Pentax 67 lens to Pentax 645 body adapter

One of the most interesting accessories for the Pentax 67 system is a lens adapter for Pentax 645. You can now buy for cheap the body of its ordinary non-AF models, and it can become a good additional or backup camera for the primary Pentax 67.

Pentax adapter 645 for 67 lens and 105mm F2.4

Pentax adapter 645 for 67 lens and 105mm F2.4

For one thing, it is possible to keep a different type of film there to be able to shoot simultaneously on the black-and-white or color film. There is also no need to take with you lenses for Pentax 645. Take, for instance, the 90mm F2.8, which may work similar to the normal lens, while the 105mm F2.4 is closer to the portrait lens.

Pentax adapter 645

This adapter allows the use of any 67 lenses on 645 bodies in full manual and aperture priority (Av) exposure modes. It has aperture coupling and automatic diaphragm release levers which allow to use Pentax 67 lenses almost like 645 lenses. It permits open-aperture metering while the aperture value is not displayed in the Pentax 645 viewfinder. It is like setting the aperture ring of the 645 lenses to the non “A” value.

Also, it is possible to use Pentax 67 macro extension tubes for shooting macro and closeups with automatic aperture release continuing to work well. In the original manual Asahi says that with some lenses corners get slightly darkened when shooting with open aperture or light falls off at corners when aperture is closed by some f-stops. I’ve used the adapter with my 90mm F2.8, 105mm F2.4, 135mm F4 Macro and 165mm F2.8 lenses and I’ve never noticed any light falling off.

Pentax adapter 645 for 67 lens – front and back views

Pentax adapter 645 for 67 lens

I have for some time enjoyed the original non-AF body, having bought it for just 100 USD. And I can say that its exposure meter works fine, and AA batteries are available everywhere. Therefore, you won’t find yourself in a situation that once happened to me.

It is also worth mentioning that gaps between frames, which can at times pose a problem in the Pentax 67, are simply non-existent with 645 cameras due to the completely different film transport mechanism in these cameras.

“Crop” factor

As we know, a lens of X mm focal length is a lens of X mm focal length, and no matter what camera you put it on. So, the difference is that the Pentax 645 is a smaller format camera, which crops the inside of the image circle more than the 67 format does. In a nutshell, it is like using the only 41.5mm of film length instead of exposing 70mm. Take a look at the examples below to understand how cropping is actually applied.

Pentax 67 165mm F2.8 - 645 crop factor example

Pentax 645 “crop” factor example #2

Pentax 67 90mm F2.8 - 645 crop factor example

Pentax 645 “crop” factor example #1

This always creates the effect of a “longer” focal length on the 645 camera as compared with the same lens installed on the 67 camera. This effect is also often called an “equivalent” focal length. The term is only needed to simplify an understanding of the focal length required on the 67 camera to match the field of view of the “cropped” 67 lens installed on the 645 camera.

To calculate it, a focal length of the 67 lens should be multiplied by a “crop” factor. The Pentax 645 has 56×41.5mm frame size, so its diagonal is 70mm. The Pentax 67 has a 55×70mm frame size and a diagonal of 89mm. The “crop” factor is 89/70=1.27 and, as a result, a 90mm lens for 67 format installed on 645 camera is like installing native 114mm lens on 67 camera. The 105mm is like installing 133mm, 135mm “turns” into 172mm, and 165mm, into 210mm on 67 camera.

Summary

Unfortunately, the 6×4.5 format proved to be not very convenient for me, if not entirely uncomfortable. And eventually, I replaced the camera and adapter with another Pentax 6X7 body with MLU which costs a bit more. I found it easier to use two almost identical cameras on a photo shoot. But Pentax 645 allows to take 15 frames on a single type 120 film roll (16 frames for Pentax Pentax 645N and 645NII), which may be important in case of a limited film stock. Do not forget that this adapter also allows you to mount lenses on digital Pentax 645d and 645z which only operate in stop-down metering mode.

Other Pentax adapter 645

There is another third party adapter with the same full-automatic functions: Fotodiox PRO PT67-PT645 (II). It is a bit cheaper than a genuine Pentax adapter 645 but still has all the same features, including 67 outer bayonet mount.

P.S.

Thanks for reading! I would be very grateful if you point out my possible mistakes, add extra information, or just share your experience. Scroll down to the Leave a reply section and share your thoughts about it. Your opinion is important for me. I enjoy answering your questions as the answers may often benefit many other readers and the process of answering allows me to better piece together my existing knowledge and find ideas to improve my articles.

© Sasha Krasnov
Pentax 67 Macro Extension Tubes © Sasha Krasnov Photography

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14 Comments

  1. Sasha, thanks so much for explaining clearly the conversion factor from 67 lenses to 645 platform. This proved to be hard to find info! I am also considering the adaptor for using 645 lenses on K-mount bodies. Why not mix it up!

    • Thank you Phil! I’ve never used Adapter K for 645 lens. I’ve used only third party adapter EF for 645 lens a couple years ago. So, I can describe this, but I think other various adapters should be included too. Anyway, I will need images for 645->K adapter to pin a note about it in the article.

  2. Richard

    Thanks for the conversion information and calculation. So for a Digital 645z which is has a 44×33 mm frame size we have
    89/55=1.62

    • Hi, Richard. Yes, sure, in case of digital Pentax 645z conversion ratio about 1.62 should be applied to the Pentax 67 lenses. So, 105mm become 170mm.

  3. Sasha, got one of these on your recommendation but had one question that I can’t seem to find the anwer to in either the manual or elsewhere. I just popped the adapter onto the 645n with a 67 90mm f2.8 lens and when I look through the viewfinder I see the shutter speed I have it set to, but not the f stop. Instead I see “F – – “. Is that normal/ok? Or is something wrong? Thank you!

    • Hi Wesley! Thank you for the question. Yes, it’s ok. On the original Pentax 645, the actual F-number is not displayed in the viewfinder too but exposure meter works fine. Moreover, on Pentax 645 body appropriate F-number is not displayed even with 645 lenses when aperture ring set to respective f/stop, i.e. not in “A” position.

  4. Eric Charles Jones

    Hello Sasha,

    I’m just curious, have you ever used the 645 adapter and 67 lens with the combination of Pentax’s extension tubes?

    Thanks and regards

    • Hi Eric,

      Yes, sure, I used Pentax 67 Extension tubes without any limitations. But Asahi recommended manual diaphragm operation when all set of extension tubes is used. In the case of 645 to 67 adapter, it’s should be more important.

  5. Hello Sasha,
    First thaks for all the work you do to make our lifes easiers.
    When you talk about the “crop factor” do we actually see the entire image through the view finder, or must we be aware of this crop and imagine where the limits of the picture are?

    Hope I explained my self.
    Thanks for your time and help.

    Regards Carlos

    • Hello Carlos,

      Thank you so much for visiting my website and for the question. So, the “crop factor” is just a concept to make understanding a bit easier. When you put Pentax 67 lenses on Pentax 645 camera you see entire 6×4.5 frame in the viewfinder of course. But in terms of 6×7 system you crop the “full” 6×7 image frame to the dimensions of a smaller 6×4.5 image frame. Both viewfinders, 67 and 645, show entire image of its format. But when you put a 67 lens on a 645 camera you may notice that the same lens on a smaller 6×4.5 format seems to get a bit longer focal length (by x1.27) compared to the original focal length and format! This is “crop factor”. For instance, you are going to use the famous 67 105mm lens on a 645 camera that crops 6×7 image produced by this lens to the 6×4.5 image frame. Multiplying 105 by 1.27 gives ~133mm. So, you may expect the field of view of a 67 105mm lens on a 645 camera became the same as for a 133mm lens on a 67 camera. I hope it explains a bit better.

      Do not hesitate to ask me further questions.

      Best regards, Sasha.

  6. jimi franklin

    Hi Sasha,

    Thanks for the info. I just bought a pentax 645 (not N) and put the adapter and 67 lenses on. I can’t seem to change shutter speeds or get the film to advance…
    Does this adapter work with the regular 645 or does it have to be a 645N?

    Thanks,
    Jimi

    • Hi Jimi,

      thank you for visiting my website. This adapter works with all 645 bodies, including digital. The camera does not display an actual aperture value in the viewfinder due to a mechanical aperture coupling of 67 lenses, but the meter works correctly. When you are turning the aperture ring of 67 lenses the shutter speed in the viewfinder of the 645 camera also changes. If you are trying to test the camera without a film inside the camera will not work. The only option to test the camera without a film is to take out the film insert. I could be wrong because I have had no 645 cameras anymore for many years.

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