[Frosty66]

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Having just revived an SP with multiple problems I started to wonder how one might test to see how accurate the shutter speeds and light meters are ?

I'm wondering if special equipment may be needed to do any meaningful test and am wondeing what, if anything, people do? I was thinking that for the light meter one might test with the same lens on a different body and compare them, but they how do I know which is correct? Is there any reason I shouldnt test it against a dSLR since this would be new and presumeable accurate ?

[pentaxus]

As far as the shutter goes you really need a shutter tester to be sure your shutter speeds are correct. It is good to be able to know the shutter curtain travel times to be able to get the shutter speeds to come in. Yes, special equipment. For the light meter you can compare with another camera body. Check in bright light and dim light. The meter could be correct in bright light but off in dim light. I have a Canon FTb that is one stop over in bright light and two stops under in dim light ( probably not fixable). Make sure your DSLR is in center weighted and not matrix/multi-zone metering.

[Frosty66]

As far as the shutter goes you really need a shutter tester to be sure your shutter speeds are correct. It is good to be able to know the shutter curtain travel times to be able to get the shutter speeds to come in. Yes, special equipment. For the light meter you can compare with another camera body. Check in bright light and dim light. The meter could be correct in bright light but off in dim light. I have a Canon FTb that is one stop over in bright light and two stops under in dim light ( probably not fixable). Make sure your DSLR is in center weighted and not matrix/multi-zone metering.

Thanks, regarding the special equipment what would that be, I'm assuming it's prohibitively expensive though ????

[AstroDave]

Thanks, regarding the special equipment what would that be, I'm assuming it's prohibitively expensive though ????

Depends on whether you have any electronics experience and equipment. If you happen to have an oscilloscope handy (or can borrow one), the light detector to put behind the shutter can be very cheap - a few bucks. If you need something like that, I can show you a simple circuit - like the one I use for flash speed measurements. The light diode in there costs less than $1 and responds at microsecond speeds.

You just open the back of the camera, shine a light through the front that will be detected by your light sensor when the shutter curtain is open, and measure how long the pulse of light which gets through is.

[TomB_tx]

Shutters could be tested very accurately at home when we all had TVs based on CRT displays, which "painted" the screen in lines at a controlled rate. By removing the lens, opening the back, and watching the TV screen as the shutter was tripped you could see a band of screen lines and determine the speed and how consistent it was across the frame. Doesn't work with modern LCD TVs though. I've kept one old TV in my office to evaluate cameras as I collect them. I also have a nice digital shutter tester made by a tech in Russia (used to sell on eBay), but it takes time to set up and use, where the TV screen shows me all I need to know. You might search for TV Shutter test, if you have an old TV available.

[Frosty66]

Depends on whether you have any electronics experience and equipment. If you happen to have an oscilloscope handy (or can borrow one), the light detector to put behind the shutter can be very cheap - a few bucks. If you need something like that, I can show you a simple circuit - like the one I use for flash speed measurements. The light diode in there costs less than $1 and responds at microsecond speeds.

You just open the back of the camera, shine a light through the front that will be detected by your light sensor when the shutter curtain is open, and measure how long the pulse of light which gets through is.

I would like to see the circuit thanks. I am 99% sure I got rid of my oscilloscope, it was ancient but hnow wonding why I would do that !

I was looking at prices recently and realise for not much money you can get a device that turns the PC into an oscilloscope.

---------- Post added 29-04-17 at 05:14 ----------

Shutters could be tested very accurately at home when we all had TVs based on CRT displays, which "painted" the screen in lines at a controlled rate. By removing the lens, opening the back, and watching the TV screen as the shutter was tripped you could see a band of screen lines and determine the speed and how consistent it was across the frame. Doesn't work with modern LCD TVs though. I've kept one old TV in my office to evaluate cameras as I collect them. I also have a nice digital shutter tester made by a tech in Russia (used to sell on eBay), but it takes time to set up and use, where the TV screen shows me all I need to know. You might search for TV Shutter test, if you have an old TV available.

Now you mention it I saw a reference to this once, I will have to have a search again. I do still have an old CRT TV in the kitchen !

[AstroDave]

For a phototransistor circuit, take a look at my measurements of the AF540FGZ flash: Pentax AF540FGZ flash. The same circuit works for even faster photodiodes. I am now using QSD2030 photodiodes, which are available from Digikey (digikey.com) - for 60 cents apiece! - and have nanosecond response. If you want one, pm me and I’ll mail you one (or I can send a SFH-309 phototransistor). I buy them by the 5 or 10, otherwise the postage is the dominant cost per unit! Data sheets for all these components are available on-line. They will help you identify which leads are which on the devices.

You bias the phototransistor with batteries or a simple dc power supply - you can buy used wall warts at Goodwill or similar for a dollar or two. Make sure you get a DC supply. Any voltage up to 12V or so should be fine.

The sensitivity of the circuit can be set by using different resistor values. The bigger the resistance, the more sensitive the circuit. Conversely, that also increases the time constant of the response. If you can stay below 10k or 20k ohms, you should be OK for shutter speed measurements. The fastest you will be trying to measure is probably 1/1000 sec, or 1000 microseconds light pulse duration.

Do a google search on “photodiode phototransistor circuits” for more info. Figure 2 in http://denethor.wlu.ca/pc300/projects/sensors/photdiod.pdf shows my simple circuit. You don’t need to worry about any of the fancier stuff!

Just put your oscilloscope input across the resistor. In a lighted room, the phototransistor may already be conducting, giving you some voltage across the resistor. If so, turn out the lights and wave a flashlight back and forth across the transistor - you should see the scope trace go up and down. Put the scope on a slow sweep speed for this.

To measure shutter speed, open the back of the camera and place the photo detector about where the film plane would be, centered where the actual image frame would have been recorded. Take the lens off the camera and put your light source near the front of the camera, centered on the lens hole. Set your scope to single trigger on the light blip that comes through the camera when you fire the shutter and just measure the duration of the resulting pulse on the scope. Set the sweep speed consistent with the expected duration of the shutter opening.

For the fastest shutter speeds, when both shutter curtains are in motion, you have to be a bit more careful to make sure everything is lined up OK.

You should be able to measure the length of the light pulses to a few percent, which is way less than one stop.

If you can’t find your old scope or borrow one, and can generate an excuse to buy a new one (acquiring electronics test equipment can be very akin to LBA!), I’d suggest some of the new digital sampling scopes. The one I have, the Owon DS6062, was less than $400. There are several other brands with similar specs and costs. Do some checks on Ebay. The digital scopes will let you measure your light pulses at leisure. You can expand the trace on a captured signal, and there are movable measurement markers that will display the time interval for you - no interpolation necessary!

I measured an old Topcon that my father had with a system like this. The shutter speeds were reasonably close to expected up to about 1/250 sec. The last two (1/500 and 1/1000) were substantially longer than they were supposed to be.

If you have questions about the circuit or measurements, please send me a pm. Go make some measurements, and let us know how close your “new” camera is.

For DSLRs, you can’t make measurements like this. I have come up with, though, an electronic shutter speed measurement light source: an array of LEDs that steps through the LED array at a rate 50 times the expected shutter speed. You take a picture of the array and count the number of LEDs that show up. The two cameras I have measured this way (a Canon and a Pentax) were very close at all shutter speeds - within 2 or 3 % of stated value.

[Bengan]

Thanks, regarding the special equipment what would that be, I'm assuming it's prohibitively expensive though ????

I have tested this low cost gadget (Camera shutter tester for shutter speed up to 1/1000th for PCs and laptops | eBay). It's a simple light to sound converter and is plugged in to a PC using a freeware program. It may not be as accurate as the other solutions described here, but it works surprisingly well. The only thing you will have to make yourself is a simple light source.


The guy also makes more advanced (and more expensive) meters. Have a look at his other listings.

[ChrisPlatt]

We used a purpose-built SLR shutter and exposure tester when I worked in camera repair at Olympus USA.
Eric Hendrickson has a photo of one on his homepage: http://www.pentaxs.com
He services all my used Pentax cameras, so no worries here...

Chris