An easier test might be just to use something on the horizon (or
infinity). Of course this must be done with a lens that you know is
calibrated properly for infinity.
If those are sharp, everything else in between will be too.
John
Shawn Wright wrote:
> 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
> (Olympus List Archives)
>
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