reflection of secondary mirror and secondary mirror holder

When using an Orion Collimating Eyepiece, if the reflection of the
secondary mirror is completely centered in the crosshairs, but the
reflection of the secondary mirror is not totally centered in the
reflection of the secondary mirror holder, is this an issue?

When I look at the secondary mirror holder reflection, I see a glassy
reflection of light on its edge, which makes the reflection of the
secondary mirror look like it is not centered in the reflection of the
secondary mirror holder.

When I cover the secondary mirror holder with my hand, the glassy
reflection of the secondary mirror is obscured and the secondary
mirror looks centered,

Should I ignore the reflection of the secondary mirror holder?

Also, when I put a piece of white paper in the tube covering blocking
the reflection of the primary mirror, the secondary mirror looks more
or less centered in the focusing tube. It is difficult to see if it is
totally centered due to viewing angles.

Comments?

Bruce

brucegooglegroups wrote:
When using an Orion Collimating Eyepiece, if the reflection of the
secondary mirror is completely centered in the crosshairs, but the
reflection of the secondary mirror is not totally centered in the
reflection of the secondary mirror holder, is this an issue?

The reflection of the secondary in the primary need not be perfectly
centered.
What needs to be centered a
1. The diagonal in the focuser drawtube, with the sighting hole at
prime focus.
2. The reflection of the primary mirror in the secondary.


When I look at the secondary mirror holder reflection, I see a glassy
reflection of light on its edge, which makes the reflection of the
secondary mirror look like it is not centered in the reflection of the
secondary mirror holder.

I would be a bit worried about this shallow angle reflection of light
off of the
diagonal holder. I can diminish contrast on bright objects such as
the moon and planets. You might want to put some low profile baffle
in the middle of the reflective surface, not much more than 1 or 2 mm
in height.


When I cover the secondary mirror holder with my hand, the glassy
reflection of the secondary mirror is obscured and the secondary
mirror looks centered,

Should I ignore the reflection of the secondary mirror holder?

No. In a well aligned newtonian, the secondary's reflection in the
primary appears just a bit more in the direction opposite the
focuser. However, really good collimation needs verification that the
optical axis of the primary (reflected in the diagonal) coincides with
the optical axis of the eyepiece.

Two methods are generally recommended:
1. A barlow-ed laser
2. Star-image collimation (which can be done without tools). See:
http://www.piscescs.com/astro/collimat/notools2.html

Good luck,
Larry G.

Also, when I put a piece of white paper in the tube covering blocking
the reflection of the primary mirror, the secondary mirror looks more
or less centered in the focusing tube. It is difficult to see if it is
totally centered due to viewing angles.

Comments?

Bruce

On Jun 12, 10:43 am, LarryG wrote:
brucegooglegroups wrote:
When using an Orion Collimating Eyepiece, if the reflection of the
secondary mirror is completely centered in the crosshairs, but the
reflection of the secondary mirror is not totally centered in the
reflection of the secondary mirror holder, is this an issue?

The reflection of the secondary in the primary need not be perfectly
centered.
What needs to be centered a
1. The diagonal in the focuser drawtube, with the sighting hole at
prime focus.
2. The reflection of the primary mirror in the secondary.



When I look at the secondary mirror holder reflection, I see a glassy
reflection of light on its edge, which makes the reflection of the
secondary mirror look like it is not centered in the reflection of the
secondary mirror holder.

I would be a bit worried about this shallow angle reflection of light
off of the
diagonal holder. I can diminish contrast on bright objects such as
the moon and planets. You might want to put some low profile baffle
in the middle of the reflective surface, not much more than 1 or 2 mm
in height.



When I cover the secondary mirror holder with my hand, the glassy
reflection of the secondary mirror is obscured and the secondary
mirror looks centered,

Should I ignore the reflection of the secondary mirror holder?

No. In a well aligned newtonian, the secondary's reflection in the
primary appears just a bit more in the direction opposite the
focuser. However, really good collimation needs verification that the
optical axis of the primary (reflected in the diagonal) coincides with
the optical axis of the eyepiece.

Two methods are generally recommended:
1. A barlow-ed laser
2. Star-image collimation (which can be done without tools). See:http://www.piscescs.com/astro/collimat/notools2.html

Good luck,
Larry G.



Also, when I put a piece of white paper in the tube covering blocking
the reflection of the primary mirror, the secondary mirror looks more
or less centered in the focusing tube. It is difficult to see if it is
totally centered due to viewing angles.

Comments?

Bruce

Hi Larry,
My star test is like the good results in http://www.piscescs.com/astro/collimat/notools2.html.
The concentric rings are not very clear but clear enough and I did it
last night when there was a little moonlight. So it looks like my
scope is collimated.
Also, the small stars are pinpoints. The brighter stars, are not
pinpoints( like Arcturus) and are slightly elongated. Is there an
issue here?
Bruce

On Jun 13, 8:54*am, brucegooglegroups
wrote:
On Jun 12, 10:43 am, LarryG wrote:



brucegooglegroups wrote:
When using an Orion Collimating Eyepiece, if the reflection of the
secondary mirror is completely centered in the crosshairs, but the
reflection of the secondary mirror is not totally centered in the
reflection of the secondary mirror holder, is this an issue?

The reflection of the secondary in the primary need not be perfectly
centered.
What needs to be centered a
1. The diagonal in the focuser drawtube, with the sighting hole at
prime focus.
2. The reflection of the primary mirror in the secondary.

When I look at the secondary mirror holder reflection, I see a glassy
reflection of light on its edge, which makes the reflection of the
secondary mirror look like it is not centered in the reflection of the
secondary mirror holder.

I would be a bit worried about this shallow angle reflection of light
off of the
diagonal holder. *I can diminish contrast on bright objects such as
the moon and planets. *You might want to put some low profile baffle
in the middle of the reflective surface, not much more than 1 or 2 mm
in height.

When I cover the secondary mirror holder with my hand, the glassy
reflection of the secondary mirror is obscured and the secondary
mirror looks centered,

Should I ignore the reflection of the secondary mirror holder?

No. *In a well aligned newtonian, the secondary's reflection in the
primary appears just a bit more in the direction opposite the
focuser. *However, really good collimation needs verification that the
optical axis of the primary (reflected in the diagonal) coincides with
the optical axis of the eyepiece.

Two methods are generally recommended:
1. A barlow-ed laser
2. Star-image collimation (which can be done without tools). *See:http://www.piscescs.com/astro/collimat/notools2.html

Good luck,
Larry G.

Also, when I put a piece of white paper in the tube covering blocking
the reflection of the primary mirror, the secondary mirror looks more
or less centered in the focusing tube. It is difficult to see if it is
totally centered due to viewing angles.

Comments?

Bruce

Hi Larry,
My star test is like the good results inhttp://www.piscescs.com/astro/collimat/notools2.html.
The concentric rings are not very clear but clear enough and I did it
last night when there was a little moonlight. So it looks like my
scope is collimated.
Also, the small stars are pinpoints. The brighter stars, are not
pinpoints( like Arcturus) and are slightly elongated. Is there an
issue here?
Bruce

Do you have astigmatism. Change the angle that you are viewing through
the eyepiece and see if the elongation rotates with your angle of
view.

On Jun 12, 3:54*pm, brucegooglegroups
wrote:
On Jun 12, 10:43 am, LarryG wrote:



brucegooglegroups wrote:
When using an Orion Collimating Eyepiece, if the reflection of the
secondary mirror is completely centered in the crosshairs, but the
reflection of the secondary mirror is not totally centered in the
reflection of the secondary mirror holder, is this an issue?

The reflection of the secondary in the primary need not be perfectly
centered.
What needs to be centered a
1. The diagonal in the focuser drawtube, with the sighting hole at
prime focus.
2. The reflection of the primary mirror in the secondary.

When I look at the secondary mirror holder reflection, I see a glassy
reflection of light on its edge, which makes the reflection of the
secondary mirror look like it is not centered in the reflection of the
secondary mirror holder.

I would be a bit worried about this shallow angle reflection of light
off of the
diagonal holder. *I can diminish contrast on bright objects such as
the moon and planets. *You might want to put some low profile baffle
in the middle of the reflective surface, not much more than 1 or 2 mm
in height.

When I cover the secondary mirror holder with my hand, the glassy
reflection of the secondary mirror is obscured and the secondary
mirror looks centered,

Should I ignore the reflection of the secondary mirror holder?

No. *In a well aligned newtonian, the secondary's reflection in the
primary appears just a bit more in the direction opposite the
focuser. *However, really good collimation needs verification that the
optical axis of the primary (reflected in the diagonal) coincides with
the optical axis of the eyepiece.

Two methods are generally recommended:
1. A barlow-ed laser
2. Star-image collimation (which can be done without tools). *See:http://www.piscescs.com/astro/collimat/notools2.html

Good luck,
Larry G.


Hi Larry,
My star test is like the good results inhttp://www.piscescs.com/astro/collimat/notools2.html.
The concentric rings are not very clear but clear enough and I did it
last night when there was a little moonlight. So it looks like my
scope is collimated.
Also, the small stars are pinpoints. The brighter stars, are not
pinpoints( like Arcturus) and are slightly elongated. Is there an
issue here?
Bruce

Elongation of bright stars may be due to a number of possible causes:
- astigmatism of the optics
- astigmatism of the observer's eye(s)
- a thermal layer over the primary mirror
- tube currents
- a diagonal that isn't quite optically flat
- coma / astigmatism from slight miscollimation
- bright diffraction spikes
- possibly the reflection from the shiny surface of the diagonal
holder

One quick check of alignment - once you have done a star collimation,
center you scope on a fairly bright star, then rack the eyepiece out
until the shadows of the diagonal and spider are fairly clear in the
bright disc.

If the disc is perfectly round, and the diagonal's shadow is centered
in it, then you primary and secondary alignment are probably OK.

However, if it looks like the outer rim of the bright disc is not
truly circular, or if other shadows intrude on the rim, then it may be
that the primary's light cone is not falling fully on the mirror
portion of the diagonal, and you will need to figure out how to get it
better aligned.

There are tests to detect or eliminate the other possibilities, which
I won't go into here. Others should be able to provide information if
you have any questions.

Good luck,
Larry G.

On Jun 12, 10:24 pm, LarryG wrote:
On Jun 12, 3:54 pm, brucegooglegroups
wrote:



On Jun 12, 10:43 am, LarryG wrote:

brucegooglegroups wrote:
When using an Orion Collimating Eyepiece, if the reflection of the
secondary mirror is completely centered in the crosshairs, but the
reflection of the secondary mirror is not totally centered in the
reflection of the secondary mirror holder, is this an issue?

The reflection of the secondary in the primary need not be perfectly
centered.
What needs to be centered a
1. The diagonal in the focuser drawtube, with the sighting hole at
prime focus.
2. The reflection of the primary mirror in the secondary.

When I look at the secondary mirror holder reflection, I see a glassy
reflection of light on its edge, which makes the reflection of the
secondary mirror look like it is not centered in the reflection of the
secondary mirror holder.

I would be a bit worried about this shallow angle reflection of light
off of the
diagonal holder. I can diminish contrast on bright objects such as
the moon and planets. You might want to put some low profile baffle
in the middle of the reflective surface, not much more than 1 or 2 mm
in height.

When I cover the secondary mirror holder with my hand, the glassy
reflection of the secondary mirror is obscured and the secondary
mirror looks centered,

Should I ignore the reflection of the secondary mirror holder?

No. In a well aligned newtonian, the secondary's reflection in the
primary appears just a bit more in the direction opposite the
focuser. However, really good collimation needs verification that the
optical axis of the primary (reflected in the diagonal) coincides with
the optical axis of the eyepiece.

Two methods are generally recommended:
1. A barlow-ed laser
2. Star-image collimation (which can be done without tools). See:http://www.piscescs.com/astro/collimat/notools2.html

Good luck,
Larry G.

Hi Larry,
My star test is like the good results inhttp://www.piscescs.com/astro/collimat/notools2.html.
The concentric rings are not very clear but clear enough and I did it
last night when there was a little moonlight. So it looks like my
scope is collimated.
Also, the small stars are pinpoints. The brighter stars, are not
pinpoints( like Arcturus) and are slightly elongated. Is there an
issue here?
Bruce

Elongation of bright stars may be due to a number of possible causes:
- astigmatism of the optics
- astigmatism of the observer's eye(s)
- a thermal layer over the primary mirror
- tube currents
- a diagonal that isn't quite optically flat
- coma / astigmatism from slight miscollimation
- bright diffraction spikes
- possibly the reflection from the shiny surface of the diagonal
holder

One quick check of alignment - once you have done a star collimation,
center you scope on a fairly bright star, then rack the eyepiece out
until the shadows of the diagonal and spider are fairly clear in the
bright disc.

If the disc is perfectly round, and the diagonal's shadow is centered
in it, then you primary and secondary alignment are probably OK.

However, if it looks like the outer rim of the bright disc is not
truly circular, or if other shadows intrude on the rim, then it may be
that the primary's light cone is not falling fully on the mirror
portion of the diagonal, and you will need to figure out how to get it
better aligned.

There are tests to detect or eliminate the other possibilities, which
I won't go into here. Others should be able to provide information if
you have any questions.

Good luck,
Larry G.

I do have astigmatism. But I find I can't view with my glasses, the
view is better without glasses.

I have taken the eyepiece out and looked at the star reflection. The
image is perfectly round, with the donut in the center.
Clear Skies.
Bruce