Archive for the ‘eyes’ Tag

Dynamic Range II: The Eye vs. The Camera   13 comments

Abandoned oilfield in western Oklahoma now blooming with flowers and a magnet for birds and coyotes.

Abandoned oilfield in western Oklahoma now blooming with flowers and a magnet for birds and coyotes.

Last week I posted an introductory article on dynamic range.  I want to start diving down into the subject a little more this week, starting with the best visual capture device I know:  the human eye.  The images here are both from my point and shoot here on the plains where I’m working, and also some from the archive.

Dynamic range, though technically expressed as a ratio, is more simply expressed in terms of stops, as in stops of light.  If you hold shutter speed (and ISO) constant and open your aperture from f/11 to f/8 you have brightened the image by 1 stop.  You’ve allowed twice the amount of light to enter the camera and be detected by your sensor or film.  For every one stop you either double or halve the amount of light.

Small waterfall along Oregon's Sandy River.

Small waterfall along Oregon’s Sandy River.

Our Amazing Eyes

So let’s start with your eyes.  Although the internet has a wide variety of answers to the question, most agree your eyes have a dynamic range of about 20 stops from darkest to brightest.  That means you can detect at least some detail in the darkest and brightest parts of that enormous range at the same time.  We don’t usually need to deploy all this range at once of course.  Instead we shift and adapt (very quickly!), using different parts of our dynamic range under varying conditions.  If you allow for pupil dilation our range increases to 24 stops!

We do have our visual limitations.  Our eyes start to fail us in very bright or very dark lighting conditions.  We nevertheless can detect enough detail for recognition of threats when either looking into deep shadows at dusk or the rising sun at dawn.  Remember each stop of light is accompanied by a doubling or halving of the amount of light.  So despite the fact that some other animals put us to shame in other visual abilities, it’s quite the impressive dynamic range we’ve got.

Given the above, you probably are not surprised that cameras, even the best, cannot match the human eye’s abilities in the dynamic range department.  At least when it comes to “normal” daylight exposures.  At night you can leave the camera aperture open for extended periods and collect the scattered light photons that, while our eyes may detect them, simply don’t end up translating into good clear images in our brains.  Our cones (color receptors) are especially lazy at night.  It’s the reason we are so amazed when objects in the night sky are rendered in stupendous color.

So unless the future sees us evolve into nocturnal creatures, our eye-brain visual system will remain limited at night.  Of course our brains have used our hands to invent devices to extend our vision into the nighttime realm.  So enjoy those images of space you see, both the deep-sky telescope images and the star-scapes that have become such popular fare on the web.

Violent storms pass (that included funnel clouds) pass away from Oklahoma farmland.

Violent storms (that included funnel clouds) pass away from Oklahoma farmland at sunset.

Wahclella Falls, Columbia Gorge, Oregon.  This is a very low-contrast image requiring virtually no dynamic range.

Wahclella Falls, Columbia Gorge, Oregon. This is a very low-contrast image requiring virtually no dynamic range.

Dynamic Range of Cameras

So let’s get to the question that sparked my interest in this subject in the first place: what can cameras see, and does it matter?  If you look into this on the internet, you’ll come across all sorts of over-complicated camera test results, graphs and data until it’s coming out your ears!  It may come as a surprise that film (at least negative film) can generally capture more dynamic range than digital sensors can.  This is debated (of course) on the internet, but it’s pretty much true.

The reason I say “generally” and “pretty much” is that firstly, comparing film and digital in terms of dynamic range is a little like comparing apples and oranges.  Film handles tonal variation differently (see Caveats below), and is nonlinear.  Digital sensors are linear.  In fact, in this way film is closer in behavior to your eyes than digital sensors are.  Secondly, film is noticeably better at handling highlight dynamic range (bright end of the scale), whereas digital has advantages on the shadow (dark) side of things.  Your eyes can also see more detail in shadow than in highlights.  Digital cameras mimic your eyes in this way, but as any film enthusiast will tell you, they don’t do quite so well with highlights (they would describe it less kindly).

It is very hot where I am right now, so here's a shot of Oregon's Faery Falls in winter freeze.

It is very hot where I am right now, so here’s a shot of Oregon’s Faery Falls in winter freeze.

All that said, digital camera makers have been working hard on increasing dynamic range, while film is not receiving that much attention.  So you can expect all this to be a moot point in the near future.  Currently, the best digital cameras for dynamic range, the Nikon D800 and other high end DSLRs, and (especially) the new digital video cameras, can supposedly record dynamic ranges of up to 14 stops.

But that’s at low ISOs.  Think about those starscapes I mentioned above, those images of an improbably colorful and bright Milky Way you see soaring over everything from mountains to farm tractors to the Eiffel Tower!  That is not really a demonstration of the camera’s dynamic range but its low-light capabilities.  When the photographer cranks up the ISO to create those images, she is cranking down on the camera’s dynamic range.

That’s enough for now.  This little miniseries on Dynamic Range will continue next week.  Thanks for reading!

The Lower Columbia River flows peacefully seaward at dusk.  Oregon's Mount Hood in the distance.

The Lower Columbia River flows peacefully seaward at dusk. Oregon’s Mount Hood in the distance.

Eyes: Our Biggest Blessing   Leave a comment

I have heard people claim that their favorite sense is their hearing, or their taste (foodies), or some other sense.  But it is the eyes, your vision, that should be your favorite.  And not just because it is my favorite sense (haha).  It’s because you are a member of the human species.  We have always relied to a great extent on our vision.  I feel rotten for the whole day when I see a blind person, and I feel inspired when I see them enjoying life.  My eyes are my most precious possession.

This I say because just yesterday I almost lost one.  I was on my horse, enjoying a long ride, when I felt a bit adventurous and took an off-trail route through the jungle that is Oregon (our moist climate has the predictable effect).  I was leading my other horse Khallie, a filly who is occasionally a pain in the butt to pony (horse-speak for leading).  We were going along, through brush where I should have dismounted and walked.  I turned briefly to see what Khallie’s problem was, and when I turned back I got a rigid stick right in my left eye.

Khallie (left) and her mom, Gold Dancer, take a break from a ride in some delicious grass.

The three amigos hang out at the barn after their post-ride bath.

Khallie and I under a full moon.

I haven’t experienced this much pain in quite awhile.  I sat on GD’s back howling, shaking with worry that I had put my eye out.  But when I slowly opened my bloody eye I realized that, just in time, I had apparently closed my eye.  Instead of eye damage, I gashed my eyelid instead.  Whew!  Now my horse GD (for Gold Dancer) normally does not like to stop.  She fidgets and tosses her head until I finally relent and give her rein.  But this time she stood stock still for a full 10 minutes while I recovered.  Actually, both horses stood like statues.  It gave me faith that should I really be hurt badly my horse would carry me home whether I could sit upright or not.

Fortunately I was near a clean stream, so I went over and washed out my bloody eye.  What a close call.  GD thought we were going to cross the stream and I had to stop her from dragging me into the water.  Khallie, as usual, believed we were all about to drown.  Her fear of water is something I’ve been working on.  This morning I woke with my eye sealed shut by the dried blood.  A little worry, some leftover pain, but I was okay.  I cleaned out the wound and will be happy to walk around for the next few days looking like I was in a barroom brawl.

Now I sit here thanking my lucky stars for a good pair of eyes.  To this point in life, I have never even come close to needing glasses.  I do not have the hawk-eyed vision at long distance that I used to have, but my eyes work just fine at all distances.  The bright blue eye color of my youth has dimmed a bit, but I still have that ice-blue going on.  I’ve been told that they can look pretty or very cold depending on whether I am happy (nearly always) or angry (almost never).  I think my eyes are one reason I have always had trouble hiding how I feel.  My feelings are always on full display.

Khallie, an arabian filly who is my special little girl, perks her hears forward in curiosity.

GD in a shot taken from the saddle.

So please consider your eyes the next time you count your blessings.  Although we no longer hunt to survive, there are so many things we do where vision is critical.

And for me, the most indispensable use of my eyes is the ability to see the incredible beauty of this planet we call home.  I am now going to go out for a hike and shoot pictures.  And all along I’ll be thanking God for giving me those two incredibly intricate organs in my face.

%d bloggers like this: