http://photo.net/large-format-photography-forum/0044cW or http://www.graflex.org/helpboard/viewtopic.php?t=6105
The infrared photo transistor/led used in the final refinement has a 10 ° angle of view. The one from the old mouse most likely has a similar angle of view.
I do all testing with the lens removed. It makes little difference if the sensor is at the center of the shutter opening or if its center is at the smallest marked aperture opening of the lens.
The photo transistor/led has a rise and fall time of .1ms. The rise time is the time delay from when the sensor is first sees light and starts to conduct to when it reaches the maximum peak for the amount of light reaching it. The fall time is the time the sensor continues to conduct once the light source has been removed.
A leaf shutter is a dual aperture device with one aperture manually set via a lever according to a calibrated scale and the other a continuously variable from full closed to full open and back to full closed via a controlled timing system.
Now my thinking or logic might be flawed here, but it seems to me on an iris shutter, the shutter is open for less time on the edges of the round opening than the center, right? The shutter takes time to open and close, nothwithstanding the time it stays open. The edges are the last to be un-covered, and the first to be re-covered, right?. So if I make my tester with the phototransistor just a couple inches away from the rear lens element, it seems like I'd get a false reading. Seems like the phototransistor would have to be at the film plane to get a true reading.
When a leaf shutter is set (cocked) high spring tension is locked onto a lever that when released will try to force the shutter blades ( continuously variable aperture) fully closed but is locked in the set position by another lever. When the shutter is tripped the shutter blade controller is released and thrown open by a weaker spring with no opposition to the blade controller moving except for its and the blades pivot pins resistance. The shutter blades go from full closed to full open in .15 to .3 milliseconds. When the shutter blades reach full open the blade controller releases the locking lever allowing the main setting lever to try to close the shutter blades via the blade controller. The main setting lever encounters resistance to closing from the delay timing gear train.
Setting a speed testing sensor close to the outer edge of the shutter will give false shutter times. Setting the speed testing sensor at the smallest marked aperture edge will give more accurate fast speed times.
Testing is normally done with the aperture wide open and the sensor at the center of the shutter opening or lens center. By the time the shutter blades have closed down to be effectively 2 stops smaller than the smallest aperture the lens is marked for the resulting extra exposure the film receives is insignificant on a properly working shutter. A installed lens may cause false shutter test speeds unless a very bright light source is used for testing. I use a minimag flashlight with fresh batteries set to spot at 2 inches held just above the shutter opening. I have the top edge of the photo sensor near center of a piece of 1/4 inch foam core and the foam core is rested against the rear edge of the shutter. Increasing the distance to or from the shutter blades only affects the intensity of the test light source needed for testing.
http://www.photographyuncapped.com/u...half/articles/ (click on the chart to download for printing)
Well, I've constructed the tester as described with a 1.5V battery and the photodiode from an old Mac mouse. It DOES move the signal strength indicator in Adobe Audition, but not nearly sensitive enough to produce a blip in the record mode. Looks like I'm going to have to step up to a 9V battery and put in a pot, till the signal strength is enough to be useful. I wonder why the designer gets away with 1.5V and I have to go through this ordeal of rewiring mine for a 9V. Seems nothing works out as described.
Scratch one mouse... Sorry that didn't work out yet...
Do you have a turntable you can view through the shutter as you fire it? Maybe lay a strip of white tape on the turntable and run at the highest speed... Work your way back from the apparent angle of the blur that you see. And the RPM's... to a shutter speed estimate.
No I'm going to go on with the shutter tester fabrication. It's been done enough times out there to where mine should work out also. The mouse has 4 photodiodes in it, and the one I used I de-soldered from the circuit board. Could be fried. Will continue on with the 9V and potentiometer design before calling it a fried photodiode. When I'm at that point I'll cut another off the circuit board and use my super-fine wire and wrap it around the legs, and keep the soldering iron out of the picture. Not time to give up just yet. This is going to work.
Try a different audio recording program such as http://audacity.sourceforge.net/
It DOES move the signal strength indicator in Adobe Audition, but not nearly sensitive enough to produce a blip in the record mode.
Try reversing the polarity on the sensor, at 1.5V you won't damage it.
Try different lead configuration as your mouse sensor may have a different lead configuration from the diagram you are using.
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Computer logic, mice, keyboards, USB ports use 5VDC; CD, DVD, hard drives use 12VDC for their drive motors and 5VDC for their logic. Industry standard.
Last edited by shutterfinger; 08-28-2013 at 05:32 PM. Click to view previous post history.
OK, I've got my little tester working. Tuns out I needed 6 volts. So now we have here a screen shot of an actual shutter test--I forgot which speed, but it's not important for now. My problem in interpretation. I'm dealing with a 100 year old Betax shutter that I worked on, and I knew all along that I had a rather week shutter-closure spring. If you will note the attached shot, you will see that after the initial exposure, there is an equally long time before the graph returns to zero, which I am supposing to be caused by the slower action of the weak spring. Would you agree, or is this to be expected? And if so, should I include some portion of this slower upward sweep in my computation? Thoughts? Thank you.
If I understand what I'm seeing, that thin line below the axis and rising to meet it is just an AC coupled circuit recovering from a change in DC input and could be ignored. That is, it's a manifestation of the tester/audio circuit and not the shutter.
(One of these days I want to build one of these, I have the parts -- but I think part of me doesn't really want to know! )
definitely different pattern from what I'm accustomed to seeing.
Last edited by shutterfinger; 09-01-2013 at 03:18 PM. Click to view previous post history.