Photography 101: Depth of Field, and taking control of your aperture

Depth of Field refers to the area of focus in your scene, from the point of sharpest focus, to the most out of focus parts, in front of and behind the point of focus.  This is one aspect of photography where the differences between SLRs and compact cameras are the most pronounced.  There are several variables that affect depth of field, but the first one is built into your camera to begin with; the size of your sensor.  DSLRs sensors are either the same size as a 35mm frame (only a few very high end DLSR have these) or APC sized sensors (which are about 2/3rds the size of a 35mm frame).  Their physical size dramatically dwarfs the tiny image sensors built into most compact cameras (and now cell phones) and this affects the depth of field they are capable of producing in an image.  Simply put, compact cameras are limited to large depths of field, due to their tiny sensors, even if their lenses have apertures.  DSLRs, on the other hand, have a much greater range of DOF (depth of field), particularly if the lens used has a wide aperture to start with.  The DOF range of cameras further increase in medium format cameras, and then on to large format cameras.  DSLRs (as well as SLRs from the film days) are popular with amateurs and professionals alike because they combine some of the portability of compact cameras with some of the DOF capabilities of medium and large format cameras, placing them as one of the most versatile class of cameras.  Aside from the format size of your camera, there are three more important variables that determine DOF.




Aperture affects Depth of Field

The illustration above shows a camera with a 50mm lens shooting at f/2.8 and f/16.  The wider aperture of f/2.8 lets in more light, but also narrows the DOF so that only the flower in focus will look sharp.  Conversely, the narrow aperture of f/16 widens the DOF, showing many more flowers in front of and behind the point of focus as relatively sharp.  I shot a series of photos of a ladder on an old fire truck to further illustrate the difference.  

Adjusting your aperture is the most cited method of controlling depth of field, and I'll go a little more into this at the end of this post, but there are two more factors that often go overlooked.


Subject distance affects Depth of Field

Above, the camera has a 50mm lens and is set at f/8 for both shots.  The difference is that first shot is focused on a flower further away, and the second shot is focused on a flower that is very close to the camera.  In spite of having identical apertures and focal lengths, the DOF for the flowers in the first shot is much wider than the closer flower in the second shot.  The nearer the subject in focus is to the camera, the narrower the depth of field will be, independent of the aperture setting.


Focal Length affects Depth of Field

Above, the camera is set at f/8, and is focused on the same flower for both shots, but the focal length of the lens is different for each shot.  In the first shot, a wide angle 24mm lens is used, which will also yield a wider DOF.   This property is one of the reasons wide angle lenses are frequently used in landscape photography, where keeping the entire scene in focus is often desired.  The second shot uses a more telephoto 105mm lens, with a narrower angle of view, which also yields a narrower DOF.  This is one quality of telephoto lenses that make them popular in portraiture, where separating the subject from the background can help the composition.  Below are two photos I shot to illustrate how focal length affects DOF.  Notice how the fence in the background is less in focus once I zoom in to 75mm.


Baby stepping...Aperture Priority Mode

This show the mode dial set to "Aperture Priority Mode" on my Nikon D40. The "A" is commonly used on other brands of cameras, although Canon will be marked "Av", for "Aperture Variable Mode", which does the same thing.At this point, I would invite the beginning photographer to take a baby step into the art and craft of photography by switching your camera from "Auto" mode to "Aperture Priority Mode".  In this mode, the camera will still make most of the decisions for determining exposure, but you are taking control of one variable - the aperture.  Once you set the aperture, the camera will adust the shutter speed and the ISO (most DSLRs are "auto ISO" by default, so that it can adjust it as needed) around your aperture setting as it's metering the scene.  As you go along, you will be incorporating DOF as an element of composition in the shots you take.  Try using a wide open aperture when shooting portraits, and notice how shallow DOF will blur what might otherwise be a busy, distracting background.  Set a small aperture of f/16 or f/22 when shooting landscape.   Of course, everything in the previous lessons about exposure and camera shake still apply, even if the camera is handling most of the exposure settings for you, so be careful in low light situations.


Photography 101: Camera shake, and how to deal with it

 I have no idea what these dials and knobs are for, but if you posess knowledge of 1950's aviation technology, or can simply read Russian, feel free to enlighten me in the comments section.

Above are two photos I shot of a dial (of some sort) inside the fuselage of an old Russian cargo plane.  Both photos have identical exposure values, but they differ drastically in their image quality.  The blurriness of the first photo was not due to missed focus (the focus was fixed for both photos), but rather the natural tendency of my hands to move or shake over time, despite trying to keep still.  Because the camera was moving, ever so slightly, the light rays reflected from the subject moved across the surface of the sensor, ever so slightly.  This exposed light rays over what would otherwise be a sharp, contrasted edge, blurring the boundary between the dark and light areas.  This can be seen when you observe the full resolution crops showing the Russian letters of both photos.  With my 35mm lens, the shutter speed was fast enough, at 1/160th of a second, that any natural movement of my hands did not have enough time to register in the exposure for the photo on the right.  At 1/5th of a second, my inability to keep my hands perfectly still is obvious in the photo on the left.  

In both cases, I was shooting in manual mode, but this is a problem that shows up for those shooting in various automatic modes as well.  The automatic modes of most cameras will fire their built in flash if their meters determine an exposure that will need a relatively slow shutter speed (anything below 1/60th, for example), but if your camera doesn't have a built in flash, or you are using a "no flash" automatic mode, then you will may find yourself pressing the shutter release button, and might be surprised when the 2nd "clack" sound of the shutter closing doesn't' take place for a while.  If this happens, it is likely you are in a low light environment (such as indoors), and your camera's metering system compensated by opening your aperture to as wide as it can go, and (for digital) your ISO as high as it can go, leaving lowering the shutter speed as the last option for arriving at a correct exposure.  When this happens, your only option to prevent blur from camera shake is to find a way to stabilize your camera.  Your best option is to mount your camera on a tripod, achieving a stillness no human being could ever hope to achieve.  Setting your camera down on a flat, even surface (like a table) can achieve the same result.  If a stable platform isn't available, you can steady yourself and your camera by bracing against something solid, like a wall, a tree, or the top of a chair - anything that will introduce another point of contact to keep the various twitching, flexing tendons and muscles fibers throughout your hands and arms from moving the camera. 

Much sharper than the f20, 1/5th photo above, but if you observe the full resolution crop, you'll notice it still isn't quite as sharp as the f/3.5, 1/160th shot.This next photo shows what you can achieve, even at lower that "safe" shutter speeds (a "safe" shutter speed being anything that is the reciprocal of your focal length, or faster - such as 1/50th or faster for a 50mm lens) if care is taken to stabilize yourself and your camera.  This was shot at 1/15th of a second, but you will notice it is much sharper than the 1/5th of a second shot seen in the first photo.  Aside from being more careful about holding my camera, it helped that I was using a 35mm lens, which has a wider angle of view and doesn't register camera movement as much as a longer telephoto lens would.  If I were using my 70-300mm lens zoomed in to 300mm, then even 1/160th of a second would be too slow for a hand held shot; it would need to be 1/320th or faster.  If you've ever looked through a pair of high powered binoculars before, than you'll remember how the slightest movement of your head or hands resulted in the image wildly jumping about.  The longer the focal length, the more sensitive to movement your image plane will be.

Aside from tripods and bracing yourself, some digital cameras and lenses have incorporated image stabilization technology, which compensate for camera shake by moving a lens element, or the sensor itself, in motion counter to the motion introduced by your hands.  For Canon and Nikon, the image stabilization is built into their lenses; for Pentax DSLRs, the image stabilization is built into the sensor of their camera bodies.  This technology results in shots that can be taken at much lower speeds than the reciprocal of your focal length.  If my 70-300mm had VR (the Nikon version of image stabilization), I could zoom in to 300mm and shoot hand held as slow as 1/80th of a second.  These technologies, as well as the increasingly higher ISO values (allowing for higher shutter speeds) achieved by the latest digital sensors, are helping to make camera shake less of an issue now and in the future.

One important caveat to keep in mind; no matter how stabilized your camera is, only a fast shutter speed can 'freeze' a moving subject.  In other words, if your camera is locked down on a tripod, shooting at 1/30th of a second, and the person you're photographing turns his or her head, or waves their arm, it will result in a blurred image for precisely the same reasons camera shake results in blur - light rays moving across the sensor.  In the photo below, despite using a shutter speed (1/80th) fast enough for a hand held shot (zoomed to 52mm), it was not fast enough to freeze the motion of the dog or the girl's left foot nearest the soccer ball.  The need to freeze action is why sports photographers frequently use massive telephoto lenses - their enormous size due to large glass elements needed to give these lenses a maximum aperture of f/2 or f/2.8, allowing for faster shutter speeds.

 A sunnier day, or higher ISO capability would have allowed for a faster shutters speed, freezing the motion of both the dog's and girl's legs.


Photography 101: The Basics of Exposure


I decided to write up a couple of blog posts for people just getting into photography, specifically people who just picked up a shiny new Nikon D3000, Canon T2i, Sony Alpha 390 or a Pentax K-something-or-other, and would like to do more than simply shoot in "Auto Mode". Of course, not everyone who buys a DSLR is interested in studying photography; some people simply want a camera that's better than a point-and-shoot, and camera manufacturers are more than happy to both claim explicitly that DSLRs are better than compact cameras , and also imply that using DSLRs will make you a better photographer. To the first point, DSLRs are indeed "better" than compacts in many respects, chief among them the larger sensors and quality lenses, which will always be physical limitations that compact cameras can never overcome, not matter how many megapixels are jammed into their tiny sensors. The second point is, as you probably already know, hogwash. Buying a Steinway & Sons grand piano won't make you a better pianist, piano lessons and practice will. The same is true of photography, and there are several concepts to learn, both technical and artistic. This post on exposure will be the most technical of those concepts, but a critical first step to taking control of your camera and crafting the photo you want, instead of settling for whatever the camera has decided on.


1. Intensity, Time, and Sensitivity

My Nikon FM - a fully manual film camera. If you can shoot with this, you can shoot with any camera.

Photography is all about recording light, and exposure is the method by which a camera achieves this. At it's most elemental level, a camera is an opaque box with a small hole on one end for light to pass through and project an image onto the inner wall on the opposite end. Artists throughout history would use camera obscuras to project a scene, such as a landscape, onto the opposite wall, tracing the contours of the image. The introduction of light sensitive chemicals in the 19th century would transform the camera from a mere projector into an actual recording device. To the small hole would be added optical glass to focus the light, further clarifying the image, and since the photo-chemicals would render a pure white image if exposed to light for too long a time, measurements were devised for both the amount of light let in and for how long it should expose the photosensitive surface. These are the basic elements of photography; the intensity of the light, the time need for exposure, and the sensitivity of the film/sensor.

As photographic technology progressed, photo-chemicals were designed to be more sensitive to light. This led to the need for faster exposure times (early photographs were taken by removing the lens cap, counting off the minutes or seconds needed, and putting the lens cap back on), and mechanical shutters were introduced to accommodate these split-second exposures times. As fast as these new shutters were, photographers were still encountering situations where the light was too intense for proper exposures. An aperture, which is a metal diaphragm that opens and closes, was added to lenses to further control the amount of light let in.


2. Intensity is measured in f-stops

A Nikon 50mm f/1.8 Series E lens - a cheap, yet good quality "fast" lens from the 1980s The intensity of the light coming through the lens is affected by both the focal length and the aperture. The focal length is the distance light rays are brought into focus by the lens. A short focal length, like 18mm, will have a wide angle of view; a long focal length, like 200mm, will have a much narrower angle of view. As focal length increases, the less light is let in, decreasing the overall intensity of the light reaching the sensor (If you've ever used binoculars or a telescope, you might remember how much dimmer the view looked). Apertures are constructed to open and close their diaphragm blades at set distances, each distance creating an opening that is double the size as the previous setting. The wider the opening, the more light is let in; the narrower the opening, the less light is let in. In order to have a uniform measure of light intensity for all lenses, a ratio of the focal length and the aperture opening was created, called an f-stop. One f-stop is equal to a doubling or halving of light's intensity (the term "stop" is also used to refer to the doubling or halving of light for shutter speeds and ISO as well). With modern DSLRs, the lens aperture is electronically controlled, but in prior decades the lens aperture was set by rotating a ring which clicked between each f-stop (the Nikon 50mm lens pictured here is one such lens). A typical range of f-stops you will encounter will be: f/1.4, f/2, f2.8, f4, f5.6, f8, f11, f16, f22, f32. f/1.4 is the most wide open of this range, and is found on a select few lenses with optics capable of letting in a large amount of light. f/22 and f/32 are available on most lenses, as the they are the result of a more closed down aperture.



3. Time is controlled by shutter speed

The shutter speed is currently set to 1/125th of a second. The ASA (a precursor to ISO) is set to 200, which allows the built in light meter to calculate exposure against this value.Just as f-stops are delineated in increments that double of halve the light, shutter speeds are set at intervals that roughly double or halve the time the shutter opens and closes. The picture you see here are the shutter speeds available for my Nikon FM (a fully manual film camera from the 1970s), and illustrates what I mean by "roughly" - 1/15th of a second isn't exactly "half" 1/8th of a second; likewise 1/125th of a second is slightly more than half of 1/60th of a second. This slight discrepancy is due to the mechanics of shutters and what delineations are possible in the timing. Still, the speeds are close enough to the 2:1 ratio mirrored in f-stops to make them reciprocal of each other; one click of the aperture ring is equal to one click of the shutter dial. For todays DSLRs (as well as more modern film cameras), f-stops and shutter speeds are further delineated into 1/3 of a stop, so that instead of going directly from f/4 to f/5.6, it goes f/4 > f/4.5 > f/5 > f/5.6. Likewise shutter speeds are divided into thirds of stop so that 1/60th to 1/125th progresses as 1/60th > 1/80th > 1/100th > 1/125th. While this gives the photographer a much greater degree of control over exposure, it does make it more daunting for someone just learning. You can set your DSLR to only progress in full stop increments, but in the long run, it's more advantageous to just bear in mind that 3 clicks of wheel equal one full stop.





4. Sensitivity is measured by ISO

The ISO rating of 400 for this black & white print negative film allows for faster shutter speeds in lower light situationsISO refers to the "International Organization for Standardization", which sets engineering standards for manufacturers to follow, allowing for more interoperability.  For photography, this includes a set standard for a film's sensitivity to light.  An ISO value is also referred to as the "film speed", since the lower the ISO value, the slower the shutter speed needs to be to properly expose the film, and vice-versa.  Like aperture and shutters speeds, ISO is also delineated in "stops", where each value is double the previous value.  The typical range of film speeds for most films is as follows: ISO 25 > 50 > 100 > 200 > 400 > 800 > 1600.  A fast film speed like ISO 1600 will need less time to expose, but the resulting image will be grainier in appearance, due to the larger silver crystals in the emulsion needed to gather more light.  Likewise, ISO 25 will take the longest to expose, but will have a finer, smoother appearance due to smaller, more evenly distributed silver crystals.

When shooting with film, the ISO (or ASA as it was called before ISO adopted this American standard) value meant that the photographer essentially makes his or her first decision about exposure when choosing which film speed to use before loading a roll of film.  Loading a roll of ISO 400 film locks in the first of your 3 exposure variables, with aperture and shutter speed then adjusted up or down to account for the sensitivity of your film.  In DSLRs, the ISO is a setting that can apply to the image sensor at any time between shots.  DSLRs typically have a "base" ISO of 100 or 200, which is the optimal setting for that image sensor for the least noise and best color saturation.  Turning up the ISO in your DSLR will amplify the sensitivity of your sensor, allowing for shorter shutter speeds, but at the cost of a noisier image (similar in effect to film grain) and less color saturation.  The limit at which ISO of a DLSR sensor can be boosted before noise overwhelms the image varies with each camera model, with the latest digital sensors being capable of the highest ISO settings.  My Nikon D70, which was first manufactured in 2004, has a range of ISO 200 to ISO 1600, though I rarely go above ISO 800.  Conversely, a Nikon D3s has an incredible range of ISO 200 to ISO 12,800, meaning a setting of ISO 6400 on a D3s produces a cleaner, more vibrant photo than ISO 1600 does on my old D70.


5. Light is measured with light meters…or an educated guess

Before the introduction and widespread use of light meters in the mid 20th century, photographers had to rely on shared experience through trial and error to determine the correct exposure for a given scene.  It helped that sunlight is a consistent source of light, particularly on clear sunny days, from which to base a rule of thumb; that rule of thumb being the Sunny 16 Rule.  I'll delve more into this in a future post; suffice it to say photographers back then relied on judgement and experience to set their apertures and shutter speeds.  With the innovation of light meters, photographers had a more consistent method of measuring light and determining exposure.  At basic level, a light meter measures the light, and then computes the combination of aperture, shutter speed and ISO setting needed to produce an exposure equivalent to a middle grey tone.  Middle grey is the tone that marks the midpoint of the tonal range of exposure from completely underexposed (pure black) to completely overexposed (pure white).  To simplify for the sake of conceptualizing, if your light meter thinks f/5.6, 1/125th, ISO 400 will achieve middle grey, then you can reasonable expect expect your scene to expose properly.  It's actually not quite this simple, which accounts for one of the reasons more experienced photographers don't use "Auto Mode".  As with the Sunny 16 Rule, I'll expand on the vagaries of metering a scene in a later post.  For now, recognize that when you camera automatically determines the settings for you, it does so by first measuring the light with it's built in light meter, then by adjusting the aperture, shutter speed, and, in digital cameras, the ISO in order to get a shot that is properly exposed.  In a DSLR, you will know how well your photo exposed fractions of a second after you press the shutter, as the camera records the image on it's sensor, processes it into a jpeg, writes the jpeg file onto your memory card, and displays on the LCD screen on the back of your camera.  If you were using a film camera, you wouldn't know until after your film has been processed, something I continually need to remind myself as I reflexively stare at the leatherette back of Nikon FM after each shot I take.


6. How it all ties together

What the inside of my viewfinder looked like when taking the shot for the first photo seen in this blog post. The difference in appearance is largely due to the off-camera flash I used when taking this photo.If you switch your camera into manual mode and look through your viewfinder, you will see numbers that represent your shutter speed and aperture (and in some cases your ISO as well) and probably as couple of symbols to indicate things like battery life, flash, etc. You will also see a scale indicating your exposure meter. This is the camera's built in light meter telling you how overexposed or underexposed your photo will be at the given aperture/shutter/ISO setting you currently have your camera set at. In this picture here, showing what my viewfinder looked like at the time, you can see that my camera was set to f/5.6 and 1/250th (the ISO was 200, but that isn't displayed in my viewfinder). At these setting, the meter is showing my photo will be severely underexposed, with little rectangles progressing towards the "minus" side of the metering scale. If I had opened up my aperture to as high as it could go (f/2.8 in this case) and/or slowed my shutter speed considerably, the little rectangles would regress toward the "0" in the middle. If I kept dropping my shutter speed even further, they would then start progressing to the "plus" side of the scale, indicating overexposure. A "correct" exposure is one where there are no little rectangles (or hash marks, or whatever symbol your camera's meter uses) on either side of the "0" at the midpoint of the scale. The "0" indicates an EV (Exposure Value) of zero, which means middle grey. You can do the same with your DLSR, and I encourage you to give it a try. As you do so, you will start to notice that several different combination of aperture/shutter/ISO settings will yield a correct exposure, but that these different combinations have different effects on your image aside from how light or dark your image turns out. These effects, specifically blurriness at slow shutter speeds and the depth of focus at differing apertures, will be the subject of the next Photography 101 blog post.


Marcella Mayo's Maternity Photos

Marci and I share a mutual friend, and through him was introduced to my photography portfolio. Marci will be having a baby girl at the end of June, and wanted some maternity photos to add to her new family album,which already has her very first baby photos; from her sonogram.




Well, as long as I'm here...

A really good friend of mine found a funky "3D" film camera, new in the box, and had to get it for me.  I'm now the proud owner of a Nishika 3D N8000, a late 80's brick of glossy black plastic, with a celebrity endorsement from Vincent Price to boot!  Basically, it's a knockoff of the Nimslo 3D camera, but with plastic lenses, a single, set shutter speed of 1/60th, and 3 aperture setting of f/8, f/11, and f/19.  Essentially, it takes 4 exposures simultaneously in a portrait orientation across two frames worth of 35mm film.  The film is then (or rather used to be) developed and combined into a lenticular photo with the 3D effect. Nishika apparently had a shady history involving telemarketing fraud, and eventually went belly up.  All of this adds up to the Nishika N8000 being my entry into the wonderful world of lomography (but without the mark-up Lomo branded cameras recieve).

I shot this at f/2.8, which allowed a fast enough shutter speed to freeze the cyclist who was zoomimg through the frameI decided to shoot half a roll of film at Upper Bidwell Park, bringing along my Nikon D40 with a 35mm f/1.8 to act as a light meter.  The Nishika is designed for ISO 100 film, but I had to settle for ISO 200 as it was the lowest speed film available off the shelf.  Fortunately, film is more forgiving of overexposure, so I think I'll be ok.  I set the aperture on the Nishika to "Sunny" and my D40 to f/18, ISO 200, and 1/60th.  I composed some shots in that cruddy viewfinder, clicked the shutter, and advanced the film.  As of my writing this blog post, I have no idea how I did, but I didn't leave empty handed either.  The Nikon 35mm AF-S f/1.8 is a nice lens, with it's small size and light weight being perfectly suited for the smaller, entry level Nikon bodies like my D40.  Typically, I set the aperture anywhere from f/4 to wide open and f/1.8 for that shallow depth of field, and to compensate for low light conditions, but I stuck with f/11 for most of the shots seen  here.









"Dog Wood" at Lake Oroville

It's rare to find anyone describing procrastination in a positive light, but it did, in fact, work in my favor this past month.  I hemmed and I hawed, lurking on eBay and Amazon, waiting for just the right deal on a AF Nikon 50mm 1.4D, when my car decided to make the buying decision for me…by overheating.  Three weeks and three hundred dollars later, I needed to give my car a little workout to make doubly sure it wouldn't be overheating on me again, so I drove it down to the Lake Oroville dam.  Thankfully, my car was back to it's old self; reliable and paid off.   So, now I can go back to spending another month or two scrolling through auction listings. 

While I was at the lake, I found a piece of driftwood with an Anubis-like dog head.  I don't shoot landscapes that often, but when I do, I've become acutely aware that my 18-55mm kit lens that originally came with my D40 is the only lens in my collection wide enough for the kind of shots I prefer when Mother Nature is the subject..  I also find my natural tendency to shoot in portrait orientation remains just as strong when shooting landscapes.  Whenever I do end up getting that 50mm 1.4, it will remain welded to one of my camera bodies, for sure…but I'll be pouring over reviews of some wide-angle lenses as well.


In the beginning, there was 100_0078.jpg

 I acquired my Kodak EasyShare as a raffle prize at my company picnic.  It wasn't even the first digital camera I had ever owned, but it did end up being the first camera that I was truly ready for.  It started with a trip to Oregon for my cousin's wedding.  I could compose the shot in the LCD screen, but I had no control over what happened after I pressed the shutter button. I was also disappointed I couldn't quite capture the quality of the fiery sunset before my eyes.  A week later I was back in Chico, walking through the dusty trail of Upper Bidwell Park.  "The best light appears at magic hour, at sunset" according to the photography blogs and podcasts I now consumed.  I could barely discern the image on the LCD screen as the setting sun blazed through the grasses along the hill.  After I uploaded all of my photos to my computer, that one particular shot stood out like a sore thumb.  100_0078.jpg100_0078.jpg is the shot that got me off the fence. I knew I wanted a much better camera, but more importantly, I knew I wanted a camera that I could take full control of.  I was done with pressing the shutter button and hoping I'd like the result.  I was done with "scene modes".  I had an order placed for a Nikon D40 by the end of the week. 100_0078.jpg is above and beyond a snapshot, and yet it isn't what I considered (even at the time) a "great" photo.  It's more of a hint, or a shadow of a great photo.  A good composition, and yet the horizon is tilted.  No problem, I'll just rotate and crop to straighten that out:

Rotated in iPhoto…but then I lose the drama that the previous incline on the right side provided in the original.  There's more about this photo to nitpick; the low contrast, the loss of sharpness, the noise in the shadow area.  This is the photo that best exemplifies where I was 2 years ago, and where I am today.  I'm on my way, but I haven't arrived yet.  I'm doing good, but I could do better.