TMB star test

http://www.tmboptical.com/itemsGrid.asp?cat_id=31


This is a fine method for star testing. I just need all the conditions for
seeing which is a
lesson in waiting in itself. Cloud, crap and light rules the night!

"OncoBilly" wrote in message news:v%9Ac.49285$eA.20615@clgrps13...
http://www.tmboptical.com/itemsGrid.asp?cat_id=31


This is a fine method for star testing. I just need all the conditions for
seeing which is a
lesson in waiting in itself. Cloud, crap and light rules the night!

Raise you right hand and say: "I do solemnly swear I have NEVER seen
a perfect star test in ANY telescope, no matter what the mfg's may claim."
But some have come very close.

Tom Back's description of the test is one of the most lucid I've seen.
The only things to ad would be:
-Make sure YOU have no eye-based astigmatism prior to doing the test and
make sure if you use a mirror diagonal that it's a top notch one, as some
have poor mirrors and or non-right angle alignment of the mirror.
Also, if you don't use a highly corrected across the field type eyepiece like
a Nagler, be sure the star is dead centre as edge aberrations in orthos
or Plossls can cause problems.
-Rich

"OncoBilly" wrote in message news:v%9Ac.49285$eA.20615@clgrps13...
http://www.tmboptical.com/itemsGrid.asp?cat_id=31


This is a fine method for star testing. I just need all the conditions for
seeing which is a
lesson in waiting in itself. Cloud, crap and light rules the night!

Raise you right hand and say: "I do solemnly swear I have NEVER seen
a perfect star test in ANY telescope, no matter what the mfg's may claim."
But some have come very close.

Tom Back's description of the test is one of the most lucid I've seen.
The only things to ad would be:
-Make sure YOU have no eye-based astigmatism prior to doing the test and
make sure if you use a mirror diagonal that it's a top notch one, as some
have poor mirrors and or non-right angle alignment of the mirror.
Also, if you don't use a highly corrected across the field type eyepiece like
a Nagler, be sure the star is dead centre as edge aberrations in orthos
or Plossls can cause problems.
-Rich

Raise you right hand and say: "I do solemnly swear I have NEVER seen
a perfect star test in ANY telescope, no matter what the mfg's may claim."
But some have come very close.

Tom Back's description of the test is one of the most lucid I've seen.
The only things to ad would be:
-Make sure YOU have no eye-based astigmatism prior to doing the test and
make sure if you use a mirror diagonal that it's a top notch one, as some
have poor mirrors and or non-right angle alignment of the mirror.
Also, if you don't use a highly corrected across the field type eyepiece
like
a Nagler, be sure the star is dead centre as edge aberrations in orthos
or Plossls can cause problems.

My eyesight is about 90% or 95%. I see small light spikes when I look up at
the stars without my
eyeglasses. If I don't use eyeglasses when I look through an EP, am I
seeing spikes too?

TMB makes clear that barlows and diagonals should not be used BTW.

Raise you right hand and say: "I do solemnly swear I have NEVER seen
a perfect star test in ANY telescope, no matter what the mfg's may claim."
But some have come very close.

Tom Back's description of the test is one of the most lucid I've seen.
The only things to ad would be:
-Make sure YOU have no eye-based astigmatism prior to doing the test and
make sure if you use a mirror diagonal that it's a top notch one, as some
have poor mirrors and or non-right angle alignment of the mirror.
Also, if you don't use a highly corrected across the field type eyepiece
like
a Nagler, be sure the star is dead centre as edge aberrations in orthos
or Plossls can cause problems.

My eyesight is about 90% or 95%. I see small light spikes when I look up at
the stars without my
eyeglasses. If I don't use eyeglasses when I look through an EP, am I
seeing spikes too?

TMB makes clear that barlows and diagonals should not be used BTW.

My eyesight is about 90% or 95%. I see small light spikes when I look
up at the stars without my eyeglasses. If I don't use eyeglasses when
I look through an EP, am I seeing spikes too?

I can't say if you're seeing spikes. However, at high powers, the exit
pupil is small, which means you use a smaller portion of your lens and
cornea. This in turn decreases the effect of astigmatism. That's one
reason it is recommended that you use high power when performing a star
test. (Another, of course, is that it makes the pattern easier to see.)
Unless your astimatism is particularly severe, just using high power
(around 40x per inch of aperture, say) should suffice.

TMB makes clear that barlows and diagonals should not be used BTW.

I agree. Sometimes people get confused because of advice that they can
be used during *collimation*, which is a separate activity that uses
some of the same techniques.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

My eyesight is about 90% or 95%. I see small light spikes when I look
up at the stars without my eyeglasses. If I don't use eyeglasses when
I look through an EP, am I seeing spikes too?

I can't say if you're seeing spikes. However, at high powers, the exit
pupil is small, which means you use a smaller portion of your lens and
cornea. This in turn decreases the effect of astigmatism. That's one
reason it is recommended that you use high power when performing a star
test. (Another, of course, is that it makes the pattern easier to see.)
Unless your astimatism is particularly severe, just using high power
(around 40x per inch of aperture, say) should suffice.

TMB makes clear that barlows and diagonals should not be used BTW.

I agree. Sometimes people get confused because of advice that they can
be used during *collimation*, which is a separate activity that uses
some of the same techniques.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

"OncoBilly" wrote in message news:RpkAc.3$K53.1@edtnps89...
Raise you right hand and say: "I do solemnly swear I have NEVER seen
a perfect star test in ANY telescope, no matter what the mfg's may claim."
But some have come very close.

Tom Back's description of the test is one of the most lucid I've seen.
The only things to ad would be:
-Make sure YOU have no eye-based astigmatism prior to doing the test and
make sure if you use a mirror diagonal that it's a top notch one, as some
have poor mirrors and or non-right angle alignment of the mirror.
Also, if you don't use a highly corrected across the field type eyepiece
like
a Nagler, be sure the star is dead centre as edge aberrations in orthos
or Plossls can cause problems.

My eyesight is about 90% or 95%. I see small light spikes when I look up at
the stars without my
eyeglasses. If I don't use eyeglasses when I look through an EP, am I
seeing spikes too?

TMB makes clear that barlows and diagonals should not be used BTW.

A good mirror diagonal (TeleVue, AP) shouldn't effect a star test,
but a barlow might make the test less accurate by eye owing to it's
pseudo-increasing of the focal ratio. Though I've never seen a barlow
turn an f5 scope into an "f10" as far as performance, it can modify
the image to a degree.
-Rich

"OncoBilly" wrote in message news:RpkAc.3$K53.1@edtnps89...
Raise you right hand and say: "I do solemnly swear I have NEVER seen
a perfect star test in ANY telescope, no matter what the mfg's may claim."
But some have come very close.

Tom Back's description of the test is one of the most lucid I've seen.
The only things to ad would be:
-Make sure YOU have no eye-based astigmatism prior to doing the test and
make sure if you use a mirror diagonal that it's a top notch one, as some
have poor mirrors and or non-right angle alignment of the mirror.
Also, if you don't use a highly corrected across the field type eyepiece
like
a Nagler, be sure the star is dead centre as edge aberrations in orthos
or Plossls can cause problems.

My eyesight is about 90% or 95%. I see small light spikes when I look up at
the stars without my
eyeglasses. If I don't use eyeglasses when I look through an EP, am I
seeing spikes too?

TMB makes clear that barlows and diagonals should not be used BTW.

A good mirror diagonal (TeleVue, AP) shouldn't effect a star test,
but a barlow might make the test less accurate by eye owing to it's
pseudo-increasing of the focal ratio. Though I've never seen a barlow
turn an f5 scope into an "f10" as far as performance, it can modify
the image to a degree.
-Rich