Would Like To Verify Exposure Duration

Started 4 months ago | Questions thread
Bernard Delley Senior Member • Posts: 1,650
Exposure nominal and precise

bclaff wrote:

Detail Man wrote:

The (in)famous Ken Rockwell published in 2006 (describing D200 image-file meta-data tag):

The exposure time in the EXIF data is recorded in seconds, to the tenth of a second. My 56 minute exposure read 3375.2 seconds.


It (may) be that tenths of Seconds are not recorded for single-digit exposure times (<10) ?

Regarding D200 exposure time meta-data:

... Tag:0x829A


I think this Tag is only accurate for Bulb mode otherwise the "nominal" exposure is reported.

FWIW, if exposure time advances in stops then we might expect 10s to actually be 2^(3 + 1/3) = 10.08s
This would mean that 30s is actually 32s. I've never tested this.

Correct !  The conventional nominal exposure times can be several percent different from the actual precise exposure times. In measuring photo response curves, I verified that the actual exposure times were in steps of third powers of two  t =  2^(M/3) with M an integer. Times in the range 1 - 1/8000 s were tested for consistency. So I assume that the rule holds for all times that can be set. The accuracy of my test suggested accuracy better than 0.1%  for timing, on Nikon cameras. It can be safely assumed that other makers adhere to same standard based on embodiment with quartz clock and precision mechanics at the shutter blades.

BTW, apertures (except at fully open aperture) obey   N = 2^(p/6) with p an integer. The accuracy of electronically controlled apertures gets near 1% for good lenses.

 Bernard Delley's gear list:Bernard Delley's gear list
Nikon AF-S Nikkor 80-400mm f/4.5-5.6G ED VR
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