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Oberwerk 15 x 70 Vs Orion Giant 16 x 80



Introduction

I have been in the market for a new pair of binoculars for a while now. Over a period of 4-5 months I read as many reviews as I could on binoculars in the 11x to 20x range. I am looking for a step up in magnification and aperture beyond my indispensable Orion Ultraview 10x50's. At least a moderate field of view is important to me, although since I am increasing power I am not expecting to get as wide a FOV as the Ultraviews, and I'm looking for a good sharp image. Finally, I narrowed my search to consider the Oberwerk 15x70's and the Orion Giant 16x80's. Both of these binoculars were well within my price range and had the power I was looking for. I read as much as I could about each of these but still could not make up my mind. I decided to purchase both. . I compared them in as many ways as I could, with the intentions of keeping the one that fit my criteria (This tactic has not always worked for me in the past, as I often discover reasons to justify keeping a lot more than I send back). Certainly, there would be issues to consider; quality vs. price (Oberwerk's $149, Orion's $399), size, performance and most important, which one best meets my needs.

While this article will remain primarily a comparison between the Oberwerk 15x70 and the Orion Giant 16x80, it seemed appropriate that I include my other two smaller binoculars in the testing, Minolta Standard XL 7x35's and Orion Ultraview 10x50's. This should provide perspective on the performance of the giant binoculars and will allow some readers to get a feel for what can really be seen with these big binos as compared to smaller binoculars, which many already own. Each of the above binos has its advantages, (the 7x35 are great for hiking but not for faint fuzzies, the 16 x 80's split double stars less than 20"), and some rate better than others for quality of build or field of view. What I found is one binocular can't have it all. Unless you have unlimited budget to get the best (Fuji FMT-SX 16x70's, $599, come to mind here), compromises must be made to get what you want. I needed to determine which one would best deliver what I wanted. I was about to learn a few things along the way.

Although I will get more use for detailed observation out of my binoculars when I am alone out back viewing a night's fill of objects, they will also be used at Astronomy Nights when I have 20, 50 or 100 people out viewing, some for the first time. I have long been an advocate of binoculars for first timers because inexpensive binoculars will far outperform inexpensive telescopes and they are far more likely to be used more often. Here in Cumberland, Rhode Island, 15miles north of the light dome of Providence, skies for our astronomy nights generally range between 4.0 and 5.0 mag. The best I've ever recorded was 5.6 mag.

I hope you find this article useful and informative.

Summary Conclusions

Out of the box, the 16 x 80's were really impressive and were my strong favorites. I expected the Orion 16 x 80's, with a higher quality of build, better bracing, laser collimated optics and a larger aperture would win hands down over the Oberwerk 15 x 70's. I expected the narrower field of view wouldn't make that much of a difference and the slightly higher power and larger aperture seemed to offer everything I wanted. It didn't turn out that way.

The 15 x 70's came closest to meeting the published specs for eye relief and field of view almost exactly. Both the 10 x 50's and the 16 x 80's measured less than published.

The most versatile binocular for finding objects are the Orion Ultraview 10 x 50's. They have a wide enough FOV to orient in perspective and the 10x magnification is satisfactory to see many faint objects including some galaxies, many globulars, open clusters, nebulae and many fairly close double stars. The 10 x 50's provide a comfortable rendition of sky as compared to the scale and magnitude limit of 'SkyAtlas 2000.0', reaching stars just beyond the atlas.

Magnification turned out to contribute more to improved performance than aperture. The results of the aperture mask test showed that about 80% of the increase in the number of stars seen in a given field was due to magnification and only a marginal increase beyond that could be attributed to aperture. The 16x versus 15x, although noted, wasn't significant.

The combination of magnification and aperture in both the 70's and the 80's, as expected, provided a substantial increase in viewing over my current 10 x 50 Ultraviews. Both 70's and 80's provided a darker sky background than the 50's. The 80's may have had a brighter image on those faint or diffuse objects that needed brightness to be seen well. Overall image quality in the 80's was sharper on-axis, but the 70's were very close and the 70's had a sharp image over a much wider field of view.

The poor edge performance of the 80's over such a wide area and the excellent edge performance of the 70's so far out from the center made a huge difference in the usable field of view, in favor of the 70's by a very wide margin.

The 70's are seeing 95% of the objects seen by the 80's in a given area and additionally the 70's are providing a useable area of view 200% to 300% larger than the 80's. The 70's will permit sharp viewing of very wide star fields and larger nebula with a greater surrounding perspective. The 70's have a wide enough field of view to be used for finding objects.

The 70's have a nice hand fit and comfortable feel against the eyecup. They are marginally hand hold-able whereas the 80's are far too heavy to hand hold. The 80's seem built much more solidly, but the 70's were not cheap by any means. The 70's are much more like using big 50's than like using small 80's.

My opinion, based on the results of my testing, indicates that the 15 x 70's provide more of what I am looking for. Also, as it turned out, my 10 x 50's fill a very important need. After you review the data and comparisons noted here, I think you will agree with me that the Oberwerk 15 x 70's really deliver. They offer a tremendous value and are an excellent choice.

Manufacturers Specifications and Measurements

7 x 35 Minolta Standard XL Wide Angle 9.3*
10 x 50 Orion Ultraview Close Focus 6.5*
15 x 70 Oberwerk Long Eye Relief 4.4*
16 x 80 Orion Giant 3.5*

Field of View Mnfr. 9.3d 6.5d 4.3d 3.5d
Lens Coatings Coated Fully Multi Coated Broadband FMC Precision FMC
all lenses and prisms all glass to air surfaces every glass to air surface
Prisms ??? BAK4 BAK4 BAK4
Weight Approx 2 # 2 # 0 oz. 3 # 2 oz. 5 # 9 oz.
Size 5 1/8 h x 6 7/8 w 7 h x 7 3/8 w 10 3/4 h x 8 1/8 w 11 1/2 h x 9 1/4 w
Eye Relief ??? 22mm 16mm 16mm
Exit Pupil 5.0mm 5.0mm 4.6mm 5.0mm
Eye Lens Diameter 22mm 22mm 22mm (21mm cup) 20mm (19mm cup)
Focus Center +/- R diopter Center +/- R diopter Center +/- R diopter Center +/- R diopter
Close Focus(by me) (14 ft) Orion 16 ft (20ft) Oberwerk 20m (65ft) (65ft)
Mount Socket Yes Yes Yes Yes
Eye Cup 40mm soft rub fold 30mm hard cup twist 38mm soft rub fold 34mm hard rub fold
Covering Rubber Armored Rubber Armored Rubber Armored Coarse Grained Vinyl
Strap camera narrow camera wide D rings wide camera narrow
Lens caps ?? 2obj + 2 eye tight 2obj + 1 eye tight 2obj + 2 eye loose
Binoc Case none soft nylon soft nylon hard case w/handle
Accessories none none cloth tripod L adapter
Collimation inaccessible accessible accessible inaccessible
Price $109 $169 $149 $399

The 10 x 50's, which I have owned for about three years now, are a very well built, high performance binocular. Based on the specifications published for the 15 x 70's and 16 x 80's, I would classify both of these binoculars in the same group. The extras that come with the 16 x 80's, the tripod adapter and the hard carry case are probably valued at about $30 to $50 if sold separately. Shipping on the 50's was $12, on the 70's it was $8 and on the 80's it was $21.

Quality of Build

7 x 35 10 x 50 15 x 70 16 x 80
Center pivot brace tight easy tight very tight
Pivot movement excellent VG VG excellent
Eyepiece bar rocking none very little little little
Bar movement excellent VG VG VG
Focus mechanism VG VG VG VG
Diopter twist range 75*+ 75*- 45*+ 45*- 60*+ 60*- 180*+ 180*-
Internal barrel dull gray shiny black fine rib shiny cuts deep rib matte gray
Internal baffle no no Yes Yes
Lens Coatings coated (lightest) FMC (darkest) Broadband FMC Precision FMC
light blue green/blue/purple green/blue green/blue/purple
Lens reflections moderate least most little
Vignetting light loss 4% - 5% 5% - 6% none 4% - 5%

Pivot Hinges

The inter-pupilary pivot motion was very good on all and excellent although very tight, on the 16x80's, due to the brace hinge at the objective lens and also the tight movement. The 10x50's had the loosest movement but still they did not move during use.

Eyepiece Bar

The eyepiece bar on the 15x70's had some slop, allowing it to rock in & out. All the others had less rocking movement. However, in all the binoculars the eyepieces moved in & out equally at all times when focusing and held focus under normal pressure.

Focus Mechanism

All the binos had a focus mechanism that operated smoothly throughout the entire dial range. All had no slip or image shift. The focus dial moves with a moderate pressure and the eyepiece bar shows no indication of allowing accidental movement.

Focus Diopter Range

The diopter adjustment on the 10x50's and the 15x70's allowed turning the right eyepiece only thru 60*+ or 60*- (1/6 turn each way), less on the 10x50's. For me, even with my glasses on, both the 10x50's and the 15x70's required a setting in the minus diopter range to focus. Without glasses, the 10x50's required all of the minus adjustment to reach focus. Without glasses, only the 15x70's did not have sufficient minus diopter adjustment to reach focus for my 20/200 nearsightedness. I consider this to be a serious quality shortfall, since the other two binoculars had far more than enough adjustment to reach focus and this seems like such a simple quality standard to meet. A 2nd pair of Oberwerk 15 x 70's had a hair more minus diopter focus than the 1st pair I tested.

NOTE: Tim Hagan of Helix Mfg., where I purchased my Oberwerk binos, took the trouble to help me by testing out numerous Oberwerk 15x70's until he found one that had the most available minus diopter adjustment. He shipped this 2nd pair to me and it made all the difference I needed. I can now reach best focus with room to spare while wearing my glasses and also, although not perfect, I can even get good performance without my glasses.

Internal Barrel Reflections - baffles

No reflections were seen in any binoculars at any time while viewing dark sky objects. In daytime viewing, only the 15x70's showed bright reflections and only when used with the eyecups folded down. With the eyecups up the field of view was reduced by about 10-15% to the point where the reflections could no longer be seen. In the 70's, the half moon caused undesirable reflections off the inside of the barrel, but only when the image was moved to the extreme edge of the FOV.

Coatings

Only the 35's make no claim to be fully multi coated, although they do appear to be multi coated. All the others are labeled FMC and have various color reflections off their surfaces. The 70's do have one reflection off the objective lens that is nearly bright white.

Vignetting

Vignetting is the obstructed area that can be seen by looking into the eyepiece end at the exit pupil and observing the dark chords at the very edges of the circle that are the images of the prism infringing on the circular light path. These chords block the available light entering the objective before it reaches the eye lens. The 15x70's were the only binoculars that DID NOT show any light loss due to impairment of the light path. All the others have a light loss calculated at about 5% based on the area of the chord of the circle.

Collimation

If you cover and then uncover one lens while looking through the binoculars, you can see if the images are in line or momentarily separated. I have noted that my eyes do pull together the images in the 15 x 70's. In the 80's, the images seem to be dead on. Both the 10x50's and the 15x70's have a collimation adjustment screw accessible just under the rubber armor. I have not yet had to make any adjustments.

Hand Held Impressions - Ergonomics

Size lb Fit
7x35 5”hx7”w 2# fairly light excellent hand fit very little shake
10x50 7”hx7.5”w 2# fairly light excellent hand fit some shake, easily braceable
15x70 11”hx8”w 3.1# mod heavy good hand hold lots of shake, braceable
16x80 11.5”hx9”w 5.5# very heavy fair hand hold lots of shake, mount only

Weight

The 16 x 80's are huge. I could not hand hold these binoculars. The 80's required tripod mount for any type of use. The 15 x 70's appear much smaller in actual comparison than the specifications would indicate. The 70's are much more like using big 50's than like using small 80's. Although it was difficult to hold the 70's still, I was able to daytime view for short periods and it was easy enough to brace these while hand holding. The 35's and the 50's are easily hand held and I have often taken either of these on day hikes or backpack trips. The 35's can be used for hand held astronomy. The 50's can be hand held for astronomy, but in order to get the maximum benefit, it is best to mount them. Nearly all night sky viewing was tripod mounted.

Focus Reach

The focus knob on the 35's and the 50's is easily reached without moving the hands from the holding position. On the 70's, the forefinger must reach out from the holding position and focus was achievable while holding although stillness of the image was a problem. On the 80's, the focus dial cannot be reached while holding the binoculars and focus cannot be adjusted successfully without the binoculars being still. Therefore, the 80's must be mounted to adjust focus.

Eye Relief, Lens Diameter, Lens Recess, Eye Cup

Lens recess was measured with the cups down and with the cups up. Eye relief was measured by attempting to bring the exit pupil image to a clear focus on a white card, then measuring the distance from the lens to the card. I found this to be a difficult task and consider the accuracy of hand held measurements of Eye Relief to be +/- 2 mm. Relative to each other, the measurements are fairly accurate. Once Exit Pupil Image distance is known, Usable Eye Relief equals the distance back to the eye guard with eyecups folded down. Exit Pupil is as stated by the manufacturer. I tried to measure this by the size of the in-focus image on the white card. I found that to be an impossible task. The best I can say is that all measured about the same at about 5mm +/-, except the 15x70's which were smaller, but they were not less than 4mm.

7 x 35 10 x 50 15 x 70 16 x 80
Eye Relief Published ??? 22mm 16mm 16mm
Eye Cup Diameter 40mm soft rub fold 30mm hard cup twist 38mm soft rub fold 34mm hard rub fold
Cup Down Recess 3mm 3mm 2mm 7mm
Cup Up Recess 15mm 14mm 13mm 10mm
Exit Pupil Image Focus 18 mm 18 mm 17 mm 17 mm
Usable Eye Relief 15 mm 15 mm 15 mm 10 mm
Eye Lens Diameter 22mm 22mm 22mm (21mm cup) 20mm (19mm cup)
Exit Pupil 5.0mm 5.0mm 4.6mm 5.0mm

With Glasses

In all cases the eyecups must be folded down to view. Only the 35's and 50's allowed 100% view to the edge of the field stop. The 80's allowed only 80% - 90% of the FOV. The field stop could not be seen in the 70's, but by looking around in the FOV, I could find it everywhere except the outside edge of the FOV.

Without Glasses

All binoculars could be used with cups folded down to view the edge of field. When the cups were folded up to shield the eyes, which is one of the intended purposes of the eyecups, only the 35's allowed seeing the edge of field. The 50's showed about 80%-90% of the FOV. The 70's showed about 85%-95% of the FOV and the 80's showed 90%-100% of the FOV.

Eye Cups

The 35's and the 70's have very comfortable soft rubber fold-up eyecups. They can be pressed against the eye socket and have some give. The 50's have a hard screw-up eyecup that is uncomfortable when pressed up against the eye socket. The 80's have a very short hard rubber eyecup that is not much more comfortable than the 50's. The eyecup on the 35's and the 70's is wide enough to cover most of the eye socket. The 50's and the 80's do not cover the eye socket and could use some supplemental light shielding.

I found in practice that the 70's and the 80's were used with glasses on and eyecups folded down. I was not pressing up against the eyecups to view. In most instances I was a few mm back away from the eyecups and viewing was fine. However this did prevent me from seeing the field stop. Also in practice, I have used the 50's for several years now. Handheld, I use them very comfortably without my glasses and with the extended eyecup tucked just under my eyebrow. I don't press them into my eye sockets.

I prefer using binoculars without my glasses, with my eyes shielded as much as possible. To me, this is much less distracting to the eyes.

Importance of Magnification

I wanted a big jump in magnification to see more stars, fainter objects and bigger images. Also, I wanted to determine how much magnification was contributing to the overall gain in viewing. A cardboard mask 50mm in diameter was placed over the objectives of the 70's and the 80's so a comparison could be made to the 10 x 50's. I would be testing 10x50, 15x50 and 16x50s. Based on my experiences at the telescope, I expected power to have a significant benefit on faint objects. When at the telescope and you want to see deeper into a cluster you don't always go looking for a larger aperture scope, you simply put in a higher power eyepiece.

The Mask Test

The aperture mask test shows the # of stars in a given field increases considerably with a jump from 10x up to 15x or 16x. In one case there was an increase from 16 up to 27 stars within the same field. At 15x the number of stars in a given field increased by about 40%. At 16x the number of stars increased by about 50%. The sky background at both 15x and 16x was slightly darker and the stars that were at the limit of vision in the 10 x 50's would pop readily into view.

Aperture Mask
10 x 50 15 x 50 15 x 70 16 x 50 16 x 80
masked masked
Lyra area1 15 18 20
I 4665 20 26 28 29 31
Lyra area2 20 27 29 27 29
Lyra area3 16 23 25 27 28
Mizar 10 11 11 12

Magnification vs Aperture

The difference in the number of stars seen at full aperture versus masked to 50mm was only a few stars, always on the order of only 1 or 2 stars more. About 80%+ of all the additional stars beyond what the 10x50's could see were seen with the aperture masked at 50mm, indicating magnification is responsible. The conclusion reached here is that most of the additional stars seen in the field are a result of the increase in magnification and only a marginal increase is due to the increase in aperture.

Binocular Index

There are a number of references out there to 'Binocular Indexes', some of which simply multiply magnification x aperture to arrive at an Index Value. Based on the test results noted above, I tend to agree with Alan Adler that magnification holds much greater importance than aperture and indexes should account for this importance. Alan uses an index based on magnification x square root of aperture. This seems definitely headed in the right direction.

Binocular Index 7 x 35 10 x 50 15 x 70 16 x 80
Magnification 7 10 15 16
Objective Diameter 35 50 70 80
Sq Root Obj Dia 5.9 7.1 8.4 8.9
Adler Index 41 71 125 143

Object Finding

Maximum Field of View = TFOV

The True FOV is related to the ease of finding objects. A certain amount of perspective is necessary to find objects and a larger FOV provides more perspective. However, FOV and magnification go hand in hand for finding and a low power binocular with a wide FOV can be just as much a disadvantage as high power with a small FOV.

True measure of the FOV was obtained by noting the limits of star fields and referring to SkyAtlas 2000.0 for a measure of the field limits. (Refer to the Accessories - Books and Charts section to see my review of SkyAtlas 2000.0). Several star fields were used to test for maximum viewable field and measures were taken more than once to confirm results. The data recorded as 'Field Measured Data separation in mm' is the measurement in mm determined from SkyAtlas 2000.0 of the actual limits of view recorded from the eyepiece. When the results of observations varied, the largest readings were used as long as that reading was confirmed by at least one other observation.

Maximum FOV
7x35 10x50 15x70 16x80 NOTES
Manufacturer's Data
FOV degrees published 9.3* 6.5* 4.4* 3.5*
FOV Ft at 1000Yd. 488 341 231 183 Tan(FOV)x3000
Field Measured Data
separation in mm 74 Herc 46 M5 fld 36 M5 fld 26 M5 fld
as measured in 49 Serp 36 Serp 27 Serp
SkyAtlas 2000.0 47 Lyra 34 Lyra 27 Lyra
10 degrees = 82mm 49 Lyra 36 Delph 26 Delph
Use Max measure mm 74 49 36 27
compared to SkyAtlas 2000.0
where 82mm = 10 degrees 74/82 49/82 36/82 27/82
Actual FOV
TFOV degrees 9 6 4.4 3.3 measured
FOV Ft at 1000Yd. 472 313 231 173 Tan(FOV)x3000
Area of View sq degrees 64 28 15 8.5 pi(FOV/2)^2
Apparent FOV
basis = TFOV=AFOV/Mag
AFOV = TFOV x Mag 63 60 66 53

Results Max FOV Tests

Only the 70's produced a measured result that agreed with the manufacturers specifications. All the others measured less.

Based on the formula TFOV = AFOV / Mag., the AFOV = TFOV x Mag. This provides the resultant apparent field of view of the eye lens. In this case the results show the 16x80's have an AFOV of 53*, similar to a plossl eyepiece in a telescope, and the 15x70's have an AFOV of 66*, more like a super-wide eyepiece.

The 70's showed almost twice as much sky area as the 80's and the 50's presented three times the area seen by the 80's.

All the binoculars showed a measurable degradation of the image at some distance out from the center of the FOV. The distance out from center varied for each and loss of this useable area will be discussed under the topic of sharpness across the field

Conclusions - Object Finding

Although the 35's showed a huge chunk of sky and are very nice for general viewing of constellations and sky background, the magnification is not enough for finding a full range of objects.

The 4.4* Max FOV in the 70's was about the smallest Max FOV for "easy" finding. The 15x magnification, as did the 16x of the 80's, made finding small objects easier. Very small objects such as M57, the Ring Nebula, which appeared almost star-like at both 15x and 16x, would be difficult to identify if you didn't already know exactly where it is located based on star chart reference.

The 3.3* Max FOV in the 80's was very noticeably smaller. It made it more difficult to acquire an area of the sky for orienting to charts. I also found the 80's to be too small a FOV when viewing star fields around the Cygnus Milky Way. Severely degraded image towards the outer edge further reduced the FOV in the 80's.

By far, the most versatile binoculars for finding objects are the 10 x 50's. They have a wide enough 6.0 FOV to orient sufficient area in perspective and the 10x magnification is satisfactory to see many faint objects including some galaxies, many globulars, open clusters, nebulae and many fairly close double stars. The 10 x 50's provide a comfortable rendition of sky as compared to the scale and magnitude limit of SkyAtlas 2000.0, reaching stars just beyond the atlas.

The 70's are much more like using big 50's than like using small 80's.

Examples of Maximum FOV

7x35 1 all of Lyra
9.0* 2 almost all of the lower half of Orion
74mm 3 can see the entire keystone of Hercules
4 all of Corona Borealis
10x50 1 just barely oncompasses the parallelogram of Lyra
6.0* 2 just gets Orion’s Belt and the entire Sword at once
49mm 3 can comfortably view the Hyades with surrounding perspective
4 just barely sees the entire head of Draco
15x70 1 the NE part of Lyra from Vega to 4,5 e Lyra to 11,12 d Lyra
4.4* 2 Orion from the lowest belt star to include the entire Sword
36mm 3 part of Delphinus from 12 Y Del to 3 n Del
4 can comfortably view the Hyades But with little surrounding perspective
16x80 1 just barely from 4,5 e Lyra to 11,12 d Lyra
3.3* 2 Orion Belt stars only or Orion’s Sword only
27mm 3 the body only of Delphinus the dolphin, no tail
4 just barely the triangular head of Serpens Caput

Examples of Maximum Field of View

Types of Viewing

Binoculars need to satisfy multiple requirements. Not only must they have On-Axis sharpness for maximum resolution, but also they must have a sharp wide area of view to encompass large objects such as cluster groups, large galaxies or extended nebula. In addition, sometimes it is desirable to frame large objects or areas with surrounding sky to view in perspective. These uses all require varying levels of sharpness across an increasingly wider field of view.

This is my approach to identifying how binoculars are used. The next step will be to measure the sharpness across the field of view to determine how much of the binocular is really usable for the desired type of viewing.

Finding Limit

Although we have established the maximum Field of View (TFOV), the Limit we will define here is that not all of the FOV is useable. Generally need as large a field of view as possible to view the sky in perspective. Usually orienting to a chart. Not observing for detail here, so the zone of view out to and including a Poor view can be considered usable. In effect, this is reducing the overall field of view of the binoculars and indicating that only a certain percentage of the Max FOV is useable. The area of view considered Bad is not considered useable.

Detail Viewing Limit

This viewing limit uses the maximum wide fairly sharp area of the FOV. In most cases the area including the Fair zone can be considered the Detail Viewing Limit. This type of viewing is used for star fields, large extended objects, cluster groups and galaxy clusters. The objects viewed in the Fair zone are not well defined. This zone is useable only for viewing the outer edges of detail for wide field objects.

Best Wide Detail Viewing

This viewing uses the maximum wide clearly sharp area of the FOV. This may be only the area considered Excellent or Good. This type of viewing is used for large extended objects, cluster groups and galaxy clusters that would all require a sharp resolution at the outer limits of the objects being viewed.

Sharp On-Axis - Detailed Observation

This is detailed observation of generally small objects using the center of the FOV. All of the binoculars had at least 40% to 50% of the FOV considered Excellent to Good. This is more than enough for double stars, galaxies, globular clusters and many open clusters

Sharpness - Useable Field of View

Sharpness

Several star fields were used to test for sharpness across the entire FOV. The binoculars were moved back and forth slightly so that star images that were focused clearly in the center were observed at various zones out to the extreme edge of the FOV. Observations were recorded several times. Sharpness is recorded as Excellent, Good, Fair, Poor or Bad. Bad results are areas of the viewable field where the star images are extremely distorted or enlarged blobs.

Poor results are areas where the images are distorted or enlarged, but might not be distracting at the outer fringes of surrounding perspective. The area out to and including Poor is considered the useable area for sharp finding and perspective.

A smaller area, the area only out to and including the Fair zone is considered the limit useable for viewing the outer edges of detail for wide field objects. Once the field enters the Poor zone images become unsatisfactory for viewing objects. Stars are flared, bloated or distorted beyond a desirable limit. As an example of the transition from Fair to Poor, Albierio - B Cygnus, a wide double at 34", becomes too blurred to separate into it's two components.

Distorted images in the Poor or Bad zones could not be refocused to improve image. No detail, even the outer edges of wide clusters, could be satisfactorily viewed in the Poor zone or beyond. The faintest stars resolvable are not seen in the Poor zone.

Sharpness
across the FOV
% of distance from NOTES
center to edge 7x35 10x50 15x70 16x80
40 and less G G G E E E E E E E E E
40 to 50 F F F G G G E E E G G G
50 to 60 F P F G G G G G G F G F
60 to 70 P P P F G F G F F P F P
70 to 80 B B B P F P F F F B P B
80 and greater VB VB VB B P B P P P VB B VB
Maximum FOV degrees 9 6 4.4 3.3 measured
Max. Area of Sky 64sq* 28sq* 15sq* 8.5sq* pi(FOV/2)^2
FINDING LIMIT
Usable Limit = Poor 70% 80% 90% 70%
Finding Limit FOV degrees 6.3 4.8 4 2.3
Usable Finding Area sq dgr 31 18 12 4 pi(FOV/2)^2
DETAIL VIEWING LIMIT
Usable Limit = Fair 60% 70% 80% 60%
Detail Limit FOV degrees 5.4 4.2 3.5 2
Usable Detail Area sq dgr 23 14 10 3 pi(FOV/2)^2
BEST DETAIL VIEWING LIMIT
Usable Limit = Good 40% 60% 60% 50%
Detail Limit FOV degrees 3.6 3.6 2.6 1.7
Usable Detail Area sq dgr 10 10 5 2 pi(FOV/2)^2

Results of Sharpness Test

The 80's were rated Poor between 60% and 70% out from the center. Images between 70% and 80% out became grossly distorted. The 80's really got Bad quickly after 70% out from the center. The already narrow 3.3* MaxFOV of the 80's is reduced to a finding limit of 2.3* out to and including the Poor zone. (It should be noted that although you are viewing at 70% out from the center, the area defined by 70% of the diameter represents only 50% of the area of the circle). The Fair zone, at 60% out from the center, reduces the usable detail-viewing limit to 2.0*. That is just enough of a FOV for the 80's to capture the area of the Pleiades with no distortion. Orion's Sword, the nebula with the surrounding star clusters, would barely fit and Praesepe would be comfortably bordered. Distortion in the 80's was much worse on the left side with all ranges degrading one step quicker.

Although the 70's were Poor at 80% out from center, they weren't Bad until near the very edge. The Poor zone was considered to extend out to 90%. The 4.4* MaxFOV of the 70's is reduced to a finding limit of 4.0* out to and including the Poor zone. (This encompassed over 80% of the area of the circle). The Fair zone, at 80% out from the center, reduces the usable detail-viewing limit to 3.5*. That is sufficient FOV for the 70's to capture all of Orion's belt stars in one view and more than enough to view Orion's Sword. A good portion of the open clusters surrounding the Rosette in Monoceros would fit comfortably. This 3.5* is about the smallest FOV that could provide a hope for seeing an object like the extended North American Nebula all in one view.

In the 50's, images were Poor between 70% and 80% out from the center. Images beyond 80% out became grossly distorted. The 6.0* MaxFOV of the 50's is reduced to a finding limit of 4.8* out to and including the Poor zone. (This encompassed over 60% of the area of the circle). The Fair zone, at 70% out from the center, reduces the usable detail-viewing limit to 4.2*. That is large enough of a FOV for the 50's to encompass all of the Coma cluster, Mel 111, or easily M24 the the Small Sagittarius Star Cloud or easily the M20-M8 the Trifid-Lagoon Nebula area.

Opinions of Sharpness

The 70's really had a far greater % of the total FOV usable for viewing than any other binocular in this comparison.

The Fair area of the 70's provides three times greater area of the sky than the Fair area of the 80's. The 50's provide 1/3 more than the area of the 70's, but at a significant reduction in magnification.

Based on these observations, the 15x70's are by far the best performers as pertains to sharp field of view and magnification for detailed viewing. The 10x50's offer a good combination of 4*+ sharp field of view at a decent 10x power, which is sufficient for a great many objects. However the 15x or 16x magnification helps bring out so many more faint objects that the magnification adds a significant advantage.

Object Viewing

Detail Viewing Limit

Open Cluster Groups like the area around Y Cygnus or the area around 2244 Mon - the Rosette, very large Open Clusters such as the Hyades or Mel 111 - Berenices Hair and small constellations such as Sagitta, Lyra or Delphinus require a fairly sharp view over a very wide area if all stars are to be seen clearly. These areas might be viewed using the FOV out to the Fair limit considered the Detail Viewing Limit. Other large area objects include M24 - Small sagitarius Star Cloud, Alpha Perseus Association, Cassiopeia clusters near M103 and objects like the California Nebula or the North American Nebula.

Best Detail Viewing

Some objects required a considerable degree of sharpness across a moderately wide FOV to be seen in sharp detail out to the edges. These objects generally are viewed entirely within the Good area of the FOV, considered the Best Detail Viewing Limit. Examples of objects in this class are galaxy groups such as M81-M82, large open clusters like NGC 752, the Pleiades, IC4665 in Oph and the Double Cluster in Perseus. Other wide detail objects include very large galaxies such as M33, M101 and M31 and areas like Orion's Sword.

On Axis Detail Viewing

Many objects require only a very sharp On-Axis view to be seen in detail. Little surrounding perspective is required, although some perspective is always helpful. These objects generally are viewed entirely within the Excellent area of the FOV. Examples of objects in this class are individual galaxies, globular clusters such as M3, M5 and M13, planetary and diffuse nebula and double stars.

Objects in the Viewing List

Several nights were spent viewing objects of interest. A lot of time was spent on various combinations of double stars to test for the limit of each binocular. Various examples of galaxies, diffuse nebula, globular and open clusters and planetary nebula are included in the viewing. In some examples, resolved stars are counted to test comparative magnitude limits. Nearly all of these objects are small enough to be viewed in the center of the FOV. Several very wide open clusters were included in the viewing list and attempts were made to see some very large nebula that could only be fully encompassed by a sharp FOV over 3*.

Binocular Observing Report

The objects viewed for detail during the hours spent developing this comparison, with log notes, are listed here.

Desired Attributes

Brightness

Brightness was sufficient in the 70's to see a star like core in eg M81 with a broad surrounding glow, a pear shaped eg M51 with the south member larger and brighter, and a bright core on gc M13 with fainter circular outer extension. The 80's showed M13 with a large bright core with a slightly dimmer outer glow and M51 had slightly more defined shape with the south member more prominent. With both binoculars a number of globular clusters were observed including M3 and M13 as the brightest examples, M5 and M10 that showed a core and fainter examples M92, M71, and M12. Last summer, my 10x50's gave a view of M22 that appeared so large and bright it seemed like an open cluster.

Contrast

Did not do specific contrast tests. I did notice considerably darker background sky in the 70' and 80's when performing the aperture mask test. I attributed the greater ability of the higher magnifications to see fainter stars to the increased contrast associated with higher power. I noticed extremely sharp images from both the 70's and the 80's on the moon in high contrast situations. I was able to easily let my vision wander around and see hundreds of clearly defined craters and mountains all along the terminator, with both the shadow side and the lit side very prominent. Two years ago, my 10x50's provided my first ever view of eg M33, an object I had searched for many times with the telescope to no avail. And now the 70's have provided me with an averted sighting of another elusive galaxy, M101.

Resolution

I was not able to test resolution on any planets, but I did a lot of double star splitting and the results are given in the tables of objects viewed. The 50's split fairly even doubles down to about 20", the 70's and the 80's down to 14", with a slight edge in performance going to the 80's. The 80's had a very nice star image that could be focused precisely.

The best example of a double star test used to compare the 70's to the 80's is the splitting of the two components of the Double's double, sigma 2470 and 2474 in Lyra. With separations of 6.6m-8.6m/13.4" and 6.7-8.8m/16.2" respectively, the 80's cleanly split the wider and elongated the closer double while the 70's split the wider with difficulty and could not see the closer double. On 100 Herc at 5.9m-6.0m/14" both binoculars cleanly split this very even double. All the binoculars had a problem splitting doubles where the components varied widely in magnitude or where the primary was very bright.

Out of Focus Star Test

This is where I realized the affects of the astigmatism in my left eye. I like to view without my glasses and when doing the star test without my glasses I noticed considerable astigmatism in the left lens. I put my glasses back on, performed the out of focus test again and found both the 70's and 80's have pretty nicely rounded out of focus images both inside and outside of focus

Aberrations

These are just the notes on the aberrations that I made a note of during my observations. The most notable aberration, sharpness across the field of view, which is not really an aberration but a limitation of the quality of lens construction, has already been discussed at length.

Rectilinear Distortion - curvature

Both the 35's and 50's had only moderate curvature. Vertically straight objects curved outwards on both sides of the center of view, but magnification wasn't high enough to make it distracting. Both the 70's and 80's exhibited considerably more curvature. It could be noticed at 20% out from center and at 50% out from center straight vertical objects were significantly curved outward to the point of distraction. This defect was not noticed during any nighttime dark sky viewing. It's affect on deep sky objects would be to move the outer stars in the field slightly from the true picture location.

Chromatic Aberration

The 80's showed a light fringe around Venus, but it was acceptable. Also the 80's show a blue-green fringe around the leading edge of the half moon. The 70's showed an unpleasant broad yellow border around the leading edge of the half moon. This would sometimes disappear as I moved my eye around the field. When I was testing both binos with a 50mm aperture mask in place, very little color fringing was apparent.

The 80's showed no apparent color fringing on bright stars. I viewed Arcturus, Spica, Deneb, Altair and Vega. The 70's seemed to show a very slight color fringe only on Vega.

Astigmatism

None noticeably present. I was pleased to find that the astigmatism I originally thought to be a defect in my lens was being induced by my eyes. Refer to the notes in Star Test above.

CREDITS

Thanks to these people, whose equipment evaluations, informative writings and help I found invaluable:

Terence Dickinson & Alan Dyer "The Backyard Astronomer's Guide" for chapters 2 & 3 on binoculars, and really for the whole book;

Todd Gross http://www.weatherman.com/ for "Binocular Reviews", so much information; and at the same site
Alan Adler "The REAL Scoop on Binoculars", for notes on the relative importance of Magnification and especially for the notes on Object Finding and Object Viewing;
Jay Freeman http://observers.org/beginner/ for his article recommending the Virtual Drop Test. If you have a virtual heart attack you probably need to buy a less expensive product;
Ed Ting - The Telescope Review Website http://www.scopereviews.com/ for Various Binocular reviews;
Tim Hagan, Helix Mfg. http://www.helix-mfg.com/ distributor for Oberwerk binoculars and University Optics eyepieces, for helping to accommodate my near-sightedness;

And to these Cloudy Nights authors, in addition to all the others whose articles appear on the website. Although some of these articles pertain to eyepieces, its all optics and the information is highly relevant, even for binoculars:

Michael Hosea "Notes on Eyepiece Evaluation" for the notes on sharpness, brightness and contrast;
Stephen Tonkin "Helios 'Stellar' 15x70 Binocular" for the notes on mis-collimation and Vignetting;
Gavin Khoo's article "Barska 15x70 Binoculars" for a review on this site of what appears visually and by stats to be exactly the same binoculars as the Oberwerk 15x70's;
Bill Brady "Eyepiece Review Pitfalls" for the comments on requirements of different targets and, in general, keeping evaluation in perspective;
David Knisely "How To Write a Product review" for how to be organized and structured;

and

Allister St. Claire for the content of his "Editorial Commentary" and for providing the forum where we all have the opportunity to try to get better at what we like to do.


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