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Air-spaced apo 70mm binoc


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Apo binocs with FPL-51 or equivalent glass are nothing new but this one has an air-spaced objective that should be better corrected. Also, the long extensions are not dewshields, they are part of the optical tube so the objectives are far away from the eyepieces, allowing for a longer focal length and another gain in correction.

https://www.teleskop-express.de/shop/product_info.php/info/p11809_William-Optics-22x70-ED-APO-Astro-Fernglas.html

Too expensive and long and heavy for me, I'm dreaming of the shorter and more affordable APM 16x70 but good to know what everybody makes.

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18 hours ago, Ben the Ignorant said:

... this one has an air-spaced objective that should be better corrected.

Worth noting there is nothing special or unusual about air-spaced lenses. I.e. all Sky-Watcher's refractors have 'air-spaced' lenses, including the humble Capricorn 70 and StarTravel-80. Air-spaced optics are the norm, not the exception. 

HTH, 

Steve 

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1 hour ago, Peter Drew said:

Agreed, but not the norm with binoculars which almost always have cemented objectives.   🙂

Is that true for large observation binoculars? If yes then you have taught me something new 🤗

Steve

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9 hours ago, FLO said:

Is that true for large observation binoculars? If yes then you have taught me something new 🤗

Steve

Up to 100mm aperture binoculars there will be few that are airspaced.  Cementing increases light transmission, or to be more correct, reduces light loss and also ensures that centering is more easily retained.  Strains that can deform images due to cementing are not usually too obvious because of the relatively low magnification.  Airspacing comes into play as an alternative in larger apertures that are designed for higher powers, mostly found at the higher priced end of the market.  At this point the distinction between binoculars and binocular telescopes can be a "grey" area.  🙂

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Nothing to do with binoculars, but I have a 600mm Solid Cat lens from the early 70s. It is called a solid cat because all the elements are bonded/glued together. It is f8, but light transmission is f11. Weighs a tonne 😀

Derek

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Soft compared to modern lenses, also very heavy. You hold the lens not the camera. Still have it in its case. But never used. Same as old F2AS Nikon it was used with, put away. Anyway as I said nothing really to do wit the subject in discussion. It was just about the lens spacing or cementing of such.

Derek

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