I found doing landscapes,in areas not all that well lit, using small apertures, for better, not good depth of field, for sharpness, i needed the mirror locked up! Speeds as low as 1second.A question often with this camera, also with Mamiya RB/RZ 67, "what ya mean no f-64?".
I'm glad many of you can handhold this monster camera, with a sound of major importance! I could not.. I added wide angle lenses, borrowed teles from a friend, had a vast system. Nothing helped! OH I had a very heavy tripod, A Schiansky ? that easily held a 8x10!
The camera did show effects from the mirror going up! My experience, not yours..I had a special mounting plate to minimize vibrations..
1/8th and 1/15th showed the most! Again we differ.
The results of the Pentax outstanding but.. any 120 TLR easily equal. It's the format not the box. My 35mm when processed carefully, filtered solutions, clean chemicals, care in focus etc easily matched the 67. Yes the 120 had a slightly better dynamic range. Slight.
The best day of my life with the Pentax 67 was trading it at Samys L.A.