Author Topic: A triumph of Swiss engineering  (Read 3025 times)

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Hans Weigum

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Re: A triumph of Swiss engineering
« Reply #15 on: October 22, 2019, 03:35:00 PM »
A couple more instruments from Kern.

Alex

https://www.kern-aarau.ch/fileadmin/user_upload/Aldo/Schnittzeichnungen/Schnitt_DKM3.jpg

This drawing refers to a different type of instrument, but sharing the same quite unique optical layout as the "Grabenfernrohr 12x72" mentioned. A specialist doing maintenance at the Swiss army  optical workshop, warned me, not to disassemble such a Grabenfernrohr, as there is nobody anymore alife, experienced to do the complicated  adjustment work.

Hans

Hans Weigum

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Re: A triumph of Swiss engineering
« Reply #16 on: October 22, 2019, 03:41:10 PM »
That's the first 6x Focalpin I've actually seen although I've seen it referenced in advertisements. 

I had one of the 10x60's and its build was unusual and highly innovative. For one thing its internal focusing was achieved not by movement of an eyelens but by movement of a 3rd objective lens located behind an air-spaced tele-objective lens. Also, its ocular end prisms are not normal Porro I prisms. One slope of the prism is set at 45 degrees to the base, but the other slope (the slope first receiving the light beam) is not necessitating a reflective coating (probably silver) be applied to its surface in order that all the light be reflected i.e. total internal reflection be achieved.

Do you have, dear Frank, an explanation for this unusual prism layout?

Hans

Frank Lagorio

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Re: A triumph of Swiss engineering
« Reply #17 on: October 22, 2019, 04:02:25 PM »
That's the first 6x Focalpin I've actually seen although I've seen it referenced in advertisements. 

I had one of the 10x60's and its build was unusual and highly innovative. For one thing its internal focusing was achieved not by movement of an eyelens but by movement of a 3rd objective lens located behind an air-spaced tele-objective lens. Also, its ocular end prisms are not normal Porro I prisms. One slope of the prism is set at 45 degrees to the base, but the other slope (the slope first receiving the light beam) is not necessitating a reflective coating (probably silver) be applied to its surface in order that all the light be reflected i.e. total internal reflection be achieved.

 

Do you have, dear Frank, an explanation for this unusual prism layout?

Hans

I think the purpose of the air-spaced objectives and unusual prism arrangement was to reduce the size and weight of the binocular in which the Kern engineers succeeded but at a cost in reduction of optical performance.
« Last Edit: October 22, 2019, 04:04:47 PM by Frank Lagorio »

Frank Lagorio

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Re: A triumph of Swiss engineering
« Reply #18 on: October 22, 2019, 04:48:53 PM »
The Focalpin is a curious binocular. Its distinguishing feature is a highly innovative internal focus arrangement using a sliding focusing lens located behind an air-spaced objective lens. You'd think that the reason for doing this would be to weatherproof the binocular, but otherwise the binocular is not well weatherproofed  the prism plates and objectives being not very well sealed lacking gaskets and O rings. And this is surprising considering how the binocular is so extremely well-built. Also, that 3rd focuser lens degrades optical performance by adding an additional two air-to-glass surfaces to the optical system. If this binocular had modern multi-layer anti-reflective coatings with light transmissions in the 90%'s and a dielectric instead of silver coated prism surface its optical performance would probably be immeasurably improved. 
« Last Edit: October 22, 2019, 04:51:13 PM by Frank Lagorio »

Uli Zeun

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Re: A triumph of Swiss engineering
« Reply #19 on: October 22, 2019, 05:06:51 PM »
The inside of the Focalpin showing the focusing system and smaller prism:
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Uli Zeun

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Re: A triumph of Swiss engineering
« Reply #20 on: October 22, 2019, 05:21:47 PM »
Here http://binopedia.info/index.php?topic=2900.0
you will find the Focalpin featured in some Kern catalogues.
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