Having purchased a used ETRS recently I was pleased to discover a webpage that explains the differences between the different models <p> http://www.smu.edu/~rmonagha/bronetr.html <p> Hope you might find it helpful. Perhaps the webmaster of this site could add a hyperlink to the above URL. <p> The rest of the website seems to contain a considerable amount of info that should be of interest to medium format enthusiasts with other cameras. <p> NB - I am not connected in anyway with the above website.