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Oberwerk 12x60 LW Binocular Review


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Oberwerk 12x60 LW Binocular Review

by Jim Van Dyke

11/29/2013

I recently attended the Eldorado Star Party here in Texas, and had the chance to look through a pair of Oberwerk 12x60 LW binoculars.  I was impressed by the image and the $109 price.

Since no one on Cloudy Nights has done an in depth12x60 review, and being a new member, I thought I would share my experiences with the Oberwerk 12x60 LW.  While this isn’t a thorough technical review, it does draw some interesting conclusions about how these binoculars work, and how the low end Chicom binocular market operates.

Published Specifications

Objective size  60mm

Magnification  12x

Porro Prism  BAK4

Optic coating  Fully broadband multi-coated

Field of view  300ft at 1000y (5.7°)

Exit pupil diameter  5mm

Exit pupil distance  14mm

Minimum focus distance  15m

Weight  2.6 lbs.

Size  9”  tall, 8” wide

Price  $109.95 + shipping in 2013

Basic Measurement Results

Aperture  51mm

TFOV  4.9 degrees

Exit pupil  4.5mm or so

Aperture was measured by focusing binoculars at infinity, then panning a laser into the ocular laterally to simulate a parallel beam.  I put paper over the objective and measured the edge to edge illuminated boundaries. I achieved consistent results of about 51mm.

True FOV was measured by noting the binocular just straddled alpha, beta, Cassiopeia in the right side, and had a little bit to spare in the left.  My Sky Atlas 2000 shows those stars to be about 4.9 degrees apart.  This is much less than the advertised 5.7 degrees.

Exit pupil of 4.5mm was the most inaccurate measurement.  With binoculars focused at infinity in daylight, it was measured with a ruler.  I also compared the 12x60 exit pupil against my 10x50 Celestron Novas which were about 5mm, and the Oberwerks were noticeably smaller.

Given those numbers, magnification is about 51mm/4.5mm = 11.4

Using this formula:

tan( AFOV/2 ) = magnification * tan( TFOV/2 )

Apparent FOV is about 51.6 degrees

These binoculars operate as the equivalent of a 5 degree 11.5x50 that uses full aperture.

You might ask “What is the point of the 60mm objectives?”

Viewing Impressions

I like the center focus.  It’s nice and stiff, and the diopter is stiff too.  I can look at Jupiter’s moons, and when I come back later, they are still sharp in focus.  I did not measure focus speed, but I had no trouble zeroing in.

When I look at the moon, the image is nice and contrasted.  There are no glass reflections.  None at any angle.  The sky is fairly black to the edge of the moon.  I can see nice detail in the terminator.  These are good coatings.

Coatings.  Looking at my face in the objectives, I can barely see my outline.  No face details.  Spotlight reflections are dark green.  These coatings are better than my Orion 10x70 FMC from the early 90s.  The oculars have variations of red and bluish coatings, but their reflections are fairly low.  It would not surprise me if these objectives have the same coatings as the top of the line Oberwerks.  People complain about the subpar coatings on the Nikon 12x50 AE.  It isn’t in Nikon’s interest to make those binoculars too good.  They want to protect their $800 SE line.  Oberwerk has no high end 12x50 binos.

The oculars are a generous 21mm across, and the objectives measure 60mm.  The binocular light shrounds extend about 5/8” past the objectives.

Jupiter showed little flaring on both sides of focus.  The blur was a smooth circle on one side of focus, and an irregular blotch on the other.  I was able to easily focus right/left sides to get a perfectly round Jupiter in both eyes, and easily seen sharp moons.  I had a lot of fun tracking them night after night at 12 power.  A moon was near Jupiter’s disk, and only the 12x60 could resolve that.  My 10x70 Orions and my 10x50 Celestron Novas could not.  Yes, the extra magnification makes it an unfair comparison, but I’m rapidly getting addicted to 12x!

Chromatic aberration.  Not noticeable with moon in the center.  Becomes visible towards edge of field.   More noticeable than expensive binoculars.

The image was well collimated at my 65mm interpupillary distance.  The binocular hinge was nice and stiff.

Focus.  I didn’t perform a formal test, but my vision is –2.5 diopters, and there still was plenty of “in” travel.

Eye relief.  I do not wear glasses while viewing, and I do not fold over eyecups.  My eyes comfortably rested against the eyecups, and I saw full FOV.  Never did my eyelashes wipe the lenses.

The image started deteriorating about 60% out, and got bad fairly quickly.  At the extreme edges, I did not see the familiar offensive seagulls; the blobs were pretty round.

I find these binoculars easy to hold, and the rubberized body pleasing in colder weather.  At 2.6 lbs, they do not seem heavy.  Yes, they are 9” long, but that also allows me to hold the barrel ends better and not allow the binoculars to pitch as much.  I can walk around and look at the sky.

My suburban sky is quite light polluted.  Ten years ago I could make out the Milky Way.  I do not know my limiting magnitude.

I could consistently spot M33 overhead as a hazy patch in the 12x60, similar to my 10x70.  I had a harder time in my 10x50.

I can easily see M37, M36 in all my binoculars, but while M38 requires hunting for the hazy patch in my 10x50 and I hardly notice it, it’s much easier to spot in the 12x60.  I can barely start to resolve individual stars in the 12x60, almost in the 10x70.

Cruising the starfields in Orion are nice and bright, and stars do not dim towards edge of field.

Field of view is wide enough that I do not feel I am looking through a tunnel as a typical 46 degree 7x50, or a Pentax gives.  The sky does not “roll” as I pan.  Because the true magnification of the 12x60 is around 11.4, rather than the 12.2 of the Nikon 12x50 AE, the Oberwerk 12x60 should be easier to hand hold.

In daytime, the sky washes out the bottom field of the image, more than any other binoculars I own.  While excellent for astronomy, there are smaller, more contrasty daytime binoculars than the Oberwerk 12x60.  These are larger than 12x50s.  These are not good dual use binoculars.

I am disapponted by the FOV spec.  I bought these for 5.7 degrees.  I got 0.8 less than that.  The 60mm objectives perform as 51mm.  What gives?

Oversized Objectives and Undersized Prisms

There’s only 51mm of effective aperture, and magnification 11.4 for a reason.  Larger prisms are a lot more expensive than larger lenses.  These binos have a round field stop right near the prisms.  The prisms are undersized.  Looking straight ahead, you're only using a 51mm circle of the objective, with a 5mm annulus of unused 60mm lens surrounding it.  When you view at an angle, you are using an off center 51mm circle of the objective that may even cross the edge of the 60mm lens!  The rest of the objective is unused at that angle!

So rather than using prisms sized for 50mm objectives in a conventional 12x50 design, Oberwerk is using smaller prisms sized only for a 50mm on axis view, and larger 60mm objectives to get a usable FOV at effective 50mm aperture.  At any given angle, you're using some offset 51mm circle of the 60mm lens, and the same surface area of the prisms!

This is a poor man's 11.5x50 masquerading as a 12x60!

The other problem is these binoculars are unsuitable for daytime use.  The sky washes out the bottom of the field.  I didn't understand this at first.  Even my cheap Orion 8x56 mini-giants don't do this much.  What's happening, is the oversized 60mm objectives are only allowing a 51mm circle of light to contribute to the image at any angle, and the rest of the lens is letting in unwanted stray light at that angle.  It’s hard to baffle this out, because  the light cone laterally moves around for different angles to the image plane.

Binoculars with 60mm objectives operating as 50mm effective aperture are physically larger than conventional 50mm binoculars.

Opinions and Conclusions

An internet inspection of other 12x60 brands shows they have similar designs because their objectives are big, and their bodies, including the prism housings are quite slender.  Every wonder why you can’t pay $100 more and get a “top the line” 12x60?  Well, you can.  It’s called a 12x50.

I suspect most people are buying budget slender body 12x60, 15x70 and 20x80 binoculars thinking they are getting full aperture, but they are not.  It’s easier for customers to parrot published specs than verify what they have bought, and that allows vendors a lot of leeway in specification inflation.  If a vender didn’t, naïve internet comparison shoppers would soon put him out of business.

I was wondering a month ago "Is this really the golden age of Chinese binoculars?" when I've been seeing prices half of what I paid for my Celestron 20x80s in 1991.  Mine laser tests to 74mm real aperture, which isn't as egregious.

I don't fault the clever design principles driven by economics at the low end.  These 12x60 Oberwerks work very well at night.  Jupiter is sharp, coatings are excellent, field is good, and I can see faint fuzzies I can't see in my other handheld binos.  The moon has a dark sky around it, and there are no glass reflections.  There’s a lot things these binoculars are doing right that my Japanese binos of 25 years ago are not.  Without this small prism large objective design, nobody would get this performance at this price.

Do I recommend the Oberwerk 12x60 for astronomy at $110?

Yes.  They perform amazingly well, are fun to use, and $110 is a great price.

But be realistic.  You are only getting equivalent 50mm light grasp, and these are not ultra wides.

I expect all competitor 12x60 binoculars to be really 50mm or so at less field than advertised.


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