Telescope Reviews: What Can Be Seen in 12 Different Sizes Binocs

For the binocular observer that intends to move up from a 10x50, 11x56, 12x50 or 12x60 binocular, there is still a lot to be gained by looking at 15x70s, or 16x70s and 20x80s.

10x50 binoculars can see many open clusters and in a good dark sky will find a large number of galaxies and nebula. A few bright globular clusters can be seen, but they will be small, however will appear nonstellar. Limiting magnitude can reach just deeper than mag 10.0 to 10.2 and you can separate stars as close as 16" to 15" and with effort 14".

With 12x50 binoculars you can see as deep as mag 10.4 to 10.5. Generally, field of view is about 5.0°. Some doubles at 14" and 13" can be separated, but a double at 10" can only be seen elongated. M57 can barely be seen as more than just starlike. Many deep sky objects can be easily found. For me 12x50 is about the limit of handheld astronomy.

Keep in mind, you will not see as much handheld as you will with mounted binoculars. It is very difficult even with the best 70mm binoculars to see stars beyond mag 10 when handheld. Seeing stars at mag 10 requires a completely quieted binocular on a stable mount, viewing without touching the eyepieces. A binocular used for scanning, with slight minor shake eliminates most stars over mag 9.0 from view. Absolute steadiness and some persistence is required to see mag 10.2 and 10.3. This translates to how much can be seen in star fields, open clusters and dense clusters. Deeper magnitude means more stars seen. A steady binocular means more resolution in clusters.

Having said all that about handheld, let me mention the Nikon 12x50 SE. This particular 12x50 is a well-balanced binocular, well-suited for handheld astronomy. On one particular morning recently, I grabbed my Nikon 12x50 SE and gave it a shot. I was easily able to acquire M1 in the 12x50s handheld. M78 took a little more time. I needed to search around for a while, but passing over it several times showed it in the movement. Even handheld in 12x50s, these two objects proved attainable. Several nights before I managed to spot mag 10.4 and 10.5 stars with arms braced in a reclining lawn chair. This is the best I have ever seen hand held, with any binocular.

Unless otherwise noted, visual comparisons here are relative to a mag 5.5 to 5.8 sky. Many more objects have been seen in each binocular, but fair comparisons are made when they are used on the same night. Except for doubles, where two or more binoculars are compared on an object, they were used side-by-side at the same time on the same night. This is most important as it has been proven that any binocular will see far more in a darker sky. Doubles can be seen in skies as low as 4.0 to 4.5, but skies must be steady and faint doubles need darker skies. Doubles represent the best ever achieved with that size binocular, not necessarily on the same night. Limiting magnitude samples were taken from best ever achieved.

A 10x70 Fujinon binocular is included here, but is considered a special purpose binocular. Not all observers can use it to it's full potential. With a 7mm exit pupil, if you do not have eye pupils large enough, you never get to use the entire aperture. If you do have eye pupils large enough, your other common foe is bright sky. In moderate 4.5-5.0 skies, the 10x70s show a background about 3 or 4 shades brighter on the grey scale than what is delivered by the 16x70s. In mag 4.5 skies, 10x70s are performing at about the same as a 12x50. With a 7mm exit pupil, there is so much light coming into the eyes from the extended sky background, it makes it more difficult to see everything. The 16x70s provide such a contrasty view against the darker backdrop, the contrast gain from the higher magnification of the 16x70s was far reaching and unmistakable. But when used under dark sky, the backdrop in the 10x70s did not appear so much brighter than the 16x70s and much more could be seen in the 10x70s. Faint nebula stood out now that they were being used in their productive element. More faint stars came into view. In dark sky the difference between the two is not nearly as great. The 16x70s still see even more stars, but on the faintest nebula, the 10x70s may have done a little better.

A 15x70 has 100% more aperture than a 50mm binocular and it still has 50% more than a 56mm binoc. Also you will be surprised at the image scale difference between 15x versus 10x. It's even a decent jump up from 12x to 15x or 16x. These binoculars in the 70mm class are big, but they don't yet get to the size that they fall into the realm of the giants. At just over 3#, they can be mounted on modestly robust camera tripods. Field of view is about 4.3°. With a good 15x70 you can see to a limit of about mag 10.8.

In 15x70s, objects like M65 /M66 can be found easily with M65 being difficult, but the companion NGC 3628 will not be seen. In the darkest local mag 5.8 skies, portions of the North America nebula are visible. You can split doubles down to 12", and sometimes 10" with difficulty. On the steadiest nights, you might suspect resolution of all four components in the Trapezium. You can positively see three components. On cluster I4665 in Ophiuchus, I counted 20 stars in a 10x50, 27* in 12x50, 28* in one sample of 15x70, 30* in a better 15x70 and 31* in a 16x80. In mag 5.5 skies faint nebula are not seen, but if you ever get the chance to visit mag 6.5 skies, objects like the North America nebula become apparently visible over a much wider area.

15x70s look really big when compared to 10x50s and 12x50s. It's not until you see 15x70s next to a pair of 22x100s or 25x100s that you see 15x70s are dwarfed by the larger binoculars.

A 16x60 is not that much different than the 15x70s. Just about the same objects are seen in both. Pentax, the occupant of this group also has the 20x60 size. By nature of its higher magnification it will see more stars and deeper magnitude. But this is another I have not used. I suspect its very small exit pupil becomes a limiting factor when you try to go for those faint diffuse objects. It is objects such as those diffuse extended nebula that will make you happy when you have a binocular with a 4mm or 5mm exit pupil.

The 16x70, a class unto itself, seems to be occupied by the sole tenant, Fujinon. These provide views much closer to the 20x80 class than any 15x70 will. With the 16x70s 4.0° field of view, you can easily see M65/M66. M65 will appear easier. NGC 3628 remains a challenge, not seen by these binoculars in mag 5.7 skies. Limiting mag will reach to mag 11.0 and you can split doubles in the 9" range more often. Difficult 10" doubles will be resolved even when they are beyond the ability of 15x70s and some 20x80s. Nebula appear brighter simply because the optical system is of a higher quality. Overall the view goes a little deeper, a little brighter, a little better than any 15x70. Portions of the Veil nebula are visible. This is a binocular to consider if you are thinking of a 20x80. Compared to good 15x70s these are better in all respects. When small and faint M78 was seen with dificulty in a fine handheld 12x50, it was found quickly and easily in the 16x70. When you get these out under the darkest of skies, imagine how much more you might see.

I had a 16x80 Orion at one time several years ago. These were closer in performance to the 15x70s than they were to the current 20x80s.

As magnification increases, you get to see more stars. Try to keep exit pupil large enough to get a good amount of light to the eye. Generally, as magnification increases, the field of view will narrow. With few exceptions, that is to be expected.

A 20x80 is another giant leap above a 15x70. But if you're already using 15x70, you won't notice as much of a gain to 20x80 as you did when you made the jump from 10x or 11x to 15x70.

15x70 vs. 10x50 is a 50% increase in image size and a 100% increase in area of aperture.
15x70 vs. 11x56 is a 36% increase in image size and a 56% increase in area of aperture.
15x70 vs. 12x50 is a 25% increase in image size and a 100% increase in area of aperture.
20x80 vs. 15x70 is a 33% increase in image size and a 30% increase in area of aperture.
22x100 vs 15x70 is a 46% increase in image size and a 100% increase in area f aperture.
25x100 vs 20x80 is a 25% increase in image and a 56% increase in area of aperture.

However 20x80s are solidly into the range of giant binoculars. There aren't too many small 20x80s. Image scale grows. The field of view narrows to about 3.2°. You see more stars in clusters just due to the increase in magnification. You can sometimes pick out all four stars in the Trapezium, the closest being 8.7". You can see magnitude as deep as 11.2 to 11.3 and occasionally elongate some not-so-bright equal doubles in the 7" range, but Mesartim at 7.8", remains unresolved with the 20x80s. Although I've had many opportunities to observe with 20x80s in mag 5.5 to 5.8 skies, I've never had the opportunity to get them to darker skies.

Lots of people don't really care how close a double you can split with a binocular, but it is a good measure of resolution. What this really means is you get to see a lot more resolution in dense clusters because binoculars with the ability to see that closer double will separate more stars in a cluster. This allows you to define that word resolved.

This is a comparison of observations made on an area with controlled boundaries around M45, The Pleaides. All observations were not made on the same night, but these are all in mag 5.4 skies and under the same controlled conditions.

16x60 Pentax PCF V WP see 141 stars to a limit of mag 10.84
15x70/’03 Oberwerk see 139 stars to a limit of mag 10.84
16x70 Fujinon FMT-SX see 156 stars to a limit of mag 10.94
20x80 Oberwerk Standard see 184 stars to a limit of mag 11.18

Likewise these observations were all made in similar conditions. Over several nights when M44 was naked eye, I recorded these observations. On dark nights M44 just swarms with stars in the larger binoculars. You almost can't believe the numbers of stars seen at 25x and 30x. All the stars around M44 don't quite fit in the 1.4° fov of the BT100 w/14mm Radian at 44x, but the total numer of stars is incredible. M44 has 80* brighter than mag10 and 100* brighter than mag 10.9. I'd say skies ranged from about Mag5.2 to about mag 5.5.

# of stars seen in and around M44
With various binoculars I have seen
48 stars using Oberwerk 8x56
54 stars using Pentax PCF WP 10x50
61 stars using Oberwerk Mariner 10x60
67 stars using Nikon Superior E 12x50
68 stars using Orion Minigiant 15x63
80 stars using Oberwerk 15x70
90 stars using Fujinon 16x70
94 stars using Burgess LW 20x80
126 stars with Garrett 20x80 triplet IF

102 stars with Oberwerk 24xBT100 (26mm Meade SP LP)
115 stars using Oberwerk IF 25x100
110 stars with Oberwerk 25xBT100 (24.8mm stock WA ep)
135 stars with Oberwerk 31xBT100 (20mm TV plossls)
160 stars with Oberwerk 44xBT100 (14mm Radians)

edit this observation added 11-11-05
166 stars with Oberwerk 25x100 IF sky 5.6-5.8
This observation is singled out for several reasons.
this reading is far more stars 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?
It includes several stars that were not seen in the BT100 at 44x.

This post is noticeably absent any info on the 20x90 size. I've never used them. They have an obvious gain in aperture over 80mm, but at magnification equal to 20x80, Everything I've experienced would indicate a slight gain in magnitude over 20x80s and with a larger exit pupil, 4.5mm vs. 4.0mm, a pretty good potential for gain on faint diffuse objects. Resolution should be equal to any other equivalent quality 20x binocular.

And now we arrive at the 100mm binocular size. In the 100mm size of fixed binoculars we have 22x100 and 25x100. If you've never seen or held or looked thru a pair of 100mm binoculars, when you first do get the chance, you will find these are dramatically different than anything else smaller you've used. These are big, real big. And they show it. They require a substantial mount, not just any tripod but a heavy-duty tripod with a heavy-duty head. Generally these binocs weigh about 8-10#. Most light or basic parallelogram mounts groan under the weight.

A 22x100 binocular is capable of seeing stars as faint as 11.7 to 11.8. You are now into a size binocular that provides only a 2.7° field of view. Some few objects are so huge that they will not fit into the binocular field of view. This is still a larger fov than the Pentax 20x60 (2.2°). At 22x, stars like Mizar resolve easily. Regular difficult double star targets become regularly viewed objects. Doubles like Gamma Delphinus at 9.6" are resolved. Challenges are doubles in the 7" and 8" range. Mesartim at 7.8" becomes a favorite test. In the 22x100s, NGC 6934 in Delphinus was an obvious globular cluster. It was just seen in 16x70s and very faintly seen in 16x60s. The 22x100 caught glimpses of another globular in Delphinus, NGC 7006. 7006 was not seen in any smaller binocular.

In a 25x100 binocular the field narrows to 2.4°. These binocular reach nearly to stars at mag 12.0. When you view faint clusters in these binoculars you see stars that just were not there in any smaller binocular. Doubles of 7.1" and 7.4" are clearly separated. Mesartim at 7.8" is a successful target. Gamma Delphinus at 9.6" becomes an easy target. The Trapezium provides none of the difficulty associated with 20x80s. M105 and its companion NGC 3384 make a nice pair. M96 is seen, but M95 remains difficult. M57 is an obvious torus.

The combination of magnification and aperture is so overwhelming in the 100mm binoculars, even the veritable 16x70 Fujinon is no match for a 22x100 or 25x100 binocular. Fainter galaxies seem to be easy pickings for these 100mm binoculars. While M66 is seen bright, and M65 is difficult in the 16x70s, both are readily seen in the 25x100s. In addition, the companion NGC 3628, not seen in any smaller binocular, was visible several times in the 25x100. M101 was found instantly in the 25x100, it was seen equally well in the 22x100, but it was only suspected in the 16x70s. Star counts on clusters like IC4665 in Ophiuchus show 51* in the 25x100, 50* in the 22x100, but only 40* in the 16x70.

Doubles, when resolved in the 16x70s, were more sharply defined than any other binocular, smaller or larger. But the higher powered 22x and 25x binoculars, even though they do not resolve to as fine a points, are capable of so much closer separations, they get to see closer doubles, which also means they are seeing more stars resolved in dense clusters.

In the area just south of M11, M26 is seen easy in the 16x70s but 6712 and 6664 are not seen at all. In 20x80s, 6712 is seen and in 6664 only 3 or 4 stars can be glimpsed. In both the 22x100s and 25x100s 6712 is seen readily and 8-10 stars can be counted directly in 6664.

On M17, the nebula was by far the best in the 25x100s. In the 20x80s, M17 was seen but not with the same size and brightness. In all smaller binoculars, M17 appeared smaller with much less prominence.

And finally, while still in the 100mm size, the next step is not necessarily a larger aperture, but changeable eyepieces for variable magnification. There are a variety of binoculars on the market in the 80mm and 100mm range that fit this bill. The one I am using is the Oberwerk BT100.

The BT100 is a different animal altogether than any other 5# to 12# binocular in the 80mm to 100mm range. The BT100, at 26# (12kg), is heavier than my largest telescope, a 4 foot long 6" refractor. The BT100 cannot be picked up while mounted on its tripod. You must first set out the tripod then attach the BT100s. You would not move it while mounted. You must first take the binocs off the tripod.

The views are simply stunning. It does come standard with two sets of WA eyepieces, a 24.5mm = 2.5°Tfov at 25x and a 10mm = 1°Tfov at 62x. Both eyepieces have an apparent fov of 62°. My binocular shows a bit of difficulty with the 62x 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 perfect view with almost no distortion present.

Magnifications I use the most often in the BT100 are 24x, 31x and 36x. Each step up increases the number of stars that can be seen and none of the fixed power 100mm binoculars can equal the performance of the BT100. The BT100 can see stars to mag 12.0 easier and more directly than any of the other 100mm binoculars.

The best low power views I had in the BT100 were with the 26mm at 24x. The only instrument I've ever own/used that was able to see a portion of the Merope nebula is the Oberwerk BT100 binocular telescope with a pair of 26mm TV plossls at 24x with a 4.2mm exit pupil and a 2.2° fov. Using the stock 25x WA eyepiece, I saw slight definition to the Rosette nebula.

Oberwerk 22x100s and Celestron 25x100s make M12, a globular cluster, look like it is on the verge of resolution in the outer edges, where the Fujinon 16x70s could not resolve M12 at all. The Oberwerk BT100, using a 17mm Orion Sirius plossl at 36x did in fact provide some resolution in the outer edges of M12.

One of the best high-powered views ever in the BT100 was with a 12.5mm ortho at 50 power when I resolved some 30 to 40 stars in the very dense open cluster M11.

Many of the above binoculars are not perfect. Some show slight flares in the image, some show a little astigmatism, some show a slightly bloated image in one or both sides of the binocular. Some are more difficult than others to bring to a fine pinpoint focus. Even with those deficiencies, these are the results achieved over a long period of months and in some cases years of use. Some have better coatings and contrast and certainly all are not equal in mechanical functions or quality of components. But what is most noticed is the dramatic increases in what can be seen with larger binoculars.

There is no question a higher quality binocular steps up the ladder when compared to its closest companion sizes. But that can take you only so far. This does not mean to indicate the largest binoculars are the best binoculars. Nor is it intended to mean the best binocular in the middle sizes is not the equal of the largest. In many ways, largest may not be best. All I have tried to do here is give a good comparative representation of what can be seen as binocular size increases. I think this should give you a pretty good idea of what can be seen with various sizes.

Keep in mind a binocular allows you to see with both eyes. A 100mm binocular has two 100mm apertures with a combined area of aperture equal to a 141mm scope. Binocular summation allows the eyes to provide information to the brain that is greater than what would be seen with one eye in one of those apertures. Depending on the type of objects observed, that summation gain can range from 1.2x to 1.4x what is seen in a single apertue.

These are the binocular sizes with which I've recorded observations. Certainly, many of you know plenty of other sizes of binoculars that would fill in between the lines here.

edz

Edited by EdZ (11/12/05 07:29 AM)

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