Photo Trip to Locatelli Meadow - Bonny Doon

July 19, 27, 31, 2006

I drove up to Locatelli Meadow on July 18... only to find that after getting all set up, I didn't have the mount plate for the GM8. Argh! The following night I made sure I had everything. It was a quiet weekday night, with classical music on KBOQ keeping me company. I did, however, have my first encounter with a mountain lion... a big one. Lurking in that big oak tree next to our set-up turnout. I poked around during one of the autoguided exposures and heard a growl and saw scat that looked and sounded an awful lot like a lion. Five minutes later, a local resident drove by and stopped and told me about the mountain lion she'd seen right there, not half an hour ago. Hmmmm. So I kept my spare steel channel iron RA axis sleeve close by for the remainder of the evening. My goal was a good long set of exposures of Rho Ophiuchi / Antares and surrounding dark nebulae. Conditions were good; no moon, and clear skies. A tiny bit of murk and the altitude by the time I got set up was already getting low. I think that's why the blue color around Rho Ophiuchi itself didn't come through well. It was HOT this night; temperature was about 80F even at midnight. The CCD could only pull the chip down to -12C, so residual noise is worse than usual.

My most important goal for this evening was to evaluate the filters I'd just bought - the Orion Skyglow 2" filter, and the Orion Ultrablock. The Skyglow lets in a fairly wide range centered on H-beta and O-III in the blue/green, and also the H-alpha area, while blocking the yellow/orange area which is where low and high pressure sodium street lights emit, and also mercury vapor lights in the far green. However, they're advertised as "not for astrophotography", yet with no explanation why. I thought it worth a gamble and bought them; they can always be used visually on campus with our 2" eyepieces in any event.

Conclusions: I'm disappointed with the filters results. The higher noise is to be expected on the filtered images above, but what I didn't expect is the rings of light surrounding each star. Probably secondary reflections off the surfaces of the filters, which apparently have no anti-reflection coating. The filters were loosely placed on my lens; I do not yet have a 48-49mm adapter ring. Perhaps not being dead perpendicular to the incoming light also hurt, but that appears to be a secondary effect. The Trifid Nebula is a good test subject because it has both strong H-alpha emission and also strong blueish reflection nebula on the lower side. This bluish reflection nebula actually came out better on the unfiltered version than in the Ultrablock version, which lets in blue/green light. The reflection light is no doubt more strongly skewed towards shorter wavelengths which are blocked. The Skyglow version looks like it has enhanced contrast in the red H-alpha, but the poor star images are a killer.

July 27: I did another photo night. Skies were a bit darker as fog rolled into Santa Cruz sooner and the marine layer was deeper. It was also a cooler night, allowing the CCD to cool to -25C.

July 31. For one more night during this dark-of-the-moon period I drove up to Locatelli Meadow... and found fog rolling over the pass. This is at 2200 ft elevation, so I retreated to Andy's lot at 2650 ft - highest point on Bonny Doon. My goal was to shoot "the Snake Nebula", but I had such a tough time trying to find the darn thing. I even resorted to pulling up my "dark horse" picture and zooming in and staring at it and the real sky, and I still couldn't get the star patterns right. And it was setting. OK, it's 2:00am by now and I'm NOT sacrificing a night's sleep for nothing. The Eagle Nebula - I thought I could improve on my previous attempt. I got 40 minutes of integration, dozing during each 5min exposure in the back of my RAV4, and listening to KBOQ playing the Beethoven violin concerto and the Chopin Piano Concerto #1. Cool temperatures allowed CCD chip to work at -25C. And, the final shot came out pretty well.