Centering the Newtonian secondary

I decided to work on my XT10 a little more today. I pulled the end ring off
the secondary end, and made a cardboard disk to fit down inside the tube. I
then measured and marked the center and cut out a circle the size of the
retaining screw on the seconary holder. I then pressed the cardboard down
into the tube flush wiith the seconday, and used the thumbscrews at the
spider rod ends to center the secondary holder, positioning the retaining
screw in the center of the cutout. This seemed to work great. A little more
precision and better materials and it might be no sweat to make one that
accounts for offset as well.

Putting the end ring back on I then proceeded to use the Orion Collimation
Tool to get the proper position and rotation under the focuser by adjusting
the center retaining screw and the three secondary alignment screws. The
Orion Collimation Tool is both a cross-hair site tube and cheshire eyepiece
(that is if I have that right g). Maybe I should just say that it is a
sight tube, has cross hairs, and one of those 45 degree angle light thingys
to project a light donut down onto the primary (which is what I'm calling a
cheshire, possibly in ignorance). g

Anway, with the centered position and the correct rotation on the secondary,
I then aligned everything to the center dot on the primary. To do this, I
had to first adjust the secondary to center the primary center mark in the
cross-hairs of the collimation tool. I then adjusted the primary to center
the light donunt in the cross-hairs. When I did this, the donut, and the
cross-hairs were not lined up with the center mark on the primary. So, I had
to readjust the secondary to get the cross-hairs back over the primary
center spot, and then adjust the primary again. It took just those two
iterations. Once complete, this gave me nice concentric rings with both the
primary center mark and the reflected light donut, centered in the shadow of
the secondary, the shadow of the secondary was then centered in the
reflection of the primary, and the reflection of the primary was centered in
the focuser. I then checked everything with the laser, and the beam went
right down the tube, hit the center mark on the primary, and reflected back
in on itself. This is evidenced by the return "dot" not being visible
anywhere on the surface of the laser faceplate when you look down into the
scope at the reflection of the focuser as seen in the primary.

Because my focuser is a little wobbly, I can rock it just enough to see this
dot appear at the edge of the emitter hole on the laser faceplate. That lets
me know that it is, in fact, exactly folded back on itself. An interesting
thing about the laser, and I didn't believe this until this past weekend
when I got into trouble and had a fit, is that the beam can fold back in on
itself like this, and the collimation can be _way_ off. I still don't really
understand exactly why that is, but I suspect it is the result of not having
a properly centered secondary. Previously, my secondary was off-center, and
when star collimated, the return beam of the laser was way off to one side
of the faceplate.

I've got the scope outside now and cooling off. Hopefully my star
collimation is going to be much easier tonight, and that once complete the
laser will agree with the alignment. Venus anyone?

Stephen Paul
Shirley, MA

"Stephen Paul" wrote in message ...

I've got the scope outside now and cooling off. Hopefully my star
collimation is going to be much easier tonight, and that once complete the
laser will agree with the alignment.

Collimation was P-E-R-F-E-C-T. Didn't need to touch a thing when I got
outside.

The seeing was poor and Venus was low and in the soup, but Saturn
looked really good considering the sky conditions. I was able to push
205x and not lose the Cassini. The Encke Minima was visible more often
than not. Polar shading, the main equatorial belt and some shading
in-between was obvious on the planet surface, as was the C ring.

The Trap showed E easily, and F made appearances. A well collimated
scope is a beautiful thing, especially when the seeing is poor. A
night like last night with less than perfect collimation, would have
been more dissapointing.

-Stephen

"Stephen Paul" wrote in message ...

I've got the scope outside now and cooling off. Hopefully my star
collimation is going to be much easier tonight, and that once complete the
laser will agree with the alignment.

Collimation was P-E-R-F-E-C-T. Didn't need to touch a thing when I got
outside.

The seeing was poor and Venus was low and in the soup, but Saturn
looked really good considering the sky conditions. I was able to push
205x and not lose the Cassini. The Encke Minima was visible more often
than not. Polar shading, the main equatorial belt and some shading
in-between was obvious on the planet surface, as was the C ring.

The Trap showed E easily, and F made appearances. A well collimated
scope is a beautiful thing, especially when the seeing is poor. A
night like last night with less than perfect collimation, would have
been more dissapointing.

-Stephen

"Stephen Paul" wrote in message ...

I've got the scope outside now and cooling off. Hopefully my star
collimation is going to be much easier tonight, and that once complete the
laser will agree with the alignment.

Collimation was P-E-R-F-E-C-T. Didn't need to touch a thing when I got
outside.

The seeing was poor and Venus was low and in the soup, but Saturn
looked really good considering the sky conditions. I was able to push
205x and not lose the Cassini. The Encke Minima was visible more often
than not. Polar shading, the main equatorial belt and some shading
in-between was obvious on the planet surface, as was the C ring.

The Trap showed E easily, and F made appearances. A well collimated
scope is a beautiful thing, especially when the seeing is poor. A
night like last night with less than perfect collimation, would have
been more dissapointing.

-Stephen

Last night was strange, it was windy and I expected poor seeing. However, I
watched a jet trail hold together pretty well for a few minutes and decided
it was worth getting the scope out. Saturn was indeed better than expected,
nothing like a couple of nights ago but better than average. It's like the
upper atmosphere was reasonably steady despite a lot of wind on the ground.
I found 200x about the limit in my 6" Mak, a couple of nights ago 300x was
easy.

"Stephen Paul" wrote in message
om...
"Stephen Paul" wrote in message
...

I've got the scope outside now and cooling off. Hopefully my star
collimation is going to be much easier tonight, and that once complete
the
laser will agree with the alignment.

Collimation was P-E-R-F-E-C-T. Didn't need to touch a thing when I got
outside.

The seeing was poor and Venus was low and in the soup, but Saturn
looked really good considering the sky conditions. I was able to push
205x and not lose the Cassini. The Encke Minima was visible more often
than not. Polar shading, the main equatorial belt and some shading
in-between was obvious on the planet surface, as was the C ring.

The Trap showed E easily, and F made appearances. A well collimated
scope is a beautiful thing, especially when the seeing is poor. A
night like last night with less than perfect collimation, would have
been more dissapointing.

-Stephen

Last night was strange, it was windy and I expected poor seeing. However, I
watched a jet trail hold together pretty well for a few minutes and decided
it was worth getting the scope out. Saturn was indeed better than expected,
nothing like a couple of nights ago but better than average. It's like the
upper atmosphere was reasonably steady despite a lot of wind on the ground.
I found 200x about the limit in my 6" Mak, a couple of nights ago 300x was
easy.

"Stephen Paul" wrote in message
om...
"Stephen Paul" wrote in message
...

I've got the scope outside now and cooling off. Hopefully my star
collimation is going to be much easier tonight, and that once complete
the
laser will agree with the alignment.

Collimation was P-E-R-F-E-C-T. Didn't need to touch a thing when I got
outside.

The seeing was poor and Venus was low and in the soup, but Saturn
looked really good considering the sky conditions. I was able to push
205x and not lose the Cassini. The Encke Minima was visible more often
than not. Polar shading, the main equatorial belt and some shading
in-between was obvious on the planet surface, as was the C ring.

The Trap showed E easily, and F made appearances. A well collimated
scope is a beautiful thing, especially when the seeing is poor. A
night like last night with less than perfect collimation, would have
been more dissapointing.

-Stephen