Montebello Ridge and first visual use of Stinger 450 cassegrain

by Richard Crisp

the weather wasn't a slam dunk when I arrived: it was hazy with high clouds and patches of lower ones. But it turned out that they were the kind of clouds that clear away after the sun set.

When I transport the big cass I take the optics out of the frame but leave the trame assembled. So when I set up in the field I just put the frame on the mount and point it up at the sky and then put the primary mirror and baffles in place, add the secondary and its baffle and then collimate the unit.

Collimation took me about 20 minutes yesterday and after the sun set I took a quick check using a bright star out of focus and touched up the secondary tilt tip just a very small amount.

Initially the seeing was not very good but it didn't take long and things got amazingly steady. For example Sirius was burning constant instead of shimmering as it usually does.

Dave Cooper was splitting some close doubles so with his help I swung the Cass over and split the same ones: this time by what seemed to be a pretty big distance.

The scope was delivering amazing views of Orion, M78 and amazingly enough the nebulosity around the brighter stars in Pleiades was visible and appeared bluish to my eyes.

Others including Marek, Dave and Mike (sorry, failed to remember the last name) all saw it too. It was a first for me. Andrew Pierce pointed out the Zodiacal light to us too and it was quite visible. Conditions were actually quite good up there.

Marek suggested I swing the scope over to the m46 and m47 area and the planetary that Pete Santangeli recently snagged in his image was amazingly prominent revealing a doughnut structure with a central star. I also examined M3 later on and it was very nicely resolved and over near M39 was a very faint and distant cluster with an NGC number that resolved nicely instead of being a fuzzy patch.

The Crab nebula was a huge blob but quite prominent against the background. I could not see it but Marek said he could see some of the detail of the nebula. My vision just isn't what it used to be I guess.

The scope performed way better than I had expected showing that is a heck of a visual performer in addition to its design use: imaging.

Marek kept commenting about what is expected from an 18" in terms of light grasp. But coming from the world of imaging I usually think in terms of focal length and focal ratio without considering how visually one can get different FOVs by changing eyepieces. So really it seems that an 18" f/12.6 versus an 18" f/5 seems like there can be little difference since they can be both used at the same magnification by appropriate choice of eyepiece. It just doesn't work that way in imaging as once the focal length and camera are selected the fov is defined. Then the focal ratio determines how long it takes to expose.

It was refreshing to reacquaint myself with visual methods and see first hand how the 18" performs with eyepieces. Mostly I was using a 35mm panoptic, and a 22/17 and 12mm nagler. The best views were with the 35 pano and 22 nag giving 164.5x and 262x respectively. It is very easy to use now that I put that spare AP 2.7" rack and pinion focuser on it. Marek said one other thing that struck a chord with me last night and that was how unique it was to him to use an 18" aperture on a GEM and not have to keep "bumping" the scope to follow the objects.

Mark Brada showed up too, along with Andrew Pierce, Mike, Marek, Dave Cooper and a nice couple that I can't remember the name that said they were new to TAC and observing.

The seeing conditions were good throughout the evening but the wind eventually picked up enough to affect the scope a bit. It also challenged the creature comfort. One other comment about the weather: it was very humid initially but dried up as the seeing improved about an hour after sunset.

I was packed up and driving by 10:45pm roughly.

Posted on sf-bay-tac Mar 19, 2006 08:58:34 PT
Converted by report.pm 1.3 Mar 19, 2006 12:56:55 PT