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Limiting Magnitude Charts and Tables

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#1 EdZ

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Posted 12 February 2004 - 04:48 PM

April 25,2005
SEE THE # NEW POSTS BELOW WITH UPDATED CHARTS
edz



M45 Star Counts and Limiting Magnitude

edited 12-2-07 added approx 30 new small binoculars
Small Binoculars Light Transmission
as measured by Limiting Magnitude

Limiting magnitude of faintest stars seen are listed under the columns titled nelm. Not all binoculars were tested each night, so in some cases space is filed with xxx. Top of column over Limiting Magnitude readings gives the naked eye limiting magnitude (nelm) for those nights. nelm of 5.2 and 5.4 are estimates. Actual measured aperture is listed and rank showing illumination of the exit pupil is listed, 5 being best, as both these have some impact on total light transmission and the ability to see magnitude limits.

It's worth noting here that it took considerable effort to see these faintest stars. For instance, in a group of binoculars where the faintest star seen on any night is mag 9.1 or 9.2, the faint stars easily seen are only mag 8.8 or 8.9, several tenths brighter than the ultimate faintest seen. Stars at mag 8.8 would be seen in the first 10-15 seconds, mag 8.9 with little effort. But it would take several minutes to confirm a sighting of a mag 9.1 or mag 9.2 star. With the Fujinon 10x50, under mag 5.5 skies, I could see a mag 10 star pretty easy, but it took 10 minutes to catch a few glimpses of a mag 10.3 star.


act * illum *nelm *nelm * nelm * nelm *
Aper * ep * 4.9 * 5.0-2 * 5.2 * 5.2-5 **
50 ** 5 ** xxx ** xxx ** 10.1 * 10.3 * Nikon SE 12x50
49 ** 3 ** 9.8 ** 9.9 ** xxx ** 10.3 * Nikon Action Extreme 12x50
69 ** 4 ** 9.8 ** xxx ** 10.0 * xxx ** Fujinon FMT-SX 10x70
53 ** 2 ** xxx ** 9.5 ** 9.6 ** 10.1 * Oberwerk Mariner 10x60
50 ** 4 ** 10.0 * 9.8 ** 10.0 * 10.3 * Fujinon FMT-SX 10x50
49 ** 2 ** 9.6 ** 9.6 ** 9.9 ** xxx ** Leupold W R Mesa 10x50
48 ** 3 ** xxx ** 9.6 ** xxx ** 10.0 * Nikon Action Extreme 10x50
49 ** 3 ** xxx ** 9.6 ** 9.6 ** 9.8 ** Pentax PCF WP 10x50
49 ** 3 ** xxx ** 9.5 ** 9.4 ** 9.8 ** Orion Ultraview 10x50
46 ** 2 ** xxx ** 9.4 ** 9.5 ** 9.9 ** Oberwerk 10x50
45 ** 3 ** 9.5 ** 9.6 ** 9.8 ** 9.5 ** Garrett Genesis 10x50
41 ** 2 ** xxx ** xxx ** 9.5 ** 9.6 ** Nikon Monarch ATB10x42 Roof
41 ** 1 ** 9.3 ** xxx ** 9.5 ** xxx ** Pentax DCFHRII 10x42 Roof
42 ** 4 ** 9.4 ** xxx ** 9.6 ** xxx ** Bushnell Legend 8x42 Roof
42 ** 4 ** 9.1 ** xxx ** 9.1 ** xxx ** Garrett DCF 8x42 ApoRoof
37 ** 1 ** 8.9 ** xxx ** 9.1 ** xxx ** Oberwerk 8x42 Roof
49 ** 1 ** xxx ** 9.4 ** 9.6 ** xxx ** Oberwerk 8x56
40 ** 5 ** 9.2 ** 9.1 ** 9.4 ** xxx ** Fujinon BFL 8x42
41 ** 1 ** 9.1 ** 9.1 ** xxx ** xxx ** Swift Ultralite 8x42
40 ** 1 ** xxx ** 9.1 ** xxx ** 9.6 ** Pentax PCF WP II 8x40
39 ** 2 ** 9.2 ** xxx ** 9.4 ** xxx ** Garrett Classic 8x45
38 ** 5 ** 9.3 ** xxx ** 9.4 ** xxx ** Nikon Action Extreme 8x40
38 ** 4 ** 9.1 ** 9.1 ** xxx ** 9.1 ** Nikon Action VII 8x40
32 ** 3 ** 9.1 ** 9.1 ** xxx ** 9.1 ** Oberwerk Mariner 8x40
32 ** 4 ** xxx ** 9.1 ** xxx ** 9.1 ** Nikon SE 8x32
44 ** 3 ** xxx ** 9.2 ** 9.2 ** xxx ** Oberwerk Mariner 7x50
50 ** 5 ** 9.1 ** 9.1 ** 9.2 ** xxx ** Captain's Storm King 7x50
50 ** 3 ** 9.2 ** 9.2 ** 9.5 ** xxx ** William Optic 7x50 ED
49 ** 4 ** 9.2 ** 9.1 ** 9.5 ** xxx ** Captain's Helmsman 7x50



I posted the tables as an attachment. See the attachment for the tables and the chart edz

I've been working on studying Limiting Magnitude with an assortment of binoculars. At the time of this original post I had made about 30 observations in various Naked Eye Lim Mag skies in the M45 area. All of the observations with star counts are on the exact same field of stars.

You can observe this same field by using one of the charts linked in the posts below in this thread.

All binoculars were mounted on stable tripods. Viewing from my front yard. Light pollution not usually evident, but city lights 15 miles away on the southern horizon.

These are the complete chart observations from this current effort on M45
NELM # of stars lim mag

8x42 Swift Ultralites 5.0 69 9.7
10x50 Orion Ultraviews 4.3 53 9.1
10x50 Orion Ultraviews 4.7 68 9.6
10x50 Orion Ultraviews 5.0 85 10.1
12x50 Pentax PCF III 5.0 92 10.25
12x50 Pentax PCF III 5.2 91 10.3
16x60 Pentax PCF V WP 4.7 97 10.2
16x60 Pentax PCF V WP 5.2 125 10.8
16x60 Pentax PCF V WP 5.4 141 10.7
10x70 Fujinon FMT-SX 4.9 90 10.1
10x70 Fujinon FMT-SX 4.9 97 10.4
10x70 Fujinon FMT-SX 5.0 100 10.4
10x70 Fujinon FMT-SX 5.0 103 10.4
10x70 Fujinon FMT-SX 6.0 128 10.85
15x70/’03 Oberwerk 4.7 106 10.7
15x70/’03 Oberwerk 5.4 128 10.84
15x70/’03 Oberwerk 5.4 139 10.80
16x70 Fujinon FMT-SX 4.7 137 10.72
16x70 Fujinon FMT-SX 5.0 147 10.88
16x70 Fujinon FMT-SX 5.4 128 10.84
16x70 Fujinon FMT-SX 5.4 133 10.84
16x70 Fujinon FMT-SX 5.4 156 10.94
20x80Oberwerk Standard 5.4 184 10.96
25x100Oberwerk BT100 5.4 209 11.18 w/24.5 WA Ober
36x100Oberwerk BT100 5.4 229 11.68 w/17 Sirius plossl

edited 4-7-04 >(some recent observations with the Oberwerk 20x80 standards in mag 5.4 skies reached stars to mag 11.2 and the Oberwerk BT100 at 50x100 using 12.5mm UO orthos in mag 5.5 skies reached stars to mag 11.9. The BT100 used with a pair of Televue 26mm plossls at 24x100 saw stars all the way down to mag 11.5, better than previously seen at 25x100 with stock WA eyepieces. Best views yet with the BT100 were with the Televue 26mm plossl 2.0°fov and with televue 20mm plossl 1.5°fov eyepieces. View is quite a bit narrower than the stock WA 2.5°fov eyepieces, but you can literally put objects right out to the edge of the field stop and still see a near fine view.)

edited 9-21-06
Under my best skies ranging from mag 5.7 to 6.0;
12x50 Nikon SE see stars to a limit of mag 10.8 in mag 5.8 skies,
10x70 Fujinon FMT-SX saw stars to mag 10.85 in mag 6.0 skies
25x100 Oberwerk IF may have reached stars to mag 12.5 in mag 5.8 skies.

all the rest of these are in mag 5.4 to mag 5.6 skies
12x50 Nikon SE see stars to a limit of mag 10.6 in mag 5.5 skies,
15x70 Oberwerk v2003 sees stars to a limit of mag 10.84 in 5.6 skies
15x70 Oberwerk Ultra sees stars to a limit of mag 11.08 in 5.6 skies
16x70 Fujinon FMT-SX see stars to a limit of mag 11.02 in 5.6 skies,
17x71 Anttler Optic (20x80) Skysweeper saw 11.05, in 5.6 skies
18x70 (20x80) Burgess LW saw mag 11.05 under mag 5.6 skies
20x80? Oberwerk Standard see stars to a limit of mag 11.2 in mag 5.4 skies,
19x69 Garrett Optical (20x80) Gemini (masked) sees 11.08, in 5.6 skies
19x72 Garrett Optical (20x80) Gemini see stars mag 11.3, in 5.6 skies
22x100 Oberwerk is capable of seeing stars as faint as 11.9,
25x100 Celestron could see stars to mag 12.0.
25x100 Oberwerk IF may have reached stars to mag 12.5 in mag 5.8 skies.

Megrez 80 with 14mm Radian 36x80 mag 11.74 (mono view) 5.6 skies
TV85 with 14mm Radian 43x85 mag 11.68 previously in mag 5.2 skies


As Naked Eye Limiting Magnitude improves, the number of stars increases. A larger aperture, used at the same magnification as a smaller aperture, will show more stars. However, mostly, as magnification increases star counts and limiting magnitude will increase, even if aperture does not increase.

NELM # of stars lim mag
A selection of observations all with 50mm objectives
10x50 Orion Ultraviews 4.7 68 9.6
12x50 Pentax PCF III 4.7 xxx 10.23
15x50 Oberwerk 4.7 xxx 10.5 15x70 masked
10x50 Orion Ultraviews 5.0 85 10.1
12x50 Pentax PCF III 5.0 92 10.25
16x50 Pentax 5.0 xxx 10.4 16x60 masked
16x50 Fujinon 5.0 xxx 10.5 16x70 masked

Note that sometimes observations with the same binocular on different nights with the same NELM skies don’t always produce the same results. There are lots of reasons for this, but one big reason is seeing. Even though transparency shows the same naked Eye limiting Magnitude, the seeing may be excellent on one night and only fair on another night. Seeing will affect stars at the limit of your binoculars. Also, keep in mind, we do not see all the stars there are to see and you must be observing a very dense field.

NELM # of stars lim mag
A selection of results all obtained using 70mm binoculars
15x70/’03 Oberwerk 4.7 106 10.7
16x70 Fujinon FMT-SX 4.7 137 10.72
10x70 Fujinon FMT-SX 4.9 90 10.1
10x70 Fujinon FMT-SX 4.9 97 10.4
10x70 Fujinon FMT-SX 5.0 103 10.4
15x70/’03 Oberwerk 5.0 xxx 10.4
16x70 Fujinon FMT-SX 5.0 147 10.88
15x70/’03 Oberwerk 5.4 128 10.84
15x70/’03 Oberwerk 5.4 139 10.80
16x70 Fujinon FMT-SX 5.4 128 10.84
16x70 Fujinon FMT-SX 5.4 133 10.84
16x70 Fujinon FMT-SX 5.4 156 10.94

On any given night when I have recorded an observation sheet of 150-200 stars, there are always some fainter stars seen and some brighter stars missed. I believe that recording observations over such a broad dense field cancels out any discrepancies due to this occurrence. When the final analysis is undertaken, I will use the top 5%-10% of star observations from every sheet. In addition to the peak, this will produce a result of expected range just a bit less than the peak. But I have found in nearly every instance, the top readings all cluster around a small range just below the top reading with maybe 5 or 6 readings within 3/10ths magnitude of the peak.

NELM # of stars lim mag
A selection of results all in mag 5.0 skies
8x42 Swift Ultralites 5.0 69 9.7
10x50 Orion Ultraviews 5.0 85 10.1
12x50 Pentax PCF III 5.0 92 10.25
16x50 Pentax 5.0 xxx 10.4 16x60 masked
16x50 Fujinon 5.0 xxx 10.5 16x70 masked
16x60 Pentax PCF V WP 5.0 xxx 10.4
10x70 Fujinon FMT-SX 5.0 103 10.4
15x70/’03 Oberwerk 5.0 xxx 10.4
16x70 Fujinon FMT-SX 5.0 147 10.88

Another selection of observations, these are all at mag 5.4
16x60 Pentax PCF V WP 5.4 141 10.7
15x70/’03 Oberwerk 5.4 128 10.84
15x70/’03 Oberwerk 5.4 139 10.80
16x70 Fujinon FMT-SX 5.4 128 10.84
16x70 Fujinon FMT-SX 5.4 133 10.84
16x70 Fujinon FMT-SX 5.4 156 10.94
20x80Oberwerk Standard 5.4 184 10.96
25x100Oberwerk BT100 5.4 209 11.18 w/24.5 WA Ober
36x100Oberwerk BT100 5.4 229 11.68 w/17 Sirius plossl

There has been considerable discussion about what magnitude limits can be achieved in binoculars. From the binocular data listed above and from the supporting scope observations, it can be seen that one of the most important contributions to limiting magnitude is MAGNIFICATION.

It's pretty obvious that magnification increases the number of stars seen and the limit of magnitude of stars reached. Magnification has a much greater impact than aperture on how many stars are seen and what magnitude is reached. Aperture and exit pupil gain in importance when it comes to viewing faint extended objects. For all else “Magnification Rules.”


Low power observations of M45 binocular field, star counts and lim.mag. seen
22x78 (22x85mono) 4.6 118 10.7 TV85 w/27Panoptic
43x78 (43x85mono) 5.2 246 11.68 TV85 w/14Radian
45x105 (45x115mono) 5.2 262 11.46 G5 5"sct w/30Ultima

Faintest stars seen at various magnifications in these scopes
32x70 (32x78mono) 4.4 xxx 10.86 AT1010 w/15 TV pl
32x70 (32x78mono) 4.4 xxx glmpsd 10.93 AT1010 w/15 TV pl
45x105 (45x115mono) 5.4 xxx 11.3 G5 5"sct w/30Ultima
40x70 (40x78mono) 5.8 xxx 11.3 AT1010 w/12Konig
65x70 (65x78mono) 5.8 xxx 11.4 AT1010 w/7.5 Tak

Lowest magnifications that a mag 12.0 star became visible
137x105 (137x115mono) 4.4 xxx glmpsd 12.0 G5 5"sct w/10Radian
171x105 (171x115mono) 4.4 xxx 12.0 G5 5"sct w/8 TV pl
76x105 (76x115mono) 5.8 xxx glmpsd 12.0 G5 5"sct w/18 UO
110x105 (110x115mono) 5.8 xxx 12.0 G5 5"sct w/12.5 UO

Maximum this scope has ever seen
183x105 (183x115mono) 5.6 xxx 13.1 G5 5"sct w/7.5 Ultm
156x105 (156x115mono) 5.8 xxx 13.1 G5 5"sct w/8.8 UWA

This is what I have so far.
edz


added
In discussions back in December/03 on the Binocular Astronomy Forum, Bill Faatz, suggested using NGC 1647 in Taurus as a target ilo M45. Bill observes with 25x150 Fujinons. Bill suggests the bright stars of M45 and the glow of the nebula interferes with observation of the faintest stars in the area. I could only wish to have the nebulosity in M45 interfere with my observations.

For several reasons I chose to stick with M45. The sampling distribution in NGC 1647 is limited. Kepple and Sanner describes NGC1647; "It includes a dozen mag 9.5-10 stars, but the majority of its members are 11th to 12th magnitude objects." In M45 you have many opportunities to hit a specific LM mark with 250+ targets ranging from mag 7 to mag 12. This provides for sufficient distribution for any size binocular in almost any sky condition. Most binoculars will be testing in the mag 9.5-11 range under most conditions. Few will be testing over mag 11. It would appear NGC1647 has an even, but limited, range of targets from mag 9 to mag 12. It may be best suited for LM testing in scopes from 6" to 10" as it does have a nice distribution of stars from mag 12 thru mag 15, as shown on the chart in "Visual Astronomy of the Deep Sky."

In M45, I find that some of the moderately bright 8th mag stars that show the patterns help as guideposts. When I take my eyes away from the binocs to work on the chart, I can easily re-acquire the location by using guideposts. There are few if any guideposts in NGC1647, making it difficult to keep track of where you are. There is no question the glare from the mag 3 stars interferes with close by observation. However, most on the targets are well away from the brightest stars.

Only once have I ever suspected seeing any of the nebulosity around M45. there is one primary area where it may interfere, to the south in section F. However, within that obscured area are only very few targets. There are other targets elsewhere on the charts that duplicate the magnitude of all of those targets. The north, northeast and southwest areas of the chart, sections C and D and most of A & B, are free of any obscuring nebulsity. With nearly fifty observation sheets recorded to date, it has not proven yet to interfere with the consistent performance of any binocular from one region to another.

NGC1647 has numerous pairs and triplets. This, in effect, reduces the number of targets and changes the target magnitudes for those pairs in medium or smaller binoculars. In medium or smaller binoculars these become close pairs with integrated magnitudes. For example, a 9.9-10.3 pair, if seen as only one star with a medium binocular, is seen at an integrated magnitude of 9.33. M45 also has quite a few integrated pairs, but M45 has so many targets that the loss of a half dozen targets is inconsequential.

A considerable amount of testing is involved to attempt to verify star mags prior to LM observations. In M45, I had already verified integrated magnitudes of close companions, observed for differences in published magnitudes and visual magnitudes, identified variable stars and charted a sizable mix of targets and performed various scope observations to verify sufficient targets were labeled. It makes far more sense to me to continue with the M45 charts for all those reasons.

edz

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#2 EdZ

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Posted 25 April 2005 - 12:34 PM

Chart updated 4-23-05

This is a link to my Limiting Magnitude Study Chart of M45. The current chart has newly added, a variety of stars between mag 12.0 and 13.0. Primarily developed for determining Limiting Magnitude in binoculars, the original charts had stars to mag 12.0. Some recent observations with the high powered BT100 Oberwerk binocular telescope maxed out the mag 12 charts. Also, verifications with small scopes required a few additional targets to mag 13. And those of you who may have opportunity to observe under mag6+ skies will need the stars in the range of mag 12-13.

These are not easy targets. Practice with the chart is advise to ensure you can comfirm you are observing the correct targets. You need to become familiar with the star patterns to confirm you are in the proper location.

Under various skies between mag 5.0 and 5.6, I have seen to the following limits:

22x100 Oberwerk to mag 11.87
25x100 Celestron to mag 11.96
BT100 Oberwerk at 24x to mag 11.5 (under mag 4.8 skies)
BT100 Oberwerk at 36x to mag 12.0 (mag 5.4 skies, maxed out, prior to upgrade charts)
5" Celestron G5 scope with 18mm SWA at 76x to mag 11.94 (mag 5.1 skies)


The attachment (see title block above) in this post is the Table of Magnitudes.

The link that follows is to the chart which resides in my photo gallery.
M45 Limiting Magnitude Chart of Stars to Mag 13.0

edz

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#3 EdZ

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Posted 25 April 2005 - 12:51 PM

Chart updated 4-23-05

This is a link to my Limiting Magnitude Study Chart of Cr399. The current chart has newly added, a variety of stars between mag 11.5 and 12.5. Primarily developed for determining Limiting Magnitude in binoculars, the original charts had stars to mag 12.0. Some recent observations with the high powered BT100 Oberwerk binocular telescope maxed out the mag 12 charts. Also, verifications with small scopes required a few additional targets to mag 13. And those of you who may have opportunity to observe under mag6+ skies will need the stars in the range of mag 12-13.

These are not easy targets. Practice with the chart is advise to ensure you can comfirm you are observing the correct targets. You need to become familiar with the star patterns to confirm you are in the proper location.

Under various skies between mag 5.0 and 5.6, I have seen to the following limits:

22x100 Oberwerk to mag 11.87
25x100 Celestron to mag 11.96
BT100 Oberwerk at 24x to mag 11.5 (under mag 4.8 skies)
BT100 Oberwerk at 36x to mag 12.0 (mag 5.4 skies, maxed out, prior to upgrade charts)
5" Celestron G5 scope with 18mm SWA at 76x to mag 11.94 (mag 5.1 skies)


The attachment (see title block above) in this post is the Table of Magnitudes.

The link that follows is to the chart which resides in my photo gallery.
Cr399 (The Coathanger) Chart Detail to mag 12.5
This chart will be useful for the next few months as Cr399 will soon be a good evening target.

edz

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#4 EdZ

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Posted 25 April 2005 - 01:05 PM

This Chart is still in progress. I have not labeled any of the magnitudes. However, some information about the population of stars in m44 gives a very good indication of magnitude ranges.

M44 has 80 stars to mag 10.0 and has 100 stars to mag 10.9. This chart has just over 200 stars plotted, 140+ stars plotted within the boundary and 60 more within the 2° square periphery. I can see every star on this chart when tested with my 5" scope that has a measured LM of 13.1, so this chart reaches to about mag 13.

Can you see single stars resolved in M44?
The 25 brightest stars all range between mag 6.3 to mag 8.0. There are a number of close pairings that would result in naked eye integrated magnitudes potentially bright enough to see as "resolved stars". While the brightest single star in M44 is 6.3, these 4 pairs all result in brighter naked eye integrated magnitudes. They would be seen as 5.8, 5.9, 6.0 and 6.1. These include all the stars in M44 brighter than mag 6.6. So after these 4 groups that have integrated magnitudes, seeing a "5th star" puts you at NELM 6.6. There are several other pairs that are not as close as 3 arcmin but more like 5-6 arcmin.

The chart has now been edited to include only those stars around this cluster that I have been viewing, even though they are outside the cluster boundary. My starting point guide post is the bright pair at upper right just outside the true boundary. On the west there is a very distinct N-S line of 5 bright stars, running almost from top to bottom of the cluster. On the south there is a distinct string of mostly bright stars just outside the true boundary that I use as my defining limits. On the left (the east) there is a very noticable barren area that helps clearly define that edge.

Here are results from recent observations over a two night period. Both nights were about mag 4.9. These recent observations overlooked 4-6 stars on the extreme periphery that were included in all the earlier observations, so all of these counts in this first group are slightly lower than the history, but these here are all comparable to each other.
39 stars - Oberwerk Mariner 7x50 (actually measures only 7x43)
39 stars - Captain's Storm King 7x50(old single coated Swift)
41 stars - William Optic 7x50
42 stars - Captain's Helmsman 7x50
40 stars - Bushnell Legend 8x42 roof
40 stars - Nikon AE 8x40
48 stars - Nikon AE 10x50
51 stars - Nikon AE 12x50
57 stars - Fujinon FMT-SX 10x50
88 stars – Oberwerk Ultra 15x70

If I were to hazard a guess, I'd say 40 stars is mag 9 and 50 stars is about mag 9.6 to 9.8. In all cases, each of these binoculars saw just a few stars on the limit borderline needing averted vision.


Here's the history - best readings from the more complete and careful observations. With various binoculars I have seen
56 stars using Pentax PCF WP 10x50 sky5.2
57 stars using Fujinon FMT-SX 10x50 sky4.7
64 stars using Oberwerk Mariner 10x60 sky5.2
67 stars using Fujinon 10x70 sky5.2
72 stars using Nikon Superior E 12x50 sky5.2
70 stars using Orion Minigiant 15x63 sky5.0
80 stars using Oberwerk 15x70 sky5.0
90 stars using Fujinon 16x70 sky5.0
97 stars using Fujinon 16x70 sky5.3
94 stars using Burgess LW 20x80 sky5.0
82 stars using Celestron Giant 20x80 sky4.7
99 stars using Anttler Optic 18.5x80 sky4.9
101 stars using Anttler 18.5x80 sky mag5.0
116 stars using Garrett 21x80 sky mag5.0
the above observations fall probably just below mag 11.

103 stars using Fujinon 16x70 sky5.5
102 stars with Oberwerk 24xBT100 (26mm Meade SP LP)sky4.8
117 stars with Oberwerk 25xBT100 (24.8mm stock WA ep)sky5.2
123 stars using Oberwerk 25x100 IF sky5.2
These observations probably reach mag 11.3 to 11.4

128 stars with Garrett 21x80 triplet IF sky5.6
127 stars with Oberwerk 25x100 IF sky5.2
125 stars with Oberwerk 25xBT100 (24.8mm stock WA ep)sky5.6
135 stars with Oberwerk 24xBT100 (26mm Meade SP LP) sky5.6
these observations probably range from mag 11.5 close to mag12

And finally these higher powered observations
135 stars with Oberwerk 31xBT100 (20mm TV plossls)sky5.0
150 stars with Oberwerk 44xBT100 (14mm Radians)sky5.2
174 stars with Oberwerk 44xBT100 (14mm Radians)sky5.5
this last observation probably reaches close to mag12.5
(+ clouds interfered)

edit. this observation added 11-11-05
166 stars seen with Oberwerk 25x100 IF sky 5.6-5.8
This observation is singled out for several reasons.
this reading is 30 stars more than I had ever seen before at 25x100
I awoke at 3:30-4:00 AM and went outside, completely dark adapted
Temp was 34°, but the binoculars had been out from the night before
the sky had very good transparency, no moisture in the air
I easily found M101 this night. There are not many times I've seen M101.
M44 was bright naked eye and looked grainy, ?suspect resolved a few?
This observation includes several stars that were not seen in the BT100 at 44x.
I think this 25x100 binocular observation reaches close to mag 12.5



Take this chart out with you and circle all the stars you can see.
80 stars within the boundary = you've reached mag 10.0
over 100 stars within the boundary = you've gone beyond mag 10.9
140-150 stars on the chart and you are at about mag 12

The smallest symbol on the chart designates all the stars I have not yet see even with 44x100. The next smallest symbol represents all the remaining faint stars that were not seen with any binocular below the 44x100. (except that quite a few were seen with the Oberwerk 25x100 on 11-11-05)

M44 Chart of stars to mag13

edit
I have in my hands a draft observation sheet marked up from an observation on Feb 06 with my C5 (5" SCT) at 150x. On that night, (nothing special as far a NELM is concerned, about 5.2-5.4), I observed over 230 stars in and around M44. There were a few stars observed that are not plotted on this chart. I have not yet edited the master chart. But rest assured, you are not going to see all of those with a binocular, I doubt even at 40x100. FWIW, adding these few extra would take these charts potentially just a little deeper than mag 13.

edz

#5 holger_merlitz

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Posted 25 April 2005 - 08:48 PM

Hello Ed,

Thank you for this extremely tedious and accurate piece of work! It appears quite complete - I wonder whether these results could be published in a professional astronomers or optics journal. The data could be a valuable tool for other researchers.

Regards,
Holger

#6 EdZ

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Posted 25 April 2005 - 09:55 PM

I have been using these numbered charts for about a year and a half for collecting Limiting Magnitude observations. Since the observations are from a consistently numbered set of charts, I am able to simply load the data into a spreadsheet by number sequence without the need to look up a magnitude for each entry. The spreadsheet does that. I know the charts so well that for most of the stars I know its number. I still need to look up the fainter ones.

In my observation logbook for the night, I might enter something like (seen C1,2,3,4,5,6... missed C13,14). Entering the data into the spreadsheet is simply a matter of putting a 1 or a zero down the list for that binocular. At this point I probably have well over a hundred observations with probably 7000 to 8000 data points. If I can ever find a few months time to myself to reduce the data, then maybe there might be something to have published.

The original version of the Cr399 chart to mag 11 was the one used for my article on Binocular Limiting Magnitude published in the CN Technical Reports. My newer larger binoculars are demanding a deeper set of data points, so all charts have been updated with deeper magnitudes.

edz

#7 KennyJ

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Posted 26 April 2005 - 01:43 AM

< Hello Ed,

Thank you for this extremely tedious and accurate piece of work! It appears quite complete - I wonder whether these results could be published in a professional astronomers or optics journal. The data could be a valuable tool for other researchers.

Regards,
Holger >

Holger , I'm sure countless members here would not only agree with you here , but also with my additional suggestion that MUCH MORE of Prof. Ed's work deserves to be professionally published.

In the meantime , the presence of so much of that work on this site goes a long way to making Cloudy Nights by far the most informative and comprehensive website for anyone interested in binocular astronomy.

Sometimes I get the impression this is not as well appreciated as it ought to be.

It seems to me that some folks come here on a brain -picking exercise , then dissapear into the sunset once they've squeezed what they want out of the "helpline" , sometimes without even so little as a polite "thank you".

I'm sure Ed and others don't mind this , so I guess I'm in a minority again by implying that it riles me.

Regards , Kenny

#8 Alby

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Posted 26 April 2005 - 06:28 AM

Hi all;

I agree with KennyJ!

For my part a big thanks to Prof EDz.
I'd say keep up the good work but I don't think Edz looks at it as work:)

Alby

#9 EdZ

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Posted 01 May 2005 - 01:14 PM

How Deep Can You See?

Incremental increases in magnification have far more influence on Binocular Limiting Magnitude (BLM) gain than incremental increases in aperture. Changes to magnification or aperture (area of the lens) show each 10% increase in magnification will increase BLM by ~0.12 to 0.15 mag and each 10% increase in area of aperture will increase BLM by ~0.03 to 0.05mag. This shows magnification was measured to have approximately three to four times the affect on the gain in BLM. When it comes to the question ”How deep can you see?” in binoculars, magnification has greater influence on performance than aperture.

The following table is not scientifically derived from formula. It is based on extrapolation from the results of my field observations. It does take into consideration separately the influence of magnification, aperture and Naked Eye Limiting Magnitude (NELM) on BLM gain. It may give a fairly good indication of what could be reached for various other binoculars that where not included in the study.

BLM Chart
See the Attachment above for the BLM Chart

if you can't open the attachment here's a link to my gallery
http://www.cloudynig...rt=7&thecat=500

Since this original study was published many more observations have been collected. In some cases, on rare occasions results were achieved about 0.2-0.3mag better than the graphs would indicate. As examples, 25x100 reached mag 11.5 in mag 4.8 skies, 25x100 reached mag 11.9 in mag 5.5 skies and premium 12x50 reached mag 10.8 in mag 5.7 skies. However, some of those observations have not been duplicated.


How is BLM Different than LM in a Scope?

You’ve heard time after time, in a scope “Aperture Rules”. It is the primary factor in light gathering and controls the LM. But what if you only use your scope with low magnification. Are you reaching LM? NO! You will not reach LM with a scope unless you use optimum magnification. The best explanation I have found for this comes from “Amateur Astronomer’s Handbook”, by Sidgwick.

That’s the biggest difference between LM in a scope and BLM in binoculars. The scope allows you to vary the magnification. In the binoculars, magnification is fixed. Sidgwick explains clearly how we arrive at the optimum magnification and it usually falls between 24D and 30D, where D is aperture in inches. Some large scope users believe they find optimum magnification at 18D to 25D, and some even say 10D. These are not magnifications that will allow you to reach the limiting magnitude of your scope, especially small scopes 8” and less.

Binoculars are a lot closer to minimum magnification than optimum magnification. Minimum is generally accepted as that which produces a 7mm exit pupil, an exit pupil that would provide maximum brightness for an observer with a 7mm eye pupil. A binocular with a 4mm exit pupil is operating at 6.3D, with a 5mm exit pupil at 5.1D and with a 7mm exit pupil is operating at 3.6D.

Based on this, it becomes apparent that normal aperture LM formulae that base calculations on optimum performance cannot always be used for binoculars. With the single exception of brightness, binoculars do not operate at optimum or utilize the full potential of the aperture. Limiting Magnitude has an impact on numbers of stars seen in loose or dense open clusters and observation of objects such as open clusters, galaxies, globular clusters and planetary nebula all benefit to varying degree from increased magnification.

Field results show magnification, more so than aperture, has a much greater impact on observed BLM. Changes to magnification or aperture (area of the lens) in increments show for every 10% change magnification was measured to have three to four times the affect on the gain on BLM.

Increases in magnification have far more influence on BLM than increases in aperture.

(Keep in mind the primary benefit of larger aperture and larger exit pupil will be realized when you are observing objects such as broad extended faint nebulae)

What it Takes to See Faint Stars

(This discussion was cut from an article that documents best observations in the range of skies from mag 5.6 to mag 5.8)

It was very difficult even with the best 70mm binoculars to see stars beyond mag 9.7. A passing glance in the eyepiece would not show stars beyond 10th mag. It required a concentrated period at the eyepiece, allowing gaze to move around. Once glimpsed, stars beyond mag10 could then be seen directly.

Even stars of 9.7mag could not be seen if the binoculars were moving. Seeing stars of this magnitude required a completely quieted binocular on a stable mount, viewing without touching the eyepieces.

More than once I noted that bumping the binoculars and causing any minor shake eliminated most stars over mag 9.0 from view. As soon as they settled quite after 5 or 10 seconds, 9.5 and 9.7 mag stars were readily seen. Absolute steadiness and some persistence is required to see mag 10.2 and 10.3. Continued persistence and effort is required to see mag 10.4. Stars beyond that are not seen in any binocular (up to 20x80) without expending a considerable concentrated effort, sometimes over as much as several minutes.

I think it is significant to note that without a steady mount the average observer is probably not seeing beyond mag 9.5 with any binocular up to 70mm, and without considerable effort is not seeing much beyond mag 10.2 to 10.3. The practiced observer using 70mm binoculars will see stars of 10.5 to 10.8 only with considerable effort and absolutely still binoculars. Quality 80mm and 100mm binoculars add roughly 0.3 to 0.6 mag respectively to the above stated for 70mm.

Move the objects slowly thru the field of view. Sometimes an object moving thru the view is easier to pick out than a stationary object.

Learn how to use your averted vision. Some areas of the vision have higher gain from averted vision than other areas. Learn where your most sensitive area of gain is by moving objects around in the field of view. Take note of where the objects are in the field, at 2 o’clock?, at 10 o’clock?, when your averted vision first picks them out.

Learn to observe for long periods of time. In the star field I used, it became relatively easy to see stars to mag10.2 to 10.4. But it never became easy to see the faintest stars of 10.6 to 10.8. Sometimes it took a concentrated effort of five minutes to gaze around the area and spot a mag10.7 star. For most observing we are not concerned with reaching the absolute limits of performance, but there are objects that will require you to develop the skill of observing. Persistence and patience are two qualities of a good observer.

in NELM 5.6-5.8 skies:
Fujinon 16x70 see 10.83 direct.
Oberwerk 15x70/03 see 10.7 direct, 10.83 glimpsed averted.
Pentax 16x60 see 10.5 direct, 10.65 averted, some brighter not seen.
Pentax 12x50 see 10.3 direct, 10.5 averted, some brighter not seen.
Orion 10x50 see 10.05 direct, none fainter averted.
Swift 8x42 see 9.5 direct, 9.75 averted.

What Factors Affect Limiting Magnitude

Many factors have an impact on LM. Some are listed here.

As aperture increases and more light is gathered, LM increases.

As magnification increases exit pupil decreases. Unlike extended sources, the light from point sources is not diminished with magnification. Extended light sources get darker but point sources do not. Sky background, because it is an extended object, gets darker. As magnification increases, the light from point sources appears amplified, as long as the point source is bright enough so that it is not viewed as an extended object. (Magnification so high as to create image blur in the Airy disk, turning the point source into an extended object, would not occur in binoculars.) This improves contrast between point sources and background light, resulting in deeper LM.

As contrast in the optical system is improved by the use of better components, i.e., higher quality coatings and baffles, glass with better light throughput, LM increases;

As the eye is kept to the eyepiece for a longer duration, dark adaptation improves to the level of the light provided by the eyepiece only and not by the surrounding ambient light, increasing observed LM;

The color of a star will have an impact on LM. For two stars of equal magnitude, a red star will appear fainter, a blue star will appear brighter. The observer would reach a deeper LM if observing a field of blue stars.

The observing conditions, affected by seeing and transparency, will have an impact on LM. In a simplified method, recorded as NELM, as it increases, LM increases.

The acuity of the observer will have an affect on LM. An observer with better acuity will record a deeper NELM observation but also the more acute observer may in fact see fainter stars in the eyepiece.

The altitude of the stars observed will have an affect on LM. Skies closer to zenith are observed through less air and also have a better chance of being darker.

The experience, persistence, concentration level and patience of the observer will have an impact on LM.


Attached Files



#10 Guest_**DONOTDELETE**_*

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Posted 01 May 2005 - 03:35 PM

Ed, the graph in the attachment is fascinating. I'd love to see some graphical indication of observational variance or degree of uncertainty, or even a verbal summary of such. (What are the areas of highest uncertainty, that could benefit from additional observations?)

One could draw a startling conclusion from the graph:

LM is a function with two independent components, one due to (aperture,magnification) and the other due to NELM. I.e., LM = f(A,M) + g(NELM).

So going from NELM 4 to 6.4, one gains 1 LM regardless of choice of aperture and magnification. (Even at NELM 4, a 9x63 outdoes a 10x50, which is surprising given the smaller eye pupil under fairly bright skies.)

Living under suburban skies, I'd love to see some data toward the left, NELM < 4. I would have thought, higher magnification helps (DeltaLM) even more when NELM is small.

Keep up the good work! -- William Chang (Saratoga, CA)

#11 EdZ

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Posted 01 May 2005 - 08:25 PM

William,

This graph was originally published in 2003. With the eventual addition of now more than twice the amout of data, it may prove to have some inconsistencies. For instance, I know from the additional data that some of the lines move slightly up. It may also turn out that some of the slopes vary somewhat. I can't even begin to see that yet. What I do know is most of the additional data for the most part, support the initial graph.

Unfortunately, I still do not have data for all the points I would like. Consider, in order to plot 15 binoculars, each in 6 different sky conditions, and verify each reading, would require nearly 200 seperate observations of an average 80 to 100 stars each, or recording over 15,000 stars.

(Even at NELM 4, a 9x63 outdoes a 10x50, which is surprising given the smaller eye pupil under fairly bright skies.)


I'm not sure at what point bright sky would reduce pupil size, but I do know that even in subdued morning light I can measure my pupils at 5.5 to 6.0mm observed in the bathroom mirror. I suspect under mag 4.0 to 4.5 skies my pupils are still dilated over 6mm. However, point well made. Extrapolating the original data did not take into consideration a potential effective aperture of less than 63mm, which it possibly could be. The 9x63 is the single case in this data which might be affected. In the additional dtat I have 8x56 and 10x70.

edz

#12 Guest_**DONOTDELETE**_*

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Posted 02 May 2005 - 01:09 AM

Ed, thanks for the clarification. Too many stars and too many pairs of binoculars :-)

You might consider using 3-4 pairs of the same/comparable brand/type and masking the apertures, to reduce the variables (such as quality/collimation/coating). More widely spaced NELMs. To simulate 3.0 NELM, maybe do it at dawn or dusk if the measurement isn't too time consuming. Just some ideas.

BTW how much does bino add to LM vs mono?

I think you have a very powerful hypothesis that should be tested and used as the basis for additional experimental work in this area -- toward an understanding of the optical and psycho-visual aspects of these observations. I'd love to see that!

Best, -- William

#13 EdZ

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Posted 02 May 2005 - 05:32 AM

William,

the answers to a few of your questions can be found in the original article in the CN Technical Reports. Follow the Pinned post Links to Web - Astro Info. You might also follow all the links to this forum to the subsequent BLM studies on M45. See Best Of links to testing aspects of binoculars. Between these two sources the mono question is answered. Some of the results were obtained by masking binoculars. That changes the focal ratio, but still provides useful info. That's what originally led to the discovery that magnification has more influence.

edz


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