Snow falling (dashes instead of lines)

[JGU1956]

Can someone explain why the falling snow in this photo looks like dashed lines instead of continuous lines?  I like the photo but this artifact spoils it.  I would have thought falling snowflakes would look like longer lines than this- not frame to frame of course, but the dashes just don't look right.

It was taken with a Panasonic GX7 and Olympus M 12-40 zoom.  No flash, ISO 3200, 1/20 sec, f2.8, and +1/3 EV exposure compensation, using mechanical shutter, not electronic shutter.  The only significant thing in post was to soften the glare from lights, but in any case that didn't make any difference to the appearance of the snow, either in the raw or as an exported jpg.  The temperature would have been below zero (celsius) but not by much so I doubt that had anything to do with it.

Thanks!

John.

[earlybird]

My first guess would be that the "street" lights are flickering.

[aduke]

I, too, think that it could be the flickering of the lights if they are powered by alternating current and decreasing output 50 or 60 times per second. The other thought I had is that perhaps the snowflakes are rotating, thus changing brightness. This is unlikely in that most of the snowflakes would be showing the same number of rotations during the 1/120 second exposure.


Alan

[JGU1956]

Thank you- that sounds very plausible.  I don't know what type of lights they were.  However if there are about 5.5 "dashes" per 1/20 second, that makes 110 Hz (I think).  I need to go back and check what sort of lights.  Any excuse to travel.

[Jeremy Roussak]

Thank you- that sounds very plausible.  I don't know what type of lights they were.  However if there are about 5.5 "dashes" per 1/20 second, that makes 110 Hz (I think).  I need to go back and check what sort of lights.  Any excuse to travel.

AC at 50Hz would give 100 flashes per second: two per cycle. If my 40-year-old physics memory is correct.

Jeremy

[NancyP]

AC flicker. Incidentally, Canon action oriented cameras, starting with 7D2, have a flicker-eliminator for high shutter speed shots, apparently the metering system feeds back to the shutter to delay shots falling on the flicker frequency. I don't shoot indoor sports, but I can see that for those who do so, this would be a great feature.

[JGU1956]

Thanks everyone.  Obviously an elementary mistake.