Is the nominal shutter speed listed on the Calument tester correct?

I finally, *finally* found my Calumet shutter speed tester. I tested some lenses and noticed that the shutter speed decimal equivalents on the label are wrong. It begins okay (1=1.000, 1/2=0.500, 1/4=0.250, 1/8=0.125) but then the label diverges and sets 1/15 to 0.0625, which is of course 1/16; likewise for 1/30 and 1/60 Calumet gives the decimals for 1/32 and 1/64 etc.:

shutter setting___actual decimal___Calumet decimal
1 sec___________1.00000_______1.00000
1/2____________0.50000________0.50000
1/4____________0.25000________0.25000
1/8____________0.12500________0.12500
1/15___________0.06667________0.06250
1/30___________0.03333________0.03125
1/60___________0.01667________0.01563
1/125__________0.00800________0.00781
1/250__________0.00400________0.00391

Am I missing something?

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Originally Posted by John Schneider

Am I missing something?

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Yep.

The decimal values are correct, proceeding by factors of 2 or 0.5, depending on which direction.

The marked speeds have changed a bit, using roughly a factor of 2 but adjusted to what folks like.

For example, 1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, 1/128 is a real factor-of-2 progression.

Similarly, 1/1000, 1/500, 1/250, 1/125, 1/62.5, 1/31.25 is a real factor-of-2 progression the other way.

The values marked on a shutter control is a combination of the two sequences.

- Leigh

As Leight correctly insinuates after 1/8 the shutter values are rounded ones instead of the not practical precise fractions.

Anything less than about 1/6-stop difference is insignificant anyway, right?

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Originally Posted by Peter Gomena

Anything less than about 1/6-stop difference is insignificant anyway, right?

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It certainly is insignificant. I would be impressed if the shutter tester were that accurate.

And thanks to Leigh for his cogent explanation.

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Originally Posted by Jac@stafford.net

It certainly is insignificant. I would be impressed if the shutter tester were that accurate.

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It surely is that accurate, especially for the relatively long times between 1s - 1/30s if it is able to measure a burst of light of 1/250s. Today's common electronics is capable of even greater accuracy than that.

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Originally Posted by Pfsor

It surely is that accurate, especially for the relatively long times between 1s - 1/30s if it is able to measure a burst of light of 1/250s. Today's common electronics is capable of even greater accuracy than that.

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That might be accurate, however, it makes no significant difference. Does anyone measure light meter accuracy, and does anyone measure the consequences of development methods. I think not.

We can measure the shutter speed, but we cannot measure the subsequent practice.
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Originally Posted by Jac@stafford.net

That might be accurate, however, it makes no significant difference. Does anyone measure light meter accuracy, and does anyone measure the consequences of development methods. I think not.

We can measure the shutter speed, but we cannot measure the subsequent practice.
.

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The light meter accuracy is surely measured at least by the manufacturer. And while it is true that there are many inaccuracy sources it is good to have at least some of them under control, isn't it?

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Originally Posted by Jac@stafford.net

Does anyone measure light meter accuracy

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Yes, absolutely.

Whenever I repair a camera that has built-in metering, I always test it with proper equipment.
The accuracy spec is always given in the service literature for the camera.

If it's not right, I fix it to make it right.
And I do not work to tolerances in that regard. I expect the meter to be right on.

- Leigh

I am not so sure about the statement on the accuracy lightmeters acros the complete spectrum. For instance: i try to avoid measurong red objects with my Gossen Spotmaster because it is way off, under exposing by several stops, where green and blue objects are pretty much spot on.

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Originally Posted by Pfsor

It surely is that accurate, especially for the relatively long times between 1s - 1/30s if it is able to measure a burst of light of 1/250s. Today's common electronics is capable of even greater accuracy than that.

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I too wondered how how much of the variation in times was from the shutter tester and how much from the shutters. When I tested my Mamiya 7 lenses, which have electronically controlled leaf shutters, I had my answer. I remember being stunned that the 1/2 came out to .50000 and the 1 was 1.00000 and the others were either dead on or off by a minuscule amount. At that point I determined for practical purposes all the error and variation was due to the shutters, or testing error.

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Originally Posted by Larry Gebhardt

I remember being stunned that the 1/2 came out to .50000 and the 1 was 1.00000...

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Due to the short time intervals being measured, shutter testers use a crystal oscillator as their time reference.
Crystal oscillators can easily hold accuracies of 10 parts-per-million (0.001%) or better.

Electronic camera shutters also use crystal timebases, for the same reason.
As long as the crystal is undamaged, they remain accurate for many decades.

- Leigh

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Originally Posted by Peter Gomena

Anything less than about 1/6-stop difference is insignificant anyway, right?

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I learned from Ken Rockwell to tape a small piece of paper to my lens boards with my tested shutter speeds so I can see at a glance what they are. Anything less than 1/2 stop off, I don't worry about writing on the paper.

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Originally Posted by Leigh

Due to the short time intervals being measured, shutter testers use a crystal oscillator as their time reference.
Crystal oscillators can easily hold accuracies of 10 parts-per-million (0.001%) or better.

Electronic camera shutters also use crystal timebases, for the same reason.
As long as the crystal is undamaged, they remain accurate for many decades.

- Leigh

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Leigh, I'm quite sure we can forget crystals for this application. There is an electronic timer circuit, probably the famous 555 that is used as an oscillator.

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Originally Posted by Larry Gebhardt

I had my answer. I remember being stunned that the 1/2 came out to .50000 and the 1 was 1.00000 and the others were either dead on or off by a minuscule amount.

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That minuscule difference could be given by the exact position of the measuring sensor with regard to the shutter centre. Because of their geometry shutters allow a slightly longer exposures passing through the centre of their opening and shorter ones passing through the shutter curtain edges. Some time difference is then measured accordingly. The shutter tester is that precise.

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Originally Posted by Alan Gales

Anything less than 1/2 stop off, I don't worry about writing on the paper.

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Really? Have you ever wondered why shutters are marked in 1/3 of stops?

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Originally Posted by Pfsor

That minuscule difference could be given by the exact position of the measuring sensor with regard to the shutter centre. Because of their geometry shutters allow a slightly longer exposures passing through the centre of their opening and shorter ones passing through the shutter curtain edges. Some time difference is then measured accordingly. The shutter tester is that precise.

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Agreed. That is a character of sensor's measuring design, but not likely enough to make a difference. Concerning the whole film, the initial small aperture when opening has light still distributing over the whole film, or as much as possible given the lens' coverage.

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Originally Posted by Jac@stafford.net

Agreed. That is a character of sensor's measuring design, but not likely enough to make a difference. Concerning the whole film, the initial small aperture when opening has light still distributing over the whole film, or as much as possible given the lens' coverage.

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For a moment I didn't understand what you agreed to but then I got it - you probably meant "but not likely enough to make a difference in film exposure"?
Of course, we're not talking about measuring shutter speeds with their lenses on. But for the shutter opening the difference is surprisingly great. Unfortunately, I don't remember if it is Stroebel or Ray that mention it but if I remember well the difference for the shutter (leaf shutter) center and the edge was about almost 1/3 stop (?). If you have the source you can find it, I don't have access to my books now. Cheers!

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Originally Posted by Pfsor

Leigh, I'm quite sure we can forget crystals for this application.
There is an electronic timer circuit, probably the famous 555 that is used as an oscillator.

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The accuracy of the 555 timer is several orders of magnitude worse than a crystal.

I would never use a 555 in the design of a shutter speed tester or any similar device.
I have used thousands of 555s in designs where absolute accuracy was not needed.

- Leigh

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Originally Posted by Pfsor

Really? Have you ever wondered why shutters are marked in 1/3 of stops?

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The deltas (time between adjacent speed settings) can be much more accurate than the absolute speed.

- Leigh

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Originally Posted by Leigh

The accuracy of the 555 timer is several orders of magnitude worse than a crystal.

I would never use a 555 in the design of a shutter speed tester or any similar device.
I have used thousands of 555s in designs where absolute accuracy was not needed.

- Leigh

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If I remember well, the 555 runs on 0.1 MHz. Enough to measure to 1/100000 s. And yes, the 555s are used in time measuring devices (with a 4026 to count the oscillation). You can always strive for better. Besides, there is no meaning to use 16-200MHz crystals to measure times long at most 1s. Not in a device with possible errors from off centre position!

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Originally Posted by Leigh

The deltas (time between adjacent speed settings) can be much more accurate than the absolute speed.

- Leigh

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So what?

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Originally Posted by Leigh

The accuracy of the 555 timer is several orders of magnitude worse than a crystal.

I would never use a 555 in the design of a shutter speed tester or any similar device.
I have used thousands of 555s in designs where absolute accuracy was not needed.

- Leigh

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As a side note - you would be probably shocked to know that Tomahawk missiles use in their time measuring device not crystals, not any timer circuits but Swiss mechanical calibres (watch movements) proudly and promptly manufactured in La Vallée de Joux...

You guys with precision metrics are going to make my head explode!
:)
When paying by check I often have to ask, "The date today, please?"
The answer is something like "September 16" to which I must respond,
"Yeah I know that, but what year is it?"

I kid you not.

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Originally Posted by Pfsor

Really? Have you ever wondered why shutters are marked in 1/3 of stops?

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Nope. It's overkill in my book.

Bracket a bunch of shots in 1/3 stop differences and see what you think.

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Originally Posted by Jac@stafford.net

You guys with precision metrics are going to make my head explode!
:)

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If it can be of some consolation to you, Leigh will measure (with a crystal oscillator!) the time of your explosion. I will just sadly confirm your instantaneous end.

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Originally Posted by Alan Gales

Nope. It's overkill in my book.

Bracket a bunch of shots in 1/3 stop differences and see what you think.

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In such a case we are probably talking apples and oranges. You probably take B&W - I take chromes and 1/3 of a stop is important to me. It can make a difference between a keeper or a botched picture.

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Originally Posted by Pfsor

If it can be of some consolation to you, Leigh will measure (with a crystal oscillator!) the time of your explosion. I will just sadly confirm your instantaneous end.

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You are funny. Thanks. Did you know that nerve messaging in the human body travels at about the speed of sound? That's good enough for me. Digressing... We are so slow.

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I take chromes and 1/3 of a stop is important to me. It can make a difference between a keeper or a botched picture.

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An old friend of mine, in fact a former employee, went on to work for National Geographic in the Kodachrome days. He was also the 1/3 stop guy. When asked about his light meter he never, ever responded.
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Originally Posted by Jac@stafford.net

You are funny. Thanks. Did you know that nerve messaging in the human body travels at about the speed of sound?

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No, I did not know. From now on I will prop my ears if I don't want to feel anything. Hope it will work in my dentist office...

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Originally Posted by Pfsor

In such a case we are probably talking apples and oranges. You probably take B&W - I take chromes and 1/3 of a stop is important to me. It can make a difference between a keeper or a botched picture.

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You are correct. I shoot mostly 8x10 B&W.

I cut my teeth on 25 ASA 35mm Kodachrome back in the 1980's. When learning, I used to bracket my shots 1 stop difference for the perfect exposure. What I learned was that usually I came out with 3 good shots. Sometimes my slightly over or under exposure shots were best. Sometimes I could not pick which was the best shot because all three looked great and I'm talking a one stop difference between each. Then of course you can talk about high key or low key which is popular in portraiture if we wanted to open another can of worms.

To be honest I'm surprised that 1/3 a stop makes that big of a difference on your chromes to you but to each their own. To be fair to you I have read that there are photographers who also feel as you do. As always I recommend that photographers experiment and find out on their own what looks good to them.

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Originally Posted by Pfsor

If I remember well, the 555 runs on 0.1 MHz. Enough to measure to 1/100000 s. And yes, the 555s are used in time measuring devices (with a 4026 to count the oscillation). You can always strive for better. Besides, there is no meaning to use 16-200MHz crystals to measure times long at most 1s. Not in a device with possible errors from off centre position!

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My but you can sure cram a lot of mis-information into a few sentences.

The highest possible frequency for a 555 would be defined by the rise time + the fall time of the output waveform.
Those are each 100ns, so 200ns total, which is a frequency of 5MHz.
Of course in a real circuit you could never achieve such fast operation reliably, but you can get to 1MHz.

The problem with the 555 is that it uses external resistors and capacitors to set its operating frequency.
While precision resistors are readily available, capacitors better than 5% are very difficult to find.
Add to that the switching time errors within the device, and you'd be lucky to hold 6% without high cost.
The actual 555 timebase circuits I've encountered usually spec their accuracy at +/-10%.

I've never encountered any crystals that operate at 200MHz.
Perhaps such do exist, but I've never found them in any equipment I've worked with.

And the position of the sensor has nothing to do with the measurement of exposure time.
A good time meter has three sensors, one in the middle and a pair at diagonally opposite corners.
This allows you to get three times for each test, regardless of the direction of shutter movement.

- Leigh

Ref: 555 datasheet from TI: www.ti.com/lit/ds/symlink/lm555.pdf

Leigh, you try hard, don't you? Of course you can use overtone with 555 but the normal frequency it runs on is 0.1 MHz. And whatever you say, 555 are widely used for time measuring. Some of us need the precision down to 1/millionth of s for measuring shutter speeds, and some of us use their Calumet testers.
To each its own. Leigh is after "the absolute" precision. When was the last time you saw a Calumet tester with 3 sensors? In your dreams perhaps.

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Originally Posted by Leigh

I've never encountered any crystals that operate at 200MHz.
Perhaps such do exist, but I've never found them in any equipment I've worked with.
- Leigh

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Don't despair Leigh, there is always something new you can learn in the life. For a starter, try to google "200 MHz crystal oscillator". It could be your first encounter with the beast, who knows.

After this exchange I became more curious about the Calumet shutter tester (which I own) and decided to see its old manual. Rightly so, the tester has 1 light sensor only and among many possible error sources when used is also indicated the precise alignment between the sensor (the tester itself) and the shutter.
A very interesting reading and it can be found on the net also. Recommended to all who are interested to know more about this shutter tester. (There is also a detailed explanation to the OP's question.)

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Originally Posted by Pfsor

After this exchange I became more curious about the Calumet shutter tester (which I own) and decided to see its old manual. Rightly so, the tester has 1 light sensor only and among many possible error sources when used is also indicated the precise alignment between the sensor (the tester itself) and the shutter.
A very interesting reading and it can be found on the net also. Recommended to all who are interested to know more about this shutter tester. (There is also a detailed explanation to the OP's question.)

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I own three Calumet shutter speed testers. When testing a shutter I test each speed three times because every once in a while the meter in error will give me the wrong speed. Sometimes it's the meter I think and sometimes it's user error on my part.

I've found that it's also a good idea to "warm up" the shutter by firing it a few times at all speeds before testing.

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Originally Posted by Pfsor

When was the last time you saw a Calumet tester with 3 sensors? In your dreams perhaps.

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I was talking about real shutter testers, not oriental toys.

- Leigh

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Originally Posted by Pfsor

For a starter, try to google "200 MHz crystal oscillator". It could be your first encounter with the beast, who knows.

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Why do you insist on talking about subjects with which you have no knowledge whatsoever?

In my earlier post, I said "crystals operating at 200MHz", NOT "crystal oscillators".

Since you obviously do not know the difference, why are you running your mouth?

- Leigh

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Originally Posted by Leigh

I was talking about real shutter testers, not oriental toys.

- Leigh

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Still trying hard? Ever noticed the title of this thread? Can you read?

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Originally Posted by Leigh

I was talking about real shutter testers, not oriental toys.

- Leigh

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Way to make a racially based buying decision!