I have a few classic SLR cameras that I'd like to bring out of retirement. I need to establish if the shutter speeds are still within spec (or not as is more likely after 35+ years). I've already thought about how I might do this: open up the camera backs and place a super- bright LED up against the shutter curtain with a light-sensitive device on the other side of the shutter. Fire the shutter and view the response time (0.004s upwards) on a storage scope. What device would be fast enough to react to the momentary flash of the LED during the instant the shutter is open? Thanks.
Any reasonably small and fast photodiode. But you have to wire it into a circuit called "transimpedance amplifier" or TIA. Give it a good reverse bias but no more than abs max from the datasheet, that reduces its capacitance. You might also want to consider doing this in the IR range with filter in front of the photodiode (from an old TV set maybe) so daylight doesn't bother your measurement.
The guru in that domain is Phil Hobbs who participates in this NG and has a web site with lots of good information, and he wrote a book about it:
Given that the fastest shutter speed is 4 ms, any silicon photodiode or phototransisor will be fast enough. A CdS cell might not be.
Can you still get film? And color processing? I sure don't miss film.
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John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers
jlarkin att highlandtechnology dott com
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Any old photodiode, or even a phototransistor would work fine.
SLRs use focal-plane shutters, with two curtains crossing the film. At speeds slower than the 'X Synch' speed, the first curtain finishes before the second one starts, so that a single fast flash can expose the whole frame.
Because the curtains move independently, they're vulnerable to speed variations, which cause exposure nonuniformity.
The easy method is to put a piece of white paper over the lens, and illuminate that with the LED. Two phototransistors at the film plane, one at the beginning of the travel and one at the end, will let you measure both the speed and uniformity. They need to be small, so that the first curtain has finished crossing the phototransistor before the second curtain arrives. With a 1/60 second X synch speed, a 1/1000 second exposure means that the two curtains are separated by only
36 mm * 60/1000 = 2.2 mm, so you need small devices.
If the shutter was cocked all that time, you might have lost some speed.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Shutter Speed Tester Uses a sound card for timing.
Shutter Speed Tester Ver. 2 Also uses a sound card and the music program Audacity for timing. Methinks you can do better with a real oscilloscope, DSO, or software scope such as:
Looks like the author sells them on eBay:
Sorry, but no specs on his choice of photodiode or phototransistor.
Shutter Speed Measuring of Analogue Film Cameras (22 mins) See schematic at 2:15.
Incidentally, in my limited experience doing camera repair on my focal plane (Leica IIIc) and various Nikon F SLR cameras, I found few problems with the higher speeds, and plenty of mechanical timer headaches with the slower speeds. Think about dissolving the gummy lubricant with some solvent, and re-lubricating the timing mechanism. Most common was a sticky shutter. Very few old cameras have any way to adjust the timing.
A few cameras will not fire if the back is open. There are tricks to bypass the interlock, but the easy way is to put a mirror onto the film plane and time the reflected light.
For slower shutter speeds, you can use a microphone and simply time between when the noisy shutter opens and closes.
More: Simple shutter speed tester (from dead mouse parts):
Camera Shutter Speed Timer. I like zero center panel meter display but it doesn't seem very accurate:
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Wouldn't it be easier to shoot a few rolls and compare to a known good came ra? I think with the right test setup and test image, you could make several "m easurements" at once. Convert everything to EV's and go from there.
If using the same lens, your test would automatically remove systemic expos ure errors relating to aperture, ISO (film speed), (no) flash and reciproci ty, etc... All that's left is shutter speed. The main variable to contro l is probably in the film processing, which I assume to be C-41.
Wouldn't you be able to discount much of the developing process by making s ure each portion of the "A/B" testing was shot on the same roll? As for pr inting, just ask the lab to not push any of the prints (i.e., no exposure c orrection). Another approach might be to compare from the negatives, and n ot the prints. Or conduct the test with color slide film.
Another plus is that by shooting actual film, one might discover other prob lems with the camera(s); not just timing errors in the shutter. Here, I'm thinking film advance & rewind mechanisms, ASA setting, light leaks, mirror /prism problems, focus plane alignment, etc... None of which you can test with a photodiode.
'm thinking film advance & rewind mechanisms, ASA setting, light leaks, mir
test with a photodiode.
You can, apart from focus problems and light meter calibration.
Rewind either works or it doesn't. Since the OP said these are 'classic' SL Rs, they'll have manual rewind cranks. Failure there is pretty obvious.
Advance problems are almost unknown in good SLRs, because the mechanisms ar e all geared. You can't c*ck the shutter unless the film cog advances a who le frame.
I've never seen a light leak in a camera with no obvious dings in it. The l ight seal is formed by interleaved black surfaces, so that any light that g ets in through a crack has to make many bounces off black surfaces before r eaching the film.
The internal meter setting is easy to test approximately, using the f/16 ru le: in bright sunlight, at f/16, the right shutter speed is 1/ASA. Testing it more accurately is quite possible but needs more apparatus.
It's hard to imagine how a camera body could have a focus error, unless you put it through a crusher or at least hit it with a baseball bat. The dista nce from the lens flange to the film plane is fixed. The mirror could conce ivably be misaligned due to sufficient trauma, which would make the visual focus different from the film focus, but I've never seen a camera that badl y damaged. (A repair guy would probably have wider experience.)
I agree that a shutter speed measurement isn't a complete camera health ass essment, and that shooting a roll or two of calibration frames might be val uable. For shutter speed specifically, though, direct measurement is a win. The logarithmic or power-law dependence of film density vs exposure, and its sensitive dependence on processing conditions, make that a tough way to measure shutter speed.
I did that for a colleague a few months ago- he's getting into film, and even clockwork, cameras.
I just illuminated the lens with a bright microscope fiber-optic illuminator and picked off the signal to a digital scope with a Thor Labs photodiode working into a 100 ohm resistor.
IIRC, the timing on the rather old camera was surprisingly good (at least in units of f-stops).
This part contains a photodiode and TIA in an 8 pin DIP. It works with a
2.7 to 36 VDC supply, the default TIA gain is 1E6 with no external parts, and the 10% to 90% risetime at the default gain is 28 us. Qty(1) cost is $7.
formatting link
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Best Regards,
ChesterW
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Dr Chester Wildey
Founder MRRA Inc.
Electronic and Optoelectronic Instruments
MRI Motion, fNIRS Brain Scanners, Counterfeit and Covert Marker Detection
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wildey at mrrainc dot com
The photodiode looks on the large side. A couple of 30-cent TO-92 phototransistors, e.g. each with a 10k resistor, would work fine. Driving a few feet of coax is no problem at that speed.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Color not so much but there is are hardcore B&W film aficionados, mostly in the more artistic field. I know an engineer who owns a company that caters especially to that group.
Yes, I should have said B&W only! It has a charm all its own. Some things never go out of style. Like vast numbers of radio hams are still nuts about using morse code - which is positively ancient!
B&W film has been extended to very nearly perfect quantum efficiency by the addition of formate ions to the emulsion--see J. Belloni et al., Nature, V. 402, p. 865 (Dec. 1999).
Pity it came too late for anybody to care very much.
Cheers
Phil Hobbs
(who used to have his own darkroom too)
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Yet morse code still provides the means to achieve realtime communication with the least amount of effort and also very low power. If I ever get back into ham radio that will again become one of my favorite modes of operation. Right now my mountain bike takes up all that time so that likely will only happen if some health reason prevents me from riding.
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