Stars, Waterfalls and Long Exposures

Well this week’s WIIW seems to have stumped people.

 I thought this image would be easy, but neither Linda G’s guess of : “Raindrops (or water drops, anyway) on a pane of glass in the dark?”; or Old Kitty’s “I'll say padding/insulation stuff!”;  were close.
I can see the water drops by the way…
So what was the image? Well the answer is kind of related to a question that Michael asked about this piccie of the day. 
Michael asked “I wonder if they used an overexposure to capture the look of the water like that?”
First up my inner child has to stamp his feet and say “MY PHOTO” – like 99.9% of piccies on this blog the Mackenzie Falls piccie is one I have taken. :-)

Now I have my tantrum out of the way  I will say, you are kind of right Michael, but it is more a case of “long exposure” rather than “over exposure”.  For a normal photograph (if there is such a thing) a camera is set for a fairly fast exposure with the shutter open for about 1/250 of a second.

If you use a shutter speed like that on a waterfall you get an image like this one I took recently of the Upper Ebor Falls. It was raining (you can see the rain on the lens) and I didn’t have a tripod so I just snapped a quick piccie.

The short exposure “freezes” the water.
 And on this piccie of the Lower Ebor Falls

SO to catch the look of motion I mount the camera on a tripod, narrow the aperture to limit the light coming in the lens and use a long exposure sometimes as long as a full second.
With a long exposure the water blurs due to its motion which generates an illusion of movement.  The only problem is sometimes the vegetation around blurs too as it moves in the wind. Like in this piccie of the Hopetoun Falls.

The trick is to get enough light reflected from the water without actually overexposing the piccie like this piccie of the lower Ebor Falls.

So what about the WIIW image?

Well other than aiming to blur motion, the other thing a long exposure is used for is when there is very low light. My WIIW piccie was taken outside here in the crystal clear skies we get in the mountains (when it isn’t raining). For this image the objects blurred a bit due to the camera moving in a breeze and in the extremely long ten second exposure the objects moved a little them selves.
I give you the Southern Cross and the “Coal Sack”