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


eddie

[cyrus]

for those just joining......
shutter tester


eddie

Or here.

[Denis Pleic]

for those just joining......
shutter tester


eddie

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

Denis