New Lens Scale: How To Convert Milliseconds To Standard Camera Fractions?

[Andy F]

Hi,

I just got this shutter tested but I don’t understand the results. Obviously I need to change the scale on the shutter to get the images to come out correctly but I am not sure how to do this because everything is written in milliseconds. I need the numbers to meet my light meter. Could someone help with letting me know what my new scale would look like or how I can make that new scale. I think the times are consistently off but I don’t know how to convert them into standard shutter speeds. Any ideas? Also, based on these numbers how bad is this shutter? It is a 210mm Fujinon in a Seiko Shutter.

I know this probably pretty basic to some people but it is new to me. Please let me know what you think?

-Andrew

[Mark J]

On a calculator you'd use the reciprocal ( '1/' ) of the amount in seconds, to get the bottom number. So 101 milliseconds is 0.101 seconds, reciprocal is about 10.

Your numbers for the right column are :

1 & 1/3
4/5ths
1/2.5
1/5
1/10
1/20
1/40
1/100
1/160
1/230

Roughly speaking, you'd not be far off to say they are all about 1/2 a stop slow ( ie. more light ) .

[BrianShaw]

It would be a lot easier to compensate using the aperture than changing the shutter speed scale. Or compensate via EI on a light meter.

[sharktooth]

Your shutter speeds seem to be around half a stop slow throughout the range, but 1/400 is pretty close to 1/250. It's not exactly half a stop, but close enough that it won't matter. Depending on the meter you use, it may not be easy to set intermediate shutter speeds. It would probably be easier to use the shutter speed indicated on the shutter, and just close down the aperture by half a stop from the meter reading.

If the shutter is set to 1/400, then just use 1/250 on your meter, and don't change the aperture.

[neil poulsen]

What I do is to give the f-stop difference (in fraction of stops) needed to correct the actual speed to the nominal speed. So, you would use the nominal speed (i.e. 1, 1/2, 1/4 1/8 etc) on the light meter, and then you would adjust the f-stop by the number of stops specified on the table.

For your data, I came up with the following table:

Nominal__ Aperture Correction (in stops)

1________ -0.4
1/2______ -0.7
1/4______ -0.7
1/8______ -0.7
1/15_____ -0.6
1/30_____ -0.7
1/60_____ -0.5
1/125____ -0.3
1/250____ -0.6
1/500____ -1.1

A negative in the table means that the aperture must be closed by the given number of stops. I used 1/500, versus 1/400, because it's 1/500 that will be found on your light meter. The aperture correction has been rounded to the nearest tenth stop.

All your aperture corrections are negative because, in each case, the actual time is longer than it should be.

The formula used to obtain the aperture correction is the following:

Correction = -log[AcutalTime/NominalTime] / log[2]

It doesn't matter which base you use for the logs. (Natural, base 10, etc.) The actual time is what you stated in your post. Nominal time is the quotient of Nominal. (i.e. nominal time for 1/250 is 0.040.)

[BrianShaw]

With many flms and photogaphic situations you'll barely notice the "error" if you don't compensate. But averaging to a half-stop compensation on all speeds except your fastest is easy to remember and do if you seek "exposure perfection".

[Doremus Scudder]

Here's my table of shutter speeds in milliseconds with corresponding approximate 1/3-stop fractions.

When I get my shutters tested, I convert the time in milliseconds to the closest 1/3-stop shutter speed. I'll then make a sticker to paste on the lensboard with the corrected shutter speed.

So, for example, let's say the 1/15th-second setting on the shutter comes in at 83 milliseconds. On my table, that's closest to 80 milliseconds, which is 1/12 second, which is 1/3 stop slower than the standard 1/15th second. So, I'll mark that as 1/15- (using the "minus" sign). And say that my 1/125th-setting comes in at around 14 milliseconds. That's closest to 12.7 milliseconds on the chart, which is 1/80th second, which is 1/3 stop faster than the standard 1/60th setting (i.e., my 1/125 setting is about 2/3-stop slow). So, I'll mark that 1/60+ (using the "plus" sign) on my sticker. Just remember that the plus and minus signs refer to the numbers: Minus means More exposure and Plus is Less exposure when working with the fractions-of-a-second shutter speeds.

Then, when setting the exposure, I'll just adjust with the aperture. Say my meter wants 1/60th at f/22. I'll set my shutter at 1/125th, which is 1/60+ (1/3 stop less exposure than 1/60th) and then set the aperture to 1/3 stop more open than f/22 to compensate. (if there are no 1/3-stop hash marks on the shutter, I just estimate). This method gets me to within 1/6 stop overall, close enough for color transparency work even.

I work in 1/3-stop increments when metering anyway, since my meters are all marked with third-stop hash marks. I'd notate the above in my exposure record as "f/22- at 1/60+." The good thing about this is that the minus sign for both shutter speeds and aperture means more exposure and the plus sign for both means less exposure.

Hope that all makes sense; it will after looking at the chart and going through the above examples again.

Best,

Doremus

[Andy F]

Hi Everyone,

This was really helpful. I guess the take away is that the shutter is a half-stop slow and the 400 should be rewritten to 250. Some of the information was a little more complex and I will need sometime to process it but everything said was so helpful.

Thanks everyone,
Andrew

[Mark J]

The other option is to adjust your film speed on the meter.
In my case I would rarely shoot at faster than 1/60th sec, so based on Neil's table above, I'd add 2/3rd of a stop to the film speed - eg. for an iso 100 film , I'd use iso 160 on the meter.

edit : sorry Brian mentioned this earlier.

[sharktooth]

If you're shooting with negative film in either B&W or color, there's usually lots of latitude, so a half stop overexposure is no problem. Negative films will often benefit from the extra exposure, so you're probably better off just ignoring the issue, and just use the marked values on your shutter, and not bothering about doing any compensation.

The only time 1/2 a stop becomes important is with color transparency films like Ektachrome or Fuji Velvia/Provia, or some high contrast specialty films. You risk washed out highlights with overexposure, since the film latitude is so small.