DIY shutter tester for Barnack style cameras

[Individual One]

Timers for focal plane shutters, using a light source and a detector located on opposite sides of a focal plane shutter are all over the internet. As they use transmitted light, they require a camera with an opening or removable back.
I wanted to adapt this existing technology to enable it to be used on a Barnack style Leica or one of the many copies, that do not have an opening. I have a Nicca, a fairly high fidelity copy of a Leica III series camera and as it is working fine I don't want to dismantle it to make shutter speed measurements in transmitted mode.
It seemed to me that a detector staring at a laser spot on the film plane should work. It should be able to detect the brightness changes as the shutter opens and closes again. To increase the signal I placed a piece of reflective fabric that I happened to have left over from a sewing project in the shutter opening on the film plane, and relayed the spot on the film plane to the detector using a lens salvaged from a magnifying glass. To my surprise it worked. Because my Nicca currently has film in it I used a FED camera as a stand-in, but I think the system would work for focal plane shuttered rangefinder cameras in general. As with transmitted systems, the camera can be moved around to measure times at any location in the shutter opening to provide information about relative curtain speed. I have not tried it on a SLR but it would have more complex reflections for the timer to discriminate.

Here is a picture of the system in use:



And, here is the detector output at 1/30 shutter speed. Note that the detector sees the change in brightness as the shutter curtain passes from cloth to metal edge to reflective fabric.



I hope this idea can be of use to others with barnack style cameras.


(edit: this is a work in progress)
After I posted this I tried a different magnifying glass to relay the image. It works much better, giving a stronger and cleaner signal for the detector to work with.
Picture attached of a 1/60 test:



And another edit. I finished the film in the Nicca, so I could test the camera on my new setup.
Turns out it is overexposing by about 1/2 stop across the range. (The dark curves on the graph are +/- 0.5 stops)
Not that bad for a 70 year old machine, and easily compensated for.



Bruce

 

[Individual One]

I have recently purchased a Leotax TV2, and tested it on this setup. It performed quite well.

The yellow dots and blue dots are the shutter speeds measured at the left and right edges of the frame. Given that they overlay so well, it suggests that the curtains are travelling at the same speed. The red lines are +/- 0.5 stop, my personal spec, so all indicated speeds are within that except for 1/500. I can offset for that.
Bruce

 

[ic-racer]

Leotax and Nicca, some nice Japanese cameras! Nice setup for testing!

 

[Individual One]

Leotax and Nicca, some nice Japanese cameras! Nice setup for testing!

I should clarify that it is actually not certain from my testing that the curtains are travelling at the same speed, but rather that the exposure is appropriate across the frame. I suspect that the shutter curtains accelerate as they move. They start from zero at the edge of the frame, and reach a maximum speed by the far side before braking abruptly back to zero. If the curtains are accelerating then the slit width must increase to maintain the same exposure, meaning that the curtains cannot be going the same speed.

 

[qqphot]

expanding your setup to have a spot left, center, and right might be a nice next step, so that it could be used to adjust uniformity as well as overall exposure. When i set up a (very janky, temporary) system like this I did it with multiple "exposures" for each position, which was too much effort but surprisingly consistent and did let me get a couple of cameras adjusted to have uniform and correct exposure.

 

[Individual One]

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I attach a graph of data taken of a badly performing camera, a Zorki 1 that has defied all my attempts at adjustment and is two stops out between centre and trailing side at higher speeds. I suppose it could have something to do with 70 year old dried up lubricants. I am currently stripping it completely and expect to either fix it or destroy it trying. For my Leotax, I did take data at left, centre, and right. But the centre was the same as the left and right in this well adjusted camera and I left it out of the graph as it added no useful information and made a crowded display. The data was taken by repositioning the laser spot across the field through multiple exposures. My setup as currently configured has only one laser, one relay optic, and one sensor. A multiple version is possible but not worth the effort. As an aside, I do have a lot of experience with imaging and autofocus systems prototyping from my time at a company building thermal laser imaging engines for the graphic arts industry. My DIY system with a reflected laser spot and relay optics is based on the principle used in high speed autofocus systems (see DE19919804B4 for an example). Instead of detecting distance my DIY setup has the easier task of detecting the presence or absence of a shutter curtain.

 

[ic-racer]

I should clarify that it is actually not certain from my testing that the curtains are travelling at the same speed, but rather that the exposure is appropriate across the frame. I suspect that the shutter curtains accelerate as they move. They start from zero at the edge of the frame, and reach a maximum speed by the far side before braking abruptly back to zero. If the curtains are accelerating then the slit width must increase to maintain the same exposure, meaning that the curtains cannot be going the same speed.

Some shutters I measured seem to come up to a terminal velocity (limited by friction) quickly and stay constant all the way across. Others do seem to conitnue to accelerate across.

Check this out showing the effect of speeding up with appropriate increase in slit width:

 

[Individual One]

Some shutters I measured seem to come up to a terminal velocity (limited by friction) quickly and stay constant all the way across. Others do seem to conitnue to accelerate across.

Check this out showing the effect of speeding up with appropriate increase in slit width:

I would sure like to have the use of one of those high speed cameras.