Review of TMB optical Monocentric eyepieces

(Bettrel) wrote:
From my personal experience, the review contains nore than a bit of hogwash
Now, understand, I don't have any stake one way or the other and don't really
have an opinion on whether the Mono's are good, bad or indifferent... but isn't
it just a bit funny that S&T, which routinely gets panned by many on here for
their glowing reviews of products is now going to get panned for a negative (to
a degree, of course) review?

AFAIK, (from the yahoo tmb group) two of the eyepieces were found to be
defective (astigmatic) at TMB upon return from S&T.

The eyepieces were sent to S&T from general inventory and purposely not
hand-picked, a commendable act.

Had Thomas Back done otherwise, and had S&T contacted TMB about possible
problems, I am sure that Gary Seronik's findings would have been more in
line with the general concensus.

I have not received my August issue of S&T yet, but this is what has
apparently happened.

I am glad that S&T has adopted a policy of pointing out flaws, a gutsy move.
However, it's always difficult to read between the lines w.r.t.
motive, integrity, and competence.

-Gavin

I think that unfortunately there might have been some sort of inadvertent Q/A
issue with the eyepieces that Mr. Seronik tested.

I know that to be fair, Thomas pulled random samples and intentionally (again,
wanting to be "fair"), did not test them prior to shipping them out.

If it had been me (with my 20/20 hindsight) I would have personally tested the
items before they went out so that I could rest assured that they were at least
representative of the product as it was designed. I would not consider this
necessarily "hand-picking" but rather standard Q/A. This action would have
neutralized the present unfortunate circumstances.

To complicate matters, to my knowledge, when Mr. Seronik found what he thought
was off-axis astigmatism, he made no attempt to contact the manufacturer to ask
him why. This action, also, would have served to neutralize the present
unfortunate circumstances.

So, as it turns out, an unfortunate series of events is now bound to result in
some sort of irreversible consequences for TMB.

You can't really blame either of them, either. It is more a comedy of errors
than anything else.

It is a damned shame, too. The TMB SuperMonos that I own show no astigmatism at
all, I was not able to detect any coma either, and I am a fairly meticulous
observer. (This is using my 6" F8 refractor).

As I understand it, at least for astigmasm, as designed the TMB Super
Monocentrics have less than either Plossls or Orthos.

There is some field curvature in the design that can be focused out when
observing objects at the edge of the field. Since I bought them for Moon and
planets, I do most of my observing with them directly on-axis.

For observing the Moon and Planets, they are equally as good, or even
surprisingly better in some cases, than any of the other eyepieces that I have
the good fortune to own.

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

rat
~( );

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

I think that unfortunately there might have been some sort of inadvertent Q/A
issue with the eyepieces that Mr. Seronik tested.

I know that to be fair, Thomas pulled random samples and intentionally (again,
wanting to be "fair"), did not test them prior to shipping them out.

If it had been me (with my 20/20 hindsight) I would have personally tested the
items before they went out so that I could rest assured that they were at least
representative of the product as it was designed. I would not consider this
necessarily "hand-picking" but rather standard Q/A. This action would have
neutralized the present unfortunate circumstances.

To complicate matters, to my knowledge, when Mr. Seronik found what he thought
was off-axis astigmatism, he made no attempt to contact the manufacturer to ask
him why. This action, also, would have served to neutralize the present
unfortunate circumstances.

So, as it turns out, an unfortunate series of events is now bound to result in
some sort of irreversible consequences for TMB.

You can't really blame either of them, either. It is more a comedy of errors
than anything else.

It is a damned shame, too. The TMB SuperMonos that I own show no astigmatism at
all, I was not able to detect any coma either, and I am a fairly meticulous
observer. (This is using my 6" F8 refractor).

As I understand it, at least for astigmasm, as designed the TMB Super
Monocentrics have less than either Plossls or Orthos.

There is some field curvature in the design that can be focused out when
observing objects at the edge of the field. Since I bought them for Moon and
planets, I do most of my observing with them directly on-axis.

For observing the Moon and Planets, they are equally as good, or even
surprisingly better in some cases, than any of the other eyepieces that I have
the good fortune to own.

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

rat
~( );

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

WayneH wrote:

My understanding is that other instruments were used also, Craig.
Nevertheless, from long years of planetary observing (my prime mover),
I feel qualified to state that the kind of aberration noted
(astigmatism) is not exacerbated by decreased focal lengths. Coma,
certainly yes, but *not* astigmatism. Thus I felt my observations to
be relevant.

Well, it has been my experience that the aberrations that an *eyepiece* alone
introduces into the system tend to get worse at shorter f/ratio systems,
especially astigmatism. For example, there is slight astigmatism near the
edge of the field in the 30mm WideScan III using an f/10 SCT, but put that
same eyepiece into a 100mm f/6 refractor and it becomes very obvious, with the
outer third of the field noticably degraded by it. I once had a 6mm "HM"
eyepiece for my first 2.4 inch refractor (rather narrow field of view), and
while it peformed well in the refractor, putting it on my newly-constructed 8
inch f/7 revealed horrid field curvature. The true test of an eyepiece comes
at the shorter f/ratios, and in that, sometimes units which seem to be
tac-sharp at long f/ratios tend to not be so at the short ones. The fact that
Seronik reported a little astigmatism with the Monocentrics in an 8 inch f/4.5
Newtonian (with the Paracorr, it would be f/5.18) is rather revealing, and I
have little reason to doubt that he reported what he saw. Clear skies to you.

--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

WayneH wrote:

My understanding is that other instruments were used also, Craig.
Nevertheless, from long years of planetary observing (my prime mover),
I feel qualified to state that the kind of aberration noted
(astigmatism) is not exacerbated by decreased focal lengths. Coma,
certainly yes, but *not* astigmatism. Thus I felt my observations to
be relevant.

Well, it has been my experience that the aberrations that an *eyepiece* alone
introduces into the system tend to get worse at shorter f/ratio systems,
especially astigmatism. For example, there is slight astigmatism near the
edge of the field in the 30mm WideScan III using an f/10 SCT, but put that
same eyepiece into a 100mm f/6 refractor and it becomes very obvious, with the
outer third of the field noticably degraded by it. I once had a 6mm "HM"
eyepiece for my first 2.4 inch refractor (rather narrow field of view), and
while it peformed well in the refractor, putting it on my newly-constructed 8
inch f/7 revealed horrid field curvature. The true test of an eyepiece comes
at the shorter f/ratios, and in that, sometimes units which seem to be
tac-sharp at long f/ratios tend to not be so at the short ones. The fact that
Seronik reported a little astigmatism with the Monocentrics in an 8 inch f/4.5
Newtonian (with the Paracorr, it would be f/5.18) is rather revealing, and I
have little reason to doubt that he reported what he saw. Clear skies to you.

--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

I am glad that S&T has adopted a policy of pointing out flaws, a gutsy move.
However, it's always difficult to read between the lines w.r.t.
motive, integrity, and competence.

You know, the more I think about it, I tend to disagree. I think the best thing
that S&T could do with its reviews would be to do everything they can to
**understand** the product that they are reviewing.

This is not Consumer Reports. And understanding optics is not strictly a casual
endeavor.

There is no reason that interviewing and working with the manufacturer on a
review could not be included as part of the review process. This would have
helped to mitigate the situation with TMB, and both the reviewer and the
readers might have come away with a bit more actual understanding of what these
eyepieces are really all about.



rat
~( );

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

I am glad that S&T has adopted a policy of pointing out flaws, a gutsy move.
However, it's always difficult to read between the lines w.r.t.
motive, integrity, and competence.

You know, the more I think about it, I tend to disagree. I think the best thing
that S&T could do with its reviews would be to do everything they can to
**understand** the product that they are reviewing.

This is not Consumer Reports. And understanding optics is not strictly a casual
endeavor.

There is no reason that interviewing and working with the manufacturer on a
review could not be included as part of the review process. This would have
helped to mitigate the situation with TMB, and both the reviewer and the
readers might have come away with a bit more actual understanding of what these
eyepieces are really all about.



rat
~( );

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

(Clif) wrote in message . com...
(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
Clif, It seems that in the article they show a diagram with the lense
arrangement for the old Monocentric design & say the new design has 3
thin elements of the same diameter in a symetrical arrangement. Can
you visualize exactly what they are talking about? I wonder how come
they didn't show the new design? DR

(Clif) wrote in message . com...
(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
Clif, It seems that in the article they show a diagram with the lense
arrangement for the old Monocentric design & say the new design has 3
thin elements of the same diameter in a symetrical arrangement. Can
you visualize exactly what they are talking about? I wonder how come
they didn't show the new design? DR

Ratboy99 wrote:


So, as it turns out, an unfortunate series of events is now bound to result in
some sort of irreversible consequences for TMB.


OTOH -- TMB is getting lots of exposure here. Maybe I am ignorant (not
much of an EP changer) but I had not even heard of his EPs until this
thread.

Phil