Limiting Magnitude in Binoculars

(edz) wrote in message . com...

Based on testing eight binoculars on many different nights
representing a range of conditions, this is some of what I found:

Binocular Limiting Magnitudes for a given size aperture are
significantly less, nearly one full magnitude lower, than a scope of
equal aperture.

Yes, certainly. I would have thought that the difference would be
more than one magnitude. Magnification helps an awful lot, especially
moving from ultra-large exit pupils like 5mm or 7mm down to respectable
exit pupils like 1mm or 2mm.

Two-eyed viewing vs. one-eyed viewing contributes only a small
fractional gain in magnitude.

Yes, that is my experience too. But small is not nothing, and
also the effect may be greater for diffuse objects than for stars.

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.

When binocular magnification and binocular aperture are each tested
separately, by incremental changes in magnification and aperture, it
is found for each equal increment that magnification has approximately
three to four times the influence as aperture on increases in limiting
magnitude.

Again, this surprises me greatly, although I suppose it might depend
what range of mag and aperture you tested. I am generally very
sceptical about the results that you report, but I eagerly await
the details.

- Tony Flanders

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

The views through my 25x100 Burgess Binos are a drasmatic improvement
over the views through my 26x70 Kronos. I thing the purported
relationship between aperture and magnification relative to limiting
magnitude is non-linear, and as aperture increases, it assumes greater
significance.

None of the available formula provided by Sidwick, Schaefer or Carlin
would support that. Nor does the results of my testing. All predict
linear gain with incremental increase.

But then again, some of what I'm saying is not supported by existing
formula either!

As most of the relationship has been established with
relatively small aperture binoculars, the existing formula makes sense
over that restricted range.

35mm to 80mm is not necessarily a small range. It might be considered
as such if you have the following at your disposal.


Next month, if the weather cooperates, comparisons by a number of
experienced observers will be done to measure the effectiveness of 22"
binoculars versus a 30". This is scheduled for October 25, and I
expect to report on the results within a couple of days of the event.

22inch? and 30 inch? binoculars??? What will you test on. Will you
attempt masking tests to incrementally reduce aperture and observe
effect? Will you attempt numerous magnifications at the same aperture
and record differences?

AAnd will you be able to test same magnifications and apertures on
several occasions of differing sky conditions? That should provide an
interesting set of data. I would imagine you could vary
magnifications all the way from minimum to optimum without varying
aperture. That should either support or disput what I'm stating.

edz

(Tony Flanders) wrote in message

Binocular Limiting Magnitudes for a given size aperture are
significantly less, nearly one full magnitude lower, than a scope of
equal aperture.

Yes, certainly. I would have thought that the difference would be
more than one magnitude. Magnification helps an awful lot, especially
moving from ultra-large exit pupils like 5mm or 7mm down to respectable
exit pupils like 1mm or 2mm.

The results of this test simply show support for what Sidgwick stated
and what Schaefer showed us ten+ years ago in his graphic
representation. Increases in magnification provide for significantly
better results in a given aperture.

Two-eyed viewing vs. one-eyed viewing contributes only a small
fractional gain in magnitude.

Yes, that is my experience too. But small is not nothing, and
also the effect may be greater for diffuse objects than for stars.

Barry Simon and I have both performed several tests to try and put a
value on this. I agree, there would appear to be more improvement in
brightness than in magnitude limit.


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.

This was a difficult measurement. I felt that NELM determination (at
lower values i.e., 4.0, 4.2, 4.5, but not at higher 5.6, 5.8, 6.0) was
so unreliable that I reported a more conservative variance. My
notebooks show wider variances than I reported here. I reduced my
spreads of NELM and increased my variance of LM. This has the affect
of making the overall differences even smaller.

I have no theoretical explanation either, only actual field data to
support it. But I propose this; What if the binoculars, operating at
4D to 6D, and not at optimum of 24D to 30D, are operating so far below
optimum they could never realize the full potential of not only the
aperture but also because they do not utilize the full potential of
the aperture they also do not realize the full affects of NELM.


When binocular magnification and binocular aperture are each tested
separately, by incremental changes in magnification and aperture, it
is found for each equal increment that magnification has approximately
three to four times the influence as aperture on increases in limiting
magnitude.

Again, this surprises me greatly, although I suppose it might depend
what range of mag and aperture you tested.

I believe this can be explained entirely by the fact that operating at
4D to 6D, and not at optimum of 24D to 30D, they are operating (with
the exception of brightness) so far below optimum they could never
realize the full potential of the aperture. Aperture is so
underutilized that there is so much more potential for improvement
from magnification increases. When the two are isolated from each
other it seems to become readily apparent. This is the third time in
the past 18 months I have tested and published similar results. It is
the first time I have measured the limiting magnitudes to put a real
value on it.


I am generally very
sceptical about the results that you report, but I eagerly await
the details.

- Tony Flanders

I hope you find the documentation supports the claim.

edz

Some distinction should be made in this thread regarding the effect of aperature on the limiting magnitude of stellar point objects,
which I believe is what edz is mostly referring to with respect to limiting magnitude, and extended objects, like emission nebulae,
globular clusters and some open clusters, which may be more sensitive to the increased light grasp from increased aperature. I am
waiting to read ed's more detailed article on Cloudy Nights before forming an impression.

Shneor Sherman wrote in message . ..
(Theo Ker) wrote in message . com...
So if that is true, what would be the difference for me when switching
from a 20x60 oberwerk to a 20x100 miyauchi fluo? Nearly none???? Hard
to believe!
(edz) wrote in message . com...

1 magnitude improvement, a factor of 2.5, is about what one would expect

The 100mm is back on my to-buy list and a 60mm Pentax PCF WP is
tempting, but I must be strong! ;-)

The jump from 60mm to 100mm aperture will provide only about 0.3 to
0.4 LM gain.

The jump from 10x to 16x and likewise the jump from 16x to 25x will
provide 0.4 to 0.6 LM gain each.

You will gain more from the magnification than you will from the
aperture. You don't need 100mm lenses in the binoculars to get the
gain.

edz

The views through my 25x100 Burgess Binos are a drasmatic improvement
over the views through my 26x70 Kronos. I thing the purported
relationship between aperture and magnification relative to limiting
magnitude is non-linear, and as aperture increases, it assumes greater
significance. As most of the relationship has been established with
relatively small aperture binoculars, the existing formula makes sense
over that restricted range.

Next month, if the weather cooperates, comparisons by a number of
experienced observers will be done to measure the effectiveness of 22"
binoculars versus a 30". This is scheduled for October 25, and I
expect to report on the results within a couple of days of the event.

Clear skies,
Shneor Sherman

Running such controlled comparisons may be a 'good trick'. I recall a
number of years back at Astrofest (two years running?) when somebody
brought a big pair of 14" or 16" dobsonian binoculars. LOTS of people
wanted to look through them, but every time I, and many others, went
over to have a peek, they were having collimation problems, or some
such. The thing was HUGE.

Moving and setting up (IF they are portable), and even just using 20" or
30" binos must be a BEAR! Gad, though, once they are working the view
must be fabulous!

My two cents worth: I have both 20 X 80 and 20 X 125 binoculars. Without
getting quantitative, the difference in image quality and brightness is
remarkably in favor to the bigger binos.

This year at astrofest I got to look through both Jim's Mobile (JMI) new
reflex (reflector) binoculars ... the 6" and the 10" versions. The 6"
(now available) was working well, and was not hard to use. The view was
wonderful, with M-13 resolving VERY nicely (at perhaps 50X). It was
noticeably better in this regard than my 5" conventional binos (they
resolve M-13 only with difficulty ... mostly due to only 20
magnifications). The JMI 10" was having problems maintaining collimation
(it's still a prototype, a "work in progress"). The views through it
were transitory, but promising.

Dan Mitchell
==========

edz wrote:

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

The views through my 25x100 Burgess Binos are a drasmatic improvement
over the views through my 26x70 Kronos. I thing the purported
relationship between aperture and magnification relative to limiting
magnitude is non-linear, and as aperture increases, it assumes greater
significance.

None of the available formula provided by Sidwick, Schaefer or Carlin
would support that. Nor does the results of my testing. All predict
linear gain with incremental increase.

But then again, some of what I'm saying is not supported by existing
formula either!

As most of the relationship has been established with
relatively small aperture binoculars, the existing formula makes sense
over that restricted range.

35mm to 80mm is not necessarily a small range. It might be considered
as such if you have the following at your disposal.


Next month, if the weather cooperates, comparisons by a number of
experienced observers will be done to measure the effectiveness of 22"
binoculars versus a 30". This is scheduled for October 25, and I
expect to report on the results within a couple of days of the event.

22inch? and 30 inch? binoculars??? What will you test on. Will you
attempt masking tests to incrementally reduce aperture and observe
effect? Will you attempt numerous magnifications at the same aperture
and record differences?

AAnd will you be able to test same magnifications and apertures on
several occasions of differing sky conditions? That should provide an
interesting set of data. I would imagine you could vary
magnifications all the way from minimum to optimum without varying
aperture. That should either support or disput what I'm stating.

edz

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

The views through my 25x100 Burgess Binos are a drasmatic improvement
over the views through my 26x70 Kronos. I thing the purported
relationship between aperture and magnification relative to limiting
magnitude is non-linear, and as aperture increases, it assumes greater
significance.

None of the available formula provided by Sidwick, Schaefer or Carlin
would support that. Nor does the results of my testing. All predict
linear gain with incremental increase.

But then again, some of what I'm saying is not supported by existing
formula either!

As most of the relationship has been established with
relatively small aperture binoculars, the existing formula makes sense
over that restricted range.

35mm to 80mm is not necessarily a small range. It might be considered
as such if you have the following at your disposal.


Next month, if the weather cooperates, comparisons by a number of
experienced observers will be done to measure the effectiveness of 22"
binoculars versus a 30". This is scheduled for October 25, and I
expect to report on the results within a couple of days of the event.

22inch? and 30 inch? binoculars??? What will you test on. Will you
attempt masking tests to incrementally reduce aperture and observe
effect? Will you attempt numerous magnifications at the same aperture
and record differences?

AAnd will you be able to test same magnifications and apertures on
several occasions of differing sky conditions? That should provide an
interesting set of data. I would imagine you could vary
magnifications all the way from minimum to optimum without varying
aperture. That should either support or disput what I'm stating.

edz

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

(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

"Daniel A. Mitchell" wrote in message ...
My two cents worth: I have both 20 X 80 and 20 X 125 binoculars. Without
getting quantitative, the difference in image quality and brightness is
remarkably in favor to the bigger binos.


Dan,

I wouldn't doubt for a moment that the views through 125s are brighter
with better image quality. That's the general basis that binoculars
are produced for. But this is not comparing brightness or image
quality.

Based on my results I would predict the gain in limiting magnitude
from 80 to 125 is only about 0.3 to 0.4 mag. If there is any
difference in quality (optics, coatings, baffles) there may be
additional gain attributed to that. Try it and see. When the article
comes out, there will be a chart with 50-60 stars labeled to mag12.
You'll have an opportunity to see if what I say holds up, or to see if
you get different results. Be prepared to expend considerable effort
to capture mag 11.5-12 stars, if you can even reach that far. My
guess is 5 to 10 minutes each, and probably averted only.

thanks
edz

"PrisNo6" wrote in message om...
Some distinction should be made in this thread regarding the effect of aperature on the limiting magnitude of stellar point objects,
which I believe is what edz is mostly referring to with respect to limiting magnitude, and extended objects, like emission nebulae,
globular clusters and some open clusters, which may be more sensitive to the increased light grasp from increased aperature. I am
waiting to read ed's more detailed article on Cloudy Nights before forming an impression.


I'm expecting that distintion will continue to be blurred, since the
attributes of brightness and image clarity are what people most
perceive as increased performance in binoculars. This and comparisons
between unequal quality instruments have been the most prevalent
argument on every forum. It will be difficult for many to accept this
even if it cannot be shown incorrect, because it is not what we have
been led to believe.

Having yourself taken part in the last discussion, you know the
prevailing thoughts on predictive formulae. They are not questioned,
just manipulated for best fit. This may be the beginning of true
field tests that will either corroborate or dispute existing formula.

You all need to keep in mind this entire study is absent of any tests
relative to diffuse extended objects. That is not the point.

thanks
edz

(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