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Kern Aspheron 5.5mm Supplementary Lens


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#1 Glenn Brady

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Posted 10 March 2012 - 08:09 AM

Recently, I bought a Kern Aspheron 5.5mm supplementary lens for use with my Kern-Paillard 10mm f/1.6 H16 RX Switar preset lens. Cosmetically both are in mint condition. The Aspheron is mechanically compatible with the Switar (both have 38mm threads), but the image formed when they're put together is very far out of focus (the Switar forms a sharp image on its own). I've attached the Aspheron with and without the stubby lens shade on the Switar, but the image remains very blurry.

Has anyone experienced this problem? Might the Aspheron, despite its new appearance, be defective? Is the Aspheron incompatible with all but the very late series all black 10mm Switar lenses?
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#2 Jean-Louis Seguin

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Posted 10 March 2012 - 08:45 AM

Hi Glenn,

The distance scale ring on the 10mm must be set to pretty close distance to get a sharp image with the Aspheron.

Cheers,
Jean-Louis
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#3 Glenn Brady

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Posted 10 March 2012 - 09:15 AM

Hi, Jean-Louis

I've run the focusing on the Switar to its near limit and the image is still significantly out of focus. The image is sharp at full aperture only when the subject is about three inches in front of the Aspheron.

Best regards,
Glenn
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#4 Glenn Brady

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Posted 10 March 2012 - 09:55 AM

Using a 0.25mm Edmund Optics Brass C-mount spacer (a component of a set - C-Mount Spacer Kit - recommended to me a while ago by Jean-Louis) to increase the ffd of the Switar lens, I managed to focus the lens at infinity with the Aspheron in place.
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#5 Jean-Louis Seguin

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Posted 10 March 2012 - 05:15 PM

That's not normal. The 10mm lens' distance scale must be improperly set.

Cheers,
Jean-Louis
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#6 Glenn Brady

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Posted 10 March 2012 - 05:53 PM

That's not normal. The 10mm lens' distance scale must be improperly set.


. . . and yet the 10mm lens focuses properly at infinity when its scale is set to infinity. It's only when the Aspheron is added that there's a problem.
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#7 Boris Belay

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Posted 23 May 2012 - 07:31 AM

. . . and yet the 10mm lens focuses properly at infinity when its scale is set to infinity. It's only when the Aspheron is added that there's a problem.


Because of the large depth of field on a wide angle like the 10mm, it's best to check the focus at closer distances too, like 20 or 30 cm. This will tell you whether your distance scale is accurate.
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