# Thread: Is the nominal shutter speed listed on the Calument tester correct?

1. ## 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?

2. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

Originally Posted by John Schneider
Am I missing something?
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

3. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

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

4. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

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

5. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

Originally Posted by Peter Gomena
Anything less than about 1/6-stop difference is insignificant anyway, right?
It certainly is insignificant. I would be impressed if the shutter tester were that accurate.

And thanks to Leigh for his cogent explanation.

6. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

Originally Posted by Jac@stafford.net
It certainly is insignificant. I would be impressed if the shutter tester were that accurate.
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.

7. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

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.
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.
.

8. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

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.
.
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?

9. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

Originally Posted by Jac@stafford.net
Does anyone measure light meter accuracy
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

10. ## Re: Is the nominal shutter speed listed on the Calument tester correct?

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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