Depth of field? What depth of field?

Giving your images a distinctive and interesting look is always a challenge but there are several tools available.  Depth of field is a popular “art” tool that enables you to quickly bring the viewer’s eye to the exact subject you want them to pay attention to right from the start.  To use effectively, though, you need to understand what is the depth of field you’re going to get for your composition?  It’s a tricky question – each lens behaves differently based on aperture, distance from subject, focal length, etc.  You almost have to experiment with your bag of lenses and learn.  Or  you can look up the depth of field chart for your lens and memorize it.  My problem with the latter option is I have a hard time visualizing what a 3 inch depth of field or a 500 foot depth of field looks like.  I usually just play around with my lenses and see what they deliver.

It’s especially daunting with telephoto lenses.  The depth of field for these starts out short and seems to only get smaller.  Here’s an example:

I liked the little snowball sitting in the sunlight so I wanted to make an image of it.  I was sitting at a picnic table with my camera on my tripod, using my 300mm manual focus Olympus lens (from the OM film camera days).  On my digital Olympus body this is equivalent to a 600mm lens on a full format camera.  I’m about 10 yards from the snowball so this long lens really gets up close.  I think the aperture was around f/11 or f/16 since I was looking for maximum sharpness.  Notice the area that’s in focus – it’s a narrow band where the snowball is in the sunlight.  The grass in the foreground and snowbank in the background are completely out of focus.  Which is what I wanted – you eye should go right to the snowball.  But how much depth of field is really there?

100% crop from previous image

If I zoom in on the image you can see the depth of field is REALLY narrow; according to one online DOF calculator it comes in at 4 inches.  Which means if I was making an image of a deer’s face using this distance and settings, their eyes would be in focus but their ears and nose might not be – and this is at a small aperture (not that I expect to be 10 yards from our local deer, at least not unless I’m holding a handful of corn for them).  It does give a cool look, though, as it centers your eye right on the subject I want you to pay attention to.  Like most specialized tools – and a long telephoto lens is definitely that – you get the best results when know the lens’ limitations and operating within them.

In my youth as a photographer I was always trying to get maximum depth of field, especially with landscapes.  I’ve learned now that shortening it up can truly bring some interesting features to your pictures.  Just have to know when and how to use the technique effectively and what tools work best to deliver on it.

Look down to see up

In September during my workshop we had the opportunity to photograph the full moon about a day or so before complete fullness.  What this means is just as the moon comes over the horizon there remains enough sunlight to illuminate the landscape and you don’t get the blown out highlights in the moon.  Most of us were working on a typical moon-over-mountains composition, something like this:

ISO 100, 200mm, 1/15 sec., f/8

Standing next to a small pond I noticed the scene’s reflection in the water but with the addition of grasses on the shore and some vegetation floating on the surface.  I thought it had a nice abstract look to it so I recomposed and make this image:

ISO 100, 200mm, 1/30 sec., f/5

Having everything razor sharp was of less interest to me for this image; I wanted to capture groups of shapes and tones that would define the composition more than simply a picture of the moon.  Reminded me of advice I got from a black-and-white photographer once.  He said as you are composing, look at the scene and squint to the point where all detail is gone and all you see are the blobs of light and dark.  Then compose to where those blobs form an interesting image.  Everything else will usually fall in place to compliment the composition.  It’s a good way to improve seeing for someone who easily gets distracted by the fine details and misses the complete picture!

By the way, reflections usually lose about one stop of light so you’ll have to adjust to keep your exposure when moving from the original scene.  And sometimes you’ll have to manually focus in order to get what you want to be in focus – autofocus sometimes can’t distinguish between the reflected image and something on the surface of the water.  For the second image I opened my aperture to shorten the depth of field and manually focused on the reflected mountain.

Sumac study

Growing up in the southeastern US my only encounter with the word sumac was when the adjective poison was used.  I never really learned what to look for in the woods in spite of years seeing drawings and photos, mostly because I’m apparently not affected by any of the “poison” weeds.  So I’d just ignore paying attention.

Here on the Plains, though, the term sumac takes on an entirely different meaning, especially this time of year.  It’s a harbinger of autumn, changing its identity from leggy, green leafed shrub to brilliant red beacon seemingly within days of the temperature going down to post-summer levels.  Drive by a place day in and day out with out noticing it and then suddenly one day there’s this near-neon hillside sea of red.

This is the smooth sumac, one of many different species of this world-wide genus.  I think it’s considered a pest in this part of the world – it’s the only reason I can think of that would explain all the farmers cutting it out of their fields.  Probably because it’s tenacious and hard to plow up, or because cows don’t eat it so it takes up valuable pasture space.

Turns out, though, it has economic value in various parts of the world.  The fruit (small seed-like objects that grow in a cluster at the plant’s top) is ground up and used as a spice in various Middle Eastern dishes to add a lemony flavor.  In Japan and other parts of East Asia fat is extracted from the plant and used to make wax candles or lacquer.  In North America the fruit is soaked in water to make a type of tea and the stems were used to make pipes.                           Source:  http://en.wikipedia.org/wiki/Sumac

With the dry weather this year I doubt the colors are going to stay long.  I’m already seeing sumac leaves turning brown and the fruit pods drying out.  I’m glad to see the colors, though, since it means autumn is right here and other plants will follow suit with their own tribute to fall.

ISO 100, 48mm, 1/640 sec., f/3.5

ISO 100, 90mm, 1/500 sec., f3.5

ISO 100, 71mm, 1/1600 sec., f/2.5

ISO 100, 100mm, 1/1000 sec., f/2.5

ISO 100, 100mm, 1/640 sec., f/2.8

Color quirks

I find it odd how my personal color palette has developed.  I don’t mean in a fashion sense (whatever’s comfortable and functional, that’s what I wear) but rather through the viewfinder.  It came to my attention when a friend was asking for advice on images to decorate their home’s interior, which is nicely done in greens and yellows (think fresh spring colors).  Looking through my portfolio I realized these are not colors that show up a lot as the primary theme in my images.  Surprising.

Even more surprising to me is how I’m drawn to the cool and warm colors – blues and reds – but hate their siblings of purple and magenta, casts I’m continually fighting in my slide scans.  For someone who enjoys cold weather it’s amazing how often warm colors of sunset and autumn show up in my images.

Some of it is simply lighting.  Using the late afternoon sun as a way to sculpt contrast on objects pretty much means you’re using warm light.  The atmosphere strips out so much of the blue wavelengths as the sun passes through it at sundown that getting a cool perspective is just about impossible (without some digital adjustments, of course).

ISO 100, 35mm, 1/60 sec., f/2.5

It’s similar in the early morning however the air at sunrise hasn’t accumulated all the dust from a day’s thermal activity so there’s less particulates in the air to scatter the light.  You can get some nice cool tones just before sunrise on a clear day as the blue sky radiates those shorter wavelengths everywhere on the ground.

Photographing flowers as much as I have now I’ve learned that truly yellow objects don’t appear to have much contrast and so the details are very hard to bring out in an image.  I don’t know if this is unique to yellow colored objects or if yellow flowers just don’t have that much detail.  It may be one reason there’s so little yellow in my portfolio – frustration at reviewing shot after shot of yellow things that just sit there without any characteristic depth to them.

ISO 100, 35mm, 1/40 sec., f/2.5

I do see one issue with these late afternoon, close-up photography quests.  With such a small depth of field it’s hard to hold focus on an object by just leaning down to photograph it.  The small swaying back and forth our bodies do in order to maintain balance, when magnified by a lens at close range, is enough to move the subject in and out of the actual focal point.  Tripod time, obviously.  Although sometimes you just can’t take the time needed to set up all that gear, get it oriented and then make the image.

ISO 100, 35mm, 1/60 sec., f/2

Because I was leaning over in the grass above this bush there’s very little of this mantis that is actually in focus but he contrasts nicely against the flower so I did get some detail in the image.  One of the more creepy aspects of mantis behavior is how they twist their head around to watch you – it’s not something we expect from insects.  This one did let me change positions a few times to get different compositions, but he kept a close eye on me the whole time.  With his antenna laid back from his head I got the sense I was disturbing something important but wasn’t so much of a threat it merited moving to a new flower.

Curse the light!

When you are setting up the exposure for your image (on any setting other than Auto/Program) it’s a game of trade-offs as to what you can do in order to get what you want.  Modern cameras have so many built-in tools to do this work for you it’s sometimes difficult to know what’s really going on in the camera.  So you get images back and think “this is not what I wanted the picture to look like” and wonder how your camera screwed it up.

Fortunately, there’s a setting on most DSLR’s that enables you to quit blaming the camera and start blaming yourself – Manual.  Yes, you get to set everything with respect to exposure settings.  And what you set is exactly what you will get.  Sometimes that’s exactly what you want….

Not that it’s any less frustrating; it’s just that you can’t beat up on your equipment any more.

Here’s an example.

ISO 100, 50mm, 0.4 sec., f/9

All I wanted was an image with the log and rock in focus, and an obvious small wave breaking on the shore.  Well, with these settings I do have both the rock and log in focus, but the wave is just a jumbled blur.  Obviously I need a faster shutter speed.

ISO 100, 50mm, 1/50 sec., f/2

There – I opened the aperture to let in more light, giving me the ability to have a faster shutter speed to keep the same exposure.  And I’ve got my wave.

Wait, though.  The log is in focus and the rock isn’t.  Obviously my bad – focusing on the wrong place.

ISO 100, 50mm, 1/60 sec., f/2

Ahh – now the rock is in focus and I’ve still got my wave.  It’s looking good.

Hey, now the log is out of focus!  What gives?

Oh, I see.  I’m fighting a depth-of-field problem.  At this aperture (f/2) the DOF is very narrow, narrow enough that focusing on one subject means the other will be out of focus.  Obviously I need to get a bigger DOF by closing down the size of the aperture.

ISO 100, 50mm, 2.5 sec., f/22

Yes – now everything is in focus.  But I’ve lost the wave!  It looks like the lake is completely still!  What’s wrong?

Nothing is actually wrong.  All four of these images are correctly exposed; i.e., capturing the same amount of light.  The camera is simply, and accurately, doing what I tell it to do.  So why can’t I get the composition I want?

I have two camera controls essentially fighting against each other.  For the amount of light I’m letting into the camera (exposure), a fast shutter speed that will render the wave I want requires I use a wide open aperture to give me enough light.  But a wide aperture results in a very narrow depth of field, meaning the rock and log won’t be in focus together.  Close the aperture down to get a wider depth of field and I let less light into the camera; to compensate I have to use a longer shutter speed to let more light in, which will not “stop” the wave as it travels to the beach.  I need enough light to use a smaller aperture AND a faster shutter speed.  What am I going to do?

There’s one more camera control I can use.  I can change my ISO setting to a higher number (notice these are all ISO 100).  Using higher ISO numbers basically makes the digital sensor more “sensitive” to light, thereby changing the exposure conditions of the scene (as seen by the camera) and allowing me to use a faster shutter speed and smaller aperture.  I imagine changing to ISO1600 will give me what I want.

There’s no picture to prove this works because I didn’t make one at that setting.  ISO1600 on this camera results in unacceptable noise in the image, especially in the shadow areas.  It will work, though.  Going from ISO100 to ISO1600 is an increase of 4 stops of light in the image.  I can go back to 1/60 sec. shutter speed (I know that will stop the wave) and close down the aperture from f/2 to f/8 (4 stops), giving me a depth of field sufficient to bring both rock and log into focus.  I could probably take care of most of the noise using software.

I could also have made this image earlier in the day when the sun was higher and giving me more light.  Possibly I could have used a reflector to concentrate more of the existing light on the scene (hard to do without an assistant).  Or I could use a small flash to increase the amount of light (but probably create undesirable shadows).

So, as I said, there are always trade-offs.  The master photographers use these to their advantage, crafting exposures that make the settings work for them instead of having to work around the settings.  Practice and experience – and paying attention to what you create and how.

Watch what you can’t see

Just because you think you know what you’re doing doesn’t mean you’ll actually get the result you expect.  The basis for some great science and technology finds or stuff to fill the waste bin of history.

Also, garbage in – garbage out.

Fighting the restrictions of a narrow depth of field you’ll find all sorts of techniques, gear, software, etc. offering to help you overcome the physics of lens design and light paths.  Focus stacking is popular – has been way back to film days – and interesting in how it assumes to provide a substitute for our eyesight.  To enable us, finally, to make an image that looks the way our eye really sees things.

Except it’s a lie.

Focus on reading the words on this screen.  Now, using your peripheral vision (you know, the corner of your eye), “look” at something about a foot to the right or left of the screen but don’t take your focus off the words on the screen.  What can you really tell about the details of that object off to the side?  A little blurry, isn’t it.  Here’s a better test.  While focusing on the words in the top part of a newspaper, “look” over the top at something in the distance, again using your peripheral vision.  What kind of details are you making out in that distant subject?  Not many, you say.

It seems our eyes have a depth of field as well, not only near to far but also around the circumference of our vision.  So, all those images of three dimensional objects that are sharply focused in all dimensions don’t actually mimic our eyesight.  They mimic the eyesight we wish to have.

Since they are artificial constructs, though, it means they lend themselves to interpretation and alternative versions.  From whence comes art, human and otherwise.

Taking a lot of images of a subject, each slightly focused on a different plane of the subject, and then “stacking” them together in software can result in one of those 3D objects with all aspects in focus.  Or it can result in what you see above.  Does this ball of bands exist in some alternative dimension, some slightly askew reality that periodically bleeds over into ours when we’re not looking?  Possibly, if you want to believe software programs have a mind of their own.

Your digital work seems to be becoming only as smart as your software.  The image above is not digitally enhanced, at least not in the manner you’d expect.  It’s the result of not turning on the right switch in my software, of selecting the wrong option (well, wrong unless I actually wanted this look to the image).  Instead of asking the software to deal with geometric distortions caused by moving the focal plane for each image in the stack, I simply told it to reposition each image to make sure it lined up with the others in the stack.  Except that’s not possible.

Each image in the stack is slightly different because when I refocused on a new part of the ball, all the other out-of-focus parts got slightly more out-of-focus.  Each variation adds up.  When the software was told to simply reposition all the images and line them up, it did the best it could, but in the face of an impossible task, decided to get creative.  The algorithm essentially said, “I’ll line up these few areas I can work with but with the rest I’m taking a wild guess.”  Apparently the wild guess included ignoring exposure information and color balance as well, resulting in the strange glow that appears to emanate from the ball itself.

The correct switch literally tells the software to correct for perspective shift, the phenomena that is occurring when I shift focal planes.  See, the software is actually smart – it’s the operator that gives poor direction.  You know, garbage.

It does raise the question of what other type of images you can make this way and what would they look like.

Like this, I guess.

How would you like to see that coming your way while on a Yellowstone hike?

 

Look deeply

More from my tabletop education, this time on expanding depth of field through a subject.  One way is to close down the aperture to a small size (more than f/16) but this diminishes the sharpness which can be noticeable in a close-up composition.  The other way is to make many images, each one focused on a different point on the subject and then stitch them all together to give a deeper depth of field.

Keep in mind your lens has only one focal point that exists as a plane parallel to the sensor (or film).  Depth of field is the distance in front of and behind the single point of focus where our eyes don’t notice a change in focus.  It’s technically defined as the circle of confusion.  Think of a point that is perfectly focused by your lens.  As you move the point of focus back and forth the original point will start looking blurred or out of focus (confused, as it were).  The depth of field is simply the bounds between which a change in focus doesn’t make the point look blurred.  Depth of field is a function of lens construction and aperture size, which is why sharper lenses with wide depths of field are usually more expensive.

Anyway, here’s an image I made using the second method – many images stitched together.  One issue with this technique is it’s almost impossible to do out in the natural world – nothing sits still for long enough!

ISO 100, 1/250 sec., f/8

This was made from 11  individual images, each one focused on a different part of the flower.  I started with the deepest part of the bloom and worked my way out to the edges of the petals.  In Photoshop there is a command that will auto-align the set of images (to make sure everything lines up and there are no ghost lines in the final image) and then auto-merge all the images together.  I guess the command was designed to look for “in focus” areas because that’s what gets selected from each image to make up the final image.

It’s almost unrealistically in focus.  Our eyes don’t see it like this unless in a photograph so initially it looks odd but our brains quickly adapt.  Cameras don’t see it this way, either.  The macro lens I used to make this, at the distance I was from the bloom, has a depth of field measured in millimeters, even with the aperture fully closed down to f/22.  A single image focused on the stamens (those yellow fluffy balls) would show the edges of the petals and back of the blossom as blurred.

Sometimes a picture is worth more than we can imagine when it shows us something we can’t normally see.

Repeating Patterns

 

ISO100, 28mm, 1/10 sec., f/22

No new techniques or processing today.  Just liked the patterns in this image where the ripples in the sand mirror the small waves at the shoreline.  It’s an example of where the color would distract from the patterns so I converted it to black & white.  This lens is usually pretty sharp; I guess the softness in the image is due to the long exposure time and the wind blowing on my tripod.  It is nice to see such a broad depth of field – I think my camera was about one foot from the nearest part of the picture at the bottom and the sand is pretty detailed.

The lure of B&W continues.  Maybe it’s my bias toward sharpness and details in an image.  I like exploring all the little elements in a picture like this without wondering if the color balance is correct or being affected by warm colors next to cool colors.  Good to see digital conversion gives good results; now to learn how to get similar images using film from medium and large format.

A look at depth of field

Photographers seem to constantly talk about depth of field as if it’s some talisman that magically converts so-so pictures into works of art.  Or that explains why the photograph you thought was in focus suddenly comes out all blurry – of course it was an artistic application of depth of field…  Actually, there’s not much mystery to the concept nor its application once you realize how a camera lens operates and how our brain reacts to photographs.

When you focus a camera lens you are making a sharp image on the film or digital sensor, but it is sharp only along a pretty narrow plane that is parallel to your film or sensor.  For example, imagine you take a picture of the side of a barn, standing so that you are exactly 90 degrees to the side of the barn.  When you focus on the barn the side you focus on is a plane that is parallel to your film or sensor and it will be in focus.  If you could look closely enough at the image coming through the lens you would find that most of what is between you and the side of the barn is not in focus.  Because we need some amount of out-of-focus before we actually notice it, there is an area in front of and behind that “plane of focus” that we perceive as still being in focus.  That is the depth of field.

So if depth of field is the distance from the camera where everything appears to be in focus, why do some pictures have lots of blurry stuff and others don’t?  Turns out you can control depth of field by adjusting the aperture of your lens – that’s the f/stop thing photographers keep talking about.  Small f/stops like f/2 or f/4 will show narrower depths of field than large f/stops like f/16 or f/22.  Simply by changing the aperture you can give your photographs a different look, just don’t forget to adjust the shutter speed as well to get the proper exposure.

Buy why would you want a narrow or wide depth of field?  Research has shown when people look at photographs their brain zeros in on objects that are in focus first, then scans around looking at other patterns, and then returns to the object in focus.  Makes sense when you think of our evolutionary heritage.  Wouldn’t you want to immediately notice the lion on the savanna that’s about to run you down and eat you?  As compared to paying more attention to the waving grass the lion is hiding in?

Some examples are in order.  This first picture has a narrow depth of field.  Notice the trees at the front of the line are in focus and then get progressively blurry as your eye travels back along the line.

ISO100, 200mm, 1/320 sec., f/3.5

The next photograph is the same image with the same settings only this time the focus is on the rock at the back of the line of trees.  Bet you didn’t even notice that rock in the first picture, did you?

ISO100, 200mm, 1/320 sec., f/3.5

As you hopefully notice as you glance from one image to the other,  your eye goes right to the place that is most sharply focused.  You almost can’t help yourself, as if your eye is not under your control.  To a great degree, it’s not.  It’s under the control of the photographer, who has decided where you should look first and most often, and put that part of the photograph in sharp focus.  And hiding elements you shouldn’t pay attention to by putting them outside the depth of field – remember the rock you didn’t see in the first image?

Besides using it as a visual sleight of hand to lure unsuspecting viewers into disreputable parts of a photograph, selective use of depth of field is an artistic device to bring order to visual chaos.  For example:

ISO100, 200mm, 1/8 sec., f/22

Here I’ve switched to a larger f/stop number (went from f/3.5 to f/22) and increased the depth of field in the image.  I focused on one of the trees in the middle of the line.  Now observe how your brain reacts.  You are probably looking all through the image with your eye wandering here and there but not really finding a place to land.  I’ll bet compared to the earlier images you find this one less pleasing, even to the point of thinking “there’s too much stuff in the picture” when there’s same amount of stuff as the earlier images.

Sometimes this “everything in focus” approach works – think of your favorite grand landscape.  You get that you-are-there sense because almost all the elements in the photograph are in the distance and look like they would if you were standing next to the photographer looking out over the scene.  But most of the time a judicious application of a shorter depth of field is a better approach.  Think of portraits, or pictures of people on a busy street, or flowers that seem to jump out from the background.  Good examples of that are not accidents – they are intended to look that way to you by the photographer.

One of my classmates from photo school makes images almost exclusively with a narrow depth of field.  She uses it very well, giving the viewer a clear sense of the subject of her photographs and where she wants you to look first.  You can see examples of how she uses this photography principle at Hailey King Photography.

Change of perspective – is that really reality?

Mountain Emperor Butterfly

Remember those posters from the ‘90s where you stared until a 3D image appeared?  That jumbled mass of colored dots suddenly transformed into recognizable shapes with depth from front to back.  It was an interesting example of how information can be hidden in seeming chaos, and how a change of perspective can reveal a new version of reality.

Photographers generally strive to make images reflecting the reality they see in front of them.  Except for the work of extreme artists photographs are expected to resemble in a recognizable way what the camera was pointed at when the shutter was released.  But that isn’t always the only version of that reality.

The scene here is simply a butterfly sitting on a tree trunk, lit by the setting sun.  With my macro lens set to f/2.8 the depth of field is very shallow and the focal point is right on the butterfly’s eye.

Photoshop has a filter called Extrude what essentially looks at each pixel and “extrudes” a column of pixels toward the viewer based on the lightness or darkness of the pixels in the picture.  You can adjust how big the column is and how high it will extrude.   What you see here is the filter applied to my original image (Settings:  square blocks, size = 20, height = 50, levels-based).

What I like about this image is how the filter effect renders the information in the picture into two distinct elements – the butterfly’s head and everything else.  The bark, wings, body – most of these have become representations of the real thing and our eye doesn’t spend much time on them.  The head, though, is very obvious and the eye goes right to it.

It’s not the 3D image of those old posters but the effect on this picture is to accentuate the depth in the picture, making the butterfly literally come off the tree toward the viewer.  I tried this filter on other images and, like most things in Photoshop, it works best on certain types of images.  Don’t know if there are any hard rules about which filter works best on what image, though.  You just have to play with them and get experience on what works for you.