I used a laser pointer and a photo transistor. I actually found that
some old transistors in a can worked the best. I cut the top off.
The transistor was a gain stage with an emitter follower.
If the OM archives are around, I probably discussed this.
Here is the original board I used, which I just happened
across last month while cleaning the basement.
http://www.zuik.net/OM-4t/shuter_test_MG_6132.jpg
I'm surprised I still have it.
The laser pointer, aimed at the transistor, made for sharper
transitions when the shutter passed. So, once I had the pointer
adjusted, I would put the camera in the path, and first test the
start of the shutter curtains, then the end, and compare the
pulse widths. The pulse width at 1/2000 would measure
the shutter speed, while testing the pulse width at the
start and end, would check for uniform travel speed of
the two curtains. There are two tension adjustments
you can access by removing the bottom plate.
(Obviously this testing is done with the lens and
camera back removed.)
But I highly recommend sending the camera to John H for
adjustment, as he is the pro and there is more to it than
just tweaking these two tensions. The shutter release
really needs to be cleaned before doing this adjustment.
The curtain travel accelerates, so the rise times are faster
at the end of the travel. I used to get quite a few cameras
from eckBay and would test them, as well as OM-2n's and
OM-1's. A good OM-4t would be less than 25% off at 1/2000.
Fortunately that speed is rarely used. Sometimes the curtains
would be completely closed by the end of travel, one catching
up to the other.
You would be surprised how often this speed is off.
You can also test by taking a picture at 1/2000 and checking
for exposure accuracy and uniform exposure.
A brand new Leica M6 at 1/1000 was off by a lot more,
which I returned for a second one, which was also off.
So I passed on using Leica cameras. The OM's in my
opinion had better accuracy, which they would
have to to get 1/2000 speed.
I tried a number of circuits, and this worked the best. It takes
a bit of tweaking to get the response right. I bet the transistor
I used was made in the 70's.
WayneS - OM geek for the day
At 09:49 PM 12/20/2008, you wrote:
>Wayne, I'm most interested in how you did so.
>
>Perhaps you're willing to tell me about this, whether on or offlist, as
>you judge better.
>
>TIA
>
>Fernando.
>
>WayneS wrote:
>> I used to check the shutter travel time. The OM-4t weakness is
>> at 1/2000, where exposure variation across the frame is most likely.
--
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