lens element swap between to yashica mats of different vintage
I posted about these yashica-mats before a half a year ago, but to reiterate: I have three 'Mats - an EM, 124, and 124g. The EM is currently a parts camera.
I discovered that my 124 was taking 'soft' negatives. Not soft like 'out of focus', but soft as in a lack of contrast. I took a look at the lenses and noticed what I thought was mild haze (that wasn't there before).
I took both elements out, and then discovered that it wasn't haze, but fungus on the rear element. I attempted to clean it but then wrecked it. (but I plan on keeping it for a future project).
Long story short: I replaced the rear element with the one that is from the EM, but noticed that the EM's rear element is different from the one on the 124, practically twice the length and probably of different formulation too. I'm not sure how I'm supposed to go about collumating it, I'm not sure if I should screw it in all the way like I would on the 124 series, or unscrew it out half way, or give up trying to pair a 124 front element with an EM rear and match it properly with the EM front.
Has anyone out there done this sort of thing? Any successes? Any weird effects?