Center-dotting

I will soon be center-dotting my 12.5 inch primary which now sports a
brilliant new surface from Spectrum Coatings. In the past, I have always
used a tad of black paint for this job, but I am aware that other options
exist and would be interested in how you did yours (and why). I do not
ever intend to use a laser collimator.




-- Martin R. Howell

Martin wrote:
I do not ever intend to use a laser collimator.


Just Curious - Why not?

Brian

I use a white ring that one would lick and attach to paper that goes in
a 3 ring binder. You can also find white rings that peel and stick.

The reason is that I use a laser to collimate the scope and the whole
in the middle of the white ring allows the laser to reflect back,
increaseing the ease of colimating the scope. In addition, the
white-ness of the ring makes it easy to see in the dark. The size does
not matter since it is in the shadow of the secondary.

On 5 Oct 2005 07:23:34 -0700, wrote:

I use a white ring that one would lick and attach to paper that goes in
a 3 ring binder. You can also find white rings that peel and stick.

The reason is that I use a laser to collimate the scope and the whole
in the middle of the white ring allows the laser to reflect back,
increasing the ease of collimating the scope. In addition, the
white-ness of the ring makes it easy to see in the dark. The size does
not matter since it is in the shadow of the secondary.



I know of this white ring thing and its application for laser collimation.
That is why I stated that I would not be laser collimating (so as to make
the group aware that I have no use for the white ring thing). For me, the
simple combination sight tube and Cheshire eyepiece has produced nice
results. Have you ever used one? Do you suppose the "ring" thing might be
a nice alternative for this device? It just could be that it would.

The last re coater of my mirror affixed a small (maybe 1/2 inch in
diameter) square right in the center of the mirror. Seems it was
constructed of nothing more than black electrical tape. So I was thinking
that maybe a small 3/8" diameter round piece of electrical tape might be
nice.

There are ways to collimate accurately without a center mark at all on the
primary and it would be good to hear from others who employ this technique.


-- Martin R. Howell

I just use a sharpie black marker pen.


--

The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Astronomy Net Online Gift Shop
http://www.cafepress.com/astronomy_net



"Martin" wrote in message
.. .

I will soon be center-dotting my 12.5 inch primary which now sports a
brilliant new surface from Spectrum Coatings. In the past, I have always
used a tad of black paint for this job, but I am aware that other options
exist and would be interested in how you did yours (and why). I do not
ever intend to use a laser collimator.




-- Martin R. Howell

"Martin" wrote in message
...
For me, the simple combination sight tube and Cheshire eyepiece has
produced nice results. Have you ever used one? Do you suppose the "ring"
thing might be a nice alternative for this device? It just could be that
it would.


-- Martin R. Howell

My mirror came with a white ring thing and it worked well with my
combination tube. After recoating, by Spectrum also, I used a permanent
marker to center dot. No great difference except the black square mark is
easier to see in the combo tube when collimating after dark.

Peace,
Jon

would be interested in how you did yours (and why).

The usual white ring for me, I find concentric circles easier to
centre roughly by eye with a simple sight tube prior to using a laser.
It's usually right first time when tried on a star diffraction disc.
jc

wrote in message
ups.com...

Martin wrote:
I do not ever intend to use a laser collimator.


Just Curious - Why not?


I only used the laser to aim the secondary as the second step of
collimation. Positioning of the secondary (first step) and adjusting of the
primary (final step) are easily done with a site tube/cheshire eyepiece
under light, with a final tweak of the primary using a star under dark of
night.

In fact, I once went on a tirade and posted a rant against the Newt design
here on SAA, simply because I struggled with the hardest part of the
process, getting the secondary positioned properly. Once you master that
with the site tube, the rest becomes easier over time using the cheshire.
Soon after you have a $60 dollar laser that goes largely unused, except when
the secondary is out of alignment.

It's s great tool for people who build Newts, but is completely unnecessary
for Newts that are fully assembled, with an already properly positioned
secondary.

How's that? I'm not Martin, but I stayed at a Holiday Inn Express....
:-)

This is how I did it: http://home.wanadoo.nl/jhm.vangastel/Astronomy/dot.htm
If necessary, the dot can easily be removed or replaced.

--
Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/


"Martin" schreef in bericht
.. .

I will soon be center-dotting my 12.5 inch primary which now sports a
brilliant new surface from Spectrum Coatings. In the past, I have always
used a tad of black paint for this job, but I am aware that other options
exist and would be interested in how you did yours (and why). I do not
ever intend to use a laser collimator.




-- Martin R. Howell

On Wed, 5 Oct 2005 13:38:39 -0400, Stephen Paul wrote:

wrote in message
ups.com...

Martin wrote:
I do not ever intend to use a laser collimator.


Just Curious - Why not?

It's s great tool for people who build Newts, but is completely unnecessary
for Newts that are fully assembled, with an already properly positioned
secondary.


Thanks for saving me some finger action on the keyboard, Steven. Well put.


-- Martin R. Howell