Hello all!
Well, I've been using old lenses for quite a time now, on the MZ-7, MZ-6, K10, K20, K7, Kx, and now K5...
I've stumbled on the infamous stop-down metering problem plaguing the K10/20, and still visible on the K7/5...
I've tried several split screens, but I quickly found that my keepers rate was the same with the stock screen, so I ditched them, as they are useless anyway when you recompose the shot and severely mess the metering... And their blank parts were limited to f/2, in the best cases...
I then took a leap of faith and ordered the
Pentax ME-60 blank screen, hoping that it was optimized for fast lenses, but, alas, it has the same f/2 limit than the stock screens... But to my surprise, I found the utterly blank viewfinder really pleasing and it helped me much in composition, as there is no disturbing element (as the focus brackets)...
Then, after a little research, I've found out that the
Canon ee-S screens were optimized for fast lenses, and were supposedly able to accurately show DoF right down to f/1.7... So I immediately bought one and took out my saw... I already made a DIY split from a MZ-M screen, so I was not adverse to a little plastic dust...
I ended with a nearly mint focus screen (got a little scratch on it, visible only at about f/8
).
OK, time for the tests...
DoF rendering:
I took out my f/1.4 lenses (Pentax FA50 and Samyang 85) and played a little with the DoF Preview, and hallelujah, I can now see a difference between f/1.4 and f/2 (try it with the stock screen)!!! Even f/1.7 produce a slight darkening of the viewfinder, so the eeS screen actually work right down to f/1.4!
Focusing:
With now an accurate DoF, seeing what is actually in focus at f/1.4 became really easy! But there was a severe back-focus, so I had to remove the metal shim and replace it by two thin strips of post-it...
Now, focus is eerily accurate, with both lenses! Even a split screen could not give me such a precision...
I'll order the proper metallic shim now that I have the exact thickness needed...
Metering:
OK, here I was worried...
So, I put the FA50 out of its A position, and took a series going from f/1.4 to f/22 in 1 stop increments... Here is what I got (repeated several times): 3000, 2000, 1000, 500, 250, 125, 60, 30, 15...
Yep, you've read it right : a near-perfect linearity on the whole range, with only a slight +0.5 overexposure at f/1.4...
With the 85mm now... 800, 500, 320, 160, 80, 40, 20, 10, 5... Really good, too, with a little +0.5 overexposure at f/1.4 and f/2...
I simply never had a screen so accurate before!!! For reference, the K5 stock screen has nearly 1Ev of leeway around the proper value...