Shutter Speed Test

[cyrus]

I built a home-made shutter tester which attaches to the sound card. What's the "acceptable" range of variation on shutter speeds? For example I have a 300mm lens that gives .03 instead of .025 seconds, and .007 instead of .008
Now I realize that there is quite a bit of error in my measurement since I am eyeballing the results from a graph...

[Patrik Roseen]

Obviously not being an expert, But...

I would look at this from two perspectives (besides your way of conducting the measurements and analysis):

1) compare the measured times vs 'right' time in matters of fractions of a stop.
I.e The 0.03 instead of 0.025 means +1/5 of a stop on the way to 0.05
i.e. 0.007 instead of 0.008 means -1/4 of a stop on the way to 0.004
And then ask how accurate is my lightmetering?

2) Variation in shutter speeds depending on temperature etc
Interesting just to figure out how much the previous delta times are to worry about.

[eddie]

you need to enlarge the graph so you can get a more accurate measurement. this will help instead of eye balling it (i click on the begining of the graph and highlight to the end. the computer tells you the times)

i also excercise the shutter before each test. as long as they are consitantly close call it good. none that i have tested tested exactly the same. (could be operator error. could be shutter)

eddie

[Alan Davenport]

If you're talking about leaf shutters (the most likely choice for large format use, and you did post this on the LF forum, after all) then the numbers you get from a sound card measurement are probably inaccurate. The amount of inaccuracy will vary from "very inaccurate" at short shutter speeds, to "fairly close" at long times.

The reason for the inaccuracy is that there is a substantial time lag from the initial "click" in a leaf shutter, until the point where it must be timed, and there is again a relatively long time from the point where the timing of the shutter ends until it is actually fully closed and your sound card hears the second "click" (if you will.)

A leaf shutter starts from fully closed, and as the blades open the illumination on the film gradually increases until the blades are fully opened. Then when it begins to close, the illumination decreases gradually. The effective start and stop times are somewhere in the middle of the "ramp up" and "ramp down" periods. So the effective timing of a leaf shutter will always be less than what a sound card timing gives.

I hope this makes some sense.

[C. D. Keth]

The reason for the inaccuracy is that there is a substantial time lag from the initial "click" in a leaf shutter, until the point where it must be timed, and there is again a relatively long time from the point where the timing of the shutter ends until it is actually fully closed and your sound card hears the second "click" (if you will.)

A leaf shutter starts from fully closed, and as the blades open the illumination on the film gradually increases until the blades are fully opened. Then when it begins to close, the illumination decreases gradually. The effective start and stop times are somewhere in the middle of the "ramp up" and "ramp down" periods. So the effective timing of a leaf shutter will always be less than what a sound card timing gives.


This is all complicated when you consider that shutter speeds for a leaf shutter also depend on the stop you are shooting at. Large apertures make a shutter quite a bit less efficient (where efficiency is time between the shutter beginning to move to where it is 100% open, and vice versa on the close) than when you are stopped down.

[cyrus]

Actually I should have clarified that I used a phototransistor that was connected to the sound card, not a microphone. Fancy shmancy, eh? I do use the highlighting technique but it is still not mathematically accurate (I wonder if there is a function in AUdacity that measures peak to peak)

BTW and off topic for LF, the worst shutter performance in my camera collection thus far is a Lomo fisheye plastic camera. They claim the lens is set at 1/100, but its more like 1/15. So in case you're thinking of making the heavy investment of $30 for a plastic fisheye camera, remember that. Surprisingly, the Lomo Smena is just fine. I want to try my Super Speed Graphic's 1/1000 setting next. I am guessing it won't be accurate.

[stompyq]

Damn, i just bought the parts to make exactly the same type of shoutter tester!!! I am going to be watching this thread carefully

[eddie]

Damn, i just bought the parts to make exactly the same type of shoutter tester!!! I am going to be watching this thread carefully

for those just joining......
shutter tester (http://www.open.hr/~dpleic/photo/Shutter.html)


eddie

[cyrus]

for those just joining......
shutter tester (http://www.open.hr/~dpleic/photo/Shutter.html)


eddie

Or here (http://www.davidrichert.com/sound_card_shutter_tester.htm).

[Denis Pleic]

for those just joining......
shutter tester (http://www.open.hr/~dpleic/photo/Shutter.html)


eddie

Heh, I'm glad to see that my page still has some use after all this time... :)

Denis

[cyrus]

Funny, my graphs are the other way around - it goes up first then falls. Anyway, if the x axis shows "no signal" why does it go below the x axis?

[Erich Hoeber]

I've been using one of these home-brewed shutter testers for years. I once had the opportunity to compare it to a real shutter tester and I found the home made one to be extremely accurate. Granted, there's a difference in both shutter timing and shutter efficiency that varies with aperture (and taken as a percentage, with shutter speed), but these tend to be insignificant at all but the shortest times and of little consequence to most LF users. The home-brew graph lets you "see" a bit more of these errors than a regular tester, however.

[Frank R]

I tried this shutter tester idea last year. It is serviceable but I never felt it was too reliable at the faster speeds.

I finally bought a Calument Shutter Tester a few months ago. Way easier and faster to use.

I also test every shutter and include the results on a standard form every time I sell a lens. I like giving this information to the buyers as a freebie.

[dikaiosune01]

I certainly like the idea.

However I have a question from the inexperienced individual standing before (me);
how is a photoresister any different from using a normal microphone?

Audacity certainly can record time for longer shutter speeds like 1 second.

Is there a significant difference in accuracy.

Personally, I would like to try something like this. I also have some experience soldering wires together (not much). However, I have no idea how to find or ask where to find the appropriate photoresistors at my electronics shop (No one really speaks any English in this country).

[Drew Wiley]

I've been using the Calumet tester for years and have been very pleased with it. In fact, I tested a lens last night with it. With leaf shutters, I make a habit of testing at
the stopped-down aperture I'm likely to most frequently use with that particular lens.
Most leaf shutters are off at the highest speeds, which we rarely use anyway; but I
am nitpicky about the slower speeds, since I shoot chromes as well as negs. The
Calumet has a table attached to show min/max readings for both a 1/6 variance, and
for 1/3.

[dikaiosune01]

Does anyone have any experience using a microphone to test shutter speed accuracy?
How does it compared to a documented CLA (if possible)?

I imagine it gets difficult to discern at 1/30 second or quicker.
Your thoughts?

[rdenney]

Does anyone have any experience using a microphone to test shutter speed accuracy?
How does it compared to a documented CLA (if possible)?

I imagine it gets difficult to discern at 1/30 second or quicker.
Your thoughts?

Sounds, as measured by microphones, are not important because shutters often make noise unrelated to when the shutter is actually opening and closing. Light is important. Wiring a photo-transistor or even a photodiode to the microphone input measures light. That is still subject to a range of errors, as we have discussed in great detail on this forum even within the last few months, but it should be good enough for shutter speeds up to perhaps 1/100 of a second. Faster speeds require more sophistication.

Microphone inputs on sound cards are filtered for DC, and it's a DC output from the sensor being measured, and that makes the waveform screwy. There is a bump when DC appears (or departs--could be either depending on how it's wired), and then the DC is filtered out. There is another bump in the opposite direction when the DC stops (or starts). The transistors/diodes are easy to saturation, which clips the waveform giving the impression that something definite happened, when it just happens to be the point where the light overloaded the sensor. At faster speeds, these bumps run into each other and the clipping seems meaningful, and it's not that easy to tell when the light actually started and stopped. When the error is small compared to the shutter open time, the error is not important. But the error is fixed and becomes a larger percentage of the shutter opening time as speeds get faster.

For large-format applications where slow shutter speeds are the norm, it's a good, cheap technique that is close enough.

Rick "suggesting some practice with the search engine" Denney