Wednesday, November 28, 2012

Apertures Explained

As I re-read my recent post about a photo I had taken, I realized that I might have left some people hanging with regard to camera apertures.  I touched on what an aperture is, but didn't really tie it back to the 50mm lens I wrote about.  Nor did I properly explain just what apertures have to do with photography other than making parts of the image blurry and others in focus.  This, then, is sort of a follow-up to my "Mockingbirds, Photoshop, and Miss Maudie" post but it's really just designed to be a tutorial on one of the basic functions of a camera. If you have not read that entry yet, I encourage you to do so as it introduces some concepts that will be covered here like depth-of-field.

Let's start at the beginning: cameras takes pictures by capturing light on an electronic sensor.  Prior to digital cameras, this sensor was a piece of film but nowadays it's a microchip that essentially performs the same function.
Kids today will have no idea what this stuff is.
The light that hits the sensor is controlled by the lens of the camera, which is the big cylinder-like object that sticks out from the front.  All cameras have a lens, even small ones like on an iPhone.  The lens is what lets light come in and hit the sensor which is inside the camera body.
Every camera camera lens also has a mechanism that controls how much light is allowed to enter through the front and pass to the shutter.  The size of this opening is called an aperture, and it is one of the three key pieces that, when put together, control much of how photography works (the other two being shutter speed and ISO, but we'll get to those another time).  It's a lot like how our own eyes work, actually.  Have you ever woke up in the morning, turned the lights on too soon, and had to squint or close your eyes quickly because things were so bright?  That's because when it's dark, our pupils open wide in order to let in more light.  And in bright light, our pupils shrink because there is so much light they simply don't need to be open in order to let enough in.  For example, in the image below the pupil on the left is dilated and will let in a lot of light. The pupil on the right is contracted and not much light will be let in.  At night or in dark conditions, our pupils open big to let in every bit of available light, but in the daytime our pupils contract because there is so much light around us that they don't need to let it all in for us to see properly.
Image courtesy of Aurora Health Care
Camera lenses work in the exact same way: when the aperture is wide open, a lot of light is able to enter.  And when the aperture is small, not much light will enter. But what does all this have to do with taking pictures?  Good question.  For what I hope is a decent answer, here's a video I made that addresses this:

When my wife and I were looking at DSLR cameras, I was surprised to find out that most of the standard lenses they came with could barely zoom in and out.  A common 18-55mm "kit" lens doesn't really zoom in that much, and this confused me.  Our Panasonic ZS7 had a monstrous zoom lens, so why wouldn't a fancy DSLR have the same thing?  Because even though our ZS7, and most pocket cameras nowadays, have lenses that can zoom in and out, they make a critical compromise in order to do so: they can't let in very much light.  And not only that, but the image sensor (or film) inside most pocket cameras is much, much smaller than those found in DSLR cameras.

When a lens goes from wide-angle (you can see lots of stuff) to telephoto (you zoom in), the physical elements of the lens's construction behave in such a way that the maximum aperture (or opening) of the lens almost always shrinks.  It's just not physically possible to keep a really big aperture when zoomed in, unless you spend thousands of dollars on a mega-fancy lens.  And in bright light situations, like a nature hike or backyard picnic or outdoor sporting event, this is fine because there is so much available light that the camera does not need a very big aperture in order to get enough light to take a nice photo.  You can even zoom in on things, like a woodland critter or a single athlete, and take a decent picture because the camera has so much light to work with.  But when taking pictures indoors or at night, it is simply not possible for the apertures on many small cameras to be big enough to let enough light in.  This is why most cameras have a built-in flash: they have to create their own light in order to make up for their small lenses, which are incapable of letting a large amount of light through the lens to reach the image sensor.
A 110 camera with a stack of single-use flash bulbs.
I actually had one of these when I was a kid :)
Image courtesy of Wikipedia
Another way to compensate for a small aperture is to leave the shutter open longer, which gives the image sensor a longer period of time to collect the available light coming in. This is fine if the subject of the photograph remains still, but in most situations either the subject is moving or the camera is moving. Using a tripod can eliminate the latter problem, but if you are taking pictures of, say, your daughter's evening soccer game it's somewhat impractical to ask the team to freeze motionless in the middle of a play while you snap a picture. But like I said earlier, in bright daylight this sort of thing is not a problem.  A camera with a small aperture doesn't need to have the shutter stay open very long in order to let in enough light for a picture to be captured, which is why a pocket camera with a long zoom lens is just fine in many circumstances. On the flip side, leaving the shutter open for a longer period of time can produce very pleasing photographs given the right conditions.

Ever wonder how photographers get shots like this? They shoot in low
light with a tripod and leave the shutter open for a long time :)
Image courtesy of user TuffTuffTuffTuff on Reddit
Let's back up for a minute here, and take a look at the 50mm prime lens now that we have discussed various aspects of a lens aperture.  This lens, and others like it, doesn't zoom in and out, but it does have a big maximum aperture of f/1.8 (for an explanation of how apertures are measured, check out the excellent Wikipedia entry on F-numbers or the DPReview glossary).  This means that it captures a lot of light--enough such that a flash is rarely necessary, even indoors or in lower-light conditions.  It is also capable of a very shallow depth-of-field, which I discussed in my Mockingbird entry as well.  These features make it an incredibly versatile lens, provided you are not trying to capture a wide angle of view. Let's compare this to the kit lens from earlier.  While the kit lens does zoom in and out, it has some significant drawbacks that must be considered.  When it is zoomed out all the way to 18mm, its maximum aperture is f/3.5.  When the lens is zoomed in all the way, its maximum aperture is f/5.6. (For an explanation of what it means to say 18mm, 50mm, etc., check out the excellent Wikipedia entry on focal lengths or the DPReview Glossary.)  This means a couple of things:

• In order to make the lens let in as much light as possible (f/3.5), the lens has to be at its widest-angle setting of 18mm.  Indoors or in low-light settings, a flash might not be necessary.
• When zoomed in all the way to 55mm, the lens is not capable of letting in much light (f/5.6). Indoors or in low-light settings, a flash is almost always necessary.

These limitations are not necessarily a bad thing, but they are important to know when shooting.  Also, a kit lens is relatively cheap, which makes it a good choice for photographers who want a lens that, while not perfect, is decently suited for a variety of settings.  For the sake of comparison, let's look at the Nikon 27-70mm f/2.8 lens.
Image courtesy of Nikon USA
This lens, while heavier and significantly more expensive than a kit lens, has the significant advantage of maintaining a maximum aperture of f/2.8 across its entire zoom range of 24-70mm.  This means that indoors or in a low-light setting, a flash is probably not necessary and the lens is capable of a very shallow depth-of-field.  These properties make this a far more versatile lens, and ideal for an incredible variety of settings...provided you are willing to fork over almost $2000 for it.

Let's bring this back to the realm of pocket cameras, like my Panasonic ZS7, which I said had a "monstrous zoom lens."  Keep in mind that in order to get a telephoto zoom lens on a little camera with a little image sensor, the lens aperture has to be (thanks to the laws of physics) super duper tiny.  Compare that to the Sigma 200-500mm lens which really is a monster, and has an incredible zoom while maintaining a freakishly large aperture of f/2.8 for the entire range:
Kind of impractical to carry around to your daughter's soccer game, eh?

Before I wrap this up, I want to touch on one critical question that many people still have: how do you set the aperture on your lens?  On many pocket cameras, you can't.  Most of the time this is controlled by the camera's internal software, though many cameras have scene-specific modes such as "Sports," "Fireworks," "Beach," etc. that contain aperture-and-shutter-specific presets for a few given scenarios.  Some pocket cameras do have manual control options that allow you to set the aperture, shutter, and ISO, but they are often hidden in various menus or control dials.  If you have a pocket camera it's worth checking out, though, and some even have dials that say something like "M A S P" or "M Av Tv P"

M = Manual. You have full control over the aperture and shutter values.
A/Av = Aperture mode.  You control the aperture of your lens, and the camera determines the appropriate shutter speed.
S/Tv = Shutter mode. You control the shutter speed, and the camera determines the appropriate aperture setting.
P = Program auto. The camera determines what it thinks are the best aperture and shutter values.

To adjust the aperture, switch to A or Av mode (you can also use the M mode, but that's a tad more complicated) and you will then be able to set the aperture of your lens using a dial or series of buttons on your camera.  Keep in mind that a smaller number means a bigger aperture, or more light coming in to the lens.  A bigger number means a smaller aperture, or less light coming in to the lens.

So that's the basics, folks! There's a lot I didn't cover here, and a lot that I didn't really explore in depth, so if you have questions just leave me a comment below and I will be happy to help as best as I can :)

Wednesday, November 14, 2012

Mockingbirds, Photoshop, and Miss Maudie

One issue that I was wondering about when we bought our Nikon D200 camera a few months ago was the lens. Like most people, I wanted to be able to zoom in and zoom out because, well, why not? Our little pocket camera has a monster zoom, and I didn't see why a big ol' DSLR would be any different.  But you probably know by now, if you have been reading this blog with any regularity, that we chose against a zooming lens and instead opted for a 50mm Prime f/1.8 lens.  It didn't take me long to realize that this was an outstanding choice, and after taking more than 6,000 photos with this lens and body since May I have come to realize why it really is such a fantastic lens.  This morning, then, was sort of a case study illustrating exactly why.

I work on a college campus and we often have birds, squirrels, and other animals running around and staking their claims on various flora outside the buildings.  Yesterday I noticed a pair of mockingbirds hanging out on top of a shrubbery across the street, and thought they were rather photogenic. So today I hauled my camera to work and managed to snap a picture of one of them. Fortunately, this little guy must have read my mind because he happily complied with my wishes and sat still long enough for me to snap his photo:
"Mockingbirds don't do one thing but make music for us to enjoy." -Miss Maudie, To Kill a Mockingbird
To take this picture I first had to figure out what angle at which to shoot.  Too high and it would seem like he was buried in the bush. Too low and he would be obscured by the shrubbery. This is when the "sneaker zoom" feature of a 50mm lens comes in handy: it forces you to move around and seek out the best angle for a given shot.  Not being able to rely on a mechanism to zoom in and out forces you to take in the surroundings and actively seek out the best angle and location from which to shoot.  I spent a few minutes walking around the bushes until I found a good spot, and thankfully he waited patiently for me while I was doing it.

Another issue to consider when planning a photo is the aperture you want to use on your lens.  The bigger the aperture, the faster the shot and the shallower the depth-of-field.  Basically, this means two things: the lens lets in more light and the shutter doesn't have to be open very long, and the area that is in focus is very small.  This made it possible to get only the bird in focus, and not the rest of the bush or the background (the blurry background is also called bokeh).  Here's an illustration of how this worked as I was taking the shot:

For this shot I used an aperture of f/2.4, which meant that given the available light the shutter was open for 1/350th of a second and the depth of field was very shallow. This helps draw the viewer's eye to the bird and not the surrounding area, which generally makes for a more visually pleasing photo.  A smaller aperture would have meant that the bushes, and possibly even the building in the background, would have been in focus too. This isn't necessarily a bad thing depending on the type of photo you want to take, but for this particular shot I thought a shallower depth of field would be more appropriate.  And that's the thing about photography: there's never one correct way to do it. As long as you find something that works for you and you're happy with it, you're all good.  Most pocket camera lenses have smaller apertures, and kit lenses (i.e. the lens that comes with the camera) on DSLR models aren't a whole lot bigger.  But again, it's all about what works for you and knowing how to use what you have.

Anyway, back to this shot for a bit.  Since a 50mm Prime lens cannot zoom in and out, and getting too close would have probably disturbed my new bird friend, the original shot is actually quite a bit larger:
I thought the surroundings were a tad distracting, so I cropped the photo to be tighter and bring the subject (the bird) in closer.  You might also notice that the colors of the original photo are not as vibrant as the one I posted at the top.  This is due to some post-processing I did in Photoshop but the same thing could be done in just about any image editing program, even basic ones like iPhoto.  I'm generally not a big fan of over-editing images, but I do think some degree of alteration is just fine.  And like I said earlier, it's all up to you.  Some people like to adjust everything in Photoshop, and some like to leave the photograph as-is.  Other times it's about the purpose of the photograph: are you trying to capture a scene, present an emotion, manipulate the viewer, tell a story, or ask a question?  Photoshop, as I see it, is just another arrow in a photographer's quiver to allow him to hit the target for which he is aiming.  Anyway, for this picture I used Adobe Camera RAW to adjust the contrast and saturation of the original, and then Photoshop to crop it down and add a bit of vignette.  I am pleased with the final result, and I hope you are too :)

Finally, I thought I would mention one other thing: megapixels.  For years I was under the impression that more megapixels equaled better pictures, but in truth this metric has almost nothing to do with the quality of the photos taken by a camera.  Don't take my word for it, though--just do a quick search on "megapixel myth" and you'll see what I mean.  But permit me, if you will, to use this mockingbird photo as a case study.  Our camera has a maximum resolution of 3872x2592, which means it's just a tad over 10 megapixels.  This is pretty low for cameras today, and even most pocket cameras have at least 14 or 16 megapixels. It works fine, though, and if you download the full-size photo at the top of this post you might notice that it clocks in at just a hair over 3 megapixels at 2638x1536.  Would a 15- or 20-megapixel camera have made the photo any better?  Probably not, though having that extra real estate would have allowed even tighter cropping for the final image.  Is a higher mexapixel number a bad thing? No, generally not. But I say all this to illustrate that lower megapixels on a camera doesn't mean it's a bad camera either.  So if you have an old model that you think isn't worth using anymore just because it has fewer pixels, I would say don't worry about it. Instead, go grab that sucker and get out and take some photos!

Monday, November 05, 2012

Moving on up

Two weeks ago Apple held one of their famous big ol' press events, at which they announced several new products including an iPad mini and updates to their current computers like the iMac, Mac mini, and Macbook.  They also updated their flagship iPad to its fourth generation which meant a faster processor, better screen, and better wireless connectivity.  This flurry of new products also meant that some of their former devices were bound for the bargain bin, such as the third generation iPad which was released to an eager tech-hungry public only a scant seven months ago in March.  That's not to say that the third generation iPad is somehow an unworthy technical device--far from it, in fact, with its zippy A5X chip and retina display which, when it launched, was a revolution in the tablet industry.
Almost immediately after the fourth generation iPad was announced, Apple started selling the former king of the tablet hill for the super-bargain price (as far as these things go, anyway) of $379. I already have an iPad, but saw this as a good opportunity for some people I know whom I thought would be able to make use of such a device.  One of these individuals is my mom, who has been doing mobile computing on an aging Windows Vista laptop for the past few years.  It works, but it's somewhat unwieldy and the battery life...well, let's just say my mom keeps her power cord close at hand at all times.  So I emailed my mom to let her know about the iPad 3, thinking she might be interested in possibly upgrading.  Much to my pleasant surprise, she was all in and ordered one that very same day.
One is an iPad 3. One is an iPad 4. Can you spot the difference?
It arrived a few days later, and as luck would have it the delivery man was a former neighbor who works for FedEx. Small world, eh? Soon my mom was busying herself with realtime video chatting, messaging, email, and internet surfing from a device about 20% the size of her laptop without worrying about battery power.  She seemed to be thoroughly enjoying her iPad, so much so that we offered the same information to my wife's mother who followed suit and bought one too.  In the space of a week both our mothers upgraded their technology by leaps and bounds, and we were thrilled to be along for the ride!

It has been about a week since they got their iPads, and in that time it has been so much fun helping them get acclimated to the various features and nuances of their new tablets.  We are making liberal use of Apple's Messages app, which allows us to send videos of our son to grandma and grandpa free of charge--and they are in turn sending videos right back to us.  My wife's mother was so enamored of her iPad she gave it a name, Padi, and was thoroughly delighted to discover things like the Siri search feature and the built-in dictation too.

There have been a few hiccups along the way, but we are thrilled with how this transition has gone and looking forward to helping our parents become certified techno-geeks :)