Review of TMB optical Monocentric eyepieces

(Brian Tung) wrote in message ...
Phil Wheeler wrote:
What is a "moncentric" EP?

As I recall, a monocentric eyepiece is a three-element, one-group
eyepiece in which every surface has the same center of curvature--hence
the name. If anyone knows differently, please speak up.

THat's what I thought too. The eyepieces reviewed in the article were described
as being thin lenses. There is no way that a cemented triplet of thin lenses can
have a common center of curvature. That was the basis for the freedom from
astigmatism in the original design. I am not sure I would call these modern
eyepieces monocentric...
Clif

Leonard wrote:
Hello Group ,

In the August issue of Sky and Telescope Mr Gary Seronik
does a review of the TMB Optical monocentric eyepiece and in my
reading of it comes to the conclusion that there is very little
difference (or none)in contrast and light scatter between the mono.
and two well known Plossls and a symmetrical . Three high quality
eyepieces to be sure but I would have thought more of a difference
would be seen between them and the mono. Mr Seronik did what appears
to be a very complete review . It comes as no surprise that in an F4.5
newtonian off-axis performance was less than excellent with the mono.
What do you all think about this review after such glowing
reviews from other people over the last few months ?
Leonard

-----------------------------------


This apparantly from Tom Back last week on The TMB Yahoo group.
Hopefully, this will explain what happened ? :-)

---------------------------

--- In , "tmboptical" TMBoptical@a...
wrote:
I don't take this matter lightly, in fact as time passes,
and I reread the review, I only feel incredibly let down.
In a previous post, I said how potentially damaging this
S&T review could be for TMB Optical, not just from the
standpoint of the Super Monos.

cut

I called S&T late today, to talk to the head Senior Editor Dennis
di Cicco, where the test reports get their final go-ahead.

He was not available, so they wanted me to talk to the reviewer
Gary Seronik. And guess what? The test eyepieces were in my
hands (UPS express just handed them to me) and I tested all
four on my double pass autocollimator, using my reference Strehl
.997 TMB 100mm f/8 objective.

Gary seem happy to hear from me, but it soon turned into a
shouting match. But when I brought up the fact that I just
tested the eyepieces, did things ever change. Of the four TMB
Super Mono eyepieces (as you know, I did not test these, they
were taken from a large stack of untested units, figuring what
could be more honest from a manufacturer than to do that -- not
hand pick a set like I'm sure so many do. Markus assured me that
the second run was flawless -- it certainly was not.

The 9mm, and 8mm showed gross astigmatism, the 7mm less, and
the 5mm none! And guess what eyepiece Gary didn't use, or used
very little, the 5mm. He tested defective eyepieces, and this
is a fact. Not only are the three astigmatic, but because of
that, they also do not perform on-axis as well as a TMB Mono
that is free from all defects, because of glass and/or the
optical centering of the three glass elements. Talk about bad
luck!

cut

Thomas Back



__________________________________________________ ______________________

Leonard wrote:
Hello Group ,

In the August issue of Sky and Telescope Mr Gary Seronik
does a review of the TMB Optical monocentric eyepiece and in my
reading of it comes to the conclusion that there is very little
difference (or none)in contrast and light scatter between the mono.
and two well known Plossls and a symmetrical . Three high quality
eyepieces to be sure but I would have thought more of a difference
would be seen between them and the mono. Mr Seronik did what appears
to be a very complete review . It comes as no surprise that in an F4.5
newtonian off-axis performance was less than excellent with the mono.
What do you all think about this review after such glowing
reviews from other people over the last few months ?
Leonard

-----------------------------------


This apparantly from Tom Back last week on The TMB Yahoo group.
Hopefully, this will explain what happened ? :-)

---------------------------

--- In , "tmboptical" TMBoptical@a...
wrote:
I don't take this matter lightly, in fact as time passes,
and I reread the review, I only feel incredibly let down.
In a previous post, I said how potentially damaging this
S&T review could be for TMB Optical, not just from the
standpoint of the Super Monos.

cut

I called S&T late today, to talk to the head Senior Editor Dennis
di Cicco, where the test reports get their final go-ahead.

He was not available, so they wanted me to talk to the reviewer
Gary Seronik. And guess what? The test eyepieces were in my
hands (UPS express just handed them to me) and I tested all
four on my double pass autocollimator, using my reference Strehl
.997 TMB 100mm f/8 objective.

Gary seem happy to hear from me, but it soon turned into a
shouting match. But when I brought up the fact that I just
tested the eyepieces, did things ever change. Of the four TMB
Super Mono eyepieces (as you know, I did not test these, they
were taken from a large stack of untested units, figuring what
could be more honest from a manufacturer than to do that -- not
hand pick a set like I'm sure so many do. Markus assured me that
the second run was flawless -- it certainly was not.

The 9mm, and 8mm showed gross astigmatism, the 7mm less, and
the 5mm none! And guess what eyepiece Gary didn't use, or used
very little, the 5mm. He tested defective eyepieces, and this
is a fact. Not only are the three astigmatic, but because of
that, they also do not perform on-axis as well as a TMB Mono
that is free from all defects, because of glass and/or the
optical centering of the three glass elements. Talk about bad
luck!

cut

Thomas Back



__________________________________________________ ______________________

Hi, I think maybe Mr Seronik may have erroneouly used a term
claiming that the TMB Monos displayed Astigmatism.

More likely, it was Coma that was displayed at the periphery of view,
and not Astigmatism. With a slower F-Ratio Instrument, I would assume
Coma would not be an issue with these. Mark

t (Ratboy99) wrote in message ...
I have four of the TMB Super Monos (2-16's and 2-14's) and I haven't been able
to detect any
astigmatism in them at all. That's using my F8 Tak FS-152 and a Binovuew w/ 2x
barlow. Nice eyepieces actually...
rat
~( );

email: remove 'et' from .com(et) in above email address

Hi, I think maybe Mr Seronik may have erroneouly used a term
claiming that the TMB Monos displayed Astigmatism.

More likely, it was Coma that was displayed at the periphery of view,
and not Astigmatism. With a slower F-Ratio Instrument, I would assume
Coma would not be an issue with these. Mark

t (Ratboy99) wrote in message ...
I have four of the TMB Super Monos (2-16's and 2-14's) and I haven't been able
to detect any
astigmatism in them at all. That's using my F8 Tak FS-152 and a Binovuew w/ 2x
barlow. Nice eyepieces actually...
rat
~( );

email: remove 'et' from .com(et) in above email address

lightshow wrote:
This apparantly from Tom Back last week on The TMB Yahoo group.
Hopefully, this will explain what happened ? :-)

Yes, indeed--if true, it explains quite a bit. That's rather unfortunate
for Tom and his company.

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

lightshow wrote:
This apparantly from Tom Back last week on The TMB Yahoo group.
Hopefully, this will explain what happened ? :-)

Yes, indeed--if true, it explains quite a bit. That's rather unfortunate
for Tom and his company.

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

Tom T. wrote:
I was loaned a couple for review - No astigmatism in the ones I saw,
but they do have a curved field that becomes fairly noticable on fast
scopes.

Since fast scopes often have significantly curved fields themselves, are
you certain you are seeing the field curvature of the eyepiece, instead
of the field curvature of the objective? After all, the field curvature
of the eyepiece shouldn't change from telescope to telescope, it seems
to me.

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

Tom T. wrote:
I was loaned a couple for review - No astigmatism in the ones I saw,
but they do have a curved field that becomes fairly noticable on fast
scopes.

Since fast scopes often have significantly curved fields themselves, are
you certain you are seeing the field curvature of the eyepiece, instead
of the field curvature of the objective? After all, the field curvature
of the eyepiece shouldn't change from telescope to telescope, it seems
to me.

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

On Fri, 25 Jun 2004 15:51:47 +0000 (UTC), (Brian Tung)
wrote:

Tom T. wrote:
I was loaned a couple for review - No astigmatism in the ones I saw,
but they do have a curved field that becomes fairly noticable on fast
scopes.

Since fast scopes often have significantly curved fields themselves, are
you certain you are seeing the field curvature of the eyepiece, instead
of the field curvature of the objective? After all, the field curvature
of the eyepiece shouldn't change from telescope to telescope, it seems
to me.

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

A good point -

The nagler and speers waler zooms, multiple types of orthos and
plossls, as well as several other types of eyepieces pretty much all
showed flatter fields (to the same off axial degree) than the monos on
the same scope(s).

Tom T.