Measuring shutter speeds on Minox cameras

[tjwspm]

Because the Photoplug app displays the progression of brightness, you can manually adjust the time period to be measured. This is done using the two blue sliders. This allows the effect in the diagram from IC Racer to be taken into account.

This example shows a Minox shutter in action:

The blades open within 1/2700 and close in 1/2800 s. In between there is 1/1000 s when the lens is fully opened. The acceleration phases of the two blades are clearly visible (blue arrows). The entire process takes 1/600 s. For the effective exposure time, the average of the opening and closing times must be added to the time in which the shutter is fully open. This results in an exposure time of approx. 1/(1/2750 +1/1000) = 1/730 s.

The deceleration of the closing blade can be seen in the purple arrow in the picture above. With the opening blade, the deceleration cannot be seen, as this happens when the shutter is fully opened. Therefore, the amount of light does not change when the opening blade is delayed.

I took this measurement with the Photoplug and the corresponding app.
(Please note that I am only a user of Photoplug and have nothing to do with the manufacturer)

 

[ic-racer]

I finally have a reliable solution to measuring speeds on Minox and other micro cameras. I use the light from my Autocollimator. Light boucnes off a shiny target placed in the film plane and the shutter tester measure the duration of illumination through the eyepiece.

 

[Individual One]

And here's another (closely related) method of measuring minox shutter speed. Same idea, I bounce a laser off the shutter blades and onto a photo detector. The result is displayed on a scope. In the linked video it is reporting 240ms for a requested 200ms (1/5 sec). Not too bad. The camera was supposedly built in 1966 and from the appearance of the fasteners it has never been serviced. It is a little less than 1/2 stop slow across the entire range, so this is easily compensated for.

link to example of measuring process

 

[ic-racer]

And here's another (closely related) method of measuring minox shutter speed. Same idea, I bounce a laser off the shutter blades and onto a photo detector. The result is displayed on a scope. In the linked video it is reporting 240ms for a requested 200ms (1/5 sec). Not too bad. The camera was supposedly built in 1966 and from the appearance of the fasteners it has never been serviced. It is a little less than 1/2 stop slow across the entire range, so this is easily compensated for.

link to example of measuring process

Does that work for the faster speeds where there is just a slit? I have not tried my setup on a Minox yet (works great on 16mm cameras) I did recently recieve my light sensor adapter from the 3D printer. In this case the light bounces off the film plane via beamsplitter. With a Minox and shiny blades, it might not work as expected. My Minox has film in it now, so I have not been able to test it.

 

[tjwspm]

Does that work for the faster speeds where there is just a slit?

The metering method will work even at the fastest shutter speeds. The Minox shutter never becomes a slit. Even with the 1/1000s, the shutter is fully open. I have described this in detail here:

How the Minox shutter works

Get to know all the details about how the mechanical Minox 8x11 shutter works. A comprehensive presentation with many photos.

moments-of-now.com

 

[Individual One]

The metering method will work even at the fastest shutter speeds. The Minox shutter never becomes a slit. Even with the 1/1000s, the shutter is fully open. I have described this in detail here:

How the Minox shutter works

Get to know all the details about how the mechanical Minox 8x11 shutter works. A comprehensive presentation with many photos.

moments-of-now.com

The method I describe appears to work at all shutter speeds. Full results for the camera I tested are in the attached image. The red lines are +/- 1/2 stop from ideal.



I use the same setup to measure speeds on cameras such as copies of early Leicas (don't own the real thing) where a beam cannot be transmitted through the film plane to a detector. In those cases I put a piece of reflective film on the pressure plate and bounce off that.

 

[ic-racer]

Thank you both for the explanation.

 

[tjwspm]

The method I describe appears to work at all shutter speeds. Full results for the camera I tested are in the attached image. The red lines are +/- 1/2 stop from ideal.

View attachment 389221

I use the same setup to measure speeds on cameras such as copies of early Leicas (don't own the real thing) where a beam cannot be transmitted through the film plane to a detector. In those cases I put a piece of reflective film on the pressure plate and bounce off that.

Great!