milt
sage
Reged: 09/13/04
Posts: 430
Loc: Arizona
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Quote:
Did you take into account that light obeys Snell's law at the transition from air to glass as it enters the prism?
Hi Peter,
NO!!! 
I had been wanting to do this calculation but never got around to it. Thanks for bringing it up and sheparding me through it.
Best Regards,
Milt
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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Bill,
I agree with your opinion that a BK7 binocular faster than f5 would work fine for most people, most of the time. However, when your dealing with psycho bino freaks from this forum (myself included)  , you better be able to deliver every last photon from objective to exit pupil whether we need them or not.
On a more serious note, there's probably a cost advantage to using BK7. I guess a f5 design is going to look long and skinny next to "normal" looking binos.
Do you know of any current f5 or greater designs? Do you know of any binos faster than f3.35 and do they bother with special prism material? I would guess not, for the same reason you gave for using BK7 below f5.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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Milt,
Cute post. I'm sure both of us feel some satisfaction after doing these mental gymnastics. I'm sure there are some optical engineers out there with just a hint of a grin. In the eye care field I work, in a practical way, with optics everyday. But its been a long time since I crunched even a simple problem like this. I feel like I'm back in physics 102. Anything that makes me feel 18 again is a good thing!
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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Bob W6PU
Carpal Tunnel
Reged: 12/23/04
Posts: 2191
Loc: Springer-N.E.NM
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Tongue in cheek humor, politics,and profuse knowledge make this one *Word deleted by the CN gnaughties gnomes* of an interesting thread to read!
I am throughly enjoying this, thank you all!
Bob/W6PU, in NM 
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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LOOK, here comes another dead horse, lets flog it!
I remembered that Miyauchi makes a long skinny binocular. The 22x71 is reported to be f8 on the Oberwerks website.
Now that I'm convinced that BK7 is superior to BaK4 for long focal ratios, I expected to see a premire f8 binocular using BK7. Nope, BaK4 is listed as the prism material.
I have a dim recollection that someone on this forum was happy but a little underwhelmed with his pair. I wonder if the abberations associated with BaK4 mentioned by EdZ and others may be responsible for the 22x71 owners impressions. I'm not sure if these abberations would be noticable, but it is a possibility.
I still havn't found a really fast ( < f 3.35 ) Bino. Probably because the false color would be oppressive even if an apo design was used. I thought the Miyauchi 25x141 would be a good candidate since they seem much more compact than the 150 Fuji's. They're apparently a "fast f4.4". Oh well.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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Henry Link
sage
Reged: 03/31/04
Posts: 316
Loc: Greensboro, NC
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Peter,
The US Army M-19 7X50 used an f 3 triplet objective. These were made by Bell&Howell in I believe the 70's. I have a pair which I just quickly checked for longitudinal CA with a magnification booster. It's surprisingly low, about the same as an f 4 achromatic doublet. Unfortunately I have no idea what kind of glass was used in the prism or the objective.
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Henry Link
sage
Reged: 03/31/04
Posts: 316
Loc: Greensboro, NC
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Oops, I forgot to mention there is no shadowing at the edge of the M-19 exit pupil in spite of the f 3 objective.
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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Henery,
Cool, thanks for the info.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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Henry,
After a little searching I found that the M-19 is an air spaced triplet objective design, f3 binocular. The document does specify the prism material to be "heavy flint" with a refractive index of 1.649. This is quite a bit larger than BaK4 at 1.569. Without running the numbers, I suspect this material operates with TIF at f3. This would explain why your pair doesn't have square or diamond shaped exit pupils.
On an unrelated note, the document says the military probably paid $500 - $600 for each M-19 and retail was about $900 in 1984.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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BillC
on a new path
Reged: 06/04/04
Posts: 2111
Loc: Washington, USA
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Beware of your Mark 19's. I think the RETAIL item you are talking about is a Steiner product. The M-19 made by Bell & Howell (the first solid producer, but third firm to become involved) was (I believe) strictly a military researched and contracted instrument.
The standards for the M-19 were so tight, that much money was lost in trying to get it right. The US government was splitting hairs with an axe decades before we started here on cloudy nights.
Cheers,
Bill
p.s. The closest flints I could find (with a quick look) to 1.649 are BaSF10 and SF17
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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Bill and all,
I was surprised by the price info also and I'm glad you chimed in. I also couldn't find an exact match for "heavy flint" either.
There was a used M-19 on that auction site yesterday at ~ $41. There's some M-19 info and pictures on fantao's website.
What is your opinion on them? In good shape are they good binos? Pros / cons? It seems like they have an interesting history during development and use in the military.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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BillC
on a new path
Reged: 06/04/04
Posts: 2111
Loc: Washington, USA
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Quote:
Bill and all,
I was surprised by the price info also and I'm glad you chimed in. I also couldn't find an exact match for "heavy flint" either.
There was a used M-19 on that auction site yesterday at ~ $41. There's some M-19 info and pictures on fantao's website.
What is your opinion on them? In good shape are they good binos? Pros / cons? It seems like they have an interesting history during development and use in the military.
Peter
Not to worry; all optical glasses are not made all the time by all companies. Considering CURRENT availability, I would say BaSF10 or SF17 is as close as you are going to get. I can guarantee those are good enough choices for those of us on CN.
Thanks for the heads-up on the website. I have never been there before.
Yep, that is the B & H military M-19. I was pleased that he even mentioned it started out as the T14, years earlier. Very impressive. He didn’t mention Yoder, or others involved with the project, but only we opto-geeks would even care. I have the complete history in a box somewhere at home. However, feeling that it is safe—and that no one would care if it wasn’t—I think I will let it rest wherever it is.
Opinions on the M-19:
When it is in good condition, it works great. I would still work on them . . . I would like to have a home in the Bahamas! The concept of making a nearly perfect, field reparable binocular, is a MASSIVE overkill. It looks great on paper, but then, so did the Edsel.
Once upon a time, the M-19 could stand out because of superior baffling. But, today, many inexpensive binos have world-class baffling. It is light, has a good image, and makes a great collectible. There are a few downsides, at least for me.
First, they are as ugly as a homemade rock. Next, the axle seems to have o-rings and tends to alter (sometimes) the exact IPD setting you want. For example: you bring the scopes together to, say, 64 mm, and then, through backlash, the bino wants to take you back to 67mm. I know I am splitting hairs, but CN is WAY FULL of that. Next, the focus mechanisms can be a bit tight and the “groves” in the diopter rings are rather large and smooth. Got sweaty hands? In a hurry? Forget it!
And then, there is the issue of reparability (Yes, that is spelled correctly; I looked it up). Of the dozen I have owned, I only kept a couple, and they, like their documentation, are in the dungeon. And, the next time I find them, they will probably go to the trash can, too. They have broken and dislodged prisms.
So, my quick opinion is that, in good working condition, they are fine binos. However, I still see their greatest value being in that they are great conversation starters.
Just my highly subjective thoughts.
Bill
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William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .
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Henry Link
sage
Reged: 03/31/04
Posts: 316
Loc: Greensboro, NC
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Bill,
Before you toss them please send me a message if you are willing to sell a pair of your M-19 eyepieces. The glass on mine appears to have been cleaned with Brillo pads.
Henry Link
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BillC
on a new path
Reged: 06/04/04
Posts: 2111
Loc: Washington, USA
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Henry: I won't have time to LOOK for them for a long time. HOWEVER, if I still have them, and you are willing to pay the postage, you may have them. Don't hold you breath. They are basket cases. But I think the EPs are okay.
Cheers,
Bill
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1501
Loc: Connecticut
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Bill and Henry,
Sounds like a happy ending to me. Thanks, both of you for bringing up info on an interesting binocular.
Peter
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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Henry Link
sage
Reged: 03/31/04
Posts: 316
Loc: Greensboro, NC
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Bill,
Thank you very much! Postage sounds like too little. Maybe I can use my bargaining skills to negotiate a higher price when the time comes.
Henry
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BillC
on a new path
Reged: 06/04/04
Posts: 2111
Loc: Washington, USA
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Things may be tight. But, I need the blessings more. Postage will be adequate.
Bill
--------------------
William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .
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Henry Link
sage
Reged: 03/31/04
Posts: 316
Loc: Greensboro, NC
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Bill,
I just saw your message above. Postage it is and thank you again. I'm in no hurry.
Henry
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