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Comparing Binoculars - GO22x85, WO22x70, Tak22x60


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Garrett Optical 22x85 Signature

William Optic 22x70 Apochromat

Takahashi Astronomer 22x60 Fluorite

First, let me say these are three fine binoculars. Oh yes, one is better than the others, but none of the three would be something you wouldn’t want to own. I've measured many binoculars of all sizes. Some of the measures put up by one or the other of these three rank among the best measures I’ve ever seen in big binoculars. I want to thank Peter Staiger for loaning me two fine binoculars, the Tak and the WO, so I was able to make these comparisons over a period of six months. Along with his two, and my two samples of the GO22x85, both bought used, there was some enjoyable viewing along the way to compiling the data for this review.

For starters, I can give you some of the preliminaries.

Basics, weight, focal length, mounting

These are all fairly large binoculars, with the 10# GO22x85 being the largest and heaviest and the Tak22x60 being the smallest and lightest. Although you can do very well with a lighter weight mount for the Tak22x60, I’d recommend a substantial mount for these binoculars simply due to the fact that observing at 22x will highlight the smallest deficiencies in any mount.

This GO22x85 is a bit smaller in physical size than the Oberwerk 25x100. It rides pretty nice atop my 028B/501 head combo. The GO Gemini 25x100 is the same binocular as the Oberwerk 25x100IF.

Both the GO85 and the WO70 have a center post type mount. Sometimes this type mount needs a 1” tall extension post under the center post to raise the binocular high enough off the tripod head to allow the binocular to close in for narrow IPD. Even on my Bogen 501 head I can get away with not using the post extension and still close in to my 61-62mm IPD, but just barely. For any closer IPD, a post extension would be needed. The Tak comes with it’s own specialized mount attachment, but I found the Tak more stable on the same very sturdy L adapter that I use for my Oberwerk 15x70.

The GO22x85 is an air-spaced doublet weighing 10#, listed as f/4.7, making it F=400mm.

The WO 22x70 Apo is based on the WO ZenithStar 70mm ED scope. The objective specs for the ZenithStar are 70mm, FL 430, f/6.2 FPL-51 doublet. It appears to be an air-spaced doublet. The WO22x70 body is the same physical length as the GO22x85.

The Tak 22x60 Astronomer objectives are 60mm fluorite doublets with a focal ratio of f/5.9. The Tak22x60 objectives are the same as those in their FS-60C telescope. The telescopes specs are 60mm, fl 355mm, f/5.9 fluorite doublet. Using a green laser pointer, as the glp touches the coatings it faintly shows the front edge of the front element of the Tak. Then the light from the GLP disappears. Then there is a blip at the front surface of the second element, then the visible green shaft thru the second element and then the blip as it exits the second element. This shows that the Tak is a doublet with the front facing element being the fluorite.

GO85 is a f/4.7 air-spaced doublet achromat

WO70 is a f/6.2 FPL-51 ED doublet (labeled an Apo)

Tak60 is a f/5.9 Fluorite doublet Apochromat

Temperature Changes

I've noticed this before with some other very large binoculars, and it came to light again recently. Using the GO22x85, I was observing intermittently from about 7pm to about 1am. During the course of that time, temperature dropped from the upper 40s to the mid 20s, and I suppose when I first set the binoculars up at about 6:30-7pm, they were still at about 65° room temperature. Throughout the course of the evening, the binoculars dropped from 65° room temp to the mid 20s, a 40 degree temperature change.

Two or three times during the course of the night I had to refocus. This is never necessary during the warm months. So, it’s worthwhile to keep in mind, in cold weather it pays to get your gear outside to acclimate. It’s not so much of an issue with small gear, but for big gear it is an issue. Temperature changes do have an affect on all that mass, especially when the focal length is nearly a half meter long.

I did not experience this issue with the Tak 22x60.

Eye Relief, Depth to Eye Lens, eyecups, metal rims

Garrett Optical 22x85 Signature
17mm distance to minimum exit pupil minus 8mm recess = 9mm usable eye relief

William Optic 22x70 Apochromat
17mm total minus 8 recess = 9mm usable

Takahashi Astronomer 22x60
14-15mm total minus 2 recess = 12mm usable

All three have fold down rubber eyecups. Those on the Tak are a bit sturdier. The thin rubber on my GO22x85 has already started to split along the edges.

For comparison, usable eye relief I've measured for some other binoculars:
Oberwerk 25x100 IF = 15mm.

Celestron Skymaster 25x100 = 9mm
Garrett Gemini TWP 20x80 = 13mm
Fujinon 16x70 = 9mm
Oberwerk Ultra 15x70 = 11mm
Fujinon 10x50 = 13mm
Nikon Action Ex 10x50 = 13mm

The GO85 accepts screw in filters at the back end of the eyepieces. I checked the fov with a screw-in filter installed. Without my glasses, I can see the full fov. With my glasses on, I can only see 40% of the fov when a filter is installed. I would never put my glasses up against the metal rim of a filter anyway, so the GO22x85 binocular with a filter installed, in my opinion, is not usable with eyeglasses.

Below Lyra is Sagitta. I centered M71 in my view and noticed I could see the stars of the arrow tip and middle at the same time. The distance from gamma Sge to delta Sge is 3° and this was observed to be in the view of both eyes at the same time. This is a clear indication that I can see the entire fov all at once. Keep in mind I observe with glasses, although thin, and I measured the max fov at 3.05° with a usable eye relief of 10mm. That is just barely enough for me, with my glasses right up against the rubber cups to see the entire fov.

It was easier to see the entire narrower fov in the WO70. The Tak60 eye relief was comfortable even with glasses.

Lack of protection for eye glasses

Notice that the GO22x85 eyepieces are very large with wide eye lens opening, but that also there is a metal rim surrounding the eye lens opening and that metal rim is less than 1mm deeper than the rubber eye guard. My eyeglass lenses hit this metal. This is a problem, because eye relief is so short to begin with that it is necessary to be right up against the eyepieces with eye glasses. The metal rim is not protected by the rubber eye guard. Eye glass lenses are not protected. This metal rim needs something to protect eyeglasses. I have applied a ring of thin stick-on felt.

The WO22x70 just like the GO22x85, has very short usable eye relief and has the same eyepieces. So I need to scrunch up tight behind them to see the entire fov. I need the eye guard to be folded down. But by doing so, on both the GO and WO eyepieces the metal rim of the eyepiece is exposed at the surface. I heard it several times during my viewing sessions, that little click/clack noise. My eye glasses were coming in contact with that metal rim. It's not a good noise. This is a poor design feature. This same feature is an issue on the Oberwerk Ultra 15x70 and requires the same attention.

The Tak22x60 rubber eye guard extends over the metal rim on the eyepieces and does not present this problem outlined above.

The GO and the WO are NOT eyeglasses friendly binoculars. You won't have any problems if you plant yourself squarely behind the binocular and look straight in without ever tilting your head a little too either side. The bridge of your glasses between the two eyepieces will hit the rubber on the inside edges of the eyepieces, and the curved surface of your eyeglasses will be up and away from the metal edges. But as soon as you press slightly to see the entire fov, your eyeglasses may come in contact with that metal rim. There is no way to avoid it. It is right at the surface, not recessed at all. This needs to be addressed.

I've been thru this before. It doesn't show up after one or two uses, but after repeated use it will show up. It won't take too long before little scratches appear all over the front of my eyeglasses. If I were to continue to view thru these binoculars without adding some kind of protection over that metal, I would ruin my very expensive eyeglasses, and perhaps ruin the binocular eye lenses also.

I’ve resolved this issue on my GO22x85 by adding a thin layer of stick-on felt.

For eyeglass wearers:

Increased usable eye relief, at the expense of depth to the eye lens or protection from the eye lens metal ring, is just as detrimental a factor in the design of the binocular as any aberrations or deficiencies anywhere else in the binocular system.

Usable eye relief is important, but so is protection from damaging contact.

If the eye lens is only 2mm recessed below the surface of the eyecups, eyeglasses may come in contact with the eye lens. Eventually, eyeglasses and binocular eye lenses are going to scratch. Binocular eye lenses, especially very wide eye lenses, should be a minimum of 3mm deeper than the eye cup to prevent contact with eye glasses.

If the eye lens is 3-4mm below the eyecup, BUT the metal retaining ring that houses the eye lens is close to, or at the surface of, the eyecup, then the metal ring may come in contact with your eyeglasses.

These two conditions represent design that can be detrimental to eyeglass wearers and you should be cognizant of this issue when choosing binoculars. It is far better to lose 5% of the field of view and be protected by a full cover rubber eye guard, than to have 2mm extra eye relief, be able to see the entire fov, but leave eye glasses exposed to potential damaging surface contact with glass or metal.

Take a look at the Fujinon FMT-SX 10x50 or the Nikon SE 10x42. The rubber eyecup completely covers the metal rim, at the expense of a slight loss of fov edge when wearing glasses. But there is no possible chance of coming in contact with the metal.

Collimation

One little disappointment was my GO22x85 arrived out of collimation. Please note I bought them second hand. I should also mention, I bought another pair second hand and they arrived in perfect collimation.

Using Nu Draco (a 1 arcmin double) I easily determined these were 2 arcmin out of alignment, and the error was predominantly vertical error. I cycled them thru a range of IPD and found they would get as close as 1 arcmin out at some IPD positions, but never merged. When I relaxed behind the lens, single star images would easily split apart. Several times while viewing, images would separate. My eyes were forcing the merge. After a few minutes of viewing, when I looked away from the eyepieces, everything was out-of-whack for a few seconds.

Vertical Alignment, a serious error, is when one image is higher than the other image. The eyes have no muscles to accommodate for vertical error. The allowable divergence is only 4 arcmin at 7x to 10x, only 3 arcmin at 12x to 15x and 2 arcminutes at 15x to 20x. Personally, I find these error standards quite lax, as I cannot tolerate 2 to 3 arcminutes of vertical error at magnifications of 10x and my eyes suffer with more than 1 arcmin at 16x. At 21x, I need to adjust the GO22x85 to within about 30-45 arcseconds to be within my personal tolerance level.

It took me only about 20 minutes to align the GO22x85. At first I aligned them perfectly to my IPD. But then I noted that they would go out again when I ranged thru IPD. So I re-adjusted, setting one side image close to the other side at my IPD. I found that by doing so, it would still move when I changed IPD setting, but the image would end up still close, only R over L at some IPDs and L over R at other IPD settings. I found a position where the images would never move more than about 20-30 arcseconds apart, no matter how I cycled thru IPD. Essentially, I've got it now where images merge easily and instantly from about 58mm to about 70mm IPD.

Aperture, Magnification, Exit Pupil

There are numerous methods that can be used to measure effective aperture and actual magnification. I have employed several, the mask method, the loupe and scale method, the simple light projection thru the eyepiece onto a scale method and the target laser thru the aperture method. All of these are outlined in detail in the CN binocular forum, so I need not take several pages here to explain them. The following results are verified by using several different methods and getting data that agrees by the several methods.

Garrett Optical 22x85 Signature
full aperture appears is very close to 84mm
when set to distance exit pupil = 3.97mm
magnification was measured at about 21.1x
21x84

William Optic 22x70 Apochromat
full aperture appears to be 70mm

when set to distance exit pupil = 3.36mm
magnification therefore is about 21.1x
21x70

Takahashi Astronomer 22x60
full aperture appears to be 60mm
when set to distance exit pupil = 2.72mm
magnification therefore is about 22x
22x60

Compare the above to several of my 20x80s, which are:
17x71, 18x70, 18x72 and 19x71 and 19x72

and compared to two 25x100s, which are:
23x94 and 25x90

The WO22x70 looks like it uses identical eyepieces as the GO22x85. In fact, if you cut these two binoculars just in front of the prisms, they appear to be identical. However, the aperture and focal length statistics between these two are not the same. I assume here the focal length of the WO is 430mm, as stated for the ZenithStar 70mm scope. Well, the power in the GO22x85 and the WO22x70 is nearly identical. So either the lens in the WO22x70 has a somewhat shorter focal length than assumed here or the GO22x85 has a longer F, or the eyepieces used in these two binoculars vary in focal length.

Field Of View

Maximum fov in the GO22x85 is just a hair over 3.0°, just slightly wider than the two western stars in the head of Draco. I could just barely see both of those stars at the same time, so my maximum fov was just a hair under 3°. So, pressed up tight with my eyeglasses, I'm getting 96% of the fov. That's about the same for me as the Fujinon 16x70.

Garrett Optical 22x85 Signature
Full Tfov is 3.05°, therefore Afov is 65°

William Optic 22x70 Apochromat
Full Tfov is 3.0°, therefore Afov is 62°

Takahashi Astronomer 22x60
Full Tfov is 2.2°, therefore Afov is 48°

Oberwerk 25x100 IF

Full Tfov is 2.4°, therefore Afov is about 55°

Coatings, baffles, reflections

All three of these binoculars have nice even coatings and as far as I can tell are fully multi-coated on all surfaces. Reflections off the lenses are really held to a minimum.

Seen pictured here is the GO22x85.

Internal Baffles

The GO22x85 (left) and the WO22x70 (center) have no internal baffles. They do have finely ribbed sides inside the barrels which helps control reflection off the insides of the barrels. Note the Tak 22x60 Astronomer (right). It has three internal baffles sized to let the light cone pass but to block any stray light rays, eliminating reflections and stray light.




The WO22x70 shows that the target laser, at the extreme edges of the aperture, never hits the prism housing. It first hits the inside walls of the barrel tube and gets baffled at the edges. That accounts for the fine illumination, since this shows the prism is larger than necessary for the light cone.

Chromatic Aberration

On the moon, none show on-axis false color.

The GO22x85 shows a band of lateral color, predominantly yellow towards the inside and purple towards the outside edge of the lens. It's a fairly thick yellow band, but not obtrusive. The GO is by far the fastest of these three binoculars and even if all else were equal (which its not), should show the most color just by nature of the faster f/4.7.

The WO22x70Apo shows a very thin band of lateral color. It can be almost not noticed. But keep in mind, the WO22x70 is f/6.2 and the GO22x85 is f/4.7.


The Tak22x60 shows no lateral color at all. I could not force any color. Not only is the Tak Astronomer a true Fluorite objective, but also it is about f/5.9, pretty slow for a binocular.

The amount of color error seen is dependant on focal ratio, an f/4 having greater potential color error than an f/5. Also, aperture plays a significant role in color correction. An f/4 40mm will show one half the color error as an identically designed f/4 80mm lens.

CA - Longitudinal Color Blur

The following will discuss the real amount of color blur inherent in typical achromat design. This is a fact of life, design does not vary much from this. It may perhaps be swayed slightly towards one end of the spectrum or the other, but overall this pretty much represents what you get in achromats. Almost all binoculars are achromats.

First, I need to spell out a few basics:
The range of correction in an achromat is generally from C (~480nm) to F (~650nm). With the primary focal point focused on green light at 550nm, the 480nm and 650nm will both be in focus at the same position, that position being at a point 1/2000 F removed from focus of green light.

in other words, an achromat is corrected to 1/2000 the focal length (F), such that when focused on green light, the focal length of red and blue are coincident and are out of focus by 1/2000 F or 0.0005 F.

both the linear and angular dimension of the Airy disk are dependant on the wavelength of light, so in formulas below wavelength is always a factor.

The actual angular diameter of the Airy disk in the focal plane is entirely dependant on aperture diameter (D), not F and not f#.

The actual linear diameter of the Airy disk in the focal plane is entirely dependant on focal ratio (N), not just F and not just D.

Acceptable color blur is 3 times the diameter of the Airy disk.

The linear diameter of the color blur circle in mm can be found as delta focal length (or distance from focus) x D, or in the case of an achromat 1/2000 x D. In the case of a semi-apochromat it may be 1/3000 or 1/4000 x D. In the case of an apochromat 1/8000 x D.

For nm=550, the angular diameter of the Airy disk is 280/D = 2.8 arcseconds for a 100mm scope.

While generally we speak in terms of the Airy disk in the units of visual measure or angular size in arcseconds, the use of linear measure gives us a convenient method to compare the size of the Airy disk to the size of the color blur, since the method of calculating the color blur is in linear measure.

The smallest resolution the eye can see is about 60-80 arcseconds apparent (60-80 arcsec on line pairs in daylight. For point sources at night it is closer to 120-160 arcseconds). For me personally it happens to be about 80” day and 140” night. My personal best resolution is based on many tests and observation of both line pairs and point sources with many different instruments. My personal best is not atypical.

So how do the low limits of the eye affect the ratio of color blur vs. Airy disk? The visual appearance of the ratio of color blur is low limit eye dependant. While color blur is always larger than the low limit of the eye, the resolution disks are almost always limited by the eye. Therefore in all cases we need to use the low limit of the eye for resolution.

Since we need to refer to visual terms as we see by the eye, which is angular measure, we can use the dual linear/angular information we have regarding the Airy disk to convert the color blur to arcseconds and make some comparisons about different types of binoculars and how color blur is perceived by our eyes.

The color correction described exclusively refers to Longitudinal CA, on-axis color error.

Color Blur Comparison of the Tak 22x60, WO22x70 and GO22x85.

Let's assume color correction is 1/8000, 1/4000, and 1/2000 respectively.

F/# respectively are

GO85 is a f/4.7 air-spaced doublet achromat

WO70 is a f/6.2 FPL-51 ED doublet (labeled an Apo, but clearly not an Apo)

Tak60 is a f/5.9 Fluorite doublet Apochromat

the linear diameter of the Airy disk is N/735mm
for the GO it is 4.7/735 = 0.0064mm, or 6.4 microns
for the WO it is 6.2/735 = 0.0084mm, or 8.4 microns
for the Tak it is 5.9/735 = 0.0080mm , or 8.0 microns.

the color blur diameter in each is
for a 85mm @ 1/2000 it is = 0.0005 x 85 = 0.043mm or 43 microns
for a 70mm @ 1/4000 = 0.00025 x 70 = 0.018mm or 18 microns
for a 60mm @ 1/8000 = 0.000125 x 60 = 0.0075mm or 7.5 microns

GO85 is a f/4.7 air-spaced doublet achromat

color blur diameter = 43 microns

Airy disk diameter = 6.4 microns

Airy disk Angular diameter is 280/D = 3.3 arcseconds.

color blur angular diameter is 3.3 x 43/6.4 = 22 arcseconds

Color blur is 22/3.3 = 6.7x Airy disk

In a f/4.7 85mm achromat at 22x, color 22x22 = 484” / disks 3.3x22 = 73”

Magnified Airy disk is 73 arcseconds, but eye limit disk is 80 arcseconds, therefore

Observed color blur in daylight is 22x22 / 80 = 6.1x visual disk

GO85 Observed color blur at night is 22x22 / 140 = 3.5x visual disk

WO70 is a f/6.2 FPL-51 ED doublet (labeled an Apo, but distinctly not Apo)

In a f/6.2 70mm ED at 22x, color 8.3x22 = 183” / disks 4x22 = 88”, therefore

Observed color blur in daylight is 8.3x22 / 88 = 2.1x visual disk

WO70 Observed color blur at night is 8.3x22 / 140 = 1.3x visual disk

Tak60 is a f/5.9 Fluorite doublet Apochromat

In a f/5.9 60mm Apo at 22x, color 4.4x22 = 97” / disks 4.7x22 = 103”, therefore

Observed color blur in daylight is 4.4x22 / 103 = 0.9x visual disk

Tak60 Observed color blur at night is 4.4x22 / 140 = 0.7x visual disk

In the Tak, there is NO false color outside the Airy disk

We can compare these to a 1/4000 semi-Apo ED 100mm f/7 scope.

In a f/7 120mm ED scope at 25x, color 7.4x25 = 185” / disks 2.8x25 = 70, therefore

Observed color blur in daylight is 7.4x25 / 80 = 2.3x visual disk

Observed color blur at night is 7.4x25 / 140 = 1.3x visual disk

Here we’ve assumed the WO22x70 and the ED scope are both 1/4000. The slight improvement of the WO over the ED scope is due to smaller aperture.

The GO85 is nearly the same as any f/4 20x80. Let’s compare to a typical 20x80 binocular, although consider that nearly all f/4 80mm binoculars are more like 19x 72-74mm and are therefore closer to f/4.4. Therefore the typical 20x80 (assuming 19x73) is:

19x73 at f/4.4 air-spaced doublet achromat

Observed color blur in daylight is 24x19 / 80 = 5.7x visual disk

Observed color blur at night is 24x19 / 140 = 3.3x visual disk

A typical 20x80, reduced to an operating size of 19x73 has a slightly smaller color blur than the GO 22x85. The biggest difference is due to the size of aperture.

Let’s look at 100mm binoculars and compare f/4 to f/6

In a f/4 25x100, color 25.9x25 = 650” / disks 2.8x25 = 70, therefore 650/80 = 8.1x
Observed color blur in daylight is 26x25 / 80 = 8.1x visual disk

Observed color blur at night is 26x25 / 140 = 4.6x visual disk

In a f/6 25x100, color 17.1x25 = 428” / disks 2.8x25 = 70, therefore 428/80 = 5.3x
Observed color blur in daylight is 17.1x25 / 80 = 5.3x visual disk

Observed color blur at night is 17.1x25 / 140 = 3.1x visual disk

An f/6 25x100mm binocular would have slightly better color correction than a typical 20x80 and better than the GO22x85. A typical f/4 25x100 would be significantly worse than both.

So which binoculars have more acceptable color blur? Those with a lower blur/disk ratio have a more acceptable color blur. It is somewhat surprising how low those ratios are for small binoculars. Smaller apertures are FAR better than larger apertures.

Higher f/# moves the color blur ratio in the right direction.
Smaller aperture moves the color blur ratio in the right direction.
Lower power (within same size aperture) moves the color blur ratio lower.

And it is never as bad as the pure numbers first make it out to be, since in every case, the low power results in a disk that is below the resolution limit of the eye. Since the low limit of the eye "increases" the effective size of the visual disk, therefore the blur ratio goes down and it is always somewhat better than first numerically calculated. That's why, for binoculars, we must always consider the limit of the eye. Other than the simple fact that we see more false color surrounding a bright point in those achromats with the higher color blur, what are the effects of this secondary color?

What are the implications if high false color blur? Higher secondary (false) color leads to;

a reduction in light grasp. Light that should be focused into the image disk, the Airy disk, is left outside the disk and is spread out. The amount of light in the focused disk is not as bright as the image could be if all light were focused into the image disk.

a reduction in contrast. Contrast of extended objects is a function of an infinite number of overlapping Airy disks. If each disk contains all the possible light, then each disk has a maximum brightness and a maximum contrast to the adjacent area in the image. However, if each point has only a portion of all the light and is surrounded by a circle of out-of-focus light, the color blur, then each ovelapping point in the extended image is dimmer at the center, larger overall, blurred at the edge, and interferes with some portion of the overlapping light in every adjacent point. This has the affect of reducing overall contrast.

That is why well corrected Apochromatic lens provides a better image. These differences could easily be seen in the comparisons between light grasp and the contrast in the Tak22x60, WO22x70 and GO22x85.

Resolution Normal on USAF 1951 Line Pairs

The Tak recorded the best direct resolution reading, actually, quite impressive resolution. At 88 yds., I could detect both vert and horz bars for 3.23 arcseconds resolution. I could clearly see 3.6 arcsec. I averaged the Tak readings and recorded them as having seen 3.4 arcsec. Still that puts the Tak among the top very few binoculars I've tested. It also correlates very well with what I saw in splitting extreme close doubles.

The WO was very close to the Tak. Whereas the Tak could see both H & V bars for 3.23 arcsec, the WO could only see the horz bars at that level. It could see both H & V bars for 3.62 arcseconds res, the next step down. Still a very good reading, better than any other 20x80 I've tested.

The GO was tested at a distance much further away. I recorded a best of 3.6 arcseconds. It could see both H & V bars for 3.6 arcseconds resolution. Likewise, a very good reading, better than any other 20x80 I've tested.

All else being equal, a binocular with a higher magnification will always be able to see a finer resolution, so direct resolution readings cannot be compared. To compare resolution readings for binoculars at different powers, multiply the resultant reading by the magnification to get the apparent resolution. In this case all three of these binoculars resulted in apparent resolution of just a bit under 80 arcseconds apparent. I can count on one hand the number of binoculars I’ve tested that could see resolution that close.

One thing to keep in mind, all these were tested near the extreme close focus, especially the GO which was right AT close focus. Well, magnification increases at close focus, and I have not adjusted for that, so, although by only a small percent change, all of these values are slightly overstated. Actual resolution is a small fraction worse than stated.

For comparison, the Oberwerk 25x100 IF could only see 4.0 arcseconds and the GO TWP 20x80 was able to achieve only 4.48 arcseconds, 95 and 85 arcseconds apparent respectively.

I was all set up on my deck to observe a resolution chart pinned to a telephone pole about 100 yds away. Problem was I couldn't focus the GO22x85 that close. I ended up moving further back, all the way thru my front yard, across the street and half way up my neighbor's drive way. As it turns out, the close focus for the GO22x85 was about 175 yards.

Stellar Resolution

On the Trapezium,
the Obie 25x100 saw 4 stars with ease, distinct separation of all 4, with bright large nebula.
the GO22x85 clearly and easily resolved 4 stars, just a bit smaller, but well separated, nebula was still easy but smaller
the GO20x80 did not see 4 stars clearly, maybe only 3, much smaller, nebula not quite as bright, quite a bit smaller.

Focusing on a pair of stars, gamma Delphinus, 9.6".
the WO22x70 does very well, gives a nice tight point for each star, has very minor spiking of the brighter star in the pair.

The GO22x85 shows the largest points when focused best. Stars don't get as small as seen in the WO22x70. On a close uneven pair it makes it just a bit more difficult to see the pair cleanly separated.

The Tak22x60 focuses to extremely fine pinpoint dots, half the size of the dots in the GO22x85. There are no minor spiking points coming off of even the brightest star. The pair is very well separated, the clean black space between the pair seemingly a bit wider that that seen in the GO22x85.

Vega
the GO22x85 shows it as a white star with an obvious blue halo.
the WO22x70 shows a cleaner white star, little halo.
the Tak 22x60 shows pure white and the smallest point of the three. Even on a star as bright as Vega, it focuses a smaller dot and shows almost no points or halo around the clean dot.

The WO22x70 refines the image to somewhat better than is shown in the GO22x85. The focused dot is a bit smaller and the tiny spikes that emanate from the brightest stars are a bit smaller. I'm not sure what I attribute this to, but it certainly doesn't hurt that it is f/6.

Although there is no question that the Tak is putting up the finest dot point image of these three binos, the GO22x85 seems to put up the brightest image. On targets such as M27, M71, M57, M15 and M11, it was the GO22x85 that to me seemed always to give the brightest image of the diffuse object and its surrounds. That shouldn't be too surprising as the GO22x85 does have far greater aperture. Even though the Tak22x60 has far better illumination than both these others, the much larger aperture of the GO22x85 seems to make up for that lower degree of illumination.

So, for Apo images and finest pinpoints try the Tak. For deep sky, but a bit less refined image, try the GO Signature. Fairly obvious, but the WO22x70 falls in between. The WO22x70 shows better pinpoints than the GO22x85 but not as good as the Tak, and the image quality of the WO22x70, although better than the GO22x85, is not the same as the Apo correction of the Tak. In fact, although the WO22x70 is better color corrected than the GO22x85, it still shows false color and I'm not sure the WO22x70 should be called an Apo by any standard. ED perhaps yes, but Apo, I think not.

I was looking at the doubles in Lyra, and at M57, and thought of a challenge for these three 22x binoculars, a special close double with three 22x binocs. First I scoped 100 Herc in all three, but it is so wide (14") for this power, it was really just for focusing. Then I turned to:

95 Hercules 18h+22 a nearly perfect equal very close double, 5.0-5.1/6.3"

In the GO, points are definitely large dots. I can still notice quite readily it's two stars, but the points are merged into one, not clearly separated.

In the WO, points are only slightly enlarged but there is a hint of a dark space between that shows total resolution.

In the Tak, I see very tiny pinpoints with a definite resolved dark space, clear dots look outstanding in the Tak.

These are probably three of the best binocular views of 95 Herc I've ever seen. I know I've split this pair using my Oberwerk 25x100 and with my BT100, but both at higher power.

Sharpness in Outer fov

In the GO22x85, Nu Draco, a 1 arcmin equal pair, was still just visible at the very edge. Total distortion was about 50 arcseconds at the edge. That's better than some 20x80s, but no better than the GO Gemini 20x80 or the Oberwerk Standard 20x80. Edge sharpness in the WO and the Tak is so fine that Nu Draco was too wide a test object for these other two binoculars.

Field Sharpness of the three binos tested on Theta Serpens, mags 4.5-5.0 @ 22".

In these 22x binocular that gives me about 460-480 arcseconds apparent. My typical measure for what I rate as usable fov would be 600 arcsec apparent, so this is a more stringent test than total usable fov. But I needed something closer and this 22" star was available and it gives me the opportunity to compare the three. I previously measured the GO22x85 and it deteriorates to worse than 600 arcseconds between 70-75% out from center. Based on what I saw in the Tak, it would do better than 600 at the very edge.

Garrett Optical 22x85 Signature (21x84) Full Tfov is 3.0°, therefore Afov is 64°

William Optic 22x70 Apochromat (21x70) Full Tfov is 3.0°, therefore Afov is 62°

Takahashi Astronomer 22x60 (22x60) Full Tfov is 2.2°, therefore Afov is 48°

For a comparison, I’ll include the Oberwerk 25x100 IF and the GO TWP 20x80. Those 25x100s measure up at about 23x95 and the GO TWP20x80 are closer to 19x72. The GO 22x85 measures 21x84, the WO70 is 21x70 and the Tak60 is 22x60. The Obie 25x100 is the closest in sixe to the GO22x85.

Garrett Optical TWP 20x80 (19x72) Full Tfov is 3.2°, therefore Afov is 61°

Oberwerk 25x100 (23x95) Full Tfov is 2.4°, therefore Afov is 55°


By nature of it's narrower Afov eyepieces, the Ob25x100, as compared to the GO22x85, actually has a sharper image further out in the outer fov. But also by nature of it's 55° Afov, the Ob25x100 starts out with a narrower 2.4° Tfov as compared to the 64° Afov of the GO
22x85, which results in a 3° Tfov. The 25x100 is equally sharp at least 10% wider out (85% vs 75%) than the 22x85, but as explained here, the 22x85 has an overall sharper wider fov. What this boils down to, when both are measured to the exact same standard of 600 arcseconds apparent total aberration, the 25x100 has a useable fov of 85% or 2.0° while the GO22x85 has a usable fov of 75% or 2.3°

field sharpness compared on same double star
Theta Serpens, mags 4.5-5.0 @ 22".


Limit of 22" sharpness:
in the Tak60, I could see it at 95% out, or 2.10° out of 2.2°
in the WO70, I could see it at 75% out, or 2.25° out of 3.0°
in the GO85, I could see it at 70% out, or 2.1° out of 3.0°


in the GO20x80, I could see it at 75% out, or 2.4° out of 3.2°
in the Ob25x100, I could see it at 80% out, or 1.9° out of 2.4°

As is often the case, the binocular with the widest Afov eyepieces seems to suffer from the least sharp % fov. I've rarely seen binoculars vary from this, the exception being some of the most expensive and highest quality.

Here we have the GO22x85 with a very slight wider Afov than the WO22x70. Both have essentially a 3° Tfov. They are nearly equal in outer field sharpness. FWIW, in these tests, the WO came up just a few percent wider in sharp fov.

Then we have the Tak22x60. Now the total fov is only 2.2° and the Afov of the eyepieces is only 48°. BUT, look what we get out of that. The outer field sharpness of the same star extends out to 95% of the Tfov and that gives us a 2.10° sharp Tfov. The narrow Tak, less that 75% of the total FOV of both the others, actually has a sharp fov as wide as the GO85, the binocular with the widest Afov of the three.


In all three of these binoculars I could see M26 and NGC6712 at the same time. In both the WO and GO, these two objects span across about 75% of the Tfov. Actually in the Tak I had to pan slightly to get each just into the edge of the fov, because they are about 5% wider apart than the Tak Tfov. But in the Tak, I could see both of those in the outer few % of the fov. Both M26 and NGC6712 are about visual mag 8. M26 has a brightest star of mag 10.3 and NGC6712 has a surface brightness approx mag 12.

Field sharpness of the three compared on same double star
100 Herc mags 4.9-5.0 @ 14.2".


Limit of 14" sharpness:

in the Tak, I could see it at 85% out, or 1.9° out of 2.2°
in the WO, I could see it at 70% out, or 2.1° out of 3.0°
in the GO, I could see it at 65% out, or 2.0° out of 3.05°

I was pretty impressed with the edge view in the Tak, but it's the WO that gives the widest very sharp fov. This star is giving about 300 arcsec, so this is easily still pretty good view.

I saw this star at 60% out in the Fujinon 16x70, and also I saw this star at 70% out in my long gone 20x80 Oberwerk Standard. That one is quite a long focal length, f/4.7 if I recall.

Vignette

A very simple check to show off-axis vignette is this; the edge of objective is lined up with the edge of internal baffle or prism stop, whichever hits first. Notice the size of clear view thru and out the back end. This mimics the measurement one gets when checking for percent illumination (refer to the next section of this report). The Ultra and the Signature are fairly typical of very good binoculars. All four of these are in the top 15% of all measured binoculars. 60 out of 70 binoculars DO NOT have as great a degree of illumination as any of these four. Look at the difference between them from smallest to largest. 60 others show a smaller exit view than the smallest seen here.

Upper left Oberwerk Ultra 15x70 Upper right Garrett Signature 22x85
Lower left William Optic Apo 22x70 Lower right Takahashi Astronomer 22x60

For clarity here is a larger image of the Tak 22x60

Illumination

Garrett Optical 22x85 Signature
36mm or 42% center of aperture provides 100% illumination of exit pupil

William Optic 22x70 Apochromat
35mm or 50% center of aperture provides 100% illumination of exit pupil

Takahashi Astronomer 22x60
50mm or 83% center of aperture provides 100% illumination of exit pupil

Well, the most outstanding measure of the above is the percent illumination of the Tak 22x60. I've now measured about 70 binoculars for illumination. Only 10 of them are over 40%. Only 4 of those reach 50%, two Fujinons, a Pentax and this WO 22x70. BUT only one exceeds 50%, the Tak Astronomer. And it shows that an astounding 83% of the center of aperture provides 100% illumination to the exit pupil.


Both the GO 22x85 and the WO 22x70 have 35-36mm of the center of the lens that is providing 100% illumination of the exit pupil. Then they both taper from 100% to about 50% illumination at the edges. Assuming illumination in both is a constant slope of dropoff, then the GO Signature will have slightly more total light delivered to the exit pupil, simply by nature of the wider aperture. But how much more? Well, surprisingly, not as much as you might think.

If you break down the light into concentric rings so you can calculate how much light from each ring, you can approximate how much light is delivered into the exit pupil. The central area of 35mm dia is full 100% lit. But, for example, take the 10mm wide ring between 45mm and 55mm diameter. 55sqrd minus 45sqrd leaves us with a ring of 3025-2025=1000sqmm. For sake of our example let’s say that ring delivers 70% of its light. Therefore it delivers effectively only about 1000sqmm x 70% = 700sqmm of light. This continues to decrease in each concentric ring further out until it drops to about 40-50% at the edges. You can do this for each concentric ring and approximate the total light in the exit pupil by adding up the subtotals for each individual ring. I call that the effective illuminated area.


Brightness affects of %Illumination






SCORE

SCORE

SCORE


dist % from center

full aper

effective

brightness

Total

Center

TOTAL

model

illum

illum

illum

total

illum

ratio

Illum

Illum



100%

75%

50%

area

area



area









max 5

max 3

max 8

GO Signature 22x85

42

74

96

5542

4078

74%

3.68

1.36

5.04

William Optic 22x70

50

75

96

3848

2896

75%

3.76

1.45

5.22

Takahashi 22x60

83

90

96

2827

2519

89%

4.46

2.34

6.79

The GO22x85 has almost 50% greater light gathering area than the WO22x70. But when you calculate total light, because the GO22x85 has a smaller percent of full illumination, the GO22x85 delivers only 40% more light than the WO22x70.

Compare the WO22x70 to the Tak22x60. Well, the WO22x70 has 36% greater light gathering area more than the Tak22x60. But the Tak has so much of it's lens area that provides 100% illumination, 83% for the Tak vs 50% for the WO, that the Tak actually delivers only about 15% less light to the exit pupil than the larger WO22x70.

Now compare the GO22x85 to the Tak22x60. The GO22x85 has 100% more light gathering area than the Tak22x60, but only 60% greater light delivered into the exit pupil.

The GO22x85 is very good at light delivery. At 40% full illumination, it ranks among the top 10 I've seen.

The WO22x70 has an even more efficient light delivery system. It measures at 50% full illumination, ranking it with 4 of the top 5 binoculars I've seen. I'd consider it excellent.

The Tak Astronomer 22x60 has such an efficient light delivery system that it is acting more like it is an excellent 22x70. It is so efficient that it is a superior 22x60 and ranks by far the best binocular I’ve ever tested.

Image Brightness

Brightness is determined by much more than exit pupil. Testing for percent illumination across the exit pupil shows illumination varies dramatically across a range of binoculars. Brightness can be compared by exit pupil only IF all instruments have equal illumination. That is rarely the case. Here is an example:


Brightness affects of %Illumination






SCORE

SCORE

SCORE


dist % from center

full aper

effective

brightness

Total

Center

TOTAL

model

illum

illum

illum

total

illum

ratio

Illum

Illum



100%

75%

50%

area

area



area









max 5

max 3

max 8

Fujinon BFL 8x42

50

70

95

1272

932

73%

3.66

1.29

4.95

Bushnell Legend 8x42

15

55

100

1342

879

65%

3.27

0.70

3.97

Zen Ray ED2 8x43

5

50

90

1299

801

62%

3.09

0.56

3.65

Here we have three binoculars of nearly equal size and exit pupil. Without analysis, we would expect them to be equally bright. But we can see from the illumination data that the Fujinon provides an effective 932 out of 1272 toal sq mm of illumination, far more light to the exit pupil than either the Bushnell Legend of the ZEN ED2, even though it is slightly smaller in total light gathering area.

Another misconception is that a larger aperture is going to provide more light into the exit pupil. Well again, all else equal that would hold true, but it may not be the case. The following data does not address power and the size of the exit pupil, but only the size of the aperture, where we know a larger aperture provides a greater light gathering area, and we might expect a larger aperture to also provide a greater effective illuminated area of exit pupil. Look at this data:


Brightness affects of %Illumination






SCORE

SCORE

SCORE


dist % from center

full aper

effective

brightness

Total

Center

TOTAL

model

illum

illum

illum

total

illum

ratio

Illum

Illum



100%

75%

50%

area

area



area









max 5

max 3

max 8

Takahashi 22x60

83

90

96

2827

2519

89%

4.46

2.34

6.79

Oberwerk 15x70

40

60

85

3071

2019

66%

3.29

0.93

4.22

Anttler 20x80

1

43

90

3937

2359

60%

3.00

0.41

3.40

The Anttler 20x80 is a binocular that is similar to some other common 20x80 LW binoculars. It is effectively about 70mm. The Oberwerk 15x70 is effectively 63mm. So here we have a 60mm, 63mm and 71mm binocular compared. The Obie and the Anttler are about 10% and 40% larger in LG area than the Tak, yet we see both have a lower effective illuminated area of the exit pupil than the Tak.

Using these examples to help understand the implications of illumination may help to realize that brightness is not simply based on exit pupil or size of aperture. If we were to base our expectations of illumination on aperture, we might expect the Antler must be brighter than the Oberwerk and both would be brighter than the Tak. But that is NOT the case. The Tak does such a good good at illuminating the exit pupil that it far outweighs the increase in aperture in either of the other two.

All else equal, you could make a comparison of exit pupil. But all else is seldom equal.

Limiting Magnitude Compared

Conditions weren't the best to reach ultimate limit, moon was nearby, but under any conditions a comparison at the same time shows differences between models.

I used my Obie 25x100, GO SS22x85 and Cel Giant 20x80
My previous measures show the three binocs as 23x96, 21x84 and 18x72

The 25x100 could see 10.6 stars pretty good, and one 10.9 barely and another 10.9 averted

The 22x85 could see 10.6 stars just barely, and both 10.9 only averted

The 20x80 could see 10.1 OK, 10.25 barely and 10.5 just barely/averted

Not definitive, since I didn't reach deep enough beyond the 85s/100s, but I couldn't see mag 11.0, 11.2 or 11.4 in either one. On a better night I would. But what I noticed most was there was a huge difference between 20x80 and 22x85 and even though things appeared brighter in the 25x100, there was not nearly as much difference from 22x85 to 25x100.

I tried for a magnitude limit comparison again. same target, M45. Moon near half full

Cel20x80 - 18x72 – 1059 seen, 1064 avert, 1072 not seen

GOTWP20x80 - 19x72 - 1064 seen, 1072 avert, 1087 not seen

GO22x85 - 21x84 - 1072 seen, 1087 avert, 1087 not seen

Ob25x100 - 23x96 - 1087 seen, 1087 seen, 1091 not seen

Didn't see any deeper than last night, but spent a little more time and tightened up the observations, also included both the Celestron 20x80 and the GO TWP 20x80. I suspect the spreads would get slightly wider under a good dark sky.

On the Trapezium, not much difference between the Celestron 20x80 and the GO TWP 20x80, although, I must admit, it looked smaller in the Celestron. It should have. Cel=18x72 and GO=19x72. Noticable difference in size moving up to the 22x85 and fully resolved, and a notable jump again to the 25x100 and easily resolved.

On another night, I made numerous attempts to reach the limit of magnitude.

Faintest star see naked eye was 5.05

The Tak 22x60 did not see any mag 11 stars. It could see mag 10.73 easy and mag 10.83 OK.

The WO 22x70 glimpsed 11.05 averted, maybe 3 times. Saw mag 10.73 easy and 10.83 OK.

The GO22x85 saw mag 10.73 readily, mag 10.83 easily. Near the mag 11.05 stars is also an 11.04, both seen numerous times averted. Mag 11.05 was seen direct a few times. Tried without success to see 11.17 and 11.18.

So the GO22x85 could see 0.2mag deeper than the Tak 22x60 and could see those stars easier than the WO22x70.

Short observing session with GO22x85 4:30 to 5:30 am. At 5am faintest star naked eye visible was mag 5.45. In M45, I observed stars of mag 11.3 direct and mag 11.5 averted. That's the deepest I've ever gone with the GO22x85.

Session in early AM, Sky LM 5.5. 4:30 to 5:30 am. At 5am faintest star naked eye visible was still mag 5.5. (the star was 57 Tau). Sky conditions were identical to my brief session two days ago.

This short observing session with WO22x70 parallels the brief session I had the other morning with the GO22x85. In M45, I observed stars of mag 11.3 averted (A18e) and mag 11.5 averted (A18d), however, I only glimpsed A18d (mag 11.5) twice and after about 5-10 minutes of trying could not see it any more than just those glimpses. It was easier to see it the other day with the GO22x85, when it was seen averted and each time for several seconds at a time. Just as with the GO22x85, this is the deepest I've ever gone with the WO22x70, however it was easier to see mag 11.5 with the GO22x85 than with the WO22x70.

A few days later, conditions again identical, sky mag 5.5.

Tak22x60 saw A18 c,d,e = mag 11.5

Also observed 11Mon 4.6-5.5/7.4” seen easily.

Could not see M74

All three of these binoculars observed a mag 11.5 star, sometimes direct, sometimes averted. It is too close to call one better than the other as conditions could have easily varied by some not noticeable margin. However, what is significant is that a 22x60, under same conditions, could see at least as deep as a 22x85. As mentioned under implications of false color blur ratio, at least in part, this may be related to the ability of the Tak60 to focus all the light into the Airy disk.

Deep Sky

Diffuse Objects and edge light loss

M71 can be seen in the Tak60 all the way to the edge whether positioned at top, bottom, left or right.

M71 in both the WO and the WO can still be seen at the edge when move to top or bottom, but when moved to left or right, is lost in the last 10% of the fov.

North America nebula section along east cost (the only portion that stood out as potential nebula) appeared brighter in the Tak than either of the other two binoculars. It appeared brighter in the GO85 than in the WO70.

In general however, faint diffuse objects were a bit easier to find in the GO85. For instance a faint mag 9 globular NGC 6712, just below M11, was seen by all three, but was easier spotted with the GO85.

FWIW, objects were always perceived as larger in the Tak60. The much narrower field of view cropped out significant sky background and presents each target in a smaller window. When going back and forth from the larger fov GO85 to the smaller fov Tak60, always for a few seconds my impression was that the object appeared larger in the Tak. Illusion only.

In the WO22x70, M1 and M78 were fairly easy and seen right away.
BT100 at 34x found M74 after some wiggling to-fro over the spot.
Garrett 22x85 and WO 22x70 both saw IC342, more difficult than M74.

On a morning with sky about mag 5.2, but very transparent, I observed the vicinity of NGC7790 near Beta Cas. Several clusters have been noted at this location, although they are not charted in SkyAtlas 2000.0 or smaller atlases, they are charted in Uranometria.

In the Garrett 22x85, 7790 was a distinct spot, and that area to the NW resolved into 12-13 stars spread over a 15 arcmin area. In the BT100 at 34x, I counted 16-17 stars over the same 15 arcmin area. The area to the NW that I’m describing is centered on the location of NGC7788. However, it seemed much too large to be 7788. It is possible that some of the stars in the center of that mix are members of 7788, but certainly not all of them. There was no concentration noticed, even in the 22x85 or the 34xBT100, that I could call cluster 7788. I then realized this area would require some research and careful observation.

Here’s what I found:

7790
L&S 8', 134*, using 150mm about a dozen * in a rectangle EW, in 250mm 25* within 4'x2', 5 brighest stars on west form a circlet. L&S has a full page 7"x10" plate of 7790 showing photometry. The densest concentration of bright stars is within about a 4' area and that area contains perhaps only a dozen stars brighter than mag13.
NSOG EW elongated mist, 10* mag 11 to 12, 30* in a 4'x2' area
A&H 5' Br* mag10.0, SfBr 12.0

7788
L&S 9' 20* nested in a group of mag 7-10 stars 15' across, 15* mostly east of a br*, in 250mm counted 14* in a 1.5' area
NSOG 9' 20*, a 5' concentration of mag 9-12 stars, mostly mag12-13
A&H 4' 20* Sb12.4

Based on these data, I doubt I saw the central area of 7788 in the 22x60 or 22x85. I may have seen some of the very brightest stars, but A&H defines this cluster as 4 arcmin. I counted 17 stars across 11-12 arcmin, well outside the bounds. I trust the Archinal and Hynes data and the L&S observations more than any other.

I noted in two observations of 7790 using my 22x85 that I measured it as 2-3 arcminutes in diameter. I could not see any more in the Tak22x60. For those of you in dark sky areas, this group may offer a difficult challenge. Here I post some observations with other equipment, just to give you an idea of what might be needed to see these objects.

Observation 9-13-09 11pm to 2am sky mag 5.2
used Oberwerk BT100 with 18mm AT Paradigm for 34x100, 1.7°fov, 2.9mm exit pupil
also used TV85 with 14mm Radian for 43x85 mono, 1.4°fov, 2mm exit pupil

Tested 33xBT100 for LM and found it could reach mag 11.4-11.5.

I spent a considerable time observing this area, recorded a page of notes and made a crude sketch. Here are the notes.

I used two measured stars that span 10 arcmin to judge comparative sizes of clusters.

NGC 7790 - brightest star on se edge of a hazy unresolved spot. Haze bordered on nw by 4 stars curved to encircle the haze spot. No resolution within the haze. Total width no more than about 4 arcmin. (A mounted Fujinon 10x50 could see this only as a small averted hazy spot). I do believe I saw the circlet in 7790.

NGC 7788 - plotted 17 stars using 33xBT100. Fainter stars centered on a brighter asterism of 3 stars in a line with a slight bend. Uranometria shows the extent of NGC7788 spans between these 3 stars. About half of all the stars I plotted are just outside the boundaries of extent plotted in Uranometria, so all may not be a part of the true cluster. My plotted stars are scattered over about 10-12 arcmin area. Considering LM test above, I would say all of these stars are brighter than mag 11, the 3-5 brightest perhaps mag 9-10. (A mounted Fujinon 10x50 could see no more than 6 stars here across the full extent of 10 arcmin, no haze noted).

More Deep Sky Objects

Short observing session with GO22x85

4:30 to 5:30 am. At 5am faintest star naked eye visible was mag 5.45. In M45, I observed stars of mag 11.3 direct and mag 11.5 averted. That's the deepest I've ever gone with the GO22x85.

OC 2194 in the upraised arm of Orion was seen as a very faint diffuse spot. M1 and M78 were fairly bright and pretty large. M33 was very large. Gamma Aries 7.8" was seen split, but not easily. Searched for M74 and suspected seeing it averted two or three times. M37 was somewhat resolved, perhaps 20-30 stars. NGC 2157, near M35, was seen as a diffuse spot.

Searched for IC342 in Camelopardalis, but did not see it. Unfortunately, when I returned inside and consulted my charts, I'd found that I was concentrating my efforts about 1° away from the correct spot. Should have taken the charts out with me! On the way to it, all the way from Cassiopeia thru Perseus, I caught NGC457 the Owl and saw the faint diffuse spot of nearby 436, also saw M103, NGC 659, 653 and 654, Stock2, Double Cluster, OStf26, NGC1502 and Stf485 within.

At the other end of Cas, NGC7789 was a large diffuse glow (perhaps 10-15 stars), and the only cluster I could make out near the recent area of intense study was NGC7790. However, I did see about 10-12 scattered stars around the area of 7788. Found NGC129 half way between gamma and beta Cas.

Other clusters seen: M38, NGC1907, M36, NGC1662 in Orion shield, 1807 and 1815 in Taurus above the shield, 2169 the 37 cluster and 2244 the cluster at the center of the Rosette neb.

I saw NGC2264 the Christmas tree cluster and Stf953, a 7" pair below the Christmas tree. This pair is a bit closer and much fainter than Mesartim and was considerably more difficult, although it did appear split in the WO, as compared to in the GO22x85 where I would say it appeared elongated but not cleanly split.

Sunday morn 9-20 Sky LM 5.5. temps 45°. 4:30 to 5:30 am. At 5am faintest star naked eye visible was still mag 5.5. (the star was 57 Tau). Sky conditions were identical to my brief session two days ago.

The "7" in NGC2169, the 37 cluster, was quite prominent. Nearby OC NGC2194 in the upraised arm of Orion was seen as a faint diffuse spot although fairly large, perhaps as large as the "7". M78 was pretty bright in comparison. NGC 2194 was similar to M1.

M33 was very large. I mistakenly reported in one report that I thought M33 filled about 1/3 of my 3° fov. I would say it filled no more than 20-25% of my fov.

All four components of the Trapezium were cleanly separated even perhaps 30-40% off the center axis. But by 60-70% out, none of the Trapezium stars could be seen individually.

I observed Sirius, Betelgeuse, Rigel and Venus looking to instigate false color and even moving these to positions well off-center could not see any false color. Betelgeuse was a distinct orange.

GO22x85 mounted on my preferred setup for large binos

Bogen 501 head on a Bogen 3246 tripod.

I've had two GO22x85s for a while and recently put one up for sale. It sold in less than 24 hours. The following was the last observing session with this binocular before I packed it up to ship to Greece. This evening and morning turned out to be a very nice last session with these GO22x85 before I sent them on their way. Good luck to their new owner.

Viewing for pleasure 10-21-09

past few nights some PM some AM

I also had my TV85 with a few eyepieces. Used mostly 24mm Tak LE (25x) 18mmTakLE(33x), 12.5mm TakLE(48x) and 10mmRadian(60x).

M31, M32 and M110 all visible at once in the
22x85. M31 extension grew with time, seemed to encompas both other small galaxies. Length appeared to extend to or at least near edges of fov.

Tried Almach with the binocs and couldn't see it. So I put the scope on it (reversed L-R) at 33x and found the secondary, beautiful blue. When I went back to the binoculars, in brief moments I could see it. Nearby M76 was seen, pretty faint, but quite obvious.

7789 in Cas in the
22x85 was a broad diffuse glow, but not resolved. In the scope at 33x, I could resolved about 20 stars, although the glow was not quite the same in the scope.

22x85 - In the double cluster, the preceeding cluster can be seen to have a small curved asterism I call the cup, almost dead center. At the open end of the cup is a single bright star. The cup can be seen clearly in the 22x85s made up of 5 stars in a curve. This made me think of the Barry Simon project to develop photos depicting what clusters look like through various binoculars. At 22x, the central core of the preceeding cluster shows this cup.

In Cas, M103 to the three nearby clusters, 659, 663, and 654. The faintest 659 showed up very well. Then from the double cluster, over to the running man, Stock 2, then to the double OSS26, it's 64" and could easily be seen anywhere within the entire fov. Mrk6 showed its little straight line. I saw the two clusters involved in IC1805, Mel15 and NGC1027, both seen fairly large. Then I saw just a spot of stars that I could call NGC1848. Tr3 was easy to find.

A drop further east and Kemble's Cascade came into view, very nice, ending at cluster NGC1502 with an 18" double in the center. From there, almost due north, I panned to a small grouping of four stars that cradle the extremely faint galaxy IC342. This is one of those nights that at best all I can say is, I thought I saw it.

M33 stood out easily in the
22x85, very large.

Mesartim was split. A nice pair for this binocular, even and only 7.8" close.

The Trapezium was beautiful! The extension glow of the nebula fanned out to make the bird shape that I see, with the little circular spot of M43 as the head. All four members of the Trap clearly resolved in the
22x85. In the scope at 48x, I could see the E component, but not F.

M78 - could barely just make out that there are stars invloved. In the scope at 48x, I could easily see two stars in M78.

In Sigma Orionis, in the scope I saw 8 stars that make up "the little Sagitta" arrow asterism. In the
22x85s, I could only see 6 of those stars.

I finished off the late morning with a view of M44, the Beehive, in each. In the binoculars at 22x, I counted about 80-90 stars in the hive. With the scope, I think at 33x, I counted between 100-110 stars.

Rating Binoculars for Performance

We should not assume just because two binoculars are specified as 10x50 that both will operate the same. Likewise, we cannot assume a simple index that calculates on only magnification and aperture will give an accurate representation of the difference between any two of different sizes. That forces you to accept that there are never differences in the quality of the delivery system. Again, we know that quite often is not the case. Simple indices give you an indication of what one size would be like compared to another size ONLY if both are actually the specified size and both are of the exact same quality. That is rarely the case.

I first wrote this in 2002, but I will reiterate it again here; Rating Binoculars needs to account for weighting of performance aspects to include variable factors such as (but not limited to) true Magnification, Effective Aperture, Resolution, Illumination of the Exit Pupil and Contrast. These all add more relevance to a total Binocular Performance Index than just accounting for aperture and magnification and exit pupil, the basis for simple common indexes.

Some indices use specified magnification and aperture, some rate brightness based on area of exit pupil and some use total light gathering area. Those are dependant on the nominal specified values being whole. Then these indices are assumed to provide a ranking of various sizes binoculars. For too long, it has been accepted that published specification values can be used to calculate a rating index. While any simple index can be developed to give some indication of relative specified sizes, these must assume the relative specified sizes are generic and apply to all binoculars across the board. Often, specifications have been shown to be not quite accurate enough, or at the very least incomplete.

This is where we really see effective aperture and illumination come into play as rating criteria. A simple area of objective or brightness of exit pupil may give a false representation when we are comparing some binoculars that have 10% reduced effective aperture and a composite effective illumination of only 50-60% of light gathering area while others may have a very high 70-75% illumination of a light gathering area that uses the full objective. For examples, see the section of this report titled Illumination.

Examples of simple indices:

Bishop: magnification x aperture (heavily weighted to aperture)

10x50 = 500

15x70 = 1050

Adler: magnification x sq rt aperture (slightly weighted towards magnification)

10xsqrt50 = 71

15xsqrt70 = 125

Light Gathering Area: area of objective lens (pi r sqrd)

10x50 = 50mm, therefore LG = pi x (50/2) sqrd = 1963

15x70 = 70mm, therefore LG = pi x (70/2) sqrd = 3848

Twilight Factor is Brightness Ratio: diameter of exit pupil squared.

10x50 exit pupil = 5mm, therefore BR= 25

15x70 exit pupil = 4.67mm, therefore BR = 22

The Adler Index, in my opinion, (and given all else equal) is a better representation of indexing, but both Bishop and Adler fail to consider actual magnification and effective aperture, both of which change the outcome. In addition, percent illumination has an affect on the Brightness Ratio and numerous other performance qualities have a dramatic affect on the resultant relative rank position when applied to specific models of binoculars. So, while perhaps good for generalization, these general indices are not good for specific ranking.

In general, across a wide range of binoculars:

magnification generally ranges +/- 5%, but can vary by 15%

aperture ranges from 100% full to 85% of full

illumination ranges from 75% of Light Gathering area to only 50% LG

and resolution varies from median by +/- 10 to 15%

Using Adler as a base, and accounting for known tested aperture:

For a best 12x50s with full aperture and 75% illumination, we get:

Adler = 12 x sqrt50 = 85

Light Gathering (LG) area = area of 50mm = (nominal) 2500

Exit Pupil (EP) = 50/12 = 4.16mm

Brightness Ratio (BR) = area of exit pupil = 4.16 squared = 17.4

True brightness (Illumination) = 17.4 x 75% = 13.1

For worst 12x50s with only 45mm effective aperture and 60% illumination

Adler = 12 x sqrt45 = 80

Light Gathering (LG) area = area of 45mm = (nominal) 2025

Exit Pupil (EP)= 45/12 = 3.75mm

Brightness Ratio (BR) = area of exit pupil = 3.75 squared = 14.1

True brightness (Illumination) = 14 x 60% = 8.5

The effective aperture in our example best 12x50 provides a 23% larger LG area, and therefore 23% larger area of EP. Because of the higher illumination over the area, 75% of 50mm vs 60% of 45mm, performance is actually a 50% improvement in illumination from worst to best 12x50. Simple indices would never show this difference in performance. That is a pitfall of depending upon simplicity to make performance judgments.


Measured affect on Index

spec

spec

spec

spec

dia

spec

real

real

real

real

real

illum

illum

effect

 

mag

aper

Adler

LG

EP

BR

mag

aper

Adler

LG

BR

area

%

BR

Oberwerk 25x100 IF

25

100

250

7854

4.0

16

23.5

96

230

7238

16.7

4723

65%

10.9

Oberwerk 22x100 A

22

100

220

7854

4.5

21

21.0

91

200

6504

18.8

3613

56%

10.4

Garrett Signature 22x85

22

85

203

5675

3.9

15

21.3

84

195

5542

15.6

4078

74%

11.4

Garrett Gem TWP 20x80

20

80

179

5027

4.0

16

19.0

72

161

4072

14.4

2750

68%

9.7

Anttler Skysweeper 20x80

20

80

179

5027

4.0

16

17.0

71

143

3959

17.4

2373

60%

10.5

Burgess LW 20x80

20

80

179

5027

4.0

16

18.0

70

151

3848

15.1

2555

66%

10.0

William Optic 22x70

22

70

184

3848

3.2

10

21.3

70

178

3848

10.8

2896

75%

8.1

Fujinon FMT-SX 16x70

16

70

134

3848

4.4

19

16.0

70

134

3848

19.1

2772

72%

13.8

Oberwerk Ultra 15x70

15

70

125

3848

4.7

22

14.5

70

121

3848

23.3

2726

71%

16.5

Takahashi 22x60

22

60

170

2827

2.7

7

22.0

60

170

2827

7.4

2519

89%

6.6

Pentax PCF WP II 20x60

20

60

155

2827

3.0

9

19.8

57

149

2552

8.3

1754

69%

5.7

Nikon SE 12x50

12

50

85

1964

4.2

17

12.0

50

85

1964

17.4

1242

63%

11.0

Oberwerk 12x50 Sprt RP

12

50

85

1964

4.2

17

12.0

48

83

1810

16.0

1090

60%

9.6

Fujinon FMT-SX 10x50

10

50

71

1964

5.0

25

10.4

50

74

1964

23.1

1393

71%

16.4

Nikon Action Ex 10x50

10

50

71

1964

5.0

25

10.2

48

70

1810

22.3

1237

68%

15.2

ZenRay ZEN ED2 8x43 RP

8

43

52

1452

5.4

29

7.8

41

50

1320

27.6

815

62%

17.0

Celestron Regal 8x42 RP

8

42

52

1385

5.3

28

8.1

42

53

1385

26.6

886

64%

17.0

Bushnell Lgnd 8x42 RP

8

42

52

1385

5.3

28

8.2

41

53

1320

24.8

864

65%

16.2

Fujinon BFL 8x42

8

42

52

1385

5.3

28

8.0

40

50

1257

25.3

920

73%

18.5

The table above accounts for only actual magnification, effective aperture and measured illumination of the exit pupil. Still to consider are primary aspects such as resolution and contrast and even some lesser aspects. Notice the significant differences in the real Light Gathering area (real LG) from spec, and note the Illuminated Area (illum area). These have real affects on the Brightness. In a simple index, twilight factor (Brightness) is exit pupil squared (spec BR). Using real magnification and real aperture we get (real BR) based on the real exit pupil size. Going one step further, applying illumination to that, gives effective brightness (effect BR) the real effective illumination or brightness of the exit pupil.

This analysis is a continuation of, and parallels, what I wrote about in my tests in 2002, and the subsequent article published in 2003 titled “Binocular Performance”, in which I introduce the binocular performance index, otherwise knows as “BPI”. Once performance qualities are determined, the Adler index can be adjusted accordingly and the outcome may provide a better indication of performance ranking. At that time, I identified that performance needed to be weighted and simply applied +/- 10% for various quality aspects. I knew real performance needed to be factored but hadn’t yet actually calculated values for some performance aspects.

In the table above, you can compare the real light gathering area, the illuminated area and the affect on brightness ratio. Take note of the illuminated area of the Tak22x60; it is almost as large as some 20x80s. The illuminated area of the WO22x70 is larger than any other 70mm or 80mm binocular. The Fujinon 8x42 BFL has the smallest real aperture of the 8x models, but it has the largest illuminated area and the highest BR of the group of 8x binoculars. The Fujinon 16x70 has a larger illuminated area than any 20x80 binocular.

In all fairness brightness (BR), since it is based on exit pupil, and not directly on aperture, should be compared between closely sized exit pupils. This gives some indication of performance on diffuse objects. However, the limit of light gathering (real LG) puts a cap on the limit of faint diffuse objects that can be seen. And the magnification/aperture (real Adler) puts a cap on the deepest stellar magnitude that can be reached (although even Adler’s Index over-weights aperture for binocular limiting magnitude – See CN Reports Binocular Limiting Magnitude). So real Adler, real LG and Illum area along with effect BR give an indication of not only how bright the image will appear, but also how deep the binocular can see. This is a far cry from any use of a simplistic factor to rank binoculars or indicate how they will perform.

As I said earlier, still to consider are primary aspects such as resolution and contrast and even some lesser aspects of performance. Earlier in this report I discussed the stellar image spot size of the three binoculars highlighted in this study. The Tak has the finest image spot size. When all the light from a point is concentrated into a smaller spot, then performance on fine detail will be enhanced, improving resolution and contrast to adjacent areas. Resolution is easy enough to quantify, but aspects such as contrast improvement are very difficult to quantify, yet have significant impact on overall performance.

I have posted in the CN Binocular Forum (in 2008) a table of scores ranking about 50-60 binoculars for a variety of performance, mechanical and handling characteristics. Even some of those scores are a simplified quantification of the several aspects outlined here in more detail. Not all binoculars reviewed here are included in that table. A link can be found thru the Binocular MiniReviews – Links to Small Binocular Reviews – The Score.

Takahashi Astronomer 22x60, William Optic 22x70 Apo, Garrett Optical 22x85 Signature

SUMMARY

The WO22x70 is very good. Although smaller in aperture, it has better image quality than the GO22x85. The WO22x70 has better resolution, sharper defined image dot quality, narrower fov BUT overall wider sharp outer field of view, better off-axis illumination, a larger center area of the objective fully illuminates the image. It's got a higher price tag, but it's got a lot going for it. It's worth more, I won't speculate how much more.

Keep in mind too that my GO22x85 used cost only half of what the WO22x70 cost new.

Neither the WO22x70 nor the GO22x85 beats the performance of the Tak22x60.

The Tak22x60 fully illuminates the exit pupil across the entire field from more than 80% of the entire objective diameter. I've never seen any other binocular that does that. That's more than TWICE the norm for a typical binocular and in fact is 5x to 8x some binoculars. Other "best" binoculars fully illuminate the exit pupil from 50% of the objective diameter. Typical 10x50s and 8x40s fully illuminate the exit pupil from about 20-30% of the objective diameter. Roof prism binoculars fully illuminate the exit pupil from only about 10-20% of the objective diameter, some less than 10%.

When you look at all the light entering across the field of view from a typical binocular, beyond about 30%-35% of the central area, light diminishes from 100% to perhaps less than 40% by the edge of view. When you look at all the light gathered across the field of view in the Takahashi 22x60, nearly every photon is delivered across nearly the entire exit pupil.

No other binocular I have ever seen does so much with so small an exit pupil. I have no doubt in my mind the illumination, and therefore brightness, of the
Tak22x60 results in it performing well above its exit pupil size class. In fact it may even perform as if it were 1/3 to 1/2 again larger.

Sometimes you have to look at the qualities that contribute to performance. I've been saying for a long time that comparing exit pupils is not a "complete" indicator of the brightness of a binocular and there is more to it than that. The
Tak22x60 is the finest example to illustrate that concept.

Although the GO22x85 has significantly greater aperture, both the WO70 and the Tak60 have significantly smaller image spot size. They can see just about equally deep in magnitude and can resolve significantly closer double stars. One aberration that can cause a larger on-axis image spot size is spherical aberration. The larger spot size in the GO85 may be a function of a greater degree of spherical aberration. Never-the-less, I still prefer to keep the GO22x85 instead of my other 20x80s.

The spot size in the WO is smaller than the GO, but to see the difference between the Tak spot size and the GO spot size is remarkable. Spot size is not all just due to CA correction in ED glass, or in the case of the Taks, true fluorite. Much of it has to do with the correction of the lenses, for instance the elimination of spherical aberration and the degree of polish. The GO spot size isn't twice as large as the Tak simply due to color correction. It’s probably more a result of finer lens figuring.

Premium contrast is achieved in instruments with better lenses. To improve contrast, the lens must be figured such that all the light in the image is concentrated into the smallest image circle. In that way, the concentrated light of the object does not have as large an image blur circle that tends to overlap with adjacent areas, and the result is sharp definition at the edges of the visible disk between light and dark areas, hence improving contrast. Therefore, improved contrast would primarily be a function of a premium lens figure, or a reduction of aberrations in the lens, or a lack of spherical aberration, astigmatism, coma and chromatic aberration. That should be a goal of all good optical design.

The Takahashi Astronomer 22x60 Apochromatic binocular certainly achieves that goal.

Thank you for spending the considerable time and effort to read this article and gain an understanding of many things optical.

edz

The author lives in Cumberland, Rhode Island, USA, with his two children and the family cat. He generally observes from his yard at home, often joined by Shadow the cat. Skies are generally mag 5, and sometimes reach mag 5.5-5.7. The author has been involved as a member of the Cloudy Nights web forum astronomy community since its inception and has been publishing articles on CN since 2001. From the Cloudy Nights Reviews homepage you can use Advanced Search – by Author to find all his reviews and CN Reports.



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