Autofocus (AF) Explained

Autofocus is just what it sounds like: the camera focuses the lens for you.

Passive vs. Active

Autofocus systems are broadly categorized as "active" or "passive".  

Active autofocus systems do not use the light coming through the lens to determine correct focus, instead they have a separate mechanism for determining the distance to the subject.  Some active autofocus systems use infrared light from two separate sensors to triangulate the position of the subject, others have sonar to "echo-locate" the subject like a bat.  Pretty slick, huh?  Well, active auto-focus is not commonly used in modern cameras.

Instead, most cameras now use "passive" autofocus.  All this means is that the camera analyzes the image coming through the lens to determine correct focus.  There are two ways this can be done, "phase detection" and "contrast measurement".

Phase Detection vs. Contrast Measurement

In phase detection, the camera uses mirrors and prisms to split the light coming through the lens into two similar images.  Because of the way the prisms are positioned in the camera, the images are focused slightly differently from each other.  The camera then compares the images to calculate the correct distance to the subject and focuses the lens.  Phase detection tends to be faster than contrast measurement and is the most common autofocus method used in DSLR cameras.

In contrast measurement, the camera analyzes the boundaries between light and dark areas of the image to determine correct focus.  While the image is out of focus, the boundary between a light and dark area will appear as a gradient (i.e. gradual change in brightness from one pixel to another, low contrast).  When the image is in focus, the boundary will be sharp (i.e. quick change in brightness from one pixel to another, high contrast).  The camera adjusts the focus until the image has the highest possible contrast, which corresponds to the edges in the image being in focus.

This is the method used in digital point and shoot cameras, most video cameras, and DSLR's when using the "Live View" or "Movie" modes.  Contrast detection is traditionally much slower than phase detection, although this technology is quickly improving.

Some Light Please?

As I mentioned above, almost all digital cameras use some form of passive autofocus.  Since passive autofocus relies on the light coming through the lens, the autofocus system can really struggle in dark environments.  To overcome this, many cameras have an AF-assist lamp, a LED that turns on whenever autofocus is engaged in a low-light situation.  However, autofocus still does best when the subject is brightly lit.  Autofocus can also struggle if your subject is strongly backlit (the sun is directly behind them), as it will struggle with the comparably dim light on your intended subject.

Not So Good Up Close

Autofocus also has trouble with very nearby subjects.  This is more of a concern for "macro" or close-up lenses on DSLRs, and also for point and shoot cameras which are sometimes able to focus from only inches away.  I couldn't tell you exactly what causes this problem, but it is a common and predictable problem for macro photography.  This is a great time to use manual focus!

Better Than You or I

Despite its limitations, autofocus generally focuses more accurately and consistently than people do, especially when it is used properly.  Most modern cameras are not optimized for manual focusing, and unless you have a big, bright viewfinder and excellent eyesight, you're probably better off using autofocus like the rest of us.

Up next, how to use autofocus properly!

Manual Focusing

Staying with our topic of lenses, let's get into focusing.

There are only two ways to go: manual focus and autofocus (often abbreviated "AF").  Let's cover manual focus first because it's simpler to describe, if more challenging to master.

Manual focusing is possible on every interchangeable lens I have ever seen (i.e. for SLR cameras), although most integrated lenses don't do this (i.e. those on point-and-shoot cameras).  On most interchangeable lenses, there is a focusing ring on the lens barrel, which you turn to manually focus the image.

On fixed focal length lenses (primes), the focusing ring is the only one on there.

On zoom lenses, the focusing ring is generally smaller than the zoom ring.  There it is, towards the bottom...

If it looks like there is only one ring on your zoom lens, look for a very small focusing ring at the very front of the lens.  See it?

Hold on, wait a minute before you start jerking the focusing ring around, I don't want to break your camera.  Many lenses don't allow you to manually override the autofocus without disengaging it first.  To do that, you'll need to flip the focusing mode lever to "M".  It's a little lever beside the lens mount, and generally the options are "M, S, C" (or just "M, AF").  If it's not on your camera body, it will be on the lens itself.  When you move it to "M", autofocus will be disabled, but you will be able to manually focus now (just don't forget to move it back when you're done).

On some newer lenses, they allow you to manually override the autofocus and turn the focusing ring whenever you want to.  Be sure to check your lens and camera manual to see if this is an option before you try it (for all the reasons I mentioned above!).  I can't speak for all brands, but the Nikon lenses that allow manual override have a "M - M/A" switch on the lens barrel.  M is manual only, M/A is autofocus with manual override.

So why focus manually?

Well, sometimes autofocus screws up.  Modern auto-focus is very, very clever, but just like automated exposure modes, it can't read your mind.  Also, manual focus can be very helpful if you are using an extremely shallow depth of field where only a tiny slice of the image is in focus.  For that reason it is preferred for close-up work where the DOF can get razor thin.

To me, manual focus is just a fall back when autofocus doesn't do the job.  Some people use manual focus exclusively, but my eyesight is too bad for all that.  If I had a larger viewfinder on my camera, and some laser eye surgery, I might change my mind though. :)

Up next, autofocus mania!

365project.org

Sorry it's been so long since I've posted, loyal readers (all 1.5 of you).  I found a cool new photographic community online and got sucked in!

Go check it out and sign up today!  It's free, unlike most things that will improve your photography...

365project.org

Don't forget the .org, .com is some random guy.

BTW, a "365" is where you take one picture everyday for a year.  It's like committing to jog every morning for a year, you might not make it out every morning, but it sure as hell will make you a better runner.  Same concept, only with photos!  Join up!

"Which Lenses Should I Buy?"

This is one of the most common questions asked by new photographers, and easier to answer than it sounds.

Start with the Kit Lens

What's the kit lens?  It's the one that came with your entry level digital SLR.  99% chance its a 18-55mm f/3.5-5.6 which is the standard these days.  Why start there?

1. It's cheap (between $100 - $200 on its own, probably less as part of an entry level DSLR kit).
2. It's reasonably sharp.  Since this is the lens most people will start with, it's also how they will judge their camera and the brand as a whole.  Manufacturers know better than to start you off with a total piece of crap.
3. It's good for general photography.  This zoom range is going to cover 95% of your typical subjects.  18mm is wide enough to get decent landscapes and 55mm is tight enough to capture a headshot without being right in someone's face.

Buy a Fast Prime Next

Fact is, the kit lens leaves a lot to be desired in terms of maximum aperture.  In low light situations, you're either married to your pop-up flash (yikes!) or you're forced to jack your ISO through the roof and cope with the horrendous noise.

So what's the solution?  Get a fast prime, something with a maximum aperture like f/1.4, f/1.8 or f/2.  Besides giving you low-light performance, large apertures produce a very shallow depth of field which is great for emphasizing your subject and turning the background into a pleasing blur.

Fast primes come in a variety of focal lengths, but I'd recommend staying around 35mm or 50mm which tend to be the most useful for general photography.  So how do you choose, 35 or 50?  Try taping down the zoom ring on your kit lens at 35mm for a while, then 50mm.  Which one do you find more natural?  There's your answer.

The good news is they can be relatively cheap (about $200).  If you're worried about not being able to zoom, relax, you've still got your kit lens.  Also, you'll be surprised how often you choose to keep your fast prime on your camera and leave the kit lens in your bag.

Save Some Money, Evaluate Your Limitations


Your next lens purchase might cost you a couple dollars, so save up some money.  While you're doing that, evaluate your limitations.  Which of the following problems do you run into the most?

1. I can't zoom in far enough on distant subjects.  This probably means you're shooting sports or wildlife a lot.  The solution?  Buy a telephoto lens.  There are a number of inexpensive telephoto zooms out there, mostly in the 55-200mm or 70-300mm zoom range.  Don't expect a large maximum aperture, f/4 - f/5.6 is typical.  It's possible to get fast telephoto zooms (f/2.8 and under) but the price tag is always four digits, so you might wanna hold off on those.
2. I can't zoom in far enough / focus on very small subjects.  Then you need to buy a macro lens.  The key spec to look for is magnification ratio: you want "1:1".  This is the realm of true close-up photography.  They tend to come in 50mm, 100mm and 200mm varieties (roughly).  The longer the focal length, the further away you can be and still get 1:1 magnification.  The longer focal lengths also cost more, so unless you are photographing poisonous snakes you'll probably be fine between 50 - 100mm.  Get ready to pay though, a decent macro lens starts at $400.
3. I can't zoom out far enough to get the whole scene.  Uh oh, you need a super-wide angle lens.  The general rule is, the wider the better.  10mm is better than 12mm is better than 14mm, etc.  You can always crop in later, and the whole reason to buy a super-wide angle lens is to get a SUPER wide view!  Keep an eye out for fisheye lenses when you're shopping, they are a different animal.  If you don't mind a distorted perspective, fisheyes are fun, but they aren't going to give you straight lines like a traditional wide-angle lens.
4. I keep having to change lenses.  Maybe you need a super zoom.  They can encompass a very large zoom range (such as 18-200mm) and give you the flexibility to capture a lot of different shots quickly without stopping to change gear.  Be warned, you get what you pay for.  The cheap super zooms are pretty junky, I suggest you spend a bit more to get real quality.

See, buying a lens isn't that hard!  There are a million choices out there, and it's easy to spend a crap load of money, so do your research before you buy!  Happy lens shopping everyone!

Mrs. Davis Speaks: Let's talk editing!

Hi everyone.  My sweet husband and I have agreed to do a little switcheroo, and while he's posting on my blog today, I am posting on his.  Today I get to discuss my favorite thing about photography and that is editing!

Before my husband flips out let me say this, and you should adhere to this like the DH and I do: you should not not NOT rely on editing to save your photographs from mistakes that could have been fixed in-camera.  In fact, working and correcting mistakes in-camera is what makes you a photographer.  See honey, I do listen to you :-)

So let's get cracking!  While everyone thinks that editing (in the photographic sense) and Photoshop are synonymous these days, that couldn't be further from the truth.  Today there are a wide variety of programs out there from beginner to advanced, and you certainly don't need to start with Photoshop.  In fact, I barely use Photoshop and try not to unless I'm touching up a blemish on someone's skin.

If you have a Mac of any variety, then you've got iPhoto and at least until you get very familiar with photographic editing, you're all set.  This program has slider bars that allow for adjustments in exposure, contrast, saturation, color temperature, and a few extras.  I think the sliders are useful for beginners because they allow a lot of control and you can visibly see the difference you're making in the photo and adjust accordingly.  After experimenting over time, you will be able to know what every control does and what your photo needs.  From my personal experience, I feel that this program is absolutely fantastic for beginners and even allows a great means of importing, exporting, and storing your photos in an organized way.  I love organization, yes I do!  So you've got a Mac?  New to photographic editing?  Start with iPhoto.  Done.

Now while I'm unwilling to admit this (and find it an absolute travesty!!!!) most people are using PC's.  That's a Windows-based operating system, for the record.  I'm not an expert on PC's and don't pretend to be, but there are plenty of photo programs out there to get the job done.  So I will only discuss programs I am familiar with.  That said Picnik.com, Photoscape, and even Adobe Photoshop Elements (the intro version of Photoshop) are great programs that all run on PCs and have rave reviews all over the internet. Two of those are free and Elements is only 99 dollars.

Adobe Lightroom is my favorite program and I use it on my Mac, but it is designed for both Windows and Mac users alike.  This is definitely a "professional" program but I found it easy to use from the beginning.  Like iPhoto, it has slider bars for editing and is fairly self-explanatory.  When I first began using it, I had no clue what I was doing, but it didn't take long to figure out the concepts, how they applied to my image, and grasp the awesomeness that is Adobe Lightroom.  My highest praise is for this program because of one reason:  you can never outgrow it.  The simplest thing it does it edit photographs into beautiful masterpieces but it can also help you with a photographic website layout, printing, watermarking, you name it.  It's my personal Gold Standard.  You can tag photos by keyword,  organize them neatly, flag, rate, you name it.  But, of course, it's not free.  The going rate for the newest version is 299 dollars and while slightly steep, if you've outgrown your free program, I suggest this.  Why?  Because the workflow is easy and I am a self-professed lover of this intuitive and amazing program!

Now I know you want to know the scoop about Adobe Photoshop right?  "Photoshop" is a term used so often it makes me laugh.  I hear it used in all sorts of contexts--always a verb and never a proper noun.  So here's the skinny.  Photoshop is truly a photographic professionals' program.  Most would say it's the industry standard and maybe it is.  But honestly, it's pretty advanced.  Okay, extremely advanced.  And if you're reading this blog, I know you're not in that category just yet and I also suspect you don't want to spend $699 on this program when you've just dropped your first wad of cash on a dSLR.  Am I right?  So is it cool and can it do amazing things?  Absolutely!  But trust me when I say, it is not for you.  Not now, at least.

So now that you've read all that, I bet you're still confused.  Buying the right software is just as confusing as buying the right intro dSLR.  Here are my final choices, but feel free to do some research if you don't believe me.

• Just starting out? GO FREE!

-iPhoto (if you have a Mac, you're set)
-Photoscape
-Picnik.com

• Outgrown both those programs?  

-Adobe Photoshop Elements (99 dollars!)

• Going a little more pro?

-Adobe Lightroom



Editing software is great, because no photos ever have to look like this:

Or this:

Instead, they can look like a better version of how they are:

Isn't editing awesome?  And we've only just begun!

Since I do all the editing in our family, I'm sure I will be doing more guest posts on editing in the future.

Now back to your regularly scheduled programming with my husband....

Focal Length and Angle of View Illustrated

When it comes to angle of view, seeing is believing, so let's look at some example images:


Fisheye.  Probably a bad one to start with, since this is the only situation where focal length does NOT translate directly to angle of view.  A fisheye is as wide as you can go, in this case a 180 degree angle of view (when measured diagonally across the frame).  Still, it makes sense to start here since this is as wide-angle as you can get...

Ok now on to normal "rectilinear" lenses that won't distort the world like a fun house mirror!  I'm going to label these starting with the actual focal length of the lens, followed by the equivalent focal length for 35mm film that would produce the same angle of view.  Remember, 35mm film is still used as the "gold standard" when comparing angle of view (see the last post if you need a refresher).


10mm (equivalent to a 15mm focal length on a 35mm film camera).  This is about the widest you can go without a fisheye and is considered a "super-wide angle" lens.

12mm (equivalent to a 18mm focal length on a 35mm film camera).  Still "super wide-angle", but you can see we lost a lot of real estate in just two millimeters.  Compare the edges of this photo to the one above.

16mm (equivalent to a 24mm focal length on a 35mm film camera).  This is the end of the "super-wide angle" range.  Coincidentally, our cat Ping jumped up on the wall in the exact center of the frame.  You'll see her more later.

18mm (equivalent to a 28mm focal length on a 35mm film camera).  This was the beginning of the traditional wide-angle range before super wide-angle lenses were developed.

24mm (equivalent to a 35mm focal length on a 35mm film camera).  This is the end of the wide-angle range and the beginning of the "standard" or "normal" angles of view.

35mm (equivalent to a 50mm focal length on a 35mm film camera).  This is the middle of the standard / normal angles of view.

50mm (equivalent to a 75mm focal length on a 35mm film camera).  This is basically the end of the standard / normal angles of view and the beginning of the telephoto range.

70mm (equivalent to a 105mm focal length on a 35mm film camera).  This is in the beginning of the telephoto range, sometimes called a "short" telephoto.  Ping is really coming in handy at this point, good cat, please stay put!

105mm (equivalent to a 160mm focal length on a 35mm film camera).  We're starting to get pretty far into the telephoto range.  I am literally on the opposite end of the house from Ping.

135mm (equivalent to a 200mm focal length on a 35mm film camera).  This is the end of the traditional telephoto range and the starting point for "super telephoto".

200mm (equivalent to 300mm focal length on a 35mm film camera).  Ok, now we are in super telephoto land.  I also cannot BELIEVE Ping is still sitting there.

300mm (equivalent to 450mm focal length on a 35mm film camera).  This is the end of the road for me kiddies.  I can't afford a telephoto bigger than this.  They don't make amateur lenses longer than 300mm right now, and I have no intentions of spending $5000+ on a 400mm or longer telephoto lens!

THANKS FOR ALL YOUR HELP PING!!!  GOOD CAT!!!

Learning Lens Basics

You know what the best part is about having a SLR camera?  Interchangeable lenses!!!  This is a HUGE advantage over the fixed lenses that are on almost all consumer cameras.  Why?  Because lenses need to specialize in order to truly be great.  Even today, there is not a perfect "one lens solution" that can shoot every type of shot well.  However, before we can talk about different kind of lenses, we'll need to get familiar with a couple of basic concepts:

Zooms vs. Primes

There are two types of lenses, the kind that zooms in and out (zoom lenses), and the kind that don't (fixed-focal length or "prime" lenses).  If you just thought, "Why in the hell would I buy a lens that doesn't zoom?!?!" then keep reading.

Zoom lenses can be wonderful things, but they are tricky to engineer.  That can result in some compromises on sharpness, weight, cost, and other specifications.  On the other hand, primes are simpler to design and have less moving parts.  This can result in lower cost, lighter weight and often increased sharpness, although you sacrifice the ability to zoom.

Angle of View

Angle of view describes how wide an area the lens can "see" at one time.  A wide-angle lens is what nature photographers use to show sweeping landscapes.  The opposite of this is generally referred to as a "telephoto" lens (not a "narrow-angle lens" as one might expect).  The same nature photographer might use a telephoto lens to capture a tight shot of a bird in a faraway tree.  In the middle of this range are "normal" or "standard" lenses.  They are well suited for general photography and are often said to approximate the natural angle of view of the human eye.

Angle of view is specified in degrees, but you don't often see this written on camera lenses.  Instead, they give you focal length, which is a little more complicated.

Focal Length

A full definition of focal length is complicated and not that helpful (go see Wikipedia if you don't believe me).  What you need to know is, focal length affects angle of view.  The shorter the focal length, the wider the angle of view.  The longer the focal length, the narrower the angle of view.  Focal length is pretty much always given in millimeters, so a 28mm lens is much wider than a 105mm lens.

It's almost that simple.  The only complication is, angle of view is also affected by the sensor size of your camera.  I really have to use an example to explain this.  Nikon's digital SLRs have one of two sensor sizes: FX or DX.  The larger FX size is the same size as a frame of 35mm film.  The smaller DX sensors are 2/3rds that size.  As a result, a 28mm lens on the larger FX sensor gives the same angle of view as an 18mm lens on the smaller DX sensor.

To try to simplify things, 35mm film is used as the standard.  Lenses often say "equivalent to such-and-such focal length on a 35mm camera".  To keep with our Nikon example, a 18-55mm zoom lens designed for a DX camera may also say "equivalent to 28-80mm on a 35mm camera".  Not the best system, but its what we're dealing with.

Maximum Aperture

Back to something easier and more familiar!  Maximum aperture is the largest available aperture setting for a lens.  This is important because a large aperture can let in more light and therefore works better in low-light situations.  A f/1.4 maximum aperture is about the largest you'll see.  f/2.8 is the standard maximum aperture for expensive professional lenses.  f/4 to f/5.6 is typical among more affordable amateur lenses.

Minimum Focus Distance & Magnification

These are the important specs for close-up photography (flowers, etc.).  Minimum focus distance is just what it sounds like: the closest distance you can focus at.  This can be anywhere from a few inches to a few feet.

Magnification is how large the subject appears in the image compared to in real life.  A "1:1" magnification ratio is basically like you laid the object right on the image sensor.  So if your sensor is the size of a postage stamp, you could take a picture of a postage stamp and fill the entire frame with it.

Compatibility

Make sure the lens you buy is compatible with your camera!  Different brands of cameras have different types of lens mounts, so you need to make sure the lens will actually attach to your camera.  Sometimes that is only lenses with the same brand as your camera, but there are also manufacturers who make lenses for multiple different brands.  Even within a brand, some lenses are not compatible with certain cameras, or limit the features you can use (such as auto-focus, metering, etc.).  Do your research before you buy so you don't get a nasty surprise!

Vibration Reduction (VR)


This feature helps minimize vibration and reduce the dreaded "camera shake" at low shutter speeds.  Also called image stabilization (IS).

Recap

Here's an example of a lens you might see for sale online:  Nikon 18-55mm f/3.5-5.6 VR AF-S DX lens.  Confusing right?  Let's break it down:

Focal length: 18-55mm (this is a zoom)
Maximum aperture: f/3.5 - f/5.6 (this means the maximum aperture changes over the zoom range: f/3.5 zoomed all the way out, f/5.6 zoomed all the way in)
VR: Has vibration reduction.
AF-S and DX:   Two examples of compatibility specs, which differ from brand to brand.  Some Nikon cameras have to have AF-S lenses in order to auto-focus.  The DX means this lens is only designed to work on DX-sized sensors.

Up next, real talk about the types of lenses you want to buy.