Shutter Speeds: How exact is necessary?

[macandal]

So, really, how exact, how precise should I expect my shutters to be? I mean if I'm shooting it at 1 second should I expect it to be shooting at one second? If I'm shooting it at 1/500 of a second should I expect it to be shooting at exactly that? Or are shutter speeds just notions that give you an idea that you're shooting faster/slower but not exactly at the time the shutter speed says?

Thanks.

[Ken Lee]

To put it politely, some people are more demanding than others.

That being said we do need to know if our shutter is off my more than a minor fraction of an f/stop, particularly if we're running a sensitometry or film speed test because that will skew all our results. For that reason it's best to shoot film speed tests with one lens, one shutter and one reliable shutter speed.

In real-world shooting a fraction of an f/stop difference is hardly noticeable since there are so many variables and we are imperfect.

If you're using an older shutter which varies widely from its claimed speeds, it's good to keep a card at hand with the actual speeds written down. Then you can work more confidently.

When I had a Calumet Electronic Shutter tester, I tested my old shutters - some 60 years old - and found them all to be acceptably close. Eventually I sold that tester because I felt confident in the shutters.

You might find this helpful: the iPhone Shutter Speed App (https://itunes.apple.com/us/app/shutter-speed/id560154244?l=de&ls=1&mt=8). The current price is a modest US $2.99

I don't know if there are similar apps available for other platforms.

[djdister]

I seem to remember hearing that shutter speed tests that are + or - 1/3 f/stop from the marked speed would still be considered within acceptable tolerances. Given the many ages of my shutters, I would be surprised if any of them were exactly the marked speed.

[jp]

On the 1s end, you can tell if it's running slow by the sound when exercising it. If it needs to be on 1/2 to be a 1s exposure, that's OK for me. Dead on accurate is only required for shooting transparency film. I think being within 1/2 stop is fine for B&W, but we all have different levels of comfort. Cold weather can slow things down too. I know my TLR will be about 1 stop overexposed in 0f weather and I can compensate by selecting a faster shutter speed or smaller aperture than what the meter suggests. You can get shutter speed testers on ebay or phone apps for testing if you must know.

[Emmanuel BIGLER]

Hi !
Plus or minus 1/3 of a f-stop translates into plus or minus 20% on the exposure time.
This is very actually very far from what we actually expect even from the cheapest wristwach we use daily ;) but this specification is actually consistent with what a skilled repair technician told me. I remember being shocked: my faithful compurs cannot be that bad !

So if you are shocked, let your shutter be serviced, and expect plus or minus 10%, which translates into plus or minus 1/6-th of a f-stop.

From an horological point of view, the kind of timing escapement in use in mechanical shutters belongs to the same class of low-precision escapements in use in watches before Christiaan Huyghens invented the spiral spring regulated escapement in the XVII-st century ;)
But if plus or minus 10% would be unacceptable for a watch (this would mean 2.5 hours of drift per day !) this is already "overkill" for a photographic shutter.

[hoffner]

From usage guidelines: Be sure to give a descriptive title to your question. For people searching or browsing the archives, a nonsensical or uninformative subject (like "Oops!", "Read this!", or even "Lenses") just makes it harder for people to find answers to questions.
Now, how exact is that?

[towolf]

Soldered a photodiode and a button battery to a 3.5mm audio jack and measured my mostly old lenses with an audio programme on my laptop.

I knew the long times would be very off on the very old shutters, but it surprised me that the short times were 50% off on all of them.

http://i.imgur.com/TGgYhrJ.png

[prendt]

Hi !
Plus or minus 1/3 of a f-stop translates into plus or minus 20% on the exposure time.

So if you are shocked, let your shutter be serviced, and expect plus or minus 10%, which translates into plus or minus 1/6-th of a f-stop.



If 1/3 of a stop translates to 20% on the exposure time then a full stop (3/3) should translate to 60% on the exposure time? And if 1/6th of a f-stop is 10% of the exposure time then a full stop (6/6) is just 60% of the exposure time? Where did the remaining 40% get lost? I don't get it.

[Doremus Scudder]

If 1/3 of a stop translates to 20% on the exposure time then a full stop (3/3) should translate to 60% on the exposure time? And if 1/6th of a f-stop is 10% of the exposure time then a full stop (6/6) is just 60% of the exposure time? Where did the remaining 40% get lost? I don't get it.

You're doing the math wrong. However, you're right that the 1/3 stop is really more like a 25% increase in time.

Ex: 10 sec. + 25% = 12.5 sec: 12.5 sec. + 25% = 15.625 sec: 15.625 sec. + 25% = 19.531 sec. - almost a whole stop.

Clockwork shutters are notoriously inaccurate at higher speeds; up to a whole stop for 1/500 very often. That doesn't mean that they aren't consistent, however. I have all my shutters tested and average about six values at each speed. I use results in milliseconds and then, assuming the shutter is running consistently (if not, it goes in for a CLA), I convert the average for a given shutter speed into the closest 1/3 stop. I make a table for each shutter I own and paste this on the lensboard. Then I know how much exposure I'm actually getting when I determine my aperture and shutter speed.

If you're shooting B&W or color neg, 1/3 stop is way close enough. You may want to be a bit more accurate if you're shooting transparency material.

Best,

Doremus

[prendt]

Thanks Doremus for your explanation. In fact, I was thinking that Emmanuel in his post was speaking about f-stops meant as optical apertures (f 16, f11 etc.) and comparing them to time exposure equivalents. Go wonder.

[Ken Lee]

I renamed the thread.

[Jim Jones]

The highest speeds of a between-the-lens shutter should be checked at the same aperture used for photography. This is due to shutter efficiency, the difference between the effective shutter speed at difference apertures. Trying to find an accurate and lucid explanation of the topic revealed much confusion over many years. Long ago some people understood it http://blog.modernmechanix.com/how-camera-shutters-work/, but even now discussions tend to degenerate into quibbling with few facts presented. A Yahoo search for "camera shutter efficiency" was largely a waste of time. I doubt that any testing that does not involve either an oscilloscope or a method of integrating and measuring the amount of light at various apertures is reliable for precise exposure. The oscilloscope can reveal shutter problems other methods can't.

[Steve Goldstein]

I believe the brochure that came with Copal shutters said the factory tolerance was 30%.

[hoffner]

I renamed the thread.

Thank you Ken.

[jbenedict]

More than anything, shutter speeds need to be predictable. If 1/50 hits at 1/15 over and over every day, it will be fine. Same with the other speeds. Some people put a list of comparative shutter speeds (marked vs. measures) right on the lens board. If you wanted to, you could calculate a =/- stop column for the same chart.

Now, will a gooey/dry shutter be predictable? Your guess is as good as mine. Shutter CLA can be expensive but how many sheets of film will be exposed all screwy if the shutter speed is not predictable? Sheets o' film are getting expensive these days!

[Jerry Bodine]

The oscilloscope can reveal shutter problems other methods can't.

Very true. Years ago I had a leaf shutter checked (while I waited) by a repair guy who used an oscilloscope, and it showed the shutter was demonstrating a "bounce" after the shutter closed. This bounce meant the shutter was opening again very briefly after it closed, and it was seen as a secondary blip on the scope. I don't know of any other device that would've detected it.

[macandal]

Shutter CLA can be expensive but how many sheets of film will be exposed all screwy if the shutter speed is not predictable? Sheets o' film are getting expensive these days!Can you recommend a place to send my lenses for CLA? I live in San Francisco and prefer local, but I will send them out too. Thanks.

[Jerry Bodine]

A lot of us here rely upon Carol at Flutot's Repair in S.Cal. She really knows her stuff and I feel the prices are reasonable. At times there's quite a backlog though and may take awhile.

http://flutotscamerarepair.com/

[Drew Wiley]

I have the Calumet tester and have tested every single lens I own, as well as the curtain shutters in the small cameras. Very few traditional leaf shutters like we
use on our view cameras are accurate at the top speeds. But then nobody seems to use those speed anyway; and if they do, it's usually in conjunction with studio
flash. How much does it matter? Plenty if you shoot chrome film in high contrast scenes. But what is far more important than the accuracy of the speed setting
per se is its repeatability. If it's always statistically off in the same direction, to about the same amount, you can just tweak your aperture a bit. If it's wacky and
all over the map, to hell with it. Plus or minus 1/3 of a stop is OK; but I'd rather see things within 1/6 at important speeds when shooting color film.

[goamules]

I've never tested a shutter. I shoot some that are 100 years old. With black and white film, I've NEVER had a shot that I didn't feel the shutter did it's job. Some of my shutters are probably 1 to 2 stops off. No problems for me. It depends on how and what you are shooting. I shoot in the middle latitudes, sometimes up to several seconds, down to maybe "as fast as I can move my hand", or 1/15th or so. If you shoot like me, don't worry.

[Jac@stafford.net]

In my modest experience speaking of leaf-shutters, the larger the shutter, then the more likely the
shutter speeds are to be inaccurate, and the higher (shorter) the indicated speed, the more likely
it is to be wrong, regardless of the size of the shutter.

But ask yourself, just how precise must it be? Consider all the other factors of your photography to
find similar deviations.

Just my 10 bits.
.