Impressive Glass

Now since I worked with Pentax 6x7, and now even with Mamiya RZ67 Sekor Z lenses - one thing appears to be clear already at an early stage; the Mamiya RZ67 lenses are better. In terms of chromatic abberation - they are way better than the Pentax 67. Simply when you use all lenses at wide open aperture - the difference is pronounced.

Mamiya RZ67 vs Pentax 67 SMC lenses

Now the Mamiya Sekor Z 110mm ƒ2.8 does exhibit a little of chromatic aberration - but it is rather little, and doesn't even need much correction at aperture ƒ2.8. Impressive !

When you compare that with the Pentax 67 SMC Takumar 105mm ƒ2.4 lens - the latter makes huge amounts of chromatic aberrations (red/green fringing) at aperture ƒ2.4

Well, the Mamiya APO 210mm, as well the Sekor Z 250mm do not show any of that, at wide open aperture. At least not yet in the rather few images I have made. Naturally, when all lenses, whether Mamiya or Pentax are stopped down a couple stops, they barely or not at all show aberrations.

Stopped down - they are all excellent.

However, the Mamiya Sekor Z lenses do play in a higher class, even those who are not have the designation APOCHROMATIC (APO).

I am sure there are some Mamiya lenses that may fringe more - I'll see that once i tested them all.

Contrast slightly compromised
due to the large image circle of 6x7 lenses

Yes, the Pentax 67 lenses have it, and with the Mamiya RZ67 lenses even more. I believe it is the enormous image / illumination circle of these lenses - up to 92mm large with the RZ67 lenses - that create interferences in which the light, which goes way beyond the sensor area - bounces around in adapter and camera, leading to a somewhat lower contrast. Like a very mild glare. But that is my assumption... i can't tell for sure.

This can however be easily adressed in post processing. Plus you get a bit more leeway with the shadoes, that are slightly lifted - and therefore are mallable. I don't see it was a true obstacle. You get digital files after all - and with it - tremendeous amount of leeway how to tweak contrast.

It is also possible - that older lenses naturally have lower contrast compared to digital lenses. But i do believe it is the huge illumination circle of these 6x7 lenses, that contribute to some lesser overall contrast. But as i said, you can correct that in post.