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Cleaning & Repairs
Shutter Speed Tester

Rev.1

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 oscilloscope output.

  

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 1/16" drill.

  

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 center itself.

 

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.

 

If 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.

 

If 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 plane shutter.

 

Here's 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.

 

Now 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