Luminous Landscape Forum

Equipment & Techniques => Landscape & Nature Photography => Topic started by: JGU1956 on October 26, 2015, 02:57:12 pm

Title: Snow falling (dashes instead of lines)
Post by: JGU1956 on October 26, 2015, 02:57:12 pm

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.

Title: Re: Snow falling (dashes instead of lines)
Post by: earlybird on October 26, 2015, 03:03:09 pm

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

Title: Re: Snow falling (dashes instead of lines)
Post by: aduke on October 26, 2015, 03:10:21 pm

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

Title: Re: Snow falling (dashes instead of lines)
Post by: JGU1956 on October 26, 2015, 03:41:07 pm

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. ;D

Title: Re: Snow falling (dashes instead of lines)
Post by: Jeremy Roussak on October 26, 2015, 03:45:49 pm

Quote from: JGU1956 on October 26, 2015, 03:41:07 pm

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. ;D

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

Jeremy

Title: Re: Snow falling (dashes instead of lines)
Post by: NancyP on October 26, 2015, 07:16:25 pm

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.

Title: Re: Snow falling (dashes instead of lines)
Post by: JGU1956 on October 30, 2015, 07:11:10 pm

Thanks everyone.  Obviously an elementary mistake.  :)