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03-23-2017, 12:26 PM   #1
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Pentacon 6 to Pentax K mount adapter

Hello folks!!!
Does anyone have expirience with this adapter? I have bought one Pentacon 6 to M42 from this manufacturer and it works perfectly. But after "M42 to K mount adapter with/without flanges" threads I'm not sure if this adapter has genuine K mount just like Pentax lenses or not.
Does anyone know that? I have beautiful Pentacon 180mm f2.8 lens...

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03-23-2017, 12:38 PM   #2
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Pentacon 6 has a much longer focal flange distance than Pentax K, so you don't have to worry about it...this sort of adapter will keep infinity focus just fine.

M42 has the same focal flange distance as K mount, that is why the adapter has to sit flush with the lens mount.

If the focal flange distance is shorter then you need optical correction. Nikon for example has a focal flange distance that is slightly longer than K, but the adapter need to mount it makes the distance longer, so you need optical correction and the adapter acts like a short tele-converter...Canon FD has a shorter focal flange distance and the mount is wider than K. So the converter acts like an even longer tele-converter...
03-23-2017, 12:52 PM   #3
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QuoteOriginally posted by boriscleto Quote
Pentacon 6 has a much longer focal flange distance than Pentax K, so you don't have to worry about it...this sort of adapter will keep infinity focus just fine.

M42 has the same focal flange distance as K mount, that is why the adapter has to sit flush with the lens mount.

If the focal flange distance is shorter then you need optical correction. Nikon for example has a focal flange distance that is slightly longer than K, but the adapter need to mount it makes the distance longer, so you need optical correction and the adapter acts like a short tele-converter...Canon FD has a shorter focal flange distance and the mount is wider than K. So the converter acts like an even longer tele-converter...
I bought an adapter like that a while ago, also to be used with the Sonnar 180mm/2.8 and the Biometar 80mm/2.8, both of which are beautiful lenses. However, my version did not fit on my camera: The K-bayonet was too tight. The seller refunded the purchase and I was able to file down the mount by a few millimetres, and now it works just fine. Mind you, I haven't tested infinity focus yet. In theory, this should be no problem (see boriscleto post). But given the tolerances of the adapter I should have tested that.
03-23-2017, 01:07 PM   #4
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The bayonet should be OK mechanically - make sure you can return it if tolerances are too big. However, Pentax cameras like the electrical contacts properly short-circuited for manual lenses, so the black bayonet is not ideal. On the other hand, the rear inside in the photos looks fairly shiny despite the grooves. With the 6cm x 6cm coverage of the lenses, it may give you internal reflection problems. Both can be tweaked, but be prepared to do so.

03-24-2017, 01:07 AM   #5
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I have not used than adapter, but the Pentacon 6 to K-mount adapters that I have used work perfectly. Mine are just marked Pentacon-Pk and other respects look the same. The issue with the flanged M42 to K-mount is with the unnecessary flange arrangement which increases the length of thread. With Pentacon 6 it is bayonet-to-bayonet and not much scope for getting it wrong if it is properly engineered.
03-24-2017, 10:49 PM   #6
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Thanks guys, I'll buy it and test my luck.
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