After reading C.H. Ling's tip on mirror/focus adjustment, I decided
to try this on my Trip 35, but quickly realised I have no way to keep
the shutter open... (yes, I know there's no mirror also, but I wanted
to check lens alignment.)
Anyway, this morning I moved on to my 4T, because after last
year's focus problem "Saga", I still suspected that mirror angle was
off, due to a high number of off focus shots compared with my OM-
10. But after 6 months away at service, and the assurance that the
Oly service centre had replaced the mirror assembly, I hesitated to
push the issue.
Here's what I found:
Using my 50/1.8 focussed on a UPC bar code at about .5m, I
placed a 1-13 screen at the film plane and checked focus on both
the prism and matte area after locking the shutter with a cable
release. I used a Radio Shack 30X magnifier, which allowed very
fine focus adjustment. I discovered that focus was consistently off
at centre of the frame by approx the distance from 16 to 8 on the
DOF scale on the lens. ie: Viewfinder focus sharp with .5m mark at
left 16, while film plane focus was sharp when .5m mark was
moved to the left "8" DOF mark.
Hmmm... Next I added one tiny square of electrical tape over the
mirror stop "rest area" on the back of the mirror.
Repeating the procedure reduced the error by about half the
amount.
I added another piece of tape, which caused the error to go too far
the other way. I then removed both pieces of tape, and carefully
made a "shim" of two smaller pieces of tape.
Repeating the test at centre frame showed almost perfect
repeatable accuracy!
I then tested again at left and right edges of the frame and
confirmed my suspicions: the left edge was out by about double
the amount I had to begin with, ie: from the 16 mark to the red
centre dot on the DOF scale. And the right edge was out by the
same amount, except in the OTHER direction, indicating the mirror
is skewed across the frame.
It is for the reason, and the fact that the mirror appears very slightly
skewed to the naked eye (as it always has) that I now suspect the
Olympus service centre did no mirror replacement at all. (I assume
this is a major, expensive repair...)
I think this may be due to unusual circumstances of the repair: the
camera was given a full checkup and cleaning by Bridgeport
Cameras before I bought it at Broad Street Cameras. Broad St sent
it back to Bridgeport, who in turn sent it to Nortown for official Oly
service. But since Bridgeport and/or would Broad St would have to
cover the cost, I suspect they opted out of the repair when they got
the estimate for a mirror replacement, and just told me it was done.
I asked for paperwork on the repair, and they said they had none.
I'm not sure whether I should try to pursue this, since it's now 8
months since I got the camera back. I was thinking if I called
Carsen (the Oly Canada rep) and explained the situation, maybe
they would look into it. Or maybe I should call Nortown and ask for
the paperwork on the work done? Or maybe even Olympus
America, although I suspect they'd shy away from getting involved,
even though they were very helpful on the phone when I did call at
the beginning of all this.
If anyone has ideas on how to proceed, please let me know.
ps: I did check the diopter adjustment before and after doing this,
and tried using both eyes to check focus. My last eye checkup
showed no astigmatism, and very minor distance vision loss (0.5
and 0.75)
Shawn & Janis Wright
swright@xxxxxxxxx
http://Zuiko.sls.bc.ca/~swright
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