Tips and Tricks

Its time for another installment of Tips and Tricks here at Photo Trek.  Each month around this time I tackle a photography related question and try to make things a bit clearer.  Sometimes I deal with advanced topics, and sometimes I deal with the basics.  This month I am going to be talking about one of the most basic aspects of photography...focus.  We are going to learn how to control the auto focus in our cameras, and also a bit about manual focus.

We've all seen photographs that are completely out of focus and blurry beyond belief, in fact, we're probably all guilty of this little photographic faux pas.  What causes it?  How can you avoid it? Shouldn't auto focus be....well....automatic?  Whether you have a camera phone, or the latest Hassleblad Medium Format camera, bad focus can happen to you.  Remember, cameras are just machines, tools that are no better or worse than the person operating them.

Lets begin with the basics.  Auto focus cameras are a relatively new technology considering how long cameras have been around.  That being said, most cameras in use today, and nearly all being sold, are capable of auto focus.  With the auto focus (AF) switched on (default in most cameras), the main thing to worry about is the shutter button.  This is your primary control over the AF sensors.  No doubt you are wondering what a "two stage shutter button" is.  I'm not sure if this term has been used before, but I find it quite descriptive of what this button does.

When you press the shutter button on your camera slightly, you will feel a detent in its travel.  This is usually about half way to the bottom of its travel.  This is not a defect in the design and it is not indicating wear in your shutter button.  What that half way point is, in fact, is the AF lock.  When the button is pressed to this point, the AF sensor begins to do its job bringing the subject into focus.  We will get into how this is done a little later.  Usually, when the AF is locked, you will hear an audible tone and will likely see a visual clue that the focus is locked.  At that point, you can finish pressing the shutter button and complete the capture.

What happens if you don't lock the AF prior to activating the shutter?  Well, two things will happen.  The most noticeable thing is a delayed shutter response.  I'm sure you have all noticed this when taking that surprise picture by just pressing the button all the way down.  It is like the camera freezes for a split second...or even longer, then fires.  Many people blame the camera for being slow, but this is a direct result of the auto focus.  You see, the camera is designed to focus prior to releasing the shutter.  If you don't give the camera the time to do so, it will delay the shutter long enough for it to get a quick focus.  This leads to the second thing that happens on these snap exposures.  You focus will likely not be as crisp as you would like.  This is because of the haste in AF's operation.  The accuracy of the focus becomes a hit and miss affair, and your results will vary.

So, how does the camera know how to focus?  Well, most cameras (higher end point and shoots, and SLR's) have multiple points within the frame that it will use as reference.  When you look through the viewfinder, these points are usually represented by boxes, or open rectangles.  The number of these points will range from one up to over 50 in the newest DSLR cameras being released.  What the camera is looking for in this situation is a prominent subject, with either strong lines, or high contrast that falls within one of these points.  Usually, the camera will choose the closest subject that fits this bill (not necessarily the subject you want to focus on). 

When you press the shutter button half way and the camera locks focus, one or more of these boxes will change color to indicate which areas are locked in focus.  By pressing the button half way, you can preview the image to see what the camera chose to focus on.  If you don't like what the camera has chosen, you can release the button and try again, until you get what youlike.

If you don't see the focus boxes, chances are you only have one focus reference point and that will be in the center of the frame.  To lock the focus with a center point AF, you will need to put your subject in the center of the frame, press the button half way down, locking the focus.  While keeping the button pressed, recompose the picture and release the shutter.  Keep in mind that this will also lock the exposure so keep that in mind as well.

This actually brings us to another option with AF on the more advanced cameras...the center point, or central AF.  By accessing the menu, you can chose this central AF option so that at any time you only have one point of reference for the focus to lock.  This option will work just like the point and shoot I just described.  A variation on this can be found in several SLR cameras where you can choose any of the focus points by scrolling through them.

Another option that is in a few cameras is a flexible spot auto focus.  This is a feature in my camera and is what I use better than 90% of the time.  What this option allows is the ability to focus on a single spot anywhere in the frame.  The box is movable by use of a joystick on the back of the camera and can be placed on your focal point within the frame while maintaining your composition.  This is extremely helpful when bracketing your exposures while keeping your composition the same.

There is another option that is pretty uniform across point and shoot cameras, and this is the macro function.  I believe this to be one of the most misunderstood settings on a camera.  Fundamentally, this doesn't change anything about the picture.  It is not a magic magnifier as many believe it is.  What this does, is tells the AF sensors that the subject to be focused on is closer than normal to the lens.  It mimics the manual focus ability on an SLR macro lens which is able to focus very close to itself.  There is nothing special about this, you are just giving the camera a bit of information about what you are shooting.

Alright, we have covered some different areas of auto focus and how the camera "sees" an image and how it knows what to focus on.  However, if you still can't get the focus just right regardless of which option you used...what now?  This is when you will need to go over to manual focus.  All but the most basic point and shoot cameras have some manual focus ability.  In an SLR, there is a toggle switch similar to the above image on the lens itself which switches from auto to manual.  There are some point and shoots that have this function as well (such as my Sony F828).  As with an SLR, once the manual focus is selected, you then control the focus by turning a focus ring which adjusts the optics to bring things into focus.  On an SLR lens, the focus ring has a range scale on it that shows the distance from the lens to the focal point.  Of course you will check the focus by looking through the viewfinder.

For those cameras without a focus ring, there is usually a menu option that will adjust the focus (see your owner's manual for details on this).  You can usually see the effects of the selection in the LCD display, but there are also distances shown that correspond with the focusing distance to help you get the focus right.  This is not very precise unfortunately, and should only be used when absolutely necessary due to low light, or other specific concern.

Hopefully, this cleared up some questions about auto focus and how it works.  While this is one of the basics of photography, it is often something that the photographer isn't really aware of.  I can't tell you how many years I just pressed the button on my 35mm point and shoots and wondered why it took so long for the shutter to release.  I had never heard of doing the AF lock with the shutter button prior to starting my self education in photography.  I still come across many people these days that are not familiar with this function.  If you happen to be one of those people, you should find that your pictures will improve greatly with this technique.

Thank you for joining me once again for Photo Trek's Tips and Tricks.  If there is a question that you would like to ask, please email me at NCPhotoTrekker@aol.com.  Lets all make the best pictures that we can.

Written by Greg A. Kiser

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