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07-01-2016, 04:27 PM   #1
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Pentax 6x7 adapter


Is there such an adapter that allows the fitting of a Takumar 500mm f4.5 to a 6x7 body by first removing the M42 mount?


07-01-2016, 06:06 PM   #2
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DIYing an adapter might be possible, but there wouldn't be much of a point as the lens would old cover a fraction of the 6x7 film.

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07-01-2016, 09:54 PM   #3
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There isn't any point in trying to mount a M42 Takumar 500mm lens to a Pentax 6x7camera.

The registration distance of the M42 lens places the flange inside the lens mount preventing the mirror from rising.

And as Adam pointed out an M42 lens only covers a small area of a 6x7 film opening.


07-02-2016, 02:20 PM - 1 Like   #4
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This is a list of the registration distance of many camera bodies

Camera Mounts Sorted by Register

07-02-2016, 03:59 PM   #5
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At one time Pentax made an adapter to put the 500 4.5 Takumar on the 6x7. You bayonet the lens apart in the middle (where you put the rear filter) and the 6x7 adapter would replace the back part of the lens. Good luck finding the adapter,though. I know of someone who took the back part off and used the lens to cover 4x5 on a Graflex 4x5 focal plane shutter camera. I never saw the results but he claimed it covered fairly well.
07-03-2016, 01:09 PM   #6
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Meyer and Kilfitt both made lenses with detachable back ends so that they could cover the various formats of the time. The lenses had image circles of around 90mm and a maximum register distance of 74.1mm (Pentacon Six) but removing the back end (no optics) and replacing it with a longer one (also Meyer or Kilfitt supplied) allows them to be used on an M42 or M39 system. I have several of these and can use them on my 645Z or Canon 35mm bodies.

I'm not suggesting that the Tak 500/4.5 has the same feature but it's not as simple as saying an M42 lens will not work on a 645 mount system.....if the rear optic is 30mm or more behind the flange and the image cirlce is large enough then it's possible.

07-03-2016, 03:30 PM   #7
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QuoteOriginally posted by pentaxus Quote
At one time Pentax made an adapter to put the 500 4.5 Takumar on the 6x7 ...
Great info, I certainly didn't know that. However, the 500 mm f/4.5 isn't that great on my K-3 so I would not spend too much energy getting the parts needed to attach it to a modern 645 system.
07-04-2016, 06:39 PM   #8
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I have an SMC Tak 500/4.5 that has been modified to fit the 6x7 system. As well as replacing the rear section of the lens, which is basically an empty metal tube, there is also a baffle that is removed. In an M42/K mount lens the baffle would reduce extraneous light and thus cut flare. This effectively reduces the image circle of the lens. Once the baffle is removed it easily covers 6x7, which is what you would expect from a lens of this size and focal length. It is a fairly simple modification, but you do need someone who can accurately machine the new rear tube so that infinity focus is correct. I don't know whether this was ever an official Pentax modification or just something carried out by repair shops. Unless you already own a 500/4.5 it probably isn't worth doing, since the cost of the lens and the modifications would probably end up more than just buying a secondhand 500/5.6 (and getting a k->67 adapter if you want to use it on both systems).


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