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David_nebenzahl
Tinkerer
Username: David_nebenzahl
Post Number: 158
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 15, 2010 - 04:25 pm: | 
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I'll talk about the one I built, and hopefully others will add their own observations and experiences.
I built a fairly simple but very accurate shutter-speed indicator. It's a small microprocessor-based unit, in a small project box about 1x2x4 (inches). It uses a SX-28 MPU, an easy-to-program 8-bit chip, complete with memory, similar to the more well-known PIC line of processors, first introduced by Ubicom, then taken over by Parallax (currently owned by some other company, forget the name: they're still available).
The tester consists of the SX-28 chip, a phototransistor used as the light sensor, an oscillator crystal, a LCD display (1x16 characters) and a few other components (including switches and a 9-volt battery). Total cost as I remember was less than $40. (Of course you need a programmer for the SX too; I borrowed one to program it.)
The program is pretty simple, consisting of the following:
o Sit in a loop waiting for the phototransistor to sense light
o Start the timer counter, wait until it goes dark again
o When it goes dark, compute and display the elapsed time in milliseconds
There's some de-bouncing code and some display routines (plus hand-coded multiply and divide routines), but that's basically it.
It shows you how long the shutter stayed open in milliseconds (1 second = 1000, 1/25 = 40, etc.).
I know it's accurate to at least +/- 0.1 millisecond, as I tested it against a known good timer circuit with a microsecond resolution, so it's plenty accurate enough, at least for the cameras I work on.
I'd be curious to hear about anyone else's DIY shutter speed test strategies. I know about the sound-card tester (basically a more primitive version of mine), using a TV set, various tricks with turntables, etc. |
Paul_ron
Tinkerer
Username: Paul_ron
Post Number: 198
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 15, 2010 - 04:50 pm: |
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Can you post the schematics n progrqming involved? This sounds like a nice project. How much did it cost you to build?
I've been using the one hooked up to my sound card. It works very well n is also very accurate. I think you can find the diagrams n instructions right here in the repair article section. |
Tom_cheshire
Tinkerer
Username: Tom_cheshire
Post Number: 268
Registered: 04-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 15, 2010 - 05:29 pm: |
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Sorry, folks. Still doing the "measure the arcs produced by the turntable" method detailed in "The Amateur Photographer's Handbook, 8th Edition" by Aaron Sussman (This even has the exploded diagram of a Rolleiflex and a few lens test charts). |
David_nebenzahl
Tinkerer
Username: David_nebenzahl
Post Number: 159
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 15, 2010 - 06:47 pm: |
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Paul: I'd be glad to post the schematic (GIF or PDF), but where? Is there some place on this site? or elsewhere? (don't know if I'm ready to post a full-blown article on that document site, what's it called?).
Programming is another story. I can give you some hints, but I'm not sure what you would do with SX assembly language, which is what I wrote the code in. (Can probably give you some pseudo-code, though.)
As I said, I think the cost was about $40. That included the metal case and all the fixin's (switches, pushbuttons, etc.). |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 64
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 15, 2010 - 08:46 pm: |
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Oh crap, I sent so much time writing my post regarding this that I missed this thread. Anyway, I will repeat that post here so that we keep this thread as the main one. So here goes.
I had wanted to check the accuracy of some recently acquired film cameras. They have horizontal traveling focal plane cloth shutter.
After going over some online tutorials and DIY project description, I started off with a very basic and reasonably accurate shutter speed tester.
My current hardware is a IR detector diode (D1) in series with a resistor (R1) and a 3 V dc battery (V1).
The drop across the resistor is put as input to a line-in socket of PC and I record the signal on that input in Audacity on a computer running Debian Linux.
The value of R1 is chosen to limit the value of current flowing through the loop to valid a valid value (I use 3.9 KOhm) and V1 = 2.8 V (2 NiMH batteries in series).
D1 is from the usual IR emitter-detector pair available at any electronic hobby store.
V1 is chosen to be 3V to get reasonably good voltage across the line-in socket.
Now, the problems is that the rise and fall time of D1 are not fast to measure speeds faster than 1/1000. So till those speeds, one can more or less measure the shutter speeds reasonably well.
I have mounted D1 on the base of a black film canister. I have cut the canister to make it around 1 cm in length and position the canister behind the camera's shutter with the back open. A pair of cables (audio speaker cables, nothing fancy, terminated with a 3.5 mm male connector) take the signal from across the resistor to line-in of a PC to be recorded by Audacity (there are other ways also to get a representative signal). The input signal is a flash light positioned in front of the camera shining through the lens.
In audacity, I configure it to record at 96 KHz. Basically, higher the sampling rate, shorter the time interval that can be measure better. This works very well for speeds up to 1/250 and reasonably well at 1/500 and 1/1000. I can tweak the sensitivity of the line in mic to increase or decrease the amplitude of the waveform being recorded (useful at different speeds).
The main problem here is the response time of the diode used. The diode usually available at hobby stores has a response time which is actually a bit slow to get more accuracy for speed ranging from 1/250 and upwards. I am next trying to get a faster diode. Apparently the ones used in optical drives are better. But that is for the second version of the hardware.
I know the details are sparse here. But circuit diagrams are easily available online. If anyone wants details, I will be happy to share. I am also hoping to make a detector with two diodes so that I can measure the curtain speeds as well. |
Hanskerensky
Tinkerer
Username: Hanskerensky
Post Number: 25
Registered: 05-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 16, 2010 - 12:53 am: |
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Hi David,
Well i must admit that once (before i got my Tubosaka Tester) i considered to build something the same as you have so wonderfully made.
Should be an inexpensive, small & portable,low power (battery), microprocessor with a nice LCD display. During my search i stumbled upon the Atmel AVR Butterfly and i think this also would be a nice candidate to build a tester as you did.
Hope to see some more info from you soon ! |
Monopix
Tinkerer
Username: Monopix
Post Number: 111
Registered: 11-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 16, 2010 - 07:47 am: |
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Mine's at http://www.monopix.co.uk/sstester.shtml. I won't repeat the whole thing here.
Main problem I found was limited accuracy at fast speeds due to the width of the sensor in relation to the slit width of the shutter. |
David_nebenzahl
Tinkerer
Username: David_nebenzahl
Post Number: 160
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 16, 2010 - 11:49 am: |
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It's true that all of these testers have limited accuracy at higher speeds. Since mine is accurate to +/-0.1 msec, it's fairly accurate up to 1/1000 sec. It certainly won't be able to measure the speed of a modern 1/8000 sec. shutter. (But then again, who actually uses such high speeds besides specialized stop-action photogs?)
By the way, Peter, I looked at your tester, which is certainly interesting. However, and not to knock your efforts, but you really might want to consider a design more like mine which is based on circuitry driven by a much faster and more accurate clock (my SX-28 runs on a 1 mHz crystal oscillator). This gives much higher accuracy, resolution and repeatability, though it is certainly not as elegantly simple as your design. Plus using a microprocessor lets you do more complex stuff like counting and displaying in software rather than hardware. |
Elwrongo
Tinkerer
Username: Elwrongo
Post Number: 59
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 17, 2010 - 06:51 am: |
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I've wonder if there isn't a simpler way (ie no building eletronic devices and programming them)and this is probably way naive - if you could shine a light through the back of the back of the camera, fire the shutter and record the process on video from the front of the camera. Then however you need a video software that can divide the frames further than the usual resolution of 1/25th of a second when you look at it in the time line. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 67
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 17, 2010 - 09:14 am: |
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There is always the trick to look at a CRT TV screen while firing the shutter with the lens removed.
A CRT is a very fast beam tracing device. One tiny ray traces horizontal lines across the screen, top to bottom. Depending on the speed, one should be able to see a band of brightness. That band of brightness relates to the shutter speed, and the width of that band of brightness relates to the curtain speeds (the width is constant with same curtain speeds). Very easy to do, on just needs a CRT television for that.
If you a search online, you will get some pages that show this procedure with explanatory photos. |
Monopix
Tinkerer
Username: Monopix
Post Number: 112
Registered: 11-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 17, 2010 - 10:32 am: |
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"you really might want to consider a design more like mine"
The display was supposed to be able to count much faster than it actually could which is why I ended up with the clock speed I did. A Xtal clock would be more accurate and I still intend to change it at some point but I actually don't use it that often and it's easy to trim the clock prior to each use so it will be almost as accurate.
I don't see the need to do anything more complex so I don't see the point of designing from scratch if you can buy an off the shelf module that does all the counting and display for you. Having said that, I would like to find one that's capable of counting at at least 100KHz.
Probably the most important thing though is the understanding that the width of the beam needs to be very small to be able to measure fast speeds with any sort of accuracy. If you don't sort that problem, no system, however it's constructed, will be accurate.
Just to complicate things further, I also think a tester really needs to be capable of measuring the speed at different points of the shutter travel to be able to check for tapering or capping. Using mine as I do, with the camera on a tripod, the laser on a support in front of the camera and the tester sat on a table behind the camera, I can move the camera around freely to align the setup with different parts of the shutter. That's been of real benefit in the past. |
Paul_ron
Tinkerer
Username: Paul_ron
Post Number: 199
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 17, 2010 - 12:02 pm: |
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David, post the JPG or whatever you have of the diagram in on a photobucket site n link it here.
How did you program it? Write to an EPROM on another computer? |
David_nebenzahl
Tinkerer
Username: David_nebenzahl
Post Number: 162
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 17, 2010 - 12:34 pm: |
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Yes, to program the SX you connect it, via a 4-conductor cable, to a small programmer (called the "SX-Key") which is connected to the computer via a serial port. At least that's the way they used to do it; the more recent versions all use USB connections. So you do need an external computer, which is where you write the source code and where you can run the software, do debugging, etc.
There are lots of other systems available. Nowadays lots of people use a little development system called Arduino, which offers programming in a high-level language (Arduino) rather than primitive assembly language (which I actually prefer). However, I'm not sure that this microprocessor would work as well for this application. The nice thing about "bare-metal" systems like the SX is that you have complete access to things like interrupt service routines, which are essential for fast response times.
And of course there is the PIC line of micros, which many more people use. There are entire development "communities" much like this forum you can access online.
Will post my stuff once I find a suitable site. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 69
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 17, 2010 - 09:36 pm: |
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Reading this info about microcontrollers,since the input is an IR diode, I suppose it would be equally good reading the audio signal from the setup I described earlier, and calculating the duration of the open shutter (or high response time). This could be done using a program that reads the audio input port of the computer.
If the audio card can sample at 96 KHz, assuming fast enough response time, it should function as good as a stand alone board.
This would be beneficial if a computer is already handy and will incur minimal cost (just a diode, a resistor and a battery source). But requires programming skills on an OS.
After having written this message, I think a near future project is already taking shape in my mind  If I do this, it would be my first program using ALSA in Linux to record sound samples. |
David_nebenzahl
Tinkerer
Username: David_nebenzahl
Post Number: 165
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 17, 2010 - 10:00 pm: |
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I doubt very much if most computer sound cards are capable of very reliable response time at 96 kHz, even though they are (theoretically) capable of that sampling rate.
Still, it would make a cheap, quick & dirty tester that would be a lot better than a guess. |
Richard_cook
Tinkerer
Username: Richard_cook
Post Number: 1
Registered: 02-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 19, 2010 - 08:22 am: |
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Elektor magazine have published a design for a shutter timer.
http://www.elektor.com/magazines/2006/january/shutter-time-meter.58018.lynkx
You can pay to download the article and buy a PCB or if you are an electronics engineer you may be able to arrange the parts in the list into the required circuit diagram. |
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