Yesterday I tried to test the MF focusing accuracy of my 5D Mark II, I
hesitate to do so as I found my Zuiko 28-48 was doing very well with it for
normal shooting. I was worried that any slightly error will be killing me,
sending such camera for calibration was not really success in the pass with
Olympus (although it was AF problem).
Anyway, I can't help myself and did the test, it was a shock to me that 80%
of the tests run with the Zuiko 50/2 at F2 were front focus! I tried
different glasses, some seems to be better than the others, I even put the
varimagnifinder and set to 2.5x, the result was not very consistant and most
of the time still front focus. Then I put another lens to test, this time
50/1.4 and the result was not much better, I stopped it down to F2.8 and it
seems started to improve.
Suddenly I remember Canon (also Sony) recommend another focusing screen for
lens of F2.8 and larger. I purchased the screen right after I bought the 40D
early this year and it seems ok but I didn't find it much easier to foucs,
anyway I did use the screen since then.
Since the 5D is a FF camera, I tried to see any of my focusing screen will
work but they are all too small at the wide end and too big for the short
end. I immediately search for the size of Sony A900 screen, it is an Acute
Matte so must be very good. I found it was slightly larger than the 5D's so
it should be ok after rework.
This afternoon I purchased a A900 Type M which is designed for manual
focusing with lenses of aperture >= F2.8. After half an hour work I
successfully put the screen on the 5D II.
Wow! it makes a big different in focusing, the successful rate was almost
100%. Now I understand the different focusing screen is not for easier
focusing, it is more precise for larger aperture lenses. But I'm a little
disappointed, the A900 screen is much darker than the orignal Canon even
just at F4, you really need the F2 lenses. It also has vignetting with many
lenses especially the 28-48. Anyway, focusing accuracy is the top piority
for me and changing focusing screen is not that difficult I will just keep
both in my bag.
BTW, I was using the Minolta screen on my OMs and they don't have the above
problem. I remember some old Minolta screen (for the AF camera) was longer
and may fit the 5D, will try to search if any of them still available.
C.H.Ling
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