I have 4 lenses which I can use with the Pentax 6x7. I have a 90mm f/2.8 normal lens, a 45mm f/4 wide angle and two telephoto lenses 135mm f/4 and 200 f/4. Bellow are my notes on those different lenses based on information I could find about them as well as my experience with them. I also include a few sample pictures taken with the different lenses.
The SUPER-TAKUMAR / 6x7 1:4 / 200mm was released in 1969 (see pentaxforum.com). It seems to have a quite good reputation in terms of sharpness, bokeh and durability. I can confirm the durability since we are in 2015 and the one I have is still fully functional with a smooth focusing ring. That is quite impressive considering its age and the fact that it has not been serviced recently (at least within the last 20 years). Interestingly, it seems to be a very good lens for astro-photography: People use it with digital sensors and get very good pictures of the stars. I may have to try that sometime! In terms of limitations, it seems to produce some chromatic aberrations and color fringing. I have not had issues with that since I mostly used it with black and white film. Another limitation is its minimum focusing distance of 2,5m. This is not close enough to be able to fill the frame when shooting portraits. To get around that, I need to use extension tubes. It would have been nice to have a closer focusing distance out of the box. Bellow are a few sample pictures taken with it. The last one has been taken using one extension tube to get closer.
The Super-Multi-Coated MACRO-TAKUMAR / 6x7 1:4 / 135mm was released in 1971 (see pentaxforum.com). I don't not think I have shot more than a couple of pictures with this lens for now. From the information I could find, this is a good lens for close-ups. It has macro in its name but its maximum magnification is only about 0.3x. The minimum focusing distance is 0.75m. I should probably use this lens over the 200mm for taking close-up portraits of the kids. In terms of sharpness it seems to be quite ok, especially when stopped down. I'll have to experiment with it. So far I do not have sample pictures for that one but stay tuned!
The Super-Multi-Coated TAKUMAR / 6x7 1:2.8 / 90mm Leaf Shutter was released in 1971 (see pentaxforum.com). This is a normal lens on 6x7. The main benefit of it is that it is one stop faster than the other lenses I have. According to the information I could find, this is not a very sharp lens.From my experince with it it is hard to say if I have noticed it. Because I am scanning the negatives with a flatbed scanner, I am not really impressed with the sharpness of the images I get but the low quality of the scan makes it difficult to blame the lens. One interesting thing about this lens is that it has a leaf shutter built-in in order to allow for flash sync at up to 1/500s. I have not use the leaf shutter so far. Because of its rather inferior optical quality compared to the other lenses, I will probably not use it too much unless this focal lens is really a must. In the same range of focal lens, the one to get seem to be a 105mm f/2.4. Bellow are a few sample pictures. More pictures taken with this lens can be found in this autumn post.
The SMC PENTAX 67 1:4 45mm is a more modern lens which was released in 1989 (see pentaxforum.com). This is a wide angle lens which field of view is approximately equivalent to a 24mm lens on a 35mm camera. It is the main lens that I am using for shooting landscapes and it is the lens I typically have attached to the camera because it is the smallest in size and weight. From what I could read it has a very good reputation in terms of sharpness, distortion and overall images quality. There seem to be no obvious cons to this lens but there is apparently a 55mm/f4 which is slightly sharper. I'll continue to use it! Bellow are a few sample pictures.
Conclusion
It seems that the set of lenses I have is pretty ok with the exception of the 90mm f/2.8 which is inferior to the others. If I get the opportunity I should get a 105mm f/2.4. Out of the other lenses, I should get some experience with the 135mm f/4 which seems to be a very good lens which I have neglected up until now. I will add more sample pictures as I go. I may also add pictures of the lenses themselves. Leave me your comments if you have any different experiences and/or recommendations for Pentax 6x7 lenses!