Telescope Reviews: Limiting Magnitude Charts and Tables

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,
18.5x80 Anttler Optic 20x80 Skysweeper saw 11.05, in 5.6 skies
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,
20.8x70 Garrett Optical 20x80 Gemini (masked) sees 11.08, in 5.6 skies
20.8x80 Garrett Optical 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

Edited by EdZ (04/17/08 03:19 PM)

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