Friday, May 6, 2011

Flying Rods

The surface of the River Wensum on Wednesday was a mass of flying 'gnats' and as they changed speed they appeared as flying rods with lots of rotating wings. I have never seen this with the naked eye before. The photos are taken at 1/1000th (not quite enough to freeze wing movement, 1/40th (about what my eye saw) and 1/15th both up wind where they moved slower and downwind with very fast movement. Has anyone else witnessed this - the multiple images seen without the camera were quite new to me.


Ian said...

An interesting effect.

First thought:

Could it be something to do with the shutter blind moving as a slit across the sensor. If the gnat flies faster than the slit moves then it might appear in several places across the sensor by "overtaking the slit".

Although I would have thought a gnat flying in the opposite direction to the slit would appear just once.

Second thought:

Maybe the image stabiliser is moving the lens?


Ann Miles said...

The effect was visible without the camera though not so obvious - it was not an effect only of shutter or stabiliser.Our eye I think records at about 1/60th second and, yes, the image taken at 1/50 was the closest to what I saw

Ian said...

I had not fully appreciated that you were seeing multiple images by eye and that the "single" gnat image was the 1/1000 sec exposure. I was thinking the image exposures were the other way round.

So it is as though the gnats were static, then moved a very short distance very rapidly and stopped again, repeated multiple times/second. If so could it be linked to their wing beat frequency?

Ian said...

One more thought. We have seen the stage affect from a stroboscopic light causing a stop-motion movement as if in a Charlie Chaplin movie.

Could you have been watching the gnats whilst a strobe type of light lit them? This was perhaps the sun through some waving branches or reflecting from ripples on the water?

Ann Miles said...

I think the best explanation would be the stop start motion to explain the images and why they were visible with the naked eye. Obviously occurring at enormously high speed. Thanks for all your suggestions!

Ann Miles Photography - My Favourite Images of the Past10 years or so