Category Archives: Aperture

How do I control macro (and other) depth of field?

On a Flickr discussion the other day, someone asked what the best way was to control and improve the limited depth of field when shooting with a macro lens.

Pollen In case you’re not familiar with the term, macro photography is very close-up photography.  Technically, it’s photography where the size of the image on your sensor is at least as big as real life, but most people use the term more loosely.  I’m not interested in picking technical nits here, so I won’t be picky.

If you’ve ever done any macro photography, you know that getting your whole subject in focus can be tremendously challenging.  When you’re shooting macro, your depth of field is extremely tiny, often measured in millimeters or fractions of millimeters.  Just a little bit of movement from you or your subject and everything goes to out-of-focus hell in a windblown handbasket.  Even when you have a perfectly still subject and your camera rests firmly on a tripod, shooting your subject at the wrong angle will get you in trouble.  For an extreme example, check out the larger version of the grains of pollen on the left.  The camera was at a slightly different angle than the pollen, and you can see the changes in focus at the top and bottom of the photo.  (You can also see some excellent examples of sensor dust if you look closely at the top right and bottom left corners.)

Back to our question:  how do you control depth of field when you’re shooting macro?  My response on Flickr was that you do it in exactly the same ways that you do for any other shooting:

  • choose your aperture wisely
  • manage your camera-to-subject distance
  • choose your focal point wisely
  • when you can, use depth of field preview to check your image before you shoot

We should all understand the first one by now– choose your aperture wisely.  If you’re new to Stop Shooting Auto! and you aren’t completely familiar with aperture and how it works, you should go reread this lesson and the few that follow it.  In short, choosing a wide aperture (a low-numbered f-stop like f/4) will give you a very shallow depth of field.  Choosing a narrow aperture (a high-numbered f-stop like f/16) will get you much more depth of field.

Don’t forget that there’s an online depth of field calculator that you can use.  If you click around on that site you can also find a PC version, an iPhone version, a PalmOS version, and several other tasty tidbits.

People often overlook the camera-to-subject distance when they think about depth of field, but it’s a key parameter.  Try pulling up the DOF calculator and enter the following values:

Camera format:  Canon Digital Rebel, XT, XTi, XS, XSi
Focal length: 100mm
Selected f-stop: f/11
Subject distance:  30cm

Note that 30cm is right about one foot.  Click the calculate button, and you’ll see that your depth of field goes from about 29.9cm to 30.1cm, for a total of .26cm.  That’s about two and a half millimeters, which doesn’t leave much margin for error.

Leave everything the same, but change the subject distance to 60cm.  Now, your depth of field is from 59.4cm to 60.7cm, for a total of 1.29cm. That’s still not a whole lot, but it’s almost five times what you had when you were a foot away.  Try it at more normal focusing distances, like ten feet and twenty feet, and you’ll see that even there, doubling the distance between the camera and the subject gives you about a 4x increase in your depth of field.  In short, if you’re having trouble focusing, move back.

IMG_5835Choosing your focal point can make a huge difference when you’re working with limited depth of field.  It’s often true that your camera can do a better job of focusing than you can, but it can’t choose what to focus on.  If you really care about a certain part of the image being in perfect focus, your best bet is to put the lens into manual focus mode and do it yourself.  This will give you absolute control over where you’re focusing.

In this image, letting the camera focus might well have meant that it chose to focus on a deeper part of the spadix (the sticky-outy part for non-botanists), leaving the tip out of focus.  This might have been an interesting effect, but it wasn’t what I wanted.

Don’t forget the depth of field preview button on your camera.  If you have a shot lined up, and you want to see how much of it will be in focus, press the depth of field preview button.  The viewfinder will get darker, sometimes very dark, but if you have enough light on your subject you can probably squint and get a good idea of how much of the image is in focus.

If you just can’t get enough depth of field, there are a couple of things you can do.  First, you can add more light to the subject.  I often use desk lamps for macro work, since I can aim the light wherever I want it.  Flashes are always an option, though they can be challenging to use.  If you’re outdoors, get your subject out of the shadows, or use a white reflector (even a piece of paper will work) to reflect light onto the subject.

Putting your camera on a tripod will let you use a longer exposure, and therefore a smaller aperture.  This only works for subjects that are stationary, though– don’t try it with moving objects or you’ll wind up with a blur.

And finally, if your camera is parallel to your subject it will be easier to get the image in focus.  If your subject is at an angle to the front of the lens, move the subject and/or the camera to get a better angle.  Look up at the pollen photo for an excellent example of what happens when you get this wrong.

While depth of field issues make macro photographers pull their hair out (and then photograph the strands), it’s challenging in lots of other situations as well.  Learn to control it and you’ll have a powerful tool for taking better photos.

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Filed under Aperture, Discussion, Lesson

Action Shots– A Quickie

IMG_8742I promised to write about histograms, but I’ve been pretty busy. However, here’s something quick I wanted to share. I went whale watching today with a couple of friends, and so of course I took the camera along. The thought process that I used here is pretty much my standard way of thinking about what I want to shoot.

Packing the camera bag was easy– the Canon 70-200 f/4L IS was the perfect lens choice, since it was long enough to bring the whales in close, and as a bonus image stabilization would help a little bit with the motion of the boat. Well, maybe, but it couldn’t hurt.

What about settings? I didn’t really care about depth-of-field other than wanting to have enough to get my subject in focus, so I set the camera to aperture priority mode and f/8. I realized that I was going to be shooting moving animals from a moving boat on choppy waters, and so shutter speed would be critical. I set the ISO to 100 and pointed the camera at the water, looked through the viewfinder, and pressed the button halfway to see what the camera would want to do. It picked 1/320 for a shutter speed. Under normal circumstances that would be fast enough, since it was faster than one over the focal length of the lens (1/200 in this case), but with all of that motion I wanted something faster. I took a wild guess and thought that 1/800 was a good minimum.

If I got 1/320 at ISO 100, then at ISO 200 I should be able to shoot 1/640. That still wouldn’t be enough, but at ISO 400 I should be able to shoot 1/1250. (Note: shutter speeds don’t always change in precise multiples of two. It’s confusing until you get used to it.) Since 1/1250 was well above my arbitrarily-chosen 1/800 threshold, ISO 400 should be perfect.

The sky was gray when we left the harbor, but I expected some of the fog to burn off over the course of the trip. I knew that I would have to doublecheck the settings if it started getting sunny– the fastest shutter speed my camera could do was 1/4000, which meant that I only had around two stops of room before my camera would be forced to overexpose the image. Sure enough, the sun came out a few hours later, but I was still able to shoot at around 1/2000. Otherwise, I would have either dropped down to ISO 200 or changed the aperture to f/11.

The thought process for this is one that you should use whenever you pick up a camera. What do I want this image to look like? What range of apertures and shutter speeds will get me the results I want? What camera settings should I use to get the right apertures and shutter speeds? As a novice you won’t always know all of the answers to those questions, but you can start guessing. “Do I want the background blurry or sharp? Do I want to capture or freeze motion?” Just answering those two questions before you pick up the camera will give you a huge leg up in getting the image you want.

Oh, yeah, a quick note about the gull. When I first looked at this picture on the camera’s LCD, I was rather shocked– the image looked blurry! It was taken at a shutter speed of 1/2500, so that hardly seemed possible. Either I’d seriously misjudged what shutter speeds would work, and I didn’t think I had, or something else was amiss. I zoomed in on the image and realized that the fuzziness I thought I was seeing was really the transition in feather colors at the rear edge of the wing. The image was actually so sharp that I could pick out individual feathers quite clearly.

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Filed under Aperture, Exposure, ISO, shutter speed

f/8 and Be There

IMG_1088

There’s an old saying among photojournalists– f/8 and be there. Sometimes the technical details of a photograph really matter, and sometimes they don’t. Perfect technique won’t help you if you don’t have your camera ready to go when the moment happens.

As you may have heard, the Olympic torch made an appearance in San Francisco today. In fact, it was scheduled to pass just a block from my office. I normally just hop in the car and drive to work, but I was worried that parking would be expensive and the neighborhood would be a zoo, so I opted for public transit. I took the ferry across the bay to San Francisco (and snapped some fun pictures, but accidentally erased them… I don’t function well in the morning), and encountered lots of protesters near the ferry building.

I knew this was likely, so I already had the camera ready to go. In particular, I put the camera in aperture priority mode, set the aperture to f/8, picked a lens that I was happy with, and made sure that autofocus and image stabilization were turned on. f/8 is the perfect middle-of-the-road aperture, since it will give you enough depth of field to compensate for minor focus mistakes, and will let in enough light to get decent shutter speed in daylight.  I also put the camera in multiple shot mode, so that if something was changing quickly I could just hold down the shutter button and hopefully get one of the shots timed perfectly.

Later in the day, I increased the ISO to 400– I was shooting a lot of stuff that was in shadows, and I wanted to make sure I had plenty of latitude in my shutter speed.

(I made one mistake in camera settings, but I was able to work around it OK. Can you spot what it was?  It’s hiding in the photo’s exif data.)

By spending a little bit of time up-front thinking about how I would be shooting, I was able to just forget about the mechanics of the camera and pay attention to what I wanted to shoot.  The picture above is one that I almost got right, but not quite… if only the bloody video guy hadn’t walked in front of me just as I pressed the shutter button.  Still, if I didn’t tell you that you might think he was another protester, and I’d almost be off the hook.

When shooting fast is really important, think about your camera settings in advance and figure out what you need in order to be able to forget about them.  In typical broad daylight shots, that’s probably aperture priority mode and f/8.

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Filed under Aperture, Controls, Equipment

Hey, where’s your homework?

Hey you… yes you! Where’s your homework? Remember the homework assignment I gave you that’s due by the end of the month? Some of you have done it, and done quite a fine job, but the rest are still slacking. No, the dog dd not eat your memory card, and I won’t take a note from your mother.

If you need to review, here are some lessons that might help you:

And if you want to go through all of the lessons, walk through Exposure Lessons, in order.

Now go out there and do your homework. I don’t want to have to give you detention. Be sure to leave a comment on the homework entry with a link to your photo(s), along with exposure details and anything else you want to say about them.

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Filed under Aperture, Exercise

Homework Assignment… with a prize!

flower f/4

April 4, 2008 @12 a.m:  The contest is now closed.  You’re still welcome to do the exercise and add your photos to the comments, of course, but you won’t be eligible for the March prize.

OK all you slackers… you have homework. Grab your cameras.

Go outside on a bright sunny day, or somewhere where you’ll have lots of light to work with. Find a subject. I don’t care what it is– a person, a tree, a flower, a fire hydrant– and a background. The only criterion is that the subject is clearly distinct from the background.

Take a picture of your subject in such a way that the background is intentionally blurred. You can use aperture priority, shutter priority, or manual modes at your discretion, though of course one of those is less-suited to this exercise than the others. Don’t just shoot a bunch and hope you get it right, but think about what settings you want to use before you take the shot.

Upload your photo to a photo sharing site (I recommend Flickr but any one will do). Leave a comment with the settings that you used, a link to your photo, and anything else you want to say about the image.

At the end of March 2008, I’ll pick one commenter at random and send them an 8×12 signed print from my flower porn collection.

OK, go out there and shoot!

Update! At a friend’s suggestion, I’m offering two prizes. If at least 20 people submit entries, I’ll give away two prints– one to someone chosen at random, and one to the best submission. Pass the word to your friends, enemies, photography groups, etc. You can enter more than one image but don’t get too carried away… a few is OK, but not a dozen.

Small print: void where prohibited by law. Anyone who clearly violates the spirit of the rules will be disqualified. Don’t put that in your mouth… you don’t know where it’s been. Please make sure your images are worksafe. You can post more than one photo, but you’ll only get one chance at the drawing. It must be a photo that you took specifically for this assignment, not something pulled out of the archives. Play nice. Judging is at my discretion, and is final. SSA might want to show your image in a future entry, but we don’t want any other rights to it– if we want to use it for anything else, we’ll play nice and ask for your permission first.

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Filed under Aperture, Exercise

How the settings play together

After trudging through all those scary numbers, we now know that ISO 200 is twice as fast as ISO 100, that 1/60 second is half the time of 1/30 second, and that f/4 is twice as fast as f/5.6. If I did my job well, we even learned that without anyone’s brain dripping out of their ears and onto their keyboards.

Note: the word “fast” in photography generally means “captures more light” when it’s talking about ISO or aperture.  When talking about shutter speed, though, “faster” means just the opposite– 1/60 is faster than 1/30, but 1/30 lets in twice as much light.  It’s confusing.

What might or might not be obvious now is that we can change two different things and keep the exact same exposure. For example, each of these settings will produce the exact same exposure:

ISO 100 f/4 1/60 sec baseline
ISO 100 f/2.8 1/120 sec faster (wider, more light) aperture, faster (less light) shutter speed
ISO 200 f/4 1/120 sec faster ISO, faster (less light) shutter speed
ISO 200 f/5.6 1/60 sec faster ISO, faster (wider, more light) aperture
ISO 400 f/5.6 1/120 sec ISO four times as fast, shutter speed twice as fast (less light), aperture half as fast (narrower, less light)

The first line is our baseline measurement. On the second one, we opened up the aperture wider to let more light in. In order to keep the exposure constant, we need to capture less of the light, so we keep the shutter open for half as long.

On the third and fourth lines, we increase the ISO, which records more light To balance it out, we either keep the shutter open for less time, or we make the aperture smaller– either of those will let less light in.

The fifth line is tricky! We’ve quadrupled the ISO, which means we’ve increased it by two stops. In order to compensate for that, we made the aperture smaller by one stop and we also made the shutter speed faster by one stop.

The fancy technical term for this is reciprocity– it really just means that if you change one setting, you can balance it out by changing another one, and get the same result.

So how would you use this? Here’s an example. Let’s say you’re taking a picture of a group of people, some of them standing behind the others. You put the camera in aperture priority mode and pick f/4 and ISO 100. When you try to take the shot, you find out that the best shutter speed is 1/30, and that’s too slow for you to hold the camera steady– you need at least 1/50 sec. What do you do?

Well, you can try using f/2.8 and 1/60. That will get you the same exposure, but at a faster shutter speed. But wait… now you’re at f/2.8, and when you focus on the front row of people the back row is out of focus, or vice versa. You really need f/4 to get everyone in focus.

Finally, you set the ISO to 200, which lets you use an aperture of f/4 with a shutter speed of 1/60. Voila! You get your shot.

The way exposure settings play together is a little bit like having a squishy ball in your hand. When you squeeze one part to make it smaller, another part gets bigger. Squish two parts, and the third one gets a lot bigger. Squish squish squish.

Easy, huh?

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Filed under Aperture, ISO, Lesson, shutter speed

How much more light? How much less?

At this point, we know what’s bigger and smaller, faster and slower. We know that f/4 is a bigger opening than f/8, and therefore lets more light in. We know that a shutter speed of 1/200 is faster than 1/100, and therefore lets less light in. We know that ISO 400 is faster than ISO 200, and therefore captures more light.

You’re with me, right? Good.

I’m about to throw a little bit of math at you, but I promise it’s only a tiny amount. No, really. All we really have to do is multiply by 2 or divide by 2. That’s easy, right? Take a deep breath. Ready? Let’s go.

How much more light does a shutter speed of 1/100 let in compared to a shutter speed of 1/200? The obvious guess is twice as much, and it’s precisely right. Any shutter speed that’s half as fast will let in twice as much light. Any shutter speed that’s twice as fast will let in half as much light. So 1/200 is half as much light as 1/100. 1/400 is half as much light as 1/200, and is therefore 1/4 as much light as 1/100. Double the bottom number means half as much light. Easy, huh?

Let’s look at ISO next. Do you think that ISO 200 is twice as much light as ISO 100? Bingo! Just like shutter speed, changing the setting by 2 means twice as much light, or half as much light. ISO 200 is half as fast as ISO 400. ISO 100 is half as fast as ISO 200, so it’s 1/4 as fast as ISO 400. Again, all you have to do is multiply or divide by 2, and you’re good.

Now aperture. Do you think f/4 is twice as fast as f/8?

Sorry, but this time it’s a tiny bit more complicated. When it comes to aperture, making the opening half as big means you’re only going to get 1/4 as much light. Making it twice as big means four times as much light. If you don’t want to know why, skip the rest of this paragraph. Our aperture is basically a circular opening. Remember back in high school, the area of a circle is pi-r-squared? Changing from f/4 to f/8 means that the radius of the opening is divided by 2. Because the area is changed by the square of the radius, the area of the opening is divided by 4. The amount of light coming in is directly related to the area of the opening, so the amount of light coming in is also divided by 4.

As it turns out, the way to cut the light in half is to change the aperture by a factor of about 1.4. In this case, f/5.6 is half as much light as f/4, and f/8 is half as much light as f/5.6.

Let me put it all into a nice tidy table, in case that’s easier to follow:

setting Starting setting 1/2 as much light 1/4 as much light
ISO 400 200 100
Shutter Speed 1/100 1/200 1/400
Aperture f/4 f/5.6 f/8

Now, a tiny bit of jargon. Whenever you increase or decrease the amount of light by a factor of 2, that’s called a stop. A shutter speed of 1/400 is one stop faster than 1/200. An aperture of f/4 is one stop wider than f/5.6. ISO 100 is one stop slower than ISO 200.

In summary: for shutter speed and ISO, changing the number by a factor of 2 means twice as fast or twice as slow. For aperture, changing the number by a factor of 2 means four times as fast or four times as slow. Half as much/twice as much is really all of the math you need to know in order to be a competent photographer.

A bonus note for those of you who are vaguely mathematically inclined. Remember that I said that changing the aperture setting by a factor of 1.4 meant twice as much or half as much light? The astute reader will note that 1.4 is (approximately) the square root of 2. That’s not a coincidence.

Next lesson:  How the settings play together

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Filed under Aperture, ISO, Lesson, shutter speed