Sleet and the dashed line

Post Reply
User avatar
YakRunabout
Posts: 784
Joined: Thu Feb 19, 2015 10:34 am
Location: Magnolia

Sleet and the dashed line

Post by YakRunabout »

Earlier this evening the weather radar indicated that the green associated with the never-ending, constant barrage of drizzle was changing to a thin line of pink and then to the blue of snow!! I went out to see if this change had actually occurred, and the sound of drops bouncing off the roof indicated that we were at least into the pink.
I went back in to get my phone to try a picture. By now there was some float associated with the fall, so closer to snow! I had a 700 lumen LED flashlight beam into which I directed the camera. The camera flashed also. So a fairly slow shutter resulted in the pic below. Just ignore the finger – you know – I was holding the phone and flashlight and trying to see that little spot on the screen to make the camera operate – I was happy to get any picture!

So, anyway - I thought the picture looked kind of cool! Better than I expected. But then the dashed lines confused me. Why the dashed line? The camera flash should be steady and quick? The shutter speed fairly slow, accounting for the track lines, and the flashlight beam should light up for the full exposure. Aren’t those lights steady? The resulting track looks like a strobe, like that picture of a bullet going through an apple! Is the LED light not steady?

A quick web search indicates that there is some flicker with LED lights and AC current, similar to the flicker of a fluorescent light. This is on a battery so a DC current – is there still some flicker that shows up due to the speed of this sleet?

Anybody have an explanation?
A diversion while we wait for better weather!
Attachments
1207172033.jpg
Kayak Kid
TKF 10,000 Club
TKF 10,000 Club
Posts: 34151
Joined: Mon Dec 29, 2003 12:01 am
Location: Houston,

Re: Sleet and the dashed line

Post by Kayak Kid »

About ten minutes ago, it started snowing pretty hard at my house. Some is actually sticking. Too bad that my grandson is already sound asleep. My wife wouldn't let me call him.
User avatar
Ron Mc
TKF 5000 Club
TKF 5000 Club
Posts: 5675
Joined: Fri Jan 20, 2006 6:12 pm
Location: downtown Bulverde, Texas
Contact:

Re: Sleet and the dashed line

Post by Ron Mc »

even Corpus is supposed to get a 3-inch snow accumulation.
Intellicast shows its snowing in the Valley and northern Mexico.
User avatar
Crusader
Posts: 613
Joined: Fri Feb 07, 2014 7:28 pm

Re: Sleet and the dashed line

Post by Crusader »

> Anybody have an explanation?

Did your camera use HDR mode by any chance? (where it takes bunch of pics and interpolates between them)

Edit: no... HDR usually takes 3 pics.

I think there were two sources of light -- one was flickering, another -- not. There are 3 streaks on the left that don't have dashed pattern. Maybe your camera flash?
User avatar
kickingback
TKF 5000 Club
TKF 5000 Club
Posts: 5178
Joined: Thu Feb 18, 2016 3:24 pm
Location: Houston, Texas

Re: Sleet and the dashed line

Post by kickingback »

I think the LED has "bursts" for brighter light. The LED takes the electricity and pumps it out and as it does it uses the highest rating and then quickly goes lower and back to full power in fractions of a second to make the LED look like a strobe. Although not noticeable by the naked eye you can see the strobe effect in pictures. I think it just the amount of power supplied to the LED. Try low batteries and see if you get the same result.
User avatar
mmwaggie
Posts: 126
Joined: Thu Jun 05, 2014 12:28 pm
Location: The Woodlands, TX

Re: Sleet and the dashed line

Post by mmwaggie »

If you used a digital camera it is called the rolling shutter effect.

https://petapixel.com/2014/10/13/math-b ... henomenon/
User avatar
YakRunabout
Posts: 784
Joined: Thu Feb 19, 2015 10:34 am
Location: Magnolia

Re: Sleet and the dashed line

Post by YakRunabout »

Rolling shutter effect - an interesting effect - thanks for the link. I will need to test out my cameras for this. The camera that I used is on my LG cell phone.

The rolling shutter effect appears to distort the moving object but not to give it the dashed line appearance. The link example was for an object with angular motion. The sleet was in linear motion, but at an angle across the screen. It seems that the rolling shutter effect would possibly bend this path, but not to dash the line - thoughts?
User avatar
Cuervo Jones
TKF 2000 club
TKF 2000 club
Posts: 2029
Joined: Thu Nov 06, 2008 1:12 pm
Location: Hurtling towards oblivion with a smile

Sleet and the dashed line

Post by Cuervo Jones »

Inter-dimensional ufo’s called “rods.”
https://en.m.wikipedia.org/wiki/Rod_(optics)
Then again, probably just weird optics.


Sent from my iPhone using Tapatalk
User avatar
Ron Mc
TKF 5000 Club
TKF 5000 Club
Posts: 5675
Joined: Fri Jan 20, 2006 6:12 pm
Location: downtown Bulverde, Texas
Contact:

Re: Sleet and the dashed line

Post by Ron Mc »

YakRunabout wrote:Rolling shutter effect - an interesting effect - thanks for the link. I will need to test out my cameras for this. The camera that I used is on my LG cell phone.

The rolling shutter effect appears to distort the moving object but not to give it the dashed line appearance. The link example was for an object with angular motion. The sleet was in linear motion, but at an angle across the screen. It seems that the rolling shutter effect would possibly bend this path, but not to dash the line - thoughts?
What you have is rolling shutter effect. Sleet ice is making a straight line (it's not a propeller) and with the digital scan recording pixels, rolling shutter accounts for the effect perfectly.
Post Reply