High Plains Drifter

A test of super-ultra long exposure with Nikon D3.  After work on Sunday night, July 6th, I decided to drive south to my favorite nearby photography location — Big Basin Prairie Preserve.  I wanted to give the Nikon D3 + 14-24mm f/2.8 lens combination a try in some really low light conditions — the night sky.  I really was curious to try a super-ultra long exposure (greater than 30 minutes) to see how the sensor noise was leaving the shutter open for so long.  Digital imaging sensors will accumulate "hot" pixels the longer the shutter is left open.  As technology has improved in digital imaging sensors, the duration one can leave the shutter open without introduction of noise has greatly improved over the years.  I remember my very first digital camera was a point and shoot Nikon Coolpix 950.  You couldn’t take 8 second exposures without introducing all sorts of horrible "hot" pixels dotting your image.  When I then got my first digital SLR (Nikon D70) one of the first things I noticed was the absence of hot pixels at 8 to 30 seconds!  They were absolutely clean of noise at low ISO.  That being said, image sensor noise ("hot" pixels) started showing up at super long exposures of 5 to 10 minutes.  Also, this thing called "amp glow" also started showing up in the form of a pink blotchy area at the corner of a frame due to the sensor heating up.  Internal camera digital noise reduction can eliminate much of this by a simple technique called frame subtraction (whereby taking another black-frame exposure of the same time length and subtracting that from the original image).  The only kind of photography really needing this kind of long exposure is star trail photography, which require 30 minutes to 3 hours worth of exposure time, depending on how much trailing you are interested in for your shot.  

Along comes the D3.  I was really curious how long I could keep the shutter open on this camera before the hot pixels and/or "amp glow" became too much of a problem.  On the old D70 I had, the amp glow started really becoming a problem at about 8 to 10 minutes exposure time.  Below are two versions of the same image from the D3 I shot last night with a shutter speed of 3,650 seconds (1hr, 0min, 50sec).  The first is the processed version adjusting the exposure compensation, levels/curves, noise reduction in Adobe Lightroom:

In the 2nd image, which is unprocessed, you can barely pick out the slight purple-ish hue at the very bottom of the frame.  You really have to look closely, but it’s there.   This is a ONE HOUR exposure, and you have to squint to find the amp glow.  I think Nikon finally got it right with the D3 and hot pixel/amp glow digital sensor issues for exposures longer than 10 minutes.  Some of the star trails, though, have some holes in them, as if it wasn’t exposing properly for a bit during the one hour.  I can’t entirely explain what was going on there.

But here is what really excited me…

Milky Way looking south.  Nikon D3, 14-24mm f/2.8 lens @ 14mm.  Exposure 99s @ f/2.8, ISO 1250 

I couldn’t believe the detail I was able to capture here.  Of course, the artificial lighting on the horizon was a bit of a pain, but given this shot, I am excited to get out on another clear, moonless night absent of any horizon lights to shoot the Milky Way again.  A full album of images from last night (just 7 images), is available. 

Mike U