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edcannon
professor emeritus


Reged: 11/19/03
Posts: 693
Loc: Austin, Texas
My BK-7 binoculars -- not so bad new
      #362057 - 03/02/05 11:28 PM

Barry Simon wrote in another thread:

"I think too, we are too quick to downgrade BK-7 prisms. We tend to think of them as worthless *bleep* where in truth I have read comments by some of the binocular repair guys and others that, done right, you can get some pretty good binoculars with BK-7 prisms. Someone else may want to expound about the relative merit of BK-7 in relation to BAK4."

My first binoculars were Tasco 10x50 with apparently a very short eye-relief and about 5-degree field of view. They were given to me, and I don't know much else about them. I learned from my observing mentor (who's joined at the hip to his old Colter 8-inch dob with the Lumicon straight-through 80mm finder scope he got for it) that since I was using those Tascos while wearing glasses I was getting a very small field of view and so went looking for long eye relief.

While I was still using those Tascos, for a few months another friend loaned me his Celestron 7x50 which had cost over $150 in the 1980s. That was a very nice binocular. Finally I had to give them back.

In a telescope and eyeglasses store in San Antonio I saw these Bushnell "GlassesOn" models. I didn't know then about BK-7 and coatings. I don't think that I knew that line was being discontinued. I bought the 10x50 for about $180 (maybe in 1998 -- not sure).

The first night out with them, I was awestruck. They were wonderful! It was like looking through a great big clear window. There were so many stars, such a big field of view (all 6.5 degrees as opposed to probably half that with the Tasco, and maybe even more FOV than the Celestron). I was very very happy with them and used them for four or five (or six?) years. Thinking back now, it seems that they would have compared very favorably to the Celestron 7x50, but I never had them side-by-side.

I finally kind of gave up on the Bushnell due to trouble that developed such that I can no longer get both sides perfectly focused at the same time. It may be partly my eye
prescription, but also I think that maybe the mechanism has
gotten loose in some way. (They don't have right-diopter adjustment, due to their theory being that your eyes are corrected 20/20, since you're using them with "GlassesOn".)

Anyway, later I learned that I had paid too much for them, that since they weren't fully multicoated they weren't tops in that factor, that BK-7 is considered second-tier, etc. In spite of all that, they served me very well for those years, when I was out under the night sky up to something like 100 nights per year. Among other things, with them one September night with +7.5 star charts I "independently discovered" the planet Uranus! I saw a number of comets and Messier objects with them, and I think a bright nova or two, and a couple of bright asteroids (not to mention hundreds of satellites). Almost all of this was from a suburban site, as it's very rare that I get out to a dark site.

I got the Orion Ultraview 8x42 (lower power, lighter weight, as well as BaK-4 and FMC) hoping for less shakes, but that hasn't been the case. Also, my Ultraview just doesn't focus as sharply on-axis as did the GlassesOn when they would focus together. Also, the GlassesOn are much less "soft" around the edges than the Ultraview. I've been tempted to see about getting the GlassesOn fixed, although of course it will make more sense to get a new model with right-diopter adjustment, fully multicoated, BaK-4, etc.

Bottom line about BK-7 prisms -- I feel very sure that I can truthfully and emphatically say based on years of experience that not all BK-7 binoculars are *bleep*, especially now in terms of price points and that type of thing.

Aside. Regarding that review in Astronomy, I think perhaps one target audience could be college students, who are notorious for tending to be poor -- due to spending all of their money on phone calls, pizza and beer, and textbooks. Another target audience might be teachers hoping to come up with 10 or 20 of some binocular to use in science classes, who clearly can't afford (nor probably can their school district either) ten Nikon 10x42 SE, much less Zeiss or Leica or Swarovski!! I think that Phil Harrington's message was that the sub-$100 binoculars he looked at could be useful for at least some astronomy. I need to read it again, but I don't think he claimed or implied that they are top-notch binoculars in any way.

Ed Cannon - Austin, Texas, USA


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Anonymous
Unregistered




Re: My BK-7 binoculars -- not so bad new [Re: edcannon]
      #362091 - 03/03/05 12:28 AM

You can have years of observing pleasure with BK-7 glass. No one sensible would dispute that. For the money, they can be quite nice and there are some poor constructed binos that use BK-4. However, optically, BK-7 material is inferior to BK-4 in terms of brightness...strictly speaking. Quality, cost, and pleasure is a mixture that is different for every person.

Your point is well taken.


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BillC
on a new path


Reged: 06/04/04
Posts: 4391
Loc: Lake Stevens, WA, USA
Re: My BK-7 binoculars -- not so bad [Re: ]
      #362121 - 03/03/05 01:15 AM

Yes, for most applications, BAK4 is a superior glass. However, the marketing twidgets who got the debates started should be shot.

BUT . . . not before they knit me a BMW out of a piece of steel wool. If they could do with steel wool what they have done with the BK7 vs. BAK4 debate, the project wouldn't take more than a few minutes.

Cheers,

Bill

--------------------
William J. Cook, Chief Opticalman, USNR-Ret.
Ophthalmic Tech, Naval Station, Everett, WA
Optical Mechanic, Puget Sound Naval Shipyard
Founder, Amateur Telescope Making Journal
21-year Mgr., Optics Dept., Captain's Nautical Supplies
Optics Mechanic, Ft. Lewis, WA.
Contributing Editor for Numerous Magazines

It's better to be a "has been" than a "never was." But only barely; the pay is about the same!


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