OK, so you got yourself a Kiev but want to know
for certain how close to exact the shutter speeds are.
The whole deal works around this Sharp PT510
Phototransistor. Unlike the Phototransistor found at Radio Shack,
this one really kicks. It has a very fast response time for both the
Rise and Fall Time. Meaning, it turns on and off really quickly,
which decreases the likelihood of erroneous data.
The other end of the deal is a bright
collimated light source, ie. a laser pointer.
Here is the schematic describing the circuit.
It's pretty simple. Feed 3-5 Volts in for power, when the light hits
the phototransistor a signal level change can be observed at
connector J1 output. The basic configuration is to mount this
circuit into a small box with jacks to hook up power and a connector
to a device to read the signal level change. The phototransistor is
mounted such that a very small hole is in front of the device and
the laser pointer shines through the small hole casting it's intense
light onto the phototransistor. Interrupt the light and a
corresponding signal level change is seen.
Here is the actual output as read on an
oscilloscope. When the shutter is fired the opening curtain allows
the laser beam to fall on the phototransistor as seen by the event
of a signal change shown by Yellow Arrow. When the closing curtain
passes in front of the laser beam another signal change is seen. The
duration between the two arrows is measured for the actual time the
shutter has remained open. As seen in this example a 956 micro
second event is recorded, or in layman's terms, a little faster than
1/1000 second. As you can see, very accurate readings can be made.
As well multiple readings can be recorded and average shutter speeds
with overall variations plotted on a graph against values of perfect
shutter speeds for any given setting.
OK, great, how do I build one? Start with one
of these handy Radio Shack experimenter boxes that measures 3x2
inches. Notice I've mounted my power jacks and coax connector for
Knock off any protruding bumps to make a nice
flat surface. This surface will be the front face or the surface
that contacts the film rails.
You'll want to determine where the
phototransistor will be placed. Measuring on the front surface these
numbers make a nice placement.
With these numbers it positions nicely in the
center of the exposure window.
Spot a modest hole. I used a .063" or
Chamfer the inside surface with a drill roughly
the same diameter as the phototransistor.
What you are trying to get is a bevelled hole
that will receive the dome shaped lens of the phototransistor. If
the phototransistor is placed into this bevelled hole is should
Take some material of the same outside diameter
as the phototransistor (4.7mm) and cut a little cylinder. Oddly
enough I used the barrel of a 1cc syringe used for insulin
injections. If you know anyone who has diabetes these are very handy
for things such as this and applying very precise amounts of
lubricants, but that's another story. Tack the cylinder in place
with some ACC (Krazy Glue) while pressing down to seat the
phototransistor into the bevelled hole.
If you are satisfied with the results, make it
more permanent with some epoxy glue. Now you have a receptacle that
will receive the phototransistor and it will be centered every time.
Build up the circuit on some perforated circuit
board. Note, I've added a second output connector for an audio level
signal to input into a computer sound card, but it will remain
unconnected for now.
With the phototransistor mounted on the other
side, you can remove the circuit for upgrades or what ever and it
will insert and re-center exactly to the bevelled hole.
Now to fine tune the light entrant part. Scribe
X-lines through the center of the pilot hole.
Take some shim material, it can be made of
anything, and drill a really small hole in it. This will act as an
aperture to reduce the acceptance angle of the light beam. A #80 or
.012" drill will do the trick. Draw a similar X mark on the
shim and align to the scribe marks on the box temporarily with some
tape. Do a quick test by shining a laser straight into the front and
if need be make adjustments to the position of the shim aperture.
satisfied with the position of the front aperture shim, fasten it
down. I use black electrical tape buy anything can be used. Pretty
much you are done.
you want to get fancy, you can even build one that has two detectors
for use on your other cameras that have a focal plane shutter that
travels horizontally. I've placed my detectors 25mm apart so that I
may measure the shutter speed at both sides of a horizontal focal
my test apparatus. With laser pointer mounted in a clamp in front of
camera and it held by another clamp system, I hold the shutter
tester in place with elastic bands.
you can test with some assurance that the shutter is performing to
factory specifications. And, if anyone makes mention that
"those old crappy Russian cameras can't possibly work at the
speeds on the dial because they are made poorly", I offer to
you an example of an honest 1/1250 second shutter speed. For those
with good eyes the reading on the scope is 811 micro-seconds which
is nearly spot on perfect.
July 20, 2008