5 June 2005

Observing Location	Parkchester South Condominium oval, The Bronx, NY
Observational Period	1745-1800 EDT
Atmospheric Conditions	Hot. The air smelled wet. About 50% of the sky was covered with building cumulus clouds.
Instruments	Canon 15x50 Image Stabilized binoculars - Charlie
Observing Party	Charlie Ridgway

Target	Sunspots
Constellation	Tau
Category	Solar
Time	5Jun05; 1745 EDT
Comments	While waiting for a cloud to move so I could see the sun observed shades of blue and rust in the brighter cloud tops through the solar filter, 772 772 is two spots. The larger one trails and has a small penumbra surrounding it. 773 In the SE quadrant. It is a small spot connected by a line to the void area around the larger spot which is without a penumbra. 775 In the NE quadrant close to the equator. This group is composed of three spots in two groups. Each group has a void area around it. There appears to be a small void area to the NE of the northern spot. I did not observe a penumbra around any of these spots but I expect that there will be one tomorrow when they have rotated farther from the limb and foreshortening isn't as severe. unnumbered This is a couple of small spots in the NW quadrant.   Groups Spots R Northern Hemisphere 3 6 36 Southern Hemisphere 2 5 25 Total 5 11 61 NOAA Boulder Sunspot Number 78

I had thought about going down to the park again tonight but Clear Sky Clock says transparency is supposed to go from fair to poor between sunset and midnight and I still have to finalize and upload my field drawings from last night. So I sat on a park bench and read for a little while after dinner.

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Last night Peter explained hot to get the mirror out of the primary cage of my CT-100 so tonight when I was finished updating the blog I did that.

I guess I misunderstood Peter because I was expecting to lift the back plate out of the cage with the mirror attached after I removed the three rusted screws from the plate. It seemed a little strange that it would work that way since the screws are centered nearly an inch from the edge of the cage and I couldn't figure a way that they would attach to it and still let me pull the back plate and mirror out of the cage. Now that I have done it I see how it all works and how crude the collimation system is.

When I broke the last screw loose I could feel the mirror begin to sag in the cage and when it came completely loose the mirror dropped free of the back plate. Fortunately I had the coffee can lid over the front of the cage and the cage resting on my thigh so no damage was done.

As you can see from the picture below, the mirror is mounted to an aluminum plate. Peter says it is held in place with double faced tape.

Notice in the picture below that there is a rim of light color around the top of the mirror. That is the aluminum backing plate. The mirror isn't centered on the plate. I don't know how much this off-centeredness will affect collimation.

When installing the mirror in the cage I found that I had to be very careful how it was oriented because the screw holes appear not to be equidistant. So when I first put it in and screwed one screw in place the edge of the mirror or the aluminum plate hit the side of the cage before I could get the other two holes to line up. It wasn't until the third try that I found how it needed to be oriented for all the screws to fit. Now it is marked so I can do it faster next time I take it apart.

The three Allen screws in the back the plate are really a joke. They hardly stick out above the surface of the inside of the plate. Since the plate is only 0.07 of an inch thick that is their maximum travel. To collimate the scope you need to loosen a rusted screw a bit and tighten the Allen screw next to it, and keep repeating this until the image is as closely collimated as you can get it. When you tighten the rusted screws at the end of the procedure everything will be changed so it hardly makes sense to try at all unless the image is just untenable. And when you slide the secondary on the rail to focus the image it will all change anyway.

While I had the scope out I measured the diameter of the secondary mirror to see how much it obstructs the light heading past it to the primary. It is 1.5" across its seminajor axis. Since it is mounted at a 45º angle in the cage I am assuming it presents a nearly circular cross section to the primary. The inside diameter of the secondary cage is 4.92 inches. So the central obstruction is 31.1% of the opening or 35.3% of the primary mirror.