If you set "1/60" shutter speed, what exposure time do you expect?

The mechanical shutter adds unavoidably some jitter and and slack. In the case of the pro Nikon D850, I find a little more than 1% jitter and a few percent slack towards the shortest exposure times. In the enthusiast model D7200 (with a wild history...) more of both.

I expect the logarithms of the shutter speeds to be evenly spaced. So, I would expect that 1/125 should yield half the exposure of 1/60, although the putative speeds don't obey that relationship.

Could you write that a different way - I fear I do not understand.

In video or stills, yes, 7% either way on exposure time is not in itself usually very significant, under stable lighting.

In video there's a minor effect on the rendition of motion, but far too small for anyone to notice. When shooting with multiple cameras, a 7% difference in exposures between cameras could be annoying.

But under lighting with 120Hz/60Hz flicker, the difference between a 7% deviation from a 1/60.00 s exposure and a 0.25% deviation is a factor of about 7/0.25 = 28 in the attenuation of flicker.

That is, the variation in exposure attributable to lighting flicker is about 28 times less at 1/60.00 s +/- 0.25% than at 1/60.00 s +/- 7%.

That is equally true for stills and video.

That would be the last thing I would expect, although most of us will get your one-line point.

One of my cameras gives the actual shutter period in meta-data as well as the nominal fractional value.

Curiously, 1/60sec is never 0.0166666 recurring .. 😟

Can you tell us what the camera is?

Ad the net frequency question above; a usual European one is 50Hz.

p.

ad the frequency usual in Europe: it is 50Hz

p.

somewhat annoying:
A "feature" of the edit arrangement here is that when one goes back to correct spelling (in this case a missing "e",) there is no obvious alternative for posting, but two butti\ons both containing "edit", Pressing the worng one may lead to double posting or a loop with "cancel" as the rational option.

Then I would expect 1/125 second. (+/- whatever the tolerance is, of course.)

Sorry for late reply ...

Sigma SD9

from meta-data in the raw file:

laptopscreen using Firefox on a W10 OS-

Implicit in this thread has been the expectation - at least in still photography - that shutter speed steps are based on a scale of stops (EV).

So we - typically - have target shutter speeds such as: 1 s, 1/2 s, 1/4 s, 1/8 s, 1/16 s, 1/32 s, 1/64 s, 1/128 s, 1/256 s, 1/512 s, 1/1024 s, 1/2048 s, 1/4096 s, ...

But these numbers have been thought to be not very digestible for most folk, so these shutter speeds are typically presented as nominal values:

1", 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000, ...

Historically, mechanically controlled shutter speeds were neither precise, accurate, nor very precisely repeatable, so the differences between target and nominal speeds were moot, and there was little point in providing intermediate shutter speed settings.

But today - for midrange to upmarket 21st century ILCs - we have shutters that give quite precise, and very precisely repeatable, exposure times, so 1/3 stop steps become worthwhile, and the differences between target and nominal speeds become more interesting.

The tolerances that you refer to - and that @xpatUSA previously referred to - have become quite small.

At "1/125", they might be well below 0.3% (0.004EV). Certainly much less than the 2.4% (0.035EV) difference between 1/125.00 s and 1/128.00 s.

This site might be helpful: www.scantips.com/lights/fstop2.html

This is what I get on D7200:

Bill Claff suggests an "FWC" of about 36k e- for D7200. So at "1/1000" shutter speed, I should have about 32k e-.

I'm doing something daft, or something odd is happening. Either the RAW data is quite non-linear, or the shutter speed steps - in EV - get smaller at higher shutter speeds. In particular, this data makes 1/8192 appear more like 1/7100. Which you don't seem to be getting with D850 in your setup. If there was some nonlinearity near "FWC", I might expect the picture to change if I re-based the test at 1/2048, but it doesn't change much.

I haven't tried directly measuring D7200 shutter speeds yet.

FWIW, I slotted a diffuser into my LED panel, and pointed the lens directly at that. The hood was in contact with the diffuser.

Mechanical shutter? Could be because the shutter is not in the same plane as the sensor, even if the slit widths are right.

The differences are so minute, it really sounds like rather pointless nit-picking.

Shutter not in the same plane as the sensor??? How can that happen??? 😀

Yes, it's mechanical shutter - D7200 only has mechanical shutter for stills.

In this case, like Bernard, I'm sampling a small square area at the centre of the sensor. I'm sampling 512x512 pixels or about 2mm x 2mm.
The exit pupil is about 73mm from the image plane. Na ~= 1/4. Slit width ~= 0.9mm at "1/8000" and full travel speed (~7m/s).

Do you have an estimate for the separation between the first and second curtains (in a direction normal to the sensor) ?

If the curtains were travelling at constant speed, I think I'd expect the overexposure on one side of the slit to roughly compensate the underesposure on the other.

More head-scratching required.

A mechanical focal plane shutter has to be above the sensor stack. That means that the light that falls on the sensor can be wider than the slit width of the shutter.