Tim wrote:
> <snip> with leaf shutters, usually the shutter open and close travel times
>become a significant part of the exposure at high shutter speeds. This means
>exactly where you set the light threshold of the detector circuit affects the
>measured speeds. Some testers integrate the recieved light signal to get
>actual light at the film plane which then takes into account travel time.
><snip>
Tim,
I was hoping you would chime in on this subject. I "think" I can see
the affect of the relatively slow speed of a leaf shutter in the traces
obtained by Cool Edit. Although I have not done any testing at anything
other than wide open on the two RF's that I have tested it will make an
interesting experiment.
I am curious as to the response of the circuit I used for this tester.
I has a very sharp (near vertical) initial rise that then decays
asymptotically to zero. If this is a long speed (i.e. 1/125 or slower)
there will be a mirror of this in response to the shutter closing.
However if the speeds are higher there is a truncation of the decay to
zero which is not as well defined as the start of the trace. I am
curious if there is a better way to utilize the photo detector to
trigger the Cool Edit software? Something that would produce a "square
wave" pattern with the width of the wave representing the time,
remembering that this was a $12 project that, so far, works Ok. If you
would like to suggest something a little more involved I will have to
warm up the circuit board router my company just acquired.
C.H.Ling wrote:
>Mike (?) said he need 50 minutes to complete one set of test for a
>camera that is also too long.
CH,
50 minutes also includes my generation of a list of shutter speeds in
1/4 and 1/3 stop "nominal" increments in order to judge the inaccuracy
of the shutter speeds on the new camera. Actual testing takes less than
5 or 10 minutes depending on how many samples at each speed. I will
often do at least 5 at each speed to gauge repeatability.
John Hermanson Wrote:
>Leaf shutters are limited to a maximum speed (even when new) of about
>1/350th (even when the ring says 1/500th. ) This was discussed in a thread
>awhile ago.
John,
Thanks for confirming what I thought had been previously discussed. I
hadn't let it stop me from putting film through the camera. I should
see the results later this week from the first couple of rolls of
prints. If they look OK I will try a roll of slides to get a better
feel for the accuracy of the auto exposure system.
Thanks again to all for the feed back on this project, it has been one
of the most useful projects I've ever built. And what's more it helps
with my Zuikoholism.
Mike Butler
Dublin, California
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