Limiting Magnitude in Binoculars

(edz) wrote in message . com...
(Shneor Sherman) wrote in message
22" binoculars vs. a 30" monocular. Testing will be on various DSOs:
limiting magnitude comparison, detail, contrast, etc. Sky condition
will be the same for both scopes, obviously, and good to very good
conditions are expected at that site at that time of the year;
elevation is approximately 4,000 feet with dark skies and little
skyglow, especially after midnight. Will try to obtain the same
magnification set for each scope per object. No attempts will be made
to reduce aperture. I'm not doing the testing, at best, I'll be one of
the observers. But I expect to spend most of my time with my own 22"
(monocular).
Clear skies,
Shneor Sherman

I take it this 22" binoculars is manufactured to diffraction limited
specs, unlike most all other except a few models of binoculars?

edz

Correct, I think they are Swayze optics.

Shneor

(edz) wrote in message . com...
(Shneor Sherman) wrote in message

22" binoculars vs. a 30" monocular. Testing will be on various DSOs:
limiting magnitude comparison, detail, contrast, etc. Sky condition
will be the same for both scopes, obviously, and good to very good
conditions are expected at that site at that time of the year;
elevation is approximately 4,000 feet with dark skies and little
skyglow, especially after midnight. Will try to obtain the same
magnification set for each scope per object. No attempts will be made
to reduce aperture. I'm not doing the testing, at best, I'll be one of
the observers. But I expect to spend most of my time with my own 22"
(monocular).
Clear skies,
Shneor Sherman

This would be the perfect opportunity to attempt capturing all manner
of data.

By keeping magnification constant and masking aperture to various
sizes, you could capture all the data needed to plot an aperture
influence curve. it would keep all other aspects of instrument
performance and quality constant. I can't think of any better way to
get realistic data.

By keeping aperture constant and recording limits at any number of
magnifications, you could plot a magnification influence curve.

The only possible way to get the necessary data to determine influence
of NELM is to repeat the same tests on the same objects at the same
apertures and magnifications on nights of different conditions.
Without that you cannot determine the influence of NELM.

I suspect that this particular instrument is one of superior quality,
diffraction limited, and not in any way comparable to products on the
common binocular market. This is probably a mirror binocular without
some of the light losses common in usual binoculars. Do you think any
results obtained with this instrument would even be relevant to this
discussion? Would the results of such an instrument be better
compared to the diffraction limited specifications of higher quality
telescopes?

No of that makes it any less interesting what results might be
achievable with such an intrument!

thanks
edz

Clearly, this is a mirror binocular. The results will hopefully
demonstrate how much the processing using input from both eyes by the
brain' optical cortex affects visual perception, especially in very
low light conditions - e.g., faint galaxies, Abell clusters, and the
like. That is the major purpose for using binoculars.
The eye's rods are sensitive to a single photon - but the brain
interprets one photon as noise; it takes two for the brain to treat it
as information. This way, each eye will get a photon (as a minima).
Clear skies,
Shneor Sherman

(Tony Flanders) wrote in message


I assume that by 4D, 6D, etc. you mean 4X, 6X, etc per inch of aperture,
i.e. exit pupils of 6mm or 4mm being less optimal than 1mm.

that's correct.

But that's just the problem! No matter how bad the exit pupil of
binoculars may be, it can never be worse than the naked eye. So
if binoculars do poorly for that reason, the naked eye should do
even worse.

Didn't you answer you own supposition here. There is obvious gain
from the binocular over the naked eye, by every attribute. There is
every indication that binoculars show gain. Certainly they do better
than the eye in every respect ( don't interject brightness here, it's
not the point of this analysis). The point is how much gain.

low-power binoculars are the closest possible mimic of naked-eye
observing.

Maybe it would help to think of this in loss rather than gain. if I
can see mag 11.0 stars in 6.0 NELM skies, it may be possible that
because i am observing point sources, I may not lose a full two
magnitudes of point source visibility if skies drop to NELM 4.0.
Certainly that is what was observed in the field. (On the contrary as
far as the brightness issue goes, I would bet if skies dropped from
NELM 6.0 down to 4.0, I would lose sight of most every faint extended
object, potentially indicating more than a 2 mag drop, but I did not
study the brightness of extended objects). It's possible that NELM
does not have a linear affect on point sources. I do not have a
difinitive answer for this. I only know it to be accurately
represented by field data.

edz

(edz) wrote in message . com...

I may not lose a full two magnitudes of point source visibility
if skies drop to [from NELM 6.0 to] NELM 4.0...
It's possible that NELM does not have a linear affect on point sources.

No, no, no, no, no!

It is *not* possible that NELM has a non-linear effect on point sources,
because NELM is *defined* in terms of point sources. You are talking
as though NELM were some objective phenomenon; it is not! NELM *is*
the visibility of point sources, as seen to the naked eye. Or, if you
prefer to think of it that way, through 1x10 binoculars.

Sky brightness and extinction are objective and objectively measurable
phenomena; NELM is not. If you tell me that under sky A you can see
mag 11 stars through your binoculars and mag 6 stars with the unaided
eye, but under sky B you can see mag 10.5 stars through binoculars
and mag 4 stars with the unaided eye, my first question will not be
with respect to the binocular observation but rather with respect
to the naked-eye observation. What is it that prevents you from
seeing mag 5.5 stars with your unaided eye, as theory suggests that
you should?

Were you, perhance, using star clusters to measure the limiting
magnitudes of your binoculars? If so, I have a suggestion about
why your results might be biased.

- Tony Flanders

In article ,
Tony Flanders wrote:

That's exactly why this result is so hard to stomach -- low-power
binoculars are the closest possible mimic of naked-eye observing.

Isn't a 1x Telrad finder an even closer approximation to naked-eye
viewing?

--
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e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

(Tony Flanders) wrote in message m...

Naked Eye Limiting Magnitude does not act linearly on Binocular
Limiting Magnitude. BLM does not increase in step equally as NELM
increases. For the tested range with a variance of 1.5+ mag NELM,
Binocular Limiting Magnitude varied by less than 0.5 mag.

That surprises me immensely, although I cannot claim to have studied
the subject rigorously. I have certainly found the limiting mag in
telescopes to track the NELM modestly well, much better than 0.5 for
1.5, and one would expect binoculars to track it even better. It is
hard to imagine a theoretical explanation for this result.


Tony, I support my claim very well with actual data and reference to
others who have found the same. You may want to do a little rersearch
on this subject to determine if you still disagree. Quotes from my
article;

"A review of the article "Telescopic Limiting Magnitudes" by Bradley
Schaefer"..."referencing Schaeffer's article, he shows clearly that as
NELM drops from 6.0 to 4.0, for magnifications at 100x, telescopic
limiting magnitude would drop only 0.3mag for a 2" lens and 0.7mag for
a 5" lens. As aperture increases, the instrument experiences a
greater affect from NELM. The entire 2.0 mag drop in NELM would not
be realized in the instrument until up in the range of 15" to 20"
aperture."..."Field results indicate, and Schaeffer's article
supports, the optical limiting magnitude does not vary equally as NELM
varies."

Schaefer, Bradley E., 1989, Telescopic Limiting Magnitudes, A.S.P.
102:212-229, February 1990, http://www.astrosociety.org/index.html

I printed out a copy of this article years ago. I could not access it
currently at the ASP site. This article is the subject of great
in-depth discussion by Carlin (his discussion also referenced in my
article). Based on that I'm quite surprised that the non-linearity of
the affect of NELM was not brought up as an very important determinant
in any recent discussions on this BLM subject. I am also quite
surprised that it does not appear to be addressed in predictive
formula. Perhaps it has and I missed it, but I don't think so. I'm
very happy to have my results falling in step with the claims made by
Bradley Schaefer more than 10 years ago!

edz

(Tony Flanders) wrote in message m...

If you tell me that under sky A you can see....
my first question will not be
with respect to the binocular observation but rather with respect
to the naked-eye observation.

Were you, perhance, using star clusters to measure the limiting
magnitudes of your binoculars? If so, I have a suggestion about
why your results might be biased.

- Tony Flanders


Tony, before you go any further with this, you need to take time and
ang go read my work. It should answer all your questions.

edz

Tony, before you go any further with this, you need to take time and
ang go read my work. It should answer all your questions.

edz

Since you opened the discussion here and have been discussing it here I think
it is appropriate for you to address this issue that Tony has raised.

Tony is not the only one interested in knowing your answer.

jon

(Jon Isaacs) wrote in message ...
Tony, before you go any further with this, you need to take time and
ang go read my work. It should answer all your questions.

edz

Since you opened the discussion here and have been discussing it here I think
it is appropriate for you to address this issue that Tony has raised.

Tony is not the only one interested in knowing your answer.

jon

Jon, since I started out by telling Tony I did not have an
explanation, only a hypothesis, I will default to Schaefer's article.
My data seems to clearly support what Schaefer shows and that is
smaller apertures are not as affected by NELM as some might believe.
In fact Schaefer clearly shows the affects of NELM are not linear.

Since aperture in fixed mag binoculars can never be utilized to its
optimum, as it can in variable magnification telescopes, I would
suspect that is even more true and a stronger case in binoculars, not
less.

I don't know if this hypothesis is correct. But as I said I do have
clear and accurate data to support what I'm saying. The affects of
NELM are non-linear in overall outcome of binocular LM performance.

edz

Tony, you have a question about the validity of how I determined MELM.

My target study area was Cr399, the coathanger. The maximum NELM
reached was 5.8. It has only 3 stars that would have been naked eye
visible throughout my weeks of observations. The NE stars are
separated by about 15arcmin. I explain clearly in my work the
difficulty of using these closely grouped stars and the unreliability
of NELM from them. On about half the nights, these three were not
even NE visible.

Other NELM targets were nearby constellations with a variety of star
magnitudes; Sge, Del, Psc, UMi. In every case I tried to confirm NELM
from more than one target location. In every instance at least one of
those locations was either my target or as close as I colud get to my
target.

I included a full written section on the determination of NELM that
should explain my procedure. there were several variables taken into
consideration in the determination of NELM, i.e., integrated
magnitudes.

I think the major difference is thru the galss and not in the
determination of NELM, as I usually had a second observation to
confirm.

edz