm UWA eyepiece
1.25" 9.7mm eyepiece
1.25" 15mm eyepiece
Collimation/Focus Mask

D7200 DSLR
iPhone 6s Plus

Clouds were approaching from the southwest so I hoped to at least get a start on improving the collimation of the optics of the 12" LX600 during the session.

As an assist to checking the collimation I would use the Astrozap Astrocap Focusing Mask in its "collimation configuration":


1915 MST: Jupiter was visible to the naked eye high in the sky (if you knew where to look). 1923 MST: sunset. It was still breezy. Took this panoramic photo using the iPhone 6s Plus showing the view from the southeast (left) to the northwest (right), with clouds visible in the south:


1931 MST: LX600 ON, StarLock OFF. Took a quick look at Jupiter, 102X. Three moons were visible.

Slewed to the star Spica to begin the collimation work. Using the mask to view a slightly out-of-focus Spica with the 9.7mm eyepiece (251X) on a visual back I could see that the three dots were not equally spaced. This photo (cropped) made with the D7200 DSLR at prime focus + visual back shows the dots, although the non-equal spacing isn't as apparent:


I then began adjusting the collimation screws (2 out of the 3) to improve the collimation while viewing Spica out-of-focus (without the mask). By 2005 MST, with clouds now at the zenith, the collimation was likely to be as good as I could get with the poor seeing conditions. These DSLR prime focus images (cropped) taken on either side of focus show the diffraction pattern:

photo photo

While the central obstruction black area is nearly entered, there is still some non-concentric circles apparent at the edges.

I then used the Bahtinov Mask configuration to focus Spica. This (cropped) DSLR prime focus shows Spica in focus with the mask:


That's actually the most symmetric diffraction pattern I've seen with the LX600 since I began imaging with it. That gave me some hope that maybe the collimation work was finally done.

2022 MST: clouds were now in much of the sky. 2028 MST: Mars, very bright, was now visible over the hill to the southeast.

I found a mostly clear patch of sky and took this image using a 10 second, ISO 1600, exposure of the star Castor and some fainter stars using the D7200 DSLR at prime focus:


While the image looks pretty good at the image scale shown, the inset shows that faint stars are doubled. That indicates that the collimation is still not quite correct. Rats, more work to do.

2036 MST: with clouds interferring I ended the collimation imaging tests. Viewed Jupiter through brief holes in the clouds, 102X, 163X, and 251X on the star diagonal. The views were actually better than on the previous night, so some improvement in the collimation had been made this session.

2045 MST: checked a satellite image and saw that more cloud cover was approaching from the southwest. It was obvious I would not get any imaging of "Mars at opposition" done this night. 2050 MST: tried to view Mars, 102X, but clouds interferred. Began closing up.

Close: Sunday, 22 May 2016, 2101 MST
Temperature: 67°F
Session Length: 2h 35m
Conditions: Mostly cloudy

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