Tag Archives: camera

March 4, 2008 · 9:32 pm

Why are there spots on my picture?

You might notice it in the blue of the sky or the white of a wedding dress. Maybe, as often happens with me, it’s the petals of a flower. Whatever the image, someday you’re going to look closely at a picture and see that it’s full of little spots. These often look like little dark spots ringed by a color that’s slightly lighter than the background, and they show up in the same place on every picture you take.

These spots usually come from dust on your sensor. You won’t see them too often at large apertures, but when you stop the camera down they start to become visible. They particularly stand out in areas that have large expanses of a single light color, but you can often see them in other areas of the image as well.

This flower was taken at f/32, which as we all know is a very tiny f-stop. It’s not a great photo, but because of the small aperture it shows every little piece of dust on the sensor. You can’t really see it at the small size, but if you were to look at the full-resolution image you’d see lots and lots of little bitty spots all over the photo.

On the right is a collection of full-size crops taken from the same image. These spots become highly-visible and quite annoying when the image is enlarged.

There’s an easy way to test to see if you have noise on your sensor. Find a brightly-lit white or light-colored wall, or a piece of plain white paper. Set your camera to manual mode, shutter speed of about two seconds, and the smallest aperture your lens will do. Point the camera at the white surface and take a picture, moving the camera around just a little bit so that the background becomes blurry.

Transfer the image to your computer and look at it full-size. Chances are good that you’ll see at least a few little specks, and if you’ve never cleaned your sensor before it may be pretty bad.

This image originally came from Flickr user djwudi, and I thank him for allowing me to use it. He works in a camera shop, and a customer came in complaining about spots on his photos. This is what the sensor looked like at f/32 before cleaning. I’ve personally never seen one this bad, but dust can start making your pictures ugly long before this point.

If you change lenses, and sometimes even if you don’t, getting dust on your sensor is inevitable. However, there are a few things you can do to reduce the amount of dust that your sensor collects:

Never store the camera without a lens or other protective cap
Minimize the number of times you change lenses, and minimize the amount of time the lens is off the camera
When you change lenses, make sure the body of the camera is pointed down and the camera is turned off
Try not to change lenses in dirty environments

My procedure for changing lenses is to turn the camera off (though sometimes I forget), then take the rear cap off of the new lens and get it ready to go. As soon as it is, I point the camera straight down, remove the lens, and put the new one on as quickly as possible. I then put the rear cap on the old lens and store it in my camera bag.

Do you have dust? Don’t worry! Here are SSA!’s instructions for cleaning your sensor.

5 Comments

Filed under Discussion, Equipment

Tagged as camera, dirt, dust, sensor, yuckypoo

January 23, 2008 · 10:55 pm

Question: Shooting At The Zoo

I recently got an excellent reader question from TJ. It was such a great question that I thought it deserved its own entry, rather than being buried in comments.

Patti, I had a really frustrating experience last year when I attempted to take pictures at a zoo. Most of the occupants were birds and were housed behind 1″ grid wire. Frequently, they were shaded and I (and the camera) were not. Sometimes they were moving. Sometimes I had to shoot up into a tree and the sun was shining directly into the lens. Often, my camera wouldn’t focus, so I had to shift to manual focus. Sometimes, it wouldn’t even snap the picture when I was doing the focusing. I have a Nikon D70s. Might you give some tips on what I could’ve been doing wrong and how to shoot these types of pictures better?

TJ, that’s a really hard set of circumstances to work under, because you have so many things working against you. This is exactly the sort of situation that will confuse automatic modes on your camera, and require you to switch to manual settings in order to get good shots. I’m not sure I have a magic formula, but let me see if I can break the problem down and show you how I’d think about it.

First the fence. It’s going to do two things– get in the way of your shooting, and confuse your autofocus. Switching to manual focus is a great way to solve the latter problem, since you’re smarter than the camera is and you know to just ignore the fence. Once you’re in manual focus, you have two choices on how to deal with the fence– you can either stand back and use the fence as part of the composition, or you can put the lens up against the fence and shoot between the grids. Using a wide aperture will help the fence blur and fade out of the picture, especially if you’re close to it.

Here’s where things are going to get hairy and conflict with each other. You’re manually focusing on a moving target, so you sort of want to leave yourself some room for error– if you have a lot of depth-of-field, you’ll still have the bird in focus even if he starts moving. However, that’s in direct conflict with wanting to use a wider aperture to make the fence fade away. I would probably opt for using something like f/5.6 (I originally said f/11, but in retrospect I think that’s probably not the best answer) and then get as close to the fence as I could, but I’d play around with it and see what worked for that particular situation.

Once I found an aperture that I liked, I’d try to find the best shutter speed that worked with it. If I couldn’t get a fast enough shutter speed to capture the birds well, I’d increase the ISO until I did. If that still didn’t work, I’d open up the aperture until I found something that worked. There’s a pretty good chance that the camera’s metering will be confused here, so use it as a starting point rather than a final answer.

This is one of those places where digital has a huge advantage over film– you can try out the shot and see how it works. The birds aren’t going anywhere, so you can afford to spend a few minutes setting up a few shots and seeing what works, then making adjustments. Whenever I’m shooting under tricky lighting conditions, I always do a few test shots beforehand so that I can get my camera set up the way I want it.

Backlighting, especially shooting into the sun, is just hard. Don’t forget that your feet are an invaluable photographic tool. If you can’t get the shot because the sun is right in front of you, take a few steps. You’ll probably be able to find a better angle on your subject. If you’re close enough that you can use a flash to fill in some front light, that often works very well.

I haven’t used a Nikon dSLR, so I don’t know what will stop it from taking a shot. I know that my Canon will stomp its foot and get pouty if it can’t focus, but if I put it into manual focus it will shoot with the lens cap on in all exposure modes.

After I answered this question, I went out and took a few photos through a fence, to see what the fence looked like at different apertures and distances. I’ll post them as a separate entry.

By the way, the bird photo at the top of this entry was taken at the St. Louis Zoo a few years ago, shortly after I got my first dSLR. I can’t remember much about the photo, but it was taken through either glass or a fence in auto mode. I included it partially because it matched the subject matter, but mostly to remind myself that just a little while ago all I really knew how to do was point the camera at something and hope for the best.

What do lens terms mean?

If you’ve just gotten your first dSLR, you’ve probably already thought about buying another lens to go with it. Maybe you want something that will let you shoot telephoto, or wide angle, or macro. Maybe you want something faster. Most likely, you don’t know what you want, but somebody told you that the kit lens wasn’t very good and you believed them.

You did what anyone would do, and started surfing the web looking at lenses. Pretty soon, your head was swimming and your eyes were glazed over after looking at all those lens terms. What’s an EF-S? What does 70-200 mean? Why is that lens so much more expensive than the one that seems like the same thing?

I’ll do my best to unravel it all for you, though I’ll warn you up front that some of this is Canon-specific. If anyone wants to write a guest entry and explain Nikon-specific terminology, or terminology for other brands, leave me a comment.

First off, an easy one. The writing on the front reads “CANON LENS EF 50mm 1:1.8 II CANON INC. (theta)52mm”. This is the Canon “Nifty Fifty” 50mm lens. (It’s a steal at around $75, and I highly recommend picking one up if you shoot Canon.) The “CANON LENS” is easy enough that I won’t insult your intelligence by explaining it.

“EF” is a Canon-specific term, and it stands for Electro-Focus. This is the type of lens that is used on the Canon EOS line of SLRs. As of this writing, all digital SLRs are EOS-type cameras, so if you have a Canon dSLR any EF lens should work. Some lenses are EF-S rather than EF. The S stands for “sticks out in back” or something like that– the back part of the lens sticks out a little farther than an EF lens. If you have the Canon 18-55 kit lens, it’s an EF-S mount. EF-S lenses work on almost all Canon dSLRs except for the high-end professional models.

“50mm” is the focal length of the lens– I explained what focal length is in the previous entry. 50mm is kind of a mid-range focal length, neither long enough to be telephoto nor short enough to be wide-angle. It’s a good general-purpose length.

“1:1.8” is the maximum aperture of the lens– the widest that it can open. The term “1:1.8” means exactly the same thing as f/1.8, and we all know what f-stops are now, right? Right?

I’ll be perfectly honest here and say that I’m not certain what the “II” means, but I’m guessing it means something like “Version 2”.

On the other side of the lens it says “CANON INC.” and then “52mm”. That last number is the size of the filter threads. Almost all lenses have threads on the outside that will let you screw a filter onto the front, either to protect the front glass from damage or to add some sort of special effect. On this particular lens, the diameter of the threads is 52mm, which means that you need to buy a 52mm filter if you want to add a filter. It is common practice and a very good idea to keep a UV filter on the front of your lens at all time, to protect the lens from damage.

Here’s the Canon kit lens. It’s a lot like the previous one, but a little bit more complicated.

Notice that instead of “CANON LENS” it says “CANON ZOOM LENS”. The word zoom means that the lens can change its focal length. In the previous example, the 50mm lens was always 50mm and you couldn’t make the focal length any longer or shorter. In the case of a zoom lens, there’s an extra ring on the lens that lets you zoom in or out to get closer or farther away from your subject. In this case, if we look just a little bit farther on the lens, we’ll see “18-55mm”. That means that the lens can zoom out to be as wide as 18mm, or zoom in to get as close as 55mm. You can, of course, use any length in-between those as well. Zoom lenses are nice because they let you have a lot of flexibility in how the image looks without having to change to a different lens.

I’ve already explained the “EF-S” part, but I’ll remind you that it’s Canon-specific.

Now it gets interesting. The maximum aperture is listed as “1:3.5-1.5.6”. We already know that means f/3.5-f/5.6, but why would a lens have more than one number? As it turns out, zoom lenses are really nice to use, but they’re harder to make than fixed-focal-length (also called “prime”) lenses. Some zoom lenses have the same maximum aperture at both their shortest and longest focal lengths, but sometimes the maximum aperture changes. When you see two numbers, the first one is what the maximum aperture is when the lens is at its shortest focal length, and the second one is at its longest.

In this case, that means that when the lens is zoomed out to 18mm, the widest possible aperture is f/3.5. When it’s zoomed in to 55mm, the widest it can open is f/5.6. As you can probably guess, if you’re in the middle of that range the maximum aperture is somewhere between those two values.

Finally, this lens has 58mm filter threads.

There are a few more terms you’ll commonly see for Canon lenses. “USM” stands for ultrasonic motor, and specifically the motor that is used for focusing. All you really need to know is that USM lenses focus faster than their non-USM counterparts, and they’re quieter.

“IS” stands for image stabilization. This is a piece of real technical magic that helps get rid of camera shake on longer exposures. It can be extremely useful for getting shots where you can’t quite hold the camera steady enough to get a solid shot. It won’t help you with moving subjects, and it won’t do any good for very long exposures, but it’s great when there’s almost but not quite enough light. IS lenses are much more expensive than their non-IS counterparts, though.

And finally, some Canon lenses have the “L” designation. This stands for “Ludicrously Expensive.” OK, not really, but it might as well. Canon L lenses are their top-of-the-line professional models. They are generally the highest-quality lenses that Canon makes, but they come with a high price tag.

I hope that helps, at least a little. Again, if someone wants to guest author a similar article about Nikon or other brand lenses, leave me a comment.

13 Comments

Filed under Equipment

Tagged as camera, lens, photography

January 11, 2008 · 12:23 am

What is focal length?

It happens to most dSLR owners. You get the camera, and you’re thrilled with it, but you’re also awed and a wee bit afraid because the whole thing is just so confusing. It doesn’t take very long before someone tells you that the kit lens, the lens that usually comes with the camera, is a piece of garbage. This sends you off to the web to find a better lens, but there are all sorts of complicated and cryptic numbers and letters and symbols and the like. The whole thing is so bewildering that you just want to go to the drugstore and buy a disposable film camera.

Don’t fear! The cryptic numbers and letters that are used to describe lenses are really (mostly) pretty straightforward. If you’ve been reading this blog, you’ll probably find that you’re already familiar with most of the terms, so this won’t be too hard.

Before we start looking at lenses, there’s on term that I may not have explained yet– focal length. In a nutshell focal length is how long the lens is. It’s a little bit more complicated than that, of course, and the technical definition isn’t all that interesting, but there is really only one thing you need to know, and it’s really easy. The longer your lens is, the more the image is magnified.

Let’s say that you’re taking a picture of the tree in your yard, and there’s a bird perched on a branch. If you use a short lens, you’ll get the whole tree into the picture, and the bird will be a tiny little blob. If you use a long lens, you’ll just get the bird and the branch that he’s sitting on, and you’ll be able to tell that he’s a blue jay. If you have a really long lens, you’ll be able to see the worm in his mouth. Cool!

If you have a zoom lens, and you probably do, you’re probably already familiar with this concept. Zoom in and everything gets closer. Zoom out and you get more of the area in the picture.

Long lenses are called telephoto lenses. The prefix tele- means distant, so telephoto lenses let you take pictures of distant things. This amazing shot of a polar bear, taken by award-winning nature photographer Joe Decker, was taken with a telephoto lens. Joe’s a smart guy, and he knows if he gets too close to a bear he runs the risk of being dinner.

Short lenses are called wide-angle lenses, because they let you get a really wide view of your surroundings. Again, I’ll use one of Joe’s photos, this one a sweeping view of sunrise in Bryce Canyon. I honestly don’t know what lens was used for this shot, but the only way to get such a grand vista is to use a wide-angle lens.

Here’s what you should remember about focal length: using a wide-angle lens is like stepping back from the picture so that you can see more of the action, while using a telephoto lens is like walking over to the subject so you can get a closer look. That’s really all you need to know for now.

Once again, I’d like to thank Joe Decker for giving me permission to use his images as examples. I highly recommend checking out his work, especially some of his recent images from Iceland and Greenland.

In the next lesson, I’ll take a closer look at a couple of lenses and explain what all of the numbers mean.

Ten Tips For Your New dSLR

Was Santa Claus good to you? Did you find a new dSLR under the Christmas tree this year? If so, then congratulations! You were definitely a good little boy or girl, and you got a very nice treat. You’re probably excited, but also a little bit intimidated by your new toy.

Here are ten Stop Shooting Auto! tips to get you started with your new dSLR:

Read part of the manual. Your camera’s manual is an invaluable guide to your dSLR, and one that you will be referencing many times in the upcoming months. It has lots of great information in it about how your camera works and what all the settings do. That’s the problem– it has too much information for getting started. If you read the whole thing right now one of two things will happen. Either your head will explode, or most of the information will go in one eye and out the other. Read the beginning of the manual now, enough to get you started with the basics, then set it aside and shoot for a while. Come back to your manual later, after you’ve used the camera for a while.
Take some pictures. Pick a theme, something not too hard, and play around. Maybe you want to take pictures of all your friends making funny faces, the tail lights of all the cars in your neighborhood, or the appliances in your kitchen. It doesn’t matter what you shoot, just do it. You probably won’t get any great masterpieces, but you’ll get some practice with your camera in a slightly structured manner.
It’s OK to use automatic modes. Did I really just say that? Yes, yes I did. Any dSLR has thirteen betrillion different knobs and modes and menu settings and gewgaws and whatchamacallits that you’ll need to learn about. Just like reading the manual, trying to learn about all of the settings at once is going to be too overwhelming. Start off by letting the camera do most of the work for you, then gradually take over the settings as you find a need for them.
Don’t obsess over better lenses and equipment. Right now, people are probably telling you that the kit lens (the lens that came with your camera) is garbage, and you have to get a better one immediately. If you’re a geek, you’re probably poring over reviews in magazines or websites so that you can compare specs and find your next lens. Stop it. The kit lens is a perfectly good starting point, and it will be a while before you find it limiting.
Start making a list of small accessories that you want. OK, this is exactly the opposite of the advice I gave in #4, but it’s a different situation. There are probably a few little things that you’ll want to pick up sometime soon, so make a list as you find them. Do you need a spare battery or charger? Is the strap cutting into your neck? You’ll almost certainly want a bigger memory card at some point. You don’t need to run out and stock up on every accessory in sight, but think about the things that will be useful to you.
Handle your camera with care, but not paranoia. Your camera is a complex, high-tech instrument, but it’s also designed to handle some degree of abuse. You don’t have to baby your camera, but exercise some common sense. Don’t bang it around. Be careful not to get dirt inside the camera. Don’t drop it into the bathtub or run over it with your Range Rover.
Experiment. One of the best was to learn about your camera is to just play around with it. Try zooming in and out on the same scene and see how the image changes. Get down on the ground and look at things from a different angle. Try different modes to see what they do. One of the beautiful things about digital photography is that “film” is cheap, and another is that you don’t have to develop the photos before you can see them. You can try out lots of different things to see what works.
Analyze your shots. One of the other wonderful things about digital photography is that your camera records the settings you used. Photographers used to keep notebooks for the shots they took so that they could record the exposure settings, focal length, etc. Today, you just have to look at some information, called the EXIF data, that’s hidden in each file. Here’s an example. You don’t care about all of the data, but Exposure (shutter speed), Aperture, Focal Length, and ISO Speed are all useful data. The software that you use for pulling pictures off of the camera and viewing them probably has a way for you to see this information.
Find a photography buddy. It can be more fun to shoot with a friend or friends, and you can learn together. Flickr has groups for most cities, and many of those groups get together to share information and go shooting. You’ll get ideas from each other, and pick up interesting tips.
Have fun! If there’s a picture you want to take, take it. Don’t worry about not doing it right or not getting a perfect shot. Play around. Climb up on the playground equipment to get a different angle. Take pictures of bright-colored things just because you like them. Break the rules. I promise that the photography police won’t arrest you for it.

What are you waiting for? Get out there and get shooting.

2 Comments

Filed under Introduction, Stuff

Tagged as camera, photography

December 28, 2007 · 12:46 am

How to take a picture of the moon

If you’re in a hurry you can ignore the discussion and skip straight to the summary

Since a couple of people have requested this, here’s the Stop Shooting Auto! lesson in shooting the moon.

Back in the olden days, when cameras were carved out of stone and didn’t have whizbang light meters and dozens of confusing exposure dials, photographers had to choose their settings manually. In fact, my first 35mm camera, a Kodak Pony IV, had printed inserts that went into a slot in the back of the camera to help you pick your settings. For bright sunlight you used this, for cloudy bright you used that, etc. And horror of horrors, there was no Photoshop– if you screwed up the exposure, you had to try to fix it in a (gasp) darkroom. And that was if you were lucky– most people just lived with whatever bad photos they took.

Back in these dark, dark days, photographers often relied on rules of thumb to help them choose their exposures. The most common of these was called the Sunny f/16 Rule. The rule went like this: for objects that are brightly lit by the sun, set your aperture to f/16. Set your shutter speed to 1/ISO of the film. (Film? Do you remember that?) So if you were shooting with ISO 100 film, you’d set the camera to f/16 and 1/100 sec, or as close to that as you could get. At ISO 200, it was f/16 and 1/200 sec.

I know what you’re thinking. That’s great, Patti. Thanks for your little stroll down memory lane, but someone has been spiking your Geritol. I want to photograph the moon, and I want to do it at night when it’s dark out. Why would I care about sunny days?

Here’s a little secret. The moon is nothing more than a bright object lit by the sun. Sure, it’s in a dark sky and everything around you is dark, but the moon is surprisingly bright. However, it’s also pretty far away, and that makes it look pretty small in the sky and even smaller through your camera’s lens. Unless you have a very long telephoto lens, your camera’s meter just won’t know what to do with the shot. If you’ve tried to take a picture of the moon in automatic mode, you probably got a small white dot on a dark but washed-out background. We can fix that, but it will mean putting your camera in manual mode. I hope that’s not as scary to you as it would have been before you started reading this blog.

Let’s go back to that telephoto lens thing for a moment. The first thing you want is the longest telephoto lens you can get, so that the moon looks like something other than a white dot. 200mm is about the shortest, 300mm is better, and 500+ is even better than that. If you don’t have a long lens, a teleconverter is a useful accessory to have. In a nutshell, a teleconverter is kind of like a magnifying glass added to your lens. With a 1.4x teleconverter, a 200mm lens acts like a 280mm lens, and with a 2x teleconverter, a 200mm lens acts like a 400mm lens. There are some serious downsides to using teleconverters, but they can also be useful tools.

[Update: I’ve recently added an article titled What lens should I use to take a picture of the moon? It has examples of moon shots at focal lengths from 200mm to 2240mm.]

OK, so you have your longest lens out. You might want to use a tripod too, lean the camera against a wall or something to stabilize it. What settings should you use?

First off, use manual focus. Because the moon is pretty small in your viewfinder, many cameras have trouble focusing on it. If yours works in autofocus that’s great, but if not just switch to manual focus and do it the old-fashioned way.

In my experience, the Sunny 16 Rule is close but not quite right for the moon. The best settings I’ve found seem to be around ISO 100, f/11, and 1/100 sec. However, sometimes something a little slower or faster does a better job. Because of this, I recommend doing something called bracketing. Bracketing is just a fancy term for taking a bunch of shots at slightly different exposures so that you can pick out the best one.

Set your camera for manual mode, ISO 100, f/11, and 1/100 of a second. Take a picture. Now without changing any other settings, set the shutter speed to 1/200 and take another picture. Do the same thing at 1/400. When you’ve done those three, go the other way. Set the shutter speed to 1/50 and take a picture, then 1/25. If you aren’t using a tripod, don’t forget to brace the camera against something solid like a wall or a pole, so you don’t get camera shake. And voila! One of those is probably a pretty good shot of the moon.

To summarize:

Manual mode, at f/11 and ISO 100
Focus manually
Use a tripod or stabilize your camera against a sturdy object like a wall
Start at 1/100 sec and take a shot
Bracket a couple of shutter speeds faster and slower (e.g., 1/60, 1/30, 1/200, 1/400, or whatever speeds are closest to those on your camera)
Look at the images on your computer and pick out the best one

The next time you have a clear, dry night and the moon is in the sky, try it yourself.

And here are a few products that may be useful in shooting the moon:

Tamron 1.4x Pro Teleconverter for Canon cameras

Tamron 1.4x Pro Teleconverter for Nikon cameras

The Tamron pro series of teleconverters are optically quite excellent. Their physical geometry makes them work with most telephoto lenses (at least on Canon… I’m less familiar with Nikons), and they give you a fair bit of extra focal length to bring the shot in closer.

Canon RC-1 Wireless Remote Control

This little gizmo is amazing. It lives on the strap of your camera, completely out of your way, but just waiting until you need it. When you do, pop it off and voila– you have a wireless infrared remote. It works with most Canon dSLRs, it’s inexpensive, and it’s incredibly useful.

108 Comments

Filed under Exposure, Lesson

Tagged as camera, moon, photography

November 6, 2007 · 8:08 pm

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?

22 Comments

Filed under Aperture, ISO, Lesson, shutter speed

Tagged as camera, lens, photography

October 19, 2007 · 11:58 pm

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

13 Comments

Filed under Aperture, ISO, Lesson, shutter speed

Tagged as camera, lens, photography

October 15, 2007 · 11:46 pm

ISO: Why You Care

In the last lesson, you learned that ISO was sort of like turning up the volume on your stereo, in that it magnified the light as it came into your camera. That sounds like a pretty good way to get a brighter picture in low light, right? It is, but unfortunately there’s a cost associated with it.

Here are two utterly unremarkable photos that I took of the corner of my office building:

The first one was taken at ISO 100, the lowest my Canon Digital Rebel XT will go, and the second one was taken at ISO 1600, which is coincidentally the highest ISO that camera can do. You probably don’t see much difference in them at this size, but I promise you that they’re very different images.

Let’s go back to music for a bit. If you have a very quiet recording on your stereo and you turn it up, the sound gets louder. Something else happens, too– any background noises in the recording get magnified. If you’re listening to a tape (remember those?) the hiss of the tape gets louder. If there’s a small bit of noise in the background, it gets louder.

Just like sound recordings, our digital images exhibit something called noise, and that noise makes the images look grittier and grainier at high ISOs. For the following images, I’ve magnified everything to 2x the original size, and cropped down to a small section of the image for illustration purposes. First, let’s look at the upper left corner of the sky at ISO 100, 400, and 1600:

As you can see, the sky in the ISO 100 image is very smooth. At ISO 400 you can start to see it getting gritty, and at ISO 1600 the image looks pretty bad. That’s noise.

Here are a few more examples, at ISO 100 and ISO 1600:

In all three cases, the ISO 100 image looks pretty smooth, while the ISO 1600 image is very grainy.

It’s important to know that different cameras can have very different performance characteristics at higher ISOs. Inexpensive point & shoot cameras tend toward really horrible noise as the ISO increases, though I’m sure there are exceptions. Consumer-grade Canon digital SLRs are known for performing reasonably well at high ISOs, and their higher-end cameras often do exceptionally well. I have gotten some excellent low-noise shots out of my 5D at ISO 1600. Of course, I didn’t use that camera to take these test images, since the difference in quality would have been much more difficult to show.

If you’d like to see the full resolution versions of the originals:

ISO 100
ISO 400
ISO 1600

That’s great, but how should use use the ISO setting on your camera? My strategy is very simple. For typical shooting I always leave my camera set on ISO 100 until I find myself unable to get the aperture and shutter speed I need to get the shot. If there’s not enough light to shoot at ISO 100, I turn the ISO up until I get to an acceptable shutter speed and aperture. If I know I’m going to be shooting in a relatively dark environment like a nightclub, I just set the ISO to the highest setting I can and cope with whatever noise I get, since I already know that lower ISOs probably won’t be useful.

It can be useful to consider what you want to do with the images you shoot. If you’re just going to use them on the web, then the extra noise at higher ISOs won’t be much of a consideration, since the noise won’t be all that visible. Likewise, if you’re printing small images, noise won’t affect the output too much. However, if you’re planning to print enlargements, or you crop the image down significantly before printing it or displaying it on the web, noise may be a factor.

I hope that ISO has been demystified for you. Has it?

A quick update from mid-2010: This article was written a couple of years ago. Since then, dSLR technology has improved considerably. Many newer dSLRs can shoot very good images at ISO 800 or even 1600, and some produce usable shots at 3200 or even higher. All of the concepts remain the same, but the top end has moved a bit. I expect that will keep happening in the future.

Next lesson: How much more light? How much less?

3 Comments

Filed under ISO, Lesson

Tagged as camera, lens, photography

October 8, 2007 · 11:25 pm

ISO: What is it?

We’ve learned that the three things that control the exposure of a digital photo are shutter speed, aperture, and ISO. We know that shutter speed is how long the shutter is open, and that the longer it’s open the more light gets in. We know that aperture is how wide the lens is open, that wider openings let more light in, and that the size of the opening also controls how much of the image is in focus.

So what’s this ISO stuff? Way back when, we learned that there are magic gnomes that live on your camera’s sensor, and that when the shutter opens they record whatever light they see.

But first, a diversion. Imagine you go to a club to see a show– it’s a weird kind of show, but bear with me. There’s someone playing ballads on the guitar and singing along. There’s a guy playing punk rock on the accordion. There’s a trio singing political songs. And then someone gets up and whispers poetry. (Hey, I live in San Francisco. This kind of thing actually happens.)

All of a sudden, you can’t hear the show. The poem whisperer is much quieter than everybody who came before him, and the microphone isn’t sensitive enough to pick up his voice. Eventually someone kicks the sound guy and wakes him up, he turns up the sensitivity on the microphone, and unfortunately you get to hear the end of Ode to a Medium Rare Hamburger With Onions. Oh well.

Now our accordion player comes back for his Sex Pistols encore, and he blasts your eardrums. Whoops! Cover your ears until the sound guy turns the microphone’s sensitivity back down.

If you’d brought your camera you might have gotten a great picture of a room full of people covering their ears while staring at an accordionist, but other than that what does this have to do with photography?

Let’s go back to our imaginary gnomes who sit on your camera’s sensor waiting for light, and then record what they see. They do a great job on a bright sunny day, but what happens when you shoot inside the dark club? All of a sudden there’s not enough light for the gnomes, and you get a very dark image. You can open the aperture, but it only goes so far. You can use a slower shutter speed, but at some point you just get a blur of motion. There’s hope, though. Just like you have to turn up the sensitivity on the microphone to pick up more of a quiet sound, you can turn up the sensitivity on your sensor to pick up more light when the scene is dark. It’s like magnifying the light so that the gnomes can see it better.

That sensitivity is called ISO. Of course, there’s a technical description with lots of math stuff for exactly what it is and how it works, but the truth is that you don’t care. It doesn’t matter. Here’s what you do need to know about ISO– it’s pretty simple:

ISO 100 is generally considered the baseline, and it’s where your camera is set by default. ISO 200 is twice as sensitive as ISO 100. ISO 400 is twice as sensitive as ISO 200, and therefore four times as sensitive as ISO 100. ISO 800 is twice as sensitive as ISO 400, and ISO 1600 is… well, I’m not telling you. You’re smart enough to figure that one out on your own.

In the olden days, you bought film with a particular ISO, and you set your up camera so that it knew what film it had in it. These days, you just tell your camera what ISO that you want it to use, and it factors the ISO into its metering. Most dSLRs have a range of ISO from 100 to 1600, often 100, 200, 400, 800, and 1600. A few will have settings in between. Some will go as low as 50 and as high as 3200, and at least one model will go as high as ISO 6400. I’m pretty sure ISO 6400 will let you take pictures without taking the lens cap off.

See? That wasn’t so hard. Turning up the ISO is basically just magnifying the light that comes into your camera.

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