Pentax 6x7 lenses on a Pentax 645 body

I see some Pentax lenses listed as "67", and some as "6x7". What is the difference, and can both be used, with an adaptor, on the Pentax 645 body?

There is no difference in lens mount, so yes, they can all be adapted to the 645 series bodies. The lenses marked 6x7 were made for the 6x7 body beginning in 1969. Lenses marked 67 were for the updated 67 body, introduced in 1990, and 67II body, in 1999. There's a wide range of 6x7 and 67 lenses available, and of course some are better than others. For user reviews of them take a look at the Pentax 67 Medium Format Lenses at https://www.pentaxforums.com/lensreviews/.

Also another good site for lens info/ratings: Dead Link Removed

PhotorioNewbie said:

I see some Pentax lenses listed as "67", and some as "6x7". What is the difference, and can both be used, with an adaptor, on the Pentax 645 body?

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Pentax 6x7 refers to the second generation lenses that came out c. 1970 when the Pentax 6x7 camera was newly minted (1969).
Asahi Pentax 6x7 Takumars preceded these lenses.
In 1989 the re-engineed Pentax 67 body came out and soon after in mid-1990, redesigned lenses to match: these are the SMC Pentax 67-designated lenses. There were a few changes to old Distagon lens designs, and upgraded engineering and cosmetics, with a few high-end and expensive lenses introduced, such as the sought-after SMC Pentax 67 75mm f2.8AL and the 400mm IF ED tele. There are quite a few members on pentaxforums.com who can speak highly of these particular lenses, but especially the SMC Pentax 67 series lenses generally. Their performance far exceeds the plain and ordinary of the early 6x7 and Takumar lenses.

An adaptor is required to use any of these lenses on teh 645 body, with the exception of the big tele lenses which mate to the external bayonet mount of the Pentax 67 cameras (that is to say there are two mounts: inner and outer, accommodating short, standard and tele to super-tele lenses).

It seems like some of the basic differences are covered here by other members.

If you're wanting some more in depth reading, I have an article on the Dead Link Removed where I talk about some other common differences.

One major difference to note between the 67 vs 6x7 versions was the use of radioactive thorium on the latter (the earlier versions). At least on the 105mm, the Super Takumar and Super Multi Coated Takumars the glass regularly yellows.

If you want to learn more, feel free to check out my article!