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Can someone please help me identify this (for me) unknown lens mount? I found it on a Pentacon (Meyer Orestegor) 500/5.6 lens, which originally was sold with either Pentacon 6 or M42 mount, but this is something different.

There is a black tube coming out 5mm from the silver base plate. The tube has an outer diameter of 38mm and an inner diameter of 35mm and is threaded only on the inside. The outer surface of the black tube is plain.

On the base plate, there are three wings in some distance from the tube. As seen on the left side of the second image, the wings are gripping inwards.

Counter-clockwise of one of these wings, there is a small, fixed pin. The pin can be seen on the first image at about 2 o'clock, on the second image at the right hand side.

enter image description here enter image description here

jarnbjo
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    Can you describe the lens / lens mount in some way in the title? As it is, imagine how many completely different questions could share this same title! – mattdm Feb 28 '17 at 02:01
  • What, if any, are the markings on the front of the lens? – Michael C Feb 28 '17 at 02:06
  • @MichaelClark Which markings do you mean? The front cover has a logo for "Meyer Optik" (the manufacturer) and around the tubus of the lens, it reads "Pentacon 5,6/500 Made in GDR". – jarnbjo Feb 28 '17 at 02:17

1 Answers1

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It appears to be an Exacta outer / external mount. The normal Exacta mount is a regular internal flange, like other manufacturers. But apparently, the external mount was used at times for some of the larger lenses.

Source:

scottbb
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    Exacta external mount? That's one I've never seen or even heard of before. – Michael C Feb 28 '17 at 02:59
  • @MichaelClark Yeah, me neither. But apparently it's a thing (at least, at those forum links). Personally, I thought the idea of that mount (as shown in photos) was just horrible. I fail to see how it is good/better for long/heavy lenses. Looks more fragile than a standard full-overlap 3-ear bayonet. – scottbb Feb 28 '17 at 03:01
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    This seems to be an inofficial modification of the lens, as it was never sold with an Exakta outer mount, but I don't see the point either. The lens I have weighs almost 4kg and the small, fragile mount does not appear to be shall we say suitable. – jarnbjo Feb 28 '17 at 14:07