Category Archives: Exposure

Aperture Priority Mode


After having read the basics of Exposure (you should really read the Understanding Exposure post before reading this one), we’re going to apply that knowledge by using my favorite camera setting: Aperture Priority Mode.  Sometimes this is displayed as an “A” on your camera’s main dial, or it may show up as “Av.”  While I wouldn’t say that Auto Mode on a digital camera is a terrible thing, I’d put it in a classification of “emergency use only.”  If you need to get a shot quickly, it usually does the job, but rarely as well as the camera is capable.  Aperture Priority still uses a number of the camera’s automatic features, while putting you in charge of others.  Particularly, something called Depth of Field (DOF).  DOF is about the relationship of what you’ve focused your camera on (the subject) and everything else in front of and behind that subject.  There’s a lot of math involved in the details, but we’ll leave that up to the nerds (not that there’s anything wrong with that), and look at the big picture perspective.

Basically, when you focus on your subject, how sharp or blurry everything else is in the picture, will be determined primarily by your aperture (remember from Exposure, that’s the f stop).  A lower aperture (like 2.8) causes everything except your subject to become blurred.  This is what’s referred to as a shallow DOF.  A higher aperture (like 22) causes everything in the entire picture to be (mostly) in focus.  Why does it matter?  If your kids are playing in such an adorable way that you have to get a picture of it, but they’re at the park and from your viewpoint, the parking lot is in the background.  In the lot are a few windowless, ratty looking, child abduction vans that you don’t want to become the focal point of your image.  What do you do?  You can’t go ask the kidnappers to move their vans…that would be politically incorrect!

This is the perfect opportunity to take control of your camera and make it do what you want.  Set it to Aperture Priority, use whatever dial on your camera controls the aperture (there are often 2 dials, try them both if unsure), and set it to something like f2, or 2.8, or 4 (whatever the lowest one is that it will go down to).  Focus on the kids and take the shot.  The parking lot behind them, and everything in it, will disappear into a beautiful, blurry mix of soft colors, leaving the focal point of the shot on your kids.

Without going into too much detail, you should know that sometimes when your lens is zoomed in, you may notice that you can’t always go as low in your f stop.  This is related to the len’s focal length.  Most zoom lens (meaning all except the really expensive ones) have self-adjusting apertures.  When you’re not zoomed in, the lens might go down to f2.8, but when you’re zoomed all the way in, it only goes down to f4 or f5.6.  Just keep this in mind and know that if you want/need to get a larger aperture (to get the background more blurred), physically move yourself closer to your subject so that you don’t have to be zoomed as much.  This will give you that lower f stop.  Just grab your camera and play with the zoom, in Aperture Priority Mode.  You’ll see that the lowest available f stop will change as you zoom in close.

Don’t forget to keep an eye on your shutter speed.  You don’t want it to drop too low.  60 to 120 if the subject is still, 250 to 500 if they are moving some, and over 500 if they are moving a good bit.  If the shutter speed drops lower than you want/need it to be, and you still want a lower f stop, you can always increase the ISO to let more light get to the sensor.  Going up to an ISO of 800 should produce good results and some cameras can go quite a bit higher.  Only raise the ISO as high as you need to, ideally keeping it at or under 400.  See how useful the Exposure post was?

This same concept of using a low f stop to blur the background, is how we get great shots with someone standing in front of the Christmas tree and all the lights are beautifully blurred behind them.

One other detail to keep in mind is that there needs to be some separation (distance) between the subject and the background in order for it to be out of focus.  The further away the subject is from the background, the more out of focus it will become.  If you want to take a shot of someone standing in front of some colorful flowers or tree leaves that produce a wonderful, soft color behind them, get the subject about 10 or 20 yards from the background…the further, the better.  Zooming in also helps the lens to distort the background.

Here’s an example of a mother and child in front of a tree shot at f8.  The tree behind them is in too sharp of focus, and as I see it, quite distracting.


Here’s another shot, but taken at f3.5.  To me, the softening of all the detail in the tree puts and keeps your focus on the subjects.  Much more pleasant to the eye.  It’s funny…to me, the shot below makes them appear to stand out from the tree, separated.  In the previous shot above, it actually looks like they are almost standing in the tree, or at least only a foot or 2 away from it.  But between these 2 shots, they never moved.  Pulling them another 10 yards away from the tree would have had a more dramatic effect, but you get the idea.


Here’s an example of some wildly colored fall leaves about 50 yards from my subject, with me zoomed in tightly.  This was shot at f 5.6, but because he was both a good distance from the leaves, and I was zoomed in pretty tight (150mm on a 200mm zoom lens), we got a great, soft blending of colors as the background.  Had the leaves only been about 10 yards from him, they would be pretty well defined.


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Understanding Exposure

Before venturing out of your camera’s Auto Mode, opening a whole new world of photographic possibilities, we need to develop a basic understanding of exposure.  Don’t worry, this is not going to hurt.  There are really only 3 things that you need to follow:

1.  ISO: the measure of a digital camera sensor’s sensitivity to light
2.  Aperture: the size of the opening in the lens when an image is created
3.  Shutter Speed:  the duration of time that the shutter is open

If you’re trying to decide whether or not this is worth your time to learn (come on…it’s only 3 things), skip down to the bottom of this post and read the last 2 paragraphs.  If any of it rings true in your photographic life, come back up here and dig in.  The whole thing is going to take about 5 minutes to turn you into an exposure pro!

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